Agent

Related Diseases/Symptoms

Mode of Transmission

Cause(s) of Emergence

Human immunodeficiency viruses 

HIV-1

HIV disease, including AIDS: severe immune system dysfunction, opportunistic infections

Sexual contact with or exposure to blood or tissues of an infected person; vertical transmission

Urbanization; changes in lifestyles/mores; increased intravenous drug use; international travel; medical technology (transfusions/transplants)

HIV-2

Similar to above

Same as above

Same as above, esp. international travel

Human papillomavirus

Skin and mucous membrane lesions (often, warts); strongly linked to cancer of the cervix and penis

Direct contact (sexual contact/contact with contaminated surfaces)

Newly recognized; perhaps changes in sexual lifestyle

Human parvovirus B19

Erythema infectiosum: erythema on face, rash on trunk; aplastic anemia

Contact with respiratory secretions of an infected person; vertical transmission

Newly recognized

Human T-cell lymphotropic viruses (HTLV-I and HTLV-II)

Leukemias and lymphomas

Vertical transmission through blood/breast milk; exposure to contaminated blood products; sexual transmission

Increased intravenous drug abuse; medical technology (transfusion)

Influenza 

Pandemic

Fever, headache, cough, pneumonia

Airborne (esp. in crowded, enclosed spaces)

Animal-human virus reassortment; antigenic shift

Drift

Same as above

Same as above

Antigenic drift

Japanese encephalitis

Encephalitis

Bite of an infective mosquito

Changing agricultural practices

La Crosse and California Group viruses

Encephalitis

Bite of an infective mosquito

Increasing interface between human activity and endemic areas; discarded tires as mosquito breeding sites



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