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West Nile Virus

Excerpts have been reprinted with permission from the APHA’s Control of Communicable Diseases Manual (CCDM). Please refer to the CCDM for more complete information.

(Dengue hemorrhagic fever and yellow fever are presented separately.)
(Central Asian hemorrhagic fever)

1. Identification – A viral disease with sudden onset of fever, malaise, weakness, irritability, headache, severe pain in limbs and loins and marked anorexia. Vomiting, abdominal pain and diarrhea occur occasionally. Flush on face and chest and conjunctival injection develop early. hemorrhagic enanthem of soft palate, uvula and pharynx, and a fine petechial rash spreading from the chest and abdomen to the rest of the body are generally associated with the disease, sometimes with large purpuric areas.

There may be bleeding from gums, nose, lungs, uterus and intestine, but only in serious or fatal cases does this occur in large amounts, often associated with severe liver damage. Hematuria and albuminuria are common but usually not massive. Fever is constantly elevated for 5-12 days or may be biphasic … Convalescence is prolonged. Other findings are leukopenia, with lymphopenia more marked than neutropenia. Thrombocytopenia is common. The reported case-fatality rate ranges from 2% to 50%. In the Russian Federation, an estimated 5 infections occur for each hemorrhagic case.

Diagnosis is through isolation of virus from blood (inoculation of cell cultures or suckling mice) or PCR. Serological diagnosis is by ELISA, reverse passive HI, IFA, CF, immunodiffusion or plaque-reduction neutralization test. Specific IgM may be present during the acute phase; convalescent sera often have low neutralization antibody titres.

2. Infectious agent – The Crimean-Congo hemorrhagic fever virus (Bunyaviridae, Nairovirus).

3. Occurrence – Observed in the steppes of western Crimea and in the Rostov and Astrakhan regions of the Russian Federation, as well as in Afghanistan, Albania, Bosnia and Herzegovina, Bulgaria, western China, the Islamic Republic of Iran, Iraq, Kazakhstan, Pakistan, South Africa, Turkey, Uzbekistan, the Arabian Peninsula and sub-Saharan Africa. Most patients are animal husbandry workers or medical personnel. Seasonal occurrence in the Russian Federation is from June to September, the period of vector activity.

4. Reservoir – In nature, believed to be hares, birds and Hyalomma spp. of ticks in Eurasia and South Africa; reservoir hosts remain undefined in tropical Africa, but Hyalomma and Boophilus ticks, insectivores and rodents may be involved. Domestic animals (sheep, goats and cattle) may act as amplifying hosts.

5. Mode of transmission – Bite of infective adult Hyalomma marginatum or H. anatolicum, or by crushing those ticks. Immature ticks are believed to acquire infection from the animal hosts and by transovarian transmission. Nosocomial infection of medical workers, occurring after exposure to blood and secretions from patients, has been important in recent outbreaks; tertiary cases have occurred in family members of medical workers. Infection is also associated with butchering infected animals.

6. Incubation period – Usually 1 to 3 days, with a range of 1-12 days.

7. Period of communicability – Highly infectious in the hospital setting. Nosocomial infections are common after exposure to blood and secretions.

8. Susceptibility – Immunity after infection probably lifelong.

9. Methods of control
A. Preventive measures: … preventive measures against ticks. An inactivated mouse brain vaccine has been used in eastern Europe and the former Soviet Union (not available in the USA).

B. Control of patient contacts and the immediate environment:
1)   Report to local health authority: In selected epidemic areas; in most countries, not a reportable disease, Class 3 (see Reporting).
2)   Isolation: Blood and body fluid precautions.
3)   Concurrent disinfection: Bloody discharges are infective; decontaminate by heat or chlorine disinfectants.
4)   Quarantine: Not applicable.
5)   Immunization: Not applicable, except in eastern Europe.
6)   Investigation of contacts and source of infection: Search for missed cases and the presence of infective animals and possible vectors.
7)   Specific treatment: Intravenous ribavirin and convalescent plasma with a high neutralizing antibody titre are regarded as useful …