8 Skin and Joints

Overview

Diseases affecting the skin and adnexal structures (e.g., mammary glands) account for many of the clinical abnormalities observed in mice and rats. As a group these diseases can be most perplexing to the clinician and pathologist concerned with rodents. Establishing definitive diagnoses frequently proves difficult or impossible, even in the most capable diagnostic laboratories, because of the complex interactions between some or all of the following: overt pathogens, opportunistic pathogens, host responses, genetic variations of hosts, environmental factors, social interactions, and other, often unknown factors.

A classification of these diseases and conditions is given in Table 12. There are 12 diseases attributed to infectious agents and 6 conditions due to other causes, such as social behavior or environmental factors. In addition to ectromelia virus, other causes of appendage amputations (Mycoplasma arthritidis, Streptobacillus moniliformis, Corynebacterium kutscheri, and "ringtail") are included because of clinical overlap with the pox diseases. Joint diseases, although rare in rodents, have been included here for clinical reasons.

By far the most frequently observed skin conditions are those categorized in Table 12 as "Dermatitis/Alopecias." It should be noted that this category is comprised of a heterogeneous group of conditions represented under both "Infectious Diseases" and "Noninfectious Conditions." The common ectoparasites (mites) and Staphylococcus aureus, a normal inhabitant of the



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 164
--> 8 Skin and Joints Overview Diseases affecting the skin and adnexal structures (e.g., mammary glands) account for many of the clinical abnormalities observed in mice and rats. As a group these diseases can be most perplexing to the clinician and pathologist concerned with rodents. Establishing definitive diagnoses frequently proves difficult or impossible, even in the most capable diagnostic laboratories, because of the complex interactions between some or all of the following: overt pathogens, opportunistic pathogens, host responses, genetic variations of hosts, environmental factors, social interactions, and other, often unknown factors. A classification of these diseases and conditions is given in Table 12. There are 12 diseases attributed to infectious agents and 6 conditions due to other causes, such as social behavior or environmental factors. In addition to ectromelia virus, other causes of appendage amputations (Mycoplasma arthritidis, Streptobacillus moniliformis, Corynebacterium kutscheri, and "ringtail") are included because of clinical overlap with the pox diseases. Joint diseases, although rare in rodents, have been included here for clinical reasons. By far the most frequently observed skin conditions are those categorized in Table 12 as "Dermatitis/Alopecias." It should be noted that this category is comprised of a heterogeneous group of conditions represented under both "Infectious Diseases" and "Noninfectious Conditions." The common ectoparasites (mites) and Staphylococcus aureus, a normal inhabitant of the

OCR for page 164
--> TABLE 12 Classification of Skin and Joint Diseases/Conditions I. Infectious diseases   A. Pox Diseases, Spontaneous Amputations in Some Cases     1. Mousepox (ectromelia)     2. Poxvirus disease(s) in rats   B. Arthritis, Spontaneous Amputations Possible     1. Mycoplasma arthritidis     2. Streptobacillus moniliformis     3. Corynebacterium kutscheri   C. Dermatitis/Alopecias     1. Common ectoparasites     2. Staphylococcus aureus     3. Pasteurella pneumotropica     4. Dermatophytosis     5. Mouse papule virus     6. Self-mutilation associated with otitis media   D. Neoplasms     1. Mouse mammary tumor viruses II. Noninfectious conditions   A. Dermatitis/Alopecias     1. Bite Wounds       a. Adults (fighting)       b. Weanlings (hunger ?)     2. "Whisker trimming," "hair nibbling," and "barbering"     3. Muzzle alopecia     4. Hair growth arrest (?)   B. Spontaneous Amputation Probable     1. "Ringtail" skin, are probably the leading causes of skin diseases in mice, while S. aureus alone probably holds that distinction in rats. Although the diseases caused by poxviruses are extremely important because of high mortality, deleterious effects on research results, and their highly contagious nature, they are relatively infrequent in occurrence or are restricted in geographic distribution. Bacterial arthritis is extremely rare in rodent stocks. Ectromelia virus Significance Low for most research uses of mice. High in those laboratories, such as immunogenetics and tumor biology laboratories, that exchange biologic materials from mice for research purposes.

OCR for page 164
--> Perspective 1930: Mousepox was first recognized by Marchal (1930) in England and called "infectious ectromelia". Since that time, mousepox has become the disease name and ectromelia virus has been accepted as the name of the virus. Recorded major outbreaks of mousepox in the United States are as follows: 1951-1953: Yale University (Trentin and Briody, 1953; Briody, 1955) 1954-1956: Roswell Park Memorial Institute, Buffalo, New York (Shope, 1954; Briody, 1955; Fenner, 1981) 1957-1958: Epizootics in 10 laboratories (Briody, 1959) 1960: Yale University (Bhatt et al., 1981) 1960-1974: National Institutes of Health (NIH), Bethesda, Maryland (Whitney et al., 1981) 1979-1980: NIH and eight other institutions in five states: Utah, Maryland, Missouri, Illinois, and Minnesota (AALAS, 1981; Held, 1981; Whitney et al., 1981). 1981: An enzyme-linked immunosorbent assay (ELISA) for ectromelia virus infection was developed (Collins et al., 1981) and subsequently shown to be far more sensitive and specific than the hemagglutination inhibition (HAI) test that traditionally had been used for serologic diagnosis (Buller et al., 1983). Agent Ectromelia virus is a large DNA virus, family Poxviridae, genus Orthopoxvirus. Virions are shaped like ovals or bricks (175 x 290 nm), have a characteristic dumbbell-shaped nucleoid, and are morphologically indistinguishable from vaccinia virus (Fenner, 1982). Many strains of ectromelia virus have been isolated. The Moscow and Hampstead strains have been studied most extensively. Moscow is the most virulent of the recognized strains. Strains are closely related antigenically. The virus is antigenically related to vaccinia (Fenner, 1982). Ectromelia virus is cultivable in tissue cultures of several cell types, including HeLa, Vero, and mouse fibroblasts (L929), and on the chorioallantoic membrane of chick embryos (Fenner, 1982). The virus is quite stable for extended periods under dry conditions at room temperature. It can be preserved for months at room temperature in glycerol and indefinitely at -70°C or by lyophilization (Fenner, 1982). The virus resists dry heat but is rapidly inactivated by moist heat. Heating of serum or other body fluids for 30 minutes at 60°C destroys infectivity (Bhatt and Jacoby, 1987c). Recommended disinfectants include sodium

