Arenaviruses are single-stranded RNA viruses which are carried principally in rodents, from which they may be transmitted to humans. One group of New World arenaviruses (the Tacaribe complex) is responsible for South American haemorrhagic fevers. Lymphocytic choriomeningitis virus occasionally produces viral meningitis in humans. Lassa is an Old World arenavirus.
LASSA FEVER
Since the first report in 1969, the disease has so far been limited to sub-Saharan West Africa, where serological studies have shown that past infection is widespread in rural areas. Isolated cases and small rural outbreaks are most common, but unlike other arenaviruses Lassa can spread person to person, and nosocomial outbreaks in hospital have also occurred .
Clinical features
The disease has the general features of a viral infection, high fever, intercostal myalgia, bradycardia, low blood pressure and leucopenia. Adherent yellow exudates on the pharynx are particularly characteristic. The fever lasts between 7 and 17 days. In severe cases liver and renal failure, electrolyte imbalance, haemorrhage and acute circulatory failure develop, hence the classification of Lassa fever as a viral haemor
| Commons viral haemorrhagic fevers | |||||
|---|---|---|---|---|---|
| Disease | Viral agent | Reservoir | Transmission | Geography | Case mortality |
| Lassa fever | Arenavirus | Multimammate rat (Mastomys natalensis) Patient |
|
West Africa | Up to 50% (responds to tribavirin) |
| Marburg/Ebola virus disease | Filovirus |
|
Via monkeys body fluids | Central Africa | 25-90% |
| Yellow fever | Flavivirus | Monkeys | Mosquitoes | Tropical Africa, South and Central America | 10-60% |
| Dengue | Flavivirus (dengue types 1-4) | Humans | Aedes aegypti et al | Tropical and subtropical coasts | Nil-10%* |
| Omsk | Togavirus | Musk rat | Ticks | Siberia | 2% |
| Crimean-Congo | Bunyavirus | Ixodes tick | Ixodes tick | Africa, Asia, Eastern Europe | 15-70% |
| Bolivian and Argentinian | Arenavirus (Machupa and Junin) | Rodents (Calomys spp.) | Urine | South America | ? |
| Haemorrhagic fever with renal syndrome | Hantavirus | Rodents | Faeces | Northern Asia, northern Europe | 30% |
| "Mortality of uncomplicated and haemorrhagic dengue fever, respectively. | |||||
rhagic fever . Case mortality is high, but mild and subclinical infections also occur.
The virus may be isolated, or antigen-detected, in maximum security laboratories from serum, pharynx, pleural exudate and urine, but diagnosis will usually be established from *paired sera', the later specimen being taken 6-8 weeks after the onset of infection. The diagnosis should be considered in the UK and other non-endemic areas in patients presenting with fever within 21 days of leaving West Africa, particularly if they have organ failure or haemorrhagic features (although most patients initially suspected of having viral haemorrhagic fevers in the UK turn out to have malaria).
Management
Strict isolation and general supportive measures, preferably in a special unit, are required. Tribavirin (ribavirin) is given intravenously (100 mg/kg, then 25 mg/kg daily for 3 days and 12.5 mg/kg daily for 4 days).
Prevention
The administration of convalescent immune plasma has been followed by recovery and is therefore recommended for prophylaxis after accidental exposure to infection.