Author: Brian Holtry

Two unique RNA viruses, the Marburg and Ebola viruses, are members of a new family known as filoviruses. These agents can cause severe or fatal hemorrhagic fevers and are endemic in Africa. Laboratory workers have been exposed to the Marburg agent while working with tissue cultures from African green monkeys.

Dengue and yellow fever are both caused by flaviviruses, and each is spread by an arthropod vector. The etiologic agents of dengue are the dengue virus types 1-4, whereas yellow fever is caused by the yellow fever virus. Flaviviruses produce a wide range of diseases including hemorrhagic fevers, arthritis, encephalitis, and hepatitis.

Many viruses causing infection of the central nervous system (CNS) are covered in chapters devoted to each type of virus. For example, enteroviruses, the agents most frequently causing meningitis and occasionally encephalitis, are covered in site. The herpes viruses that cause meningitis, encephalitis, or both, especially herpes simplex virus (HSV), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV), are discussed in site.

Creutzfeldt-Jakob disease is a progressive, fatal illness of the central nervous system that is seen most frequently in the sixth and seventh decades of life. The disease is sporadic and found worldwide, with an incidence of disease of 1 case/million people per year. The mode of acquisition is unknown, but a higher incidence of the disease among Israelis of Libyan origin who eat sheep eyeballs has led to speculation that the disease may be transmitted by the ingestion of scrapie-infected tissue.

Rabies is an acute fatal viral illness of the CNS. It can affect all mammals and is transmitted between them by infected secretions, most often by bite. It was first recognized more than 3000 years ago and has been among the most feared of infectious diseases.

Arthropod-borne (arbo) viruses causing encephalitis are members of the toga-, flavi-, and bunyavirus families. The medically important togaviruses include rubella virus, which is discussed in site, and the equine encephalitis viruses. The flavivirus family, which includes St.

Parvoviruses are widespread bird and mammalian viruses. More than 50 types have been identified, but the most common identified human pathogen is parvovirus B19. It is the cause of erythema infectiosum (Fifth disease) and is responsible for episodes of aplastic crises in patients with chronic anemia, especially those with hemolytic anemia and AIDS (Box 1). B19 is also associated with arthritis and intrauterine infection.

Poxviruses are a large, complex family of viruses that cause disease in humans and other animals (Table 1). Of the many genera in this family, only species of Orthopoxvirus and Molluscipoxvirus are associated specifically with humans.

Two major groups of retroviruses are considered in this chapter: the oncoviruses (“onco-,” related to a tumor) and the lentiviruses (“lenti-,” slow). Oncoviruses have long been associated with a variety of cancers in animals, including leukemia, lymphoma, and sarcoma; however, until recent years, oncoviruses had not been found to infect humans. The first human retrovirus, human T-lymphotropic virus type 1 (HTLV-1), was discovered in the late 1970s. It was shown to cause adult T-cell leukemia, a rare malignancy found only in Japan, Africa, and the Caribbean (although serologic evidence shows that the virus also occurs in the United States and may be associated with some chronic neurologic conditions).

The causes of hepatitis are varied and include viruses, bacteria, and protozoa, as well as drugs and toxins (eg, isoniazid, carbon tetrachloride, and ethanol). The clinical symptoms and course of acute viral hepatitis can be similar, regardless of etiology, and determination of a specific cause depends primarily on the use of laboratory tests (Box 1). Hepatitis may be caused by at least six different viruses whose major characteristics are summarized in Table 1. Non-A-non-B (NANB) hepatitis is a term previously used to identify cases of hepatitis not caused by hepatitis A or B.