OCR for page 164
--> hypochlorite (100 µg/ml [ppm] available chlorine), vapor-phase formaldehyde (paraformaldehyde, 5-10 g/m3), and iodophores (150-300 µg/ml [ppm]) (Fenner, 1982; Allen et al., 1986; Bhatt and Jacoby, 1986). Hosts Mice (Mus musculus). There is one unconfirmed report of the virus being recovered from wild rodents of three genera (Microtus, Apodemus, and Clethrionomys) in East Germany, but wild rodents are not known to serve as reservoir hosts. Some wild mouse species, including Mus caroli, Mus cookii, and Mus cervicolor popaeus, are highly susceptible to experimental infection. Limited replication of the virus and seroconversion occur in members of the genus Rattus after experimental infection (Burnet and Lush, 1936; Fenner, 1981, 1982; Buller et al., 1986). Epizootiology Ectromelia virus infections have been reported in many countries. The infection is thought to be enzootic in some institutional mouse colonies in Europe. Periodic epizootics have occurred in the United States since 1950. Some have been traced to imported mice or mouse specimens (Fenner, 1981; Osterhaus et al., 1981). Ectromelia virus infection has not been reported in commercial barrier colonies in the United States. The infection is most commonly seen in those research laboratories that exchange live mice, mouse tissues, mouse sera, and transplantable mouse tumors (e.g., immunogenetics and experimental oncology laboratories) (Fenner, 1981). Natural transmission usually is dependent on direct contact and fomites (Wallace and Buller, 1986; Bhatt et al., 1988). Skin abrasions are thought to provide the main route of entry. Aerosol transmission and infection via the respiratory route also is thought to be possible but of relatively little importance (Briody, 1966; Bhatt and Jacoby, 1986; Bhatt et al., 1988). Infected animals begin shedding virus about 10 days after infection when characteristic skin lesions appear (Fenner, 1982). Persistent infection ("the carrier state") was previously thought to be important in the epizootiology of mousepox. Recovered mice have been reported to shed virus in the feces or from skin lesions for up to 116 days (Gledhill, 1962). However, more recent data indicate that significant numbers of virus particles are shed from infected mice for only about 3 weeks even though the virus can persist for months in the spleen of an occasional mouse (Fenner, 1948c; Bhatt and Jacoby, 1987b). Thus, long-term persistent shedding of virus probably is not as important in the epizootiology of the infection as previously thought (Wallace and Buller, 1985). Cage-to-cage

OCR for page 164
--> transmission is low unless favored by husbandry practices, e.g., mixing mice from different cages or handling mice from different cages without changing gloves (Wallace and Buller, 1986; Bhatt and Jacoby, 1987b). Clinical Inapparent infection. This form of infection occurs mainly in the highly resistant strains, such as C57BL/6 or C57BL/10. Resistance of these strains to clinical disease (not to infection) has been reported to be due to a single dominant H-2 linked gene (Schell, 1960a,b; Wallace et al., 1985: O'Neill and Brenan, 1987). Clinical disease. Highly variable, ranging from less than 1% to nearly 100%, depending on many factors such as strain of mouse, strain of virus, length of time infection has been present in the colony, and husbandry practices (Briody et al., 1956; Briody, 1966). The spectrum includes: Minimal enzootic disease. The disease can smolder for long periods in small subpopulations (e.g., 2-4% of cages or total mice within a room) with little spread of infection, few if any clinical signs, and negligible mortality (Werner et al., 1981). Explosive epizootic disease. May result in sudden morbidity and mortality affecting 80-90% of a colony. This form of the disease most often has been seen in the more susceptible strains, including A, CBA, C3H, DBA/2, and BALB/c, as a result of the first introduction of the infection into a colony (Briody et al., 1956; Briody, 1966; AALAS, 1981; Bhatt and Jacoby, 1986; Wallace and Buller, 1986). Clinical manifestations can include any or all of the following: variable (<1% to >80%) mortality; ruffled hair coat; hunched posture; facial edema; conjunctivitis; swelling of the feet; cutaneous papules, erosions, or encrustations mainly on face, ears, feet, or tail; or necrotic amputation (ectromelia) of limbs or tails (Werner et al., 1981; Fenner, 1982). Pathology All mice are probably equal in susceptibility to infection, but clinical disease and mortality are virus- and mouse strain-dependent (Bhatt and Jacoby, 1986, 1987a). In general, mice of the A, CBA, C3H, DBA/2, and BALB/c strains are highly susceptible, the AKR and SJL strains are moderately susceptible, and the C57BL/6 and C57BL/10 strains are highly resistant to disease (Briody et al., 1956; Briody, 1966; AALAS, 1981; Wallace and Buller, 1985, 1986; Wallace et al., 1985; Bhatt and Jacoby, 1986, 1987a; Buller et al., 1987a). The incubation period is 7 to 10 days. Virus ordinarily enters via the

OCR for page 164
--> skin. There is local replication and extension to regional lymph nodes via lymphatics, where replication also occurs, resulting in a mild "primary viremia" as virus escapes into the blood via efferent lymphatics. Virus is taken up by splenic and hepatic macrophages, and extensive multiplication occurs in these target organs (sometimes with death due to diffuse splenic and hepatic necrosis), resulting in a massive "secondary viremia." Virus from the secondary viremia localizes in a wide variety of tissues, especially the skin (basal cells), and in the conjunctiva and lymphoid tissues. A primary lesion (frequently on the head) may appear at the site of skin inoculation about 4-7 days post infection. Foot swelling and secondary (generalized) rash (pocks) may appear 7-10 days post infection. Skin lesions heal rapidly (within 2 weeks), leaving scars on survivors (Fenner, 1948a,b, 1949). In acute mousepox there is severe necrosis of the liver, spleen, lymph nodes, Peyer's patches, and thymus. Jejunal hemorrhage often results from mucosal erosions. Inclusions may be present in the cytoplasm of hepatocytes and other infected cells. Characteristic large eosinophilic cytoplasmic inclusions may be present in skin lesions. Necrotic amputation of limbs (ectromelia) and tails can be seen in mice that survive the acute disease (Roberts, 1962a,b, 1963; Allen et al., 1981). Diagnosis Inapparent infections and low prevalence of enzootic disease may create major problems in establishing a diagnosis of mousepox. In the former, there may be no reason to suspect the infection. In the latter, extensive testing may be necessary to identify the low percentage of infected mice in a large population (Wallace et al., 1981; Werner et al., 1981). Diagnosis of acute disease is based on the presence of typical lesions, with confirmation by: (a) demonstration of characteristic large virus particles in affected tissues by using transmission electron microscopy, or (b) serologic testing of survivors of acute disease (Allen et al., 1981; Bhatt and Jacoby, 1986). Differential diagnosis of the hepatic and splenic lesions should consider infections due to Salmonella enteritidis and Streptobacillus moniliformis. Differential diagnosis of skin lesions should exclude fight wounds, bite lesions of the type in mice described by Les (1972), and loss of limbs due to bacterial infections such as Streptobacillus moniliformis or Mycoplasma arthritidis (Freundt, 1959). Serologic testing is of special value because of the feasibility of testing large numbers of animals rapidly in the event of a suspected outbreak. The enzyme-linked immunosorbent assay (ELISA) is particularly useful for this purpose in unvaccinated mice because it is sensitive and specific. The ELISA has been reported to give false-positive results in NZW and NZB

OCR for page 164
--> mice. The hemagglutination inhibition (HAI) test is relatively insensitive but has the advantage that it does not give positive reactions in testing sera from mice that have been vaccinated with the IHD-T strain (Collins et al., 1981; Buller et al., 1983). The indirect immunofluorescence assay (IFA) for many years was considered the most sensitive and specific procedure for serologic testing, but the impracticality of maintaining live antigen in the laboratory limited its usefulness for research purposes (Christensen et al., 1966). Recently, the ELISA was found to be 10-fold more sensitive than the IFA (Buller et al., 1983). Biologic materials, such as cells and blood, can be screened for mousepox (and other agents) by injecting the tissue into known pathogen-free mice followed by serologic testing. Alternatively, virus isolation may be attempted using BS-C-1 and other cell lines (Bhatt and Jacoby, 1986). Failure of skin lesion development at the site of vaccination with vaccinia virus by scarification of tail skin is considered suggestive of prior infection with mousepox (Fenner, 1982). Control Institutions that must receive mice, mouse tissues, or tumors from sources other than commercial barrier facilities should have a disease surveillance program for quarantine and testing of incoming mice and mouse tissues for infectious agents, including ectromelia virus. This approach constitutes the only practical way by which laboratories with a high risk of introducing ectromelia virus can effectively avoid the periodic disastrous consequences of mousepox outbreaks (Small and New, 1981). In the past, accepted practice for eradicating mousepox required disposal of mouse colonies and all infected biologic materials (e.g., tumors and sera), plus rigorous decontamination of rooms and equipment (AALAS, 1981). Cesarean derivation of infected mouse stocks was not considered an acceptable alternative since it may not eliminate the virus; intrauterine infection is known to occur in mice infected during pregnancy (Fenner, 1982). More recently, it has been suggested that quarantine and cessation of breeding may be successful in eliminating ectromelia virus (Bhatt and Jacoby, 1987b). Vaccination with a live virus vaccine, the IHD-T strain of vaccinia adapted to growth in embryonated eggs, may be useful in eliminating the infection from small, closed colonies where all offspring can be vaccinated at around 6 weeks of age (Tuffery, 1958; Trentin and Ferrigno, 1959; Flynn, 1963a). Vaccination can protect mice from fatal mousepox, but does not prevent infection or virus transmission (Wallace and Buller, 1986; Bhatt and Jacoby, 1987d). Vaccination with the IHD-T strain causes seroconversion and resultant

OCR for page 164
--> false positive ELISA and IFA test results, but not to the HAI test because the vaccine does not stimulate production of HAI antibody (Collins et at., 1981; Buller et al., 1983). Immunodeficient mice are highly susceptible to infection with the IHD-T strain and must be protected when vaccinating. Interference with Research Mousepox is one of the most feared diseases of mice because of (a) the potential for explosive outbreaks in which mortality can approach 100%, (b) known major effects on research results, and (c) known serious problems of detection once latent infection becomes established in a mouse population (AALAS, 1981). Manipulations that have been reported to promote mousepox epizootics include: experimental infection with tubercle bacilli, x-irradiation, administration of various toxic chemicals, shipment, tissue transplantation, castration, and tumors (Briody, 1959). In addition: Mousepox infection can alter phagocytic response (Blanden and Mims, 1973). Conversely, procedures that decrease phagocytosis may increase susceptibility to mousepox, e.g., large doses of endotoxin or splenectomy (Schell, 1960b). Intraperitoneal injection of Freund's adjuvant enhances the severity of experimental mousepox (McNeill and Killen, 1971). C57BL/6 mice infected experimentally with LP-BM5 murine leukemia virus had increased susceptibility to ectromelia virus, possibly due to inability to generate an ectromelia virus-specific cytotoxic T cell response (Buller et al., 1987c). Ectromelia virus can replicate in vitro in lymphoma and hybridoma cell lines from mice. Potentially, passage of such contaminated cell lines in mice can introduce the virus into mouse colonies (Buller et al., 1987b; Wallace and Buller, 1986). Poxvirus(es) in Rats Significance Unknown. Perspective Two large outbreaks of a highly fatal poxvirus disease occurred in laboratory rats in the USSR during 1973 and 1974 (Marennikova and Shelukhina, 1976; Marennikova et al., 1978b). A poxvirus disease with symptoms resembling mousepox was reported in Romania in 1976 (Iftimovici et al.,

OCR for page 164
--> 1976). More recently, rat tissues received from the USSR, but originating in Czechoslovakia, were found to contain poxvirus. The animals from which the tissues were obtained had a clinically inapparent poxvirus infection (Kraft et al., 1982). Whether these reports concerned the same or different viruses is unknown. Agent Poxvirus (or perhaps more than one virus). Possibly a virus of wild rodents, Turkmenia rodent poxvirus, that is related to cowpox virus but that is distinctly different from mousepox virus (Marennikova et al., 1978a). The strain isolated from rats in the USSR was designated 012-Moscow 73 (Krikun, 1977; Marennikova et al., 1978b; Kraft et al., 1982). Hosts Laboratory rats and wild rodents, Felidae (zoo animals fed infected rats), and humans (Marennikova and Shelukhina, 1976; Marennikova et al., 1978b). Laboratory mice are highly susceptible to experimental infection (Majboroda and Lobanova, 1980; Majboroda et al., 1980). Of 40 personnel exposed to infected rats, four became ill. Symptoms included headache, fatigue, cough, rhinitis, tickling in the throat, and digestive upset. Two of the four had a rash on the head, shoulders, knees, and back of the hands (Marennikova et al., 1978b). Epizootiology Infections in rats have been reported only in animals from the USSR and Eastern Europe. Wild rodents might serve as reservoir hosts in the USSR. Outbreaks of disease in the USSR were explosive, possibly associated with the entry of wild rodents into animal facilities. Clinical Infection can be inapparent (Kraft et al., 1982) or occur as an epizootic with 50% mortality (Marennikova and Shelukhina, 1976; Marennikova et al., 1978b). Disease in rats during epizootics occurred in three forms: pulmonary, dermal, and mixed pulmonary and dermal. Pulmonary form. Rats became anorexic, extremely dyspneic, and moribund, with death occurring uniformly by the third or fourth day of clinical signs. Dermal form. Relatively mild. Partial anorexia; papular rash on tail, paws, and muzzle, with transition to dry crusts in 1-2 days; sometimes partial amputation of the tail and possibly also the paws; and deaths occurring rarely.

OCR for page 164
--> Mixed form. Symptoms were transient, lasting only two to three days. Suckling rats were most susceptible. Adults most often had the dermal form of the disease and survived (Marennikova et al., 1978b). Pathology Lesions seen in the pulmonary form are severe interstitial pneumonia and pulmonary edema with serous or hemorrhagic pleural effusion. In addition to pox lesions and occasional spontaneous amputation of feet and tail, rats with the dermal form of the disease also had focal pneumonia and sometimes mucosal exanthema involving the mouth, nasopharynx, and rectum (Marennikova et al., 1978b). Kraft et al. (1982) studied a group of rats received from Czechoslovakia via the USSR that had inapparent infection. They found desquamative lesions containing poxvirus virions in the nasal mucosa. Diagnosis Definitive information is lacking. The hemagglutination inhibition test or enzyme-linked immunosorbent assay for mousepox might be useful. Virus isolation and characterization are essential. Control Definitive information is lacking, but until proven otherwise, measures comparable to those used for mousepox should be employed. Great caution should be used when importing rodents from Eastern Europe and the USSR. Interference with Research No data are available. Probably similar to mousepox in mice. Mycoplasma arthritidis Significance Uncertain. Subclinical infection may be very common in rats and mice. Perspective Experimental models of arthritis: Most of the recent literature on this agent concerns laboratory models of arthritis produced by inoculating large

OCR for page 164
--> doses of Mycoplasma arthritidis intravenously or into the footpad of rats and mice (Lindsey et al., 1978b; Cole and Cassell, 1979; Cole and Ward, 1979). It must be emphasized that these models are highly artificial and may have little relevance to the understanding of the host-parasite relationships in the natural infection. Natural infections in rats: Natural infections of M. arthritidis in rats have been reported infrequently since 1938, with the organism having one of the following four roles: Incidental infection has been reported (sometimes in association with Mycoplasma pulmonis) in various sites, including the nasopharynx (Ito et al., 1957; Ward and Cole, 1970; Stewart and Buck, 1975), middle ears (Preston, 1942; Stewart and Buck, 1975; Eamons, 1984), the lung (Cole et al., 1967), a paraovarian abscess (Preston, 1942), the submaxillary gland (Klieneberger, 1938), and multiple organs (Davidson et al., 1983). Subclinical infection has been a complicating factor in studies of experimental arthritis (Pearson, 1959; Mielens and Rozitis, 1964; Cole et al., 1969). As a contaminant of transplantable tumors M. arthritidis has caused polyarthritis and/or abscesses at the injection site in recipient rats (Woglom and Warren, 1938; Howell and Jones, 1963). M. arthritidis has been a cause of spontaneous polyarthritis in wild (Collier, 1939) and laboratory (Findlay et al., 1939; Preston, 1942; Ito et al., 1957) rats. Thus, the literature contains less than a dozen reports of natural arthritis due to M. arthritidis in rats, with the most recent such report appearing in 1969. Natural infections in mice: Natural infections of M. arthritidis in mice were first reported in 1983 (Davidson et al., 1983). In that study the organism was isolated from the nasal passages, the conjunctiva, and the uterus and by laryngo-tracheo-bronchial lavage from approximately 10% of otherwise pathogen-free mice and rats housed in the same room. No gross or microscopic lesions attributable to M. arthritidis were found in either host. Agent M. arthritidis is a bacterium, class Mollicutes, order Mycoplasmatales, family Mycoplasmataceae (sterol-requiring mycoplasmas). It is Gram negative, lacks a cell wall, pleomorphic, and may occur in filaments 2 to 30 µm long. It will grow on conventional horse serum-yeast extract mycoplasma medium, usually under facultatively anaerobic conditions at pH 7.8, 37°C, and 95% relative humidity. M. arthritidis requires arginine and usually produces "fried egg" appearance when grown on solid medium. For specific methods of cultural isolation, see Cassell et al. (1983a).

OCR for page 164
--> Diagnosis For detection of asymptomatic carriers, the fur of several animals can be brushed while the animals are held over opened plates of culture medium and then the plates can be cultured for dermatophytes (Mackenzie, 1961). For clinical cases, hair can be plucked or skin scrapings can be taken from the periphery of lesions and mounted onto slides in 10% potassium hydroxide for visualization of hyphae and endospores. Definitive diagnosis is dependent on culture and identification of organisms by using Sabouraud's or other dermatophyte medium (Georg, 1960; Emmons et al., 1977). Control Where feasible, infected stocks should be destroyed and replaced by dermatophyte-free stock after thorough sterilization and disinfection of facilities and equipment. Cesarean derivation of valuable stocks may be desirable. Treatment of affected animals is not recommended. For prevention of infection, barrier maintenance is effective. Rodents should be housed well away from laboratory animal species known to be more frequently infected, e.g., cats and dogs (Kunstyr, 1980). Dermatophyte infections of mice and rats do not represent important zoonoses. The most common of these infections, T. mentagrophytes infection in mice, has been reported as a source of infection for humans in only six instances (Fox and Brayton, 1982), and these occurred in the 1950s and 1960s before cesarean-derivation and barrier-maintenance methods were in common practice. Interference with Research There are no known examples of dermatophyte infections interferring with research in contemporary mice and rats. Pasteurella pneumotropica Significance Low. Perspective 1948-1950: Jawetz (1948, 1950) and Jawetz and Baker (1950) published papers that seemed to implicate Pasteurella pneumotropica as an ubiquitous respiratory tract pathogen of major importance in mice.

OCR for page 164
--> 1973: Moore et al. (1973) reported on a stock of gnotobiotic rats maintained in isolators and found that they were monocontaminated with P. pneumotropica, suggesting that the organism might normally inhibit the gastrointestinal tract. 1974: Jakab (1974) reported on the first in a series of studies in which mice experimentally infected with Sendai virus showed decreased clearance of intranasally inoculated P. pneumotropica. Although this and subsequent studies by Jakab and associates (Jakab, 1981) were entirely experimental, they possibly gave further impetus to the belief that P. pneumotropica is a respiratory pathogen. 1980s: More than 3 decades after the reports of Jawetz (1948, 1950) and Jawetz and Baker (1950) P. pneumotropica has not been incriminated as being responsible for outbreaks of respiratory disease in mice, i.e., their findings have not been confirmed in a natural outbreak. Perhaps their experimentally infected mice also had Sendai virus and/or Mycoplasma pulmonis infections. The gross and microscopic lesions they described were compatible with murine respiratory mycoplasmosis. Also, their mice were stated to have natural Chlamydia trachomatis infection and spontaneous pulmonary consolidation (Jawetz, 1950). Agent Pasteurella pneumotropica is a Gram-negative, coccobacillus bacterium, family Pasteurellaceae, measuring 0.5 x 1.2 µm. It is nonhemolytic. Colonies on sheep blood agar are convex, measuring 0.5-1.5 mm at 24 hours, and gray or yellow in color. Oxidase, urease, and catalase are produced, and nitrate is reduced to nitrite (Carter, 1984). Hosts Mice, rats, hamsters, guinea pigs, and many others. Epizootiology P. pneumotropica can be isolated from a high percentage (up to 95%) of healthy animals in some colonies and from feces of gnotobiotic rats (Moore et al., 1973; Sparrow, 1976; Saito et al., 1978). It can be isolated from numerous organs: respiratory tract, oral cavity, intestine, uterus, urinary bladder, skin, and conjunctiva (Jawetz, 1948, 1950; Hoag et al., 1962; Heyl, 1963; Wheater, 1967; Kunstyr and Hartman, 1983). Transmission is probably by contact and fomites.

OCR for page 164
--> Clinical This agent has been associated with a wide range of clinical manifestations and disease processes in laboratory rodents, including the following: In mice: Conjunctivitis (Wagner et al., 1969; Needham and Cooper, 1975) Panophthalmitis (Weisbroth et al., 1969) Dacryoadenitis (Wagner et al., 1969; Needham and Cooper, 1975) Subcutaneous and cervical abscesses (Weisbroth et al., 1969; Wilson, 1976; Moore and Aldred, 1978) Bulbourethral gland infections (Sebesteny, 1973) Respiratory disease? (Hoag et al., 1962; Goldstein and Green. 1967; Brennan et al., 1969a,b; Saito et al., 1978) Uterine infections (Hoag et al., 1962; Brennan et al., 1965; Blackmore and Casillo, 1972; Ward et al., 1978) Otitis media (Harkness and Wagner, 1975) In rats: Ophthalmitis (Roberts and Gregory, 1980) Conjunctivitis (Hill, 1974b; Young and Hill, 1974; Moore, 1979) Subcutaneous abscesses (Van der Shaaf et al., 1970) Mastitis (Hong and Ediger, 1978c) Respiratory disease? (Burek et al., 1972) Pathology P. pneumotropica is an opportunist that most frequently causes lesions of the skin and adnexal structures. Lesions caused by P. pneumotropica usually are characterized by suppurative inflammation. Eye lesions of rats attributed to P. pneumotropica in past reports could have been caused by sialodacryoadenitis virus, with P. pneumotropica present merely as an opportunist or incidental inhabitant. Diagnosis Many colonies of mice and rats have P. pneumotropica infections of the upper respiratory tract, digestive tract, conjunctiva, and other sites but no demonstrable disease. Diagnostic efforts must discriminate between P. pneumotropica infection and P. pneumotropica-induced disease, and rule out other possible causative agents and disease processes. Pasteurella spp., Actinobacillus spp., Haemophilus spp., and Yersinia spp., which are commonly found in mice and rats, give similar reactions in

OCR for page 164
--> many biochemical tests. Therefore, extensive biochemical testing is required to accurately identify these organisms (Hooper and Sebesteny, 1974; Lentsch and Wagner, 1980; Simpson and Simmons, 1980; Ackerman and Fox, 1981: Kunstyr and Hartman, 1983: Carter, 1984; Wullenweber-Schmidt et al., 1988). Control Since this agent is usually an opportunist, control of important primary pathogens and other factors that compromise host defenses may be more important than efforts to control P. pneumotropica infection. Cesarean derivation and maintenance in a gnotobiotic isolator may be necessary to exclude the organism completely. Antibiotic therapy has been attempted in a few instances (Gray and Campbell, 1953; Moore and Aldred, 1978), but it has limited value. Interference with Research Lesions due to P. pneumotropica in the skin and adnexal tissues can interfere with research involving those organs. Mouse Papule Virus Significance Very low. Perspective Knowledge of this agent is limited to a single report in which a group of mice with skin lesions resembling those of mousepox was described (Kraft and Moore, 1961). Agent The agent is an unclassified virus. It is ether sensitive and heat labile and can pass through a filter of 450 nm pore size. Inclusions found in skin lesions were considered suggestive of poxvirus etiology. Sera from infected animals were negative by the hemagglutination test for antibodies to vaccinia virus. No isolates of the agent are available for further study (L. M. Kraft, Moffett Field, Calif., personal communication, 1985).

OCR for page 164
--> Hosts Mice. Epizootiology Unknown. Clinical Papular skin lesions are characterized as areas of edema and hyperemia, with central indentation or dimple formation, randomly distributed over the body, including the feet and tail. Subsequently, there is keratinization and scab formation, followed by healing without scar formation. Lesions are most noticeable in nursing mice prior to the appearance of hair (Kraft and Moore, 1961). Pathology Raised papules are seen scattered over the entire body, particularly in neonatal mice before growth of hair. Microscopically, acidophilic, intracytoplasmic inclusions are present in the epidermis, and the dermis has variable infiltrates of neutrophils, lymphocytes, and histiocytes (Kraft and Moore, 1961). Diagnosis Diagnosis of a suspected occurrence of the disease should include isolation, characterization, and identification of the agent; fulfillment of Koch's postulates; and characterization of the clinical and pathological aspects of both the natural and experimental disease. Control Unknown. Interference with Research There are no known examples in which this agent interferes with research.

OCR for page 164
--> Mouse Mammary Tumor Virus Significance Infections of different mouse strains with variants of this agent provide a large assortment of valuable models for experimental viral carcinogenesis. Perspective 1933: Workers at the Jackson Laboratory (Little, Bittner, Green, and Murray) announced the discovery of a nonchromosomal influence of maternal origin that played a decisive role in the development of mouse mammary cancer (Gross. 1970). 1936: This "influence" was reported to be a virus transmitted through the mother's milk (Bittner, 1936; Visscher et al., 1942). 1959: DeOme et al. (1959) developed an assay for premalignant changes in the mouse mammary gland based on the outgrowth pattern of transplanted cells in mammary fat pads free of mammary rudiments. 1974: Lasfargues et al. (1974) successfully grew the virus in vitro. 1976: The ubiquity of the mouse mammary tumor virus (MMTV) provirus in cellular DNA of GR (substrain not given) mice was demonstrated through molecular hybridization studies (van Nie and Hilgers, 1976). 1979: Inbred strains of mice were shown to have different MMTV proviruses (Cohen and Varmus, 1979). Agent MMTV is a medium-sized RNA virus, family Retroviridae. It is the prototype of a morphologically distinct subclass of retrovirus, type B, that is characterized by an eccentric location of the nucleocapsid within the viral envelope (Bernhard, 1958; Bentvelzen and Hilgers, 1980; Schlom, 1980). Four major variants of the virus have been identified. MMTV-S (S for standard; the Bittner virus) is transmitted through the milk to nursing young and is highly oncogenic. MMTV-L (L for low oncogenic) is transmitted through germ cells and is weakly oncogenic. MMTV-P (P for pregnancydependent) is transmitted through both milk and germ cells and is highly oncogenic. MMTV-O (O for overlooked) is considered an endogenous virus in the genome of most mice (Bentvelzen and Hilgers, 1980; Medina, 1982).

OCR for page 164
--> Hosts Mus musculus (laboratory and wild). Similar viruses have been reported in other species, including Mus cervicolor, Mus cookii. and Mus caroli (Bentvelzen and Hilgers, 1980; Teramoto et al., 1980). Epizootiology Mouse strains such as C3H, DBA/2, and A readily express MMTV-S, and the virus can be demonstrated in a variety of locations throughout the body, especially in mammary tissue and milk. Molecular studies indicate that other mouse strains have proviral copies in their cellular DNA (van Nie and Hilgers, 1976). MMTV proviruses can influence the incidence of malignancy, but most are cryptic, having no discernible effect (Traina-Dorge and Cohen, 1983). Foster nursing experiments have demonstrated that transmission of MMTVS occurs via ingestion of infected milk, and results in a high incidence of mammary tumors early in life (6-12 months) when the associated genetic and hormonal factors are also present (Bittner, 1936; Medina, 1982; Traina-Dorge and Cohen, 1983). Clinical Mammary tumors in female mice can be located on virtually any part of the body (ventral, lateral, and dorsal surfaces) from the chin to the pelvic region. A variable frequency of metastases to distant sites occurs, but the lungs are the most common site (Dunn, 1959; Medina, 1982). Pathology Current theory holds that the virus initially induces "hyperplastic alveolar nodules," which are preneoplastic lesions. The average latency period from infection to tumor expression is 6-9 months. The development of tumors is enhanced by administration of estrogen to male and female mice, forced breeding, and administration of carcinogens (e.g., 3-methylcholanthrene and 7,12-dimethylbenzanthracene). Glucocorticoid hormones appear to promote mammary tumor production through the induction of intracellular MMTV RNA (Ringold, 1983). Susceptibility to MMTV is controlled by host genetic factors, i.e., it is strain dependent (Medina, 1982; Michalides et al., 1983; Traina-Dorge and Cohen, 1983). Mammary tumors usually are circumscribed, round to nodular, gray to white masses located in the subcutaneous tissue. They can become very large. Ulcerations and hemorrhages are common in large tumors. Most

OCR for page 164
--> mammary tumors are adenocarcinomas of Dunn's histologic types A or B (Dunn, 1959). Type A tumors are characterized by uniform acini lined by a single layer of cuboidal cells, while type B tumors are variable in the extent of differentiation, but usually consist of irregular cords and sheets of cells. Other types include adenocarcinomas of types C, Y, L, and P; carcinomas with squamous cell differentiation; and carcinosarcomas. Other histologic types are rare (van Nie, 1967; Sass and Dunn, 1979). Mice of many strains develop humoral and cellular immune responses to MMTV, indicating that mice infected early in life are not immunologically tolerant (Bentvelzen and Brinkhof, 1980). Diagnosis Mouse mammary tumors appear as nodules or masses of varying size in the subcutaneous tissue. They are diagnosed and classified on the basis of histopathologic characteristics (Dunn, 1959; Sass and Dunn, 1979). Detection and characterization of MMTV requires test procedures normally available only in specialized viral oncology laboratories. Some of the more common procedures are nucleic acid hybridization, immunologic assays for viral antigens, and bioassays for infectivity in different strains of mice (Medina, 1982). A better alternative for investigators whose studies require the presence or absence of MMTV or specific MMTV proviruses may be to obtain mice with the desired characteristics from either the National Institutes of Health (Dr. S. Potkay, Chief, Veterinary Resources Branch, Division of Research Services, Building 14A, Room 103, National Institutes of Health, Bethesda, MD 20205) or the National Cancer Institute (NCI) (Dr. J. G. Mayo, NCI-Frederick Cancer Research Facility, Biological Testing Branch, P.O. Box B, Frederick, MD 21701). Control For most studies, control of MMTV is not required. The most practical method of control is through selection of mouse strains. Foster nursing on mouse strains that are free of the virus has been used to eliminate MMTV-S. Interference with Research MMTV infection in mice is an extremely valuable model of mammary cancer, especially for studies of the interactions of the virus, hormones, genetics, and carcinogens. It is the only known animal model of virus-induced mammary cancer. The infection also can be a complicating factor in experimental carcinogenesis studies.

OCR for page 164
--> Concurrent infection of mice with the lactic dehydrogenase-elevating virus and MMTV-S reduces the incidence of virus-induced mammary tumors (Riley, 1966). Self-Mutilation Associated with Otitis Media Harkness and Wagner (1975) reported on a single incident in which a small percentage of adult mice in a colony exhibited violent scratching of the external ears and adjacent tissues. Histologic sections of the external ears showed ulceration and acute inflammation of the ear pinnas, external canals, and adjacent tissues. The mice also had purulent otitis media from which Mycoplasma pulmonis, Pasteurella pneumotropica, and other agents were isolated. The skin condition was considered secondary to the otitis media. Noninfectious Skin Conditions Important In Differential Diagnosis Bite Wounds in Adult Mice and Rats Fighting can be a serious problem in some strains of mice (Wimer and Fuller, 1966). It is usually worst among mature males but also occurs among females in some strains. Some of the most notorious fighters are mature males of the BALB/c, SJL/J, and HRS/J strains, which generally must be housed one per cage. Bite wounds can appear anywhere on the body, but they usually are most concentrated on the rump and lumbar regions, with few or none on the shoulders or head. The characteristic pattern of open and healing wounds along dorsal surfaces of the trunk is virtually diagnostic (Scott and Fredericson, 1951; Fredericson and Birnbaum, 1954). Among male mice housed in groups, the submissive cage mates, which are bitten most frequently, often develop anemia and splenomegaly and have a much greater incidence of amyloidosis than do dominant males (Page and Glenner, 1972). In one colony of SW (Swiss Webster) mice, complication of bite wounds by group G streptococci reportedly caused necrotizing dermatitis and 35% mortality (Stewart et al., 1975). Skin lesions caused by fighting also can occur in old male rats, but fighting among rats is usually of little consequence compared with that among mice. Housing in compatible groups or singly usually results in dramatic healing of bite wounds within a few days in both rats and mice. Bite Wounds in Weanling Mice This syndrome was first reported in C3H/HeJ and C3HeB/FeJ mice, occurring usually at 5-8 weeks of age (Les, 1972). It was associated with

OCR for page 164
--> the housing of weanling mice in groups of 40 per cage and sometimes affected all mice in a cage. Lesions varied from small red foci to encrusted excoriations up to 3 mm in diameter on the tail skin. Some tails became swollen, and the part distal to some lesions sloughed. As healing occurred, the lesions became small white scars readily visible on the tails of pigmented C3H mice. Koopman et al. (1984) have confirmed these observations for C3H/He mice. A similar, if not identical, condition has been seen in weanling mice of the BALB/c strain (Cox et al., 1977). In addition to lesions on tails, these mice also had the lesions on their feet and ears. Using histologic methods, these investigators demonstrated that the dermis beneath the lesions regularly contained fragments of keratinized epithelium from the skin surface, suggesting that the skin lesions were bite wounds inflicted by cage mates. A major difference between C3H/He and BALB/c mice with this condition is that healing results in small but prominent white foci of scarring on the tails of pigmented C3H/He mice but leaves almost imperceptible scars on the tails of albino BALB/c mice. The cause of this condition is unknown. Les (1972) and Koopman et al. (1984) have suggested that "social stress" plays a role. However, the cause may simply be hunger resulting from the sudden separation of weanlings from their dams, the simultaneous crowding of weanlings into large groups where access to food and water is limited, and/or poor palatability of food (e.g., due to hardness of the pelleted diet). Control is accomplished by housing smaller numbers of weanlings per cage (i.e., avoiding crowding). The major importance of the condition is that it be recognized as a distinct entity that can be readily differentiated from mousepox by clinical and pathological features. "Whisker-Trimming," "Hair-Nibbling," and "Barbering" These are descriptive terms that have been applied to an assortment of patterns of alopecia associated with social behavior in mice. C57BL/6, C57BL/10, C3H, and SW mice have been the most studied, and heredity is thought to play a role. The dominant cage mate chews off the whiskers or hair of other cage mates giving the affected area a smoothly shaved appearance. The sites affected most are the whiskers and hair of the face, head, neck, and back. Usually, hair chewing occurs without injury to the underlying skin, although chronic hair chewing can result in thickening and increased pigmentation of the epidermis or even formation of foreign body granulomas in the dermis. If such chronically chewed mice are separated from the more dominant mouse, the regrowth of hair may be sparse and unpigmented, often with residual partial alopecia (Hauschka, 1952; Long, 1972; Thornburg et al., 1973).

OCR for page 164
--> Muzzle Alopecia Small patches of alopecia are located on the lateral surfaces of the muzzle. They can result from mechanical trauma associated with repeatedly inserting the muzzle through holes in the cage cover or between metal rods forming the food hopper (but is probably more often due to whisker-trimming by cagemates). Histologically, the affected skin may show hyperkeratosis, acanthosis, and mild inflammation (Litterst, 1974). Hair Growth Cycling Arrest Mice are known to grow hair in distinct patterns or cycles (Borum, 1954; Chase, 1954; Chase and Eaton, 1959; Argyris, 1963). Occasionally, one may see an entire litter of runted mice about weaning age with complete loss of hair on the torso. A small tuft of hair remains at the base of the tail and normal-appearing hair is present on the head and legs. Such mice generally have severe systemic disease (e.g., mouse hepatitis virus infection) and, presumably, are experiencing a temporary arrest of normal hair growth cycling (J. R. Lindsey, Department of Comparative Medicine, University of Alabama at Birmingham, unpublished). "Ringtail" This condition has been reported in mice (Nelson, 1960), laboratory rats (Njaa et al., 1957; Flynn, 1959; Totton, 1958), and the South African white-tailed hamster (Stuhlman and Wagner, 1971). It is characterized by the appearance of concentric rings around the tail, frequently followed by sloughing of all or part of the tail. The feet also may be swollen and reddened. The cause is thought to be environmental conditions of low (less than 40%) relative humidity and high (more than 80°F) temperature.