Lábrea fever, also known as Lábrea's black fever and Lábrea hepatitis, is a lethal tropical viral infection discovered in the 1950s in the city of Lábrea, in the Brazilian Amazon basin, where it occurs mostly in the area south of the Amazon River, in the states of Acre, Amazonas and Rondônia . The disease has also been diagnosed in Colombia and Peru. The similar form in Colombia has been named Santa Marta fever.

Its main manifestation is a fulminant hepatitis which may kill in less than a week, and which characteristically affects children and young adults, and more males than females. It is accompanied also by an encephalitis in many cases. The disease is highly lethal: in a study carried out in 1986 at Boca do Acre, also in the Amazon, 39 patients out of 44 died in the acute phase of the disease. Survivors may develop chronic disease.

Symptoms and signs

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Lábrea fever has a sudden onset, with jaundice (bilious color of the skin), anorexia (lack of appetite), hematemesis (blood vomits), headache, fever and severe prostration. Death occurs by acute liver failure (ALF). In the last phase, neurological symptoms such as agitation, delirium, convulsions and hemorrhagic coma commonly appear.

Etiology

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Lábrea fever is a coinfection or superinfection of hepatitis D (HDV) and hepatitis B (HVB). The infection by HDV may occur in a patient who already has the HVB, or both viruses may infect at the same time a previously uninfected patient. VHD can only multiply in the presence of VHB, therefore vaccination against VHB prevents infection. Thus, American and Brazilian scientists have determined that the HVD, or delta, virus, which is a small circular RNA virus, is normally unable to cause illness by itself, due to a defect. When it is combined with the hepatitis B virus, Lábrea hepatitis may ensue. The main discovery of HVD and HVB association was done by Dr. Gilberta Bensabath, a leading tropical virologist of the Instituto Evandro Chagas, of Belém, state of Pará, and her collaborators.

Infected patients show extensive destruction of liver tissue, with steatosis of a particular type (microsteatosis, characterized by