chronic brucellosis and determines criteria for linking long-term adverse health outcomes to infection during military service in the Gulf War, OEF, or OIF.

Brucellae are small, gram-negative coccobacilli that are facultative intracellular pathogens with the ability to survive and multiply in mononuclear phagocytic cells of infected hosts. Eight Brucella species have been identified, but only a subgroup is associated with human disease (Table 5.2). At present, all Brucella species are considered biovars of B. melitensis.

B. melitensis contains two circular replicons of 1.1 and 1.2 Mb. Its genome contains 3,197 open reading frames. B. melitensis, B. abortus biotypes 1 and 4, and B. suis biotype 1 are very similar. In contrast, B. suis biotypes 2 and 4 contain two replicons of 1.35 and 1.85 Mb, and B. suis biotype 3 contains a single circular replicon of 3.3 Mb (Pappas et al. 2005).

TABLE 5.2 Nomenclature and Characteristics of Brucella spp.



Animal Hosts

Human Virulencea

B. melitensis


Goats, sheep, camels


B. abortus

1-6, 9

Cows, camels, yaks, buffalo

++ to +++

B. suis


Pigs (biotypes 1-3), wild hares (biotype 2), caribou (biotype 4), reindeer (biotype 4), wild rodents (biotype 5)


B. canis




B. ovis




B. neotomae




B. pinnipediae and B. cetaceae


Minke whales, dolphins, porpoises, seals


a Virulence is graded on a scale from no virulence (-) to the highest degree of virulence (++++).

SOURCE: Adapted with permission from Pappas et al. 2005.

Transmission and Endemicity of Brucellosis

Human brucellosis is a zoonosis; almost all infections are derived directly or indirectly from exposure to animals. Humans may be infected through direct contact of abraded skin or cuts with infected animals, their tissues or fluids, inhalation, inoculation of mucosal or conjunctival membranes, or ingestion of infective animal products (most often unpasteurized dairy products) (Lulu et al. 1988).

Human brucellosis occurs sporadically in many developed or industrialized countries, including the United States, but most cases occur in three distinct endemic zones: the Near East and Middle East, including Iran, Iraq, Kuwait, Saudi Arabia, Israel, Jordan, and Turkey; the Mediterranean region, including Spain, Portugal, Italy, and Greece; and Latin American countries, including Peru, Argentina, and Mexico (Abo-Shehada et al. 1996; Bodur et al. 2003; Geyik et al. 2002; Gottesman et al. 1996; Gungor et al. 2002; Gur et al. 2003; Hasanjani Roushan et al. 2004; Khateeb et al. 1990; Lubani et al. 1989b; Lulu et al. 1988; McLean et al. 1992; Memish and Venkatesh 2001; Mousa et al. 1987; Norton 1984; Tasova et al. 1999; Trujillo et al. 1994; Zaks et al. 1995). Endemic disease in those regions is usually associated with B. melitensis infection.

In the endemic zones, infections are acquired typically through consumption of dairy products, especially unpasteurized goat cheese and untreated milk. Human-to-human transmission of brucellosis species is rare but has been associated with transplantation of infected bone marrow, blood transfusion, and possibly sexual transmission of the organism in semen

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