intermediate using an enzyme, reverse transcriptase. HIV-I and the related virus HIV-2 are further classified as lentiviruses (‘slow’ viruses) because of their slowly progressive clinical effects. HIV-I and HIV-2.
Arenaviruses are pleomorphic, round or oval viruses with diameters ranging from 50 to 300 nm. The virion surface has club-shaped projections, and the virus itself contains a variable number of characteristic electron-dense granules that represent residual, non-functional host ribosomes.The prototype virus of this group is lymphocytic choriomeningitis viruses, which is a natural infection of mice. Arenav iruses are also responsible for Argentinian and Bolivian haemorrhagic fevers and Lassa fever.Lassa fever This illness was first documented in the town of Lassa, igeria, in 1969 and is confined to sub-Saharan West Africa (Nigeria, Liberia and Sierra Leone). The multimammate rat, Mastomys natalensts, is known to be the reservoir. Humans are infected by ingesting foods contaminated by rat urine or saliva containing the virus. Direct inoculation is also a common mode of spread of this disease.
The incubation period varies from 7 to 18 days. The disease is insidious in onset and is characterized by fever, myalgia, severe backache, malaise and headache. A transient maculopapular rash may be present. Sore throat and lymphadenopathy occur in over 50% of patients. In severecases epistaxis and gastrointestinal bleeding may occur, hence the classification of Lassa fever as a viral haemorrhagic fever. The fever usually lasts from 1 to 3 weeks and recovery within 1 month of the onset of illness is usual. However, death occurs in 15-20% of hospitalized patients, usually from irreversible hypovolaemic shock.
The diagnosis is established by serial serological tests (including the Lassa-specific IgM titre) or by culturing the virus from the throat, serum or urine.
Treatment is supportive and, in addition, clinical benefit and reduction in mortality can be achieved with ribavirin therapy. In non-endemic countries, strict isolation procedures should be used, the patient ideally being nursed in a flexible-film isolator. Specialized units for the management of Lassa fever and other haemorrhagic fevers have beenestablished in the UK.
Lymphocytic choriomeningitis (LCM)
This infection is a zoonosis, the natural reservoir of the LCM virus being the house mouse. Infection is characterized by:
NON-NERVOUS SYSTEM ILLNESS, with fever, malaise, myalgia, headache, arthralgia and vomiting.
ASEPTIC MENINGITIS in addition to the above symptoms. Occasionally, a more severe form occurs, with encephalitis leading to disturbance of consciousness. This illness is generally self-limiting and requires no specific treatment.
MARBURG VIRUS DISEASE AND
EBOLA VIRUS DISEASE
These severe, haemorrhagic, febrile illnesses are discussed together because their clinical manifestations are similar. The diseases are named after Marburg in Germany and the Ebola river region in the Sudan and Zaire where these viruses were first isolated. The natural reservoir for these viruses has not been identified and the precise mode of spread from one individual to another has not been elucidated. The illness is characterized by the acute onset of severe headache, severe myalgia and high fever, followed by prostration. On about the fifth day of illness a non-pruritic maculopapular rash develops on the face and then spreads to the rest of the body. Diarrhoea is profuse and is associated with abdominal cramps and vomiting. Haematemesis, melaena or haemoptysis may occur between the seventh and sixteenth day. Hepatosplenomegaly and facial oedema are usually present. In Ebola virus disease, chest pain and a dry cough are prominent symptoms. Treatment is symptomatic. Convalescent human serum appears to decrease the severity of the attack.
Viral illnesses have been implicated aetiologically, including those due to EBV, Coxsackie B viruses, echoviruses, CMV and hepatitis A virus. Non-viral causes such as allergy to Candida spp. have also been proposed.The proportion of patients with ‘organic’ diagnoses remains uncertain. Recent studie suggest that two-thirds of patients with a symptom duration of more than 6 months have an underlying psychiatric disorder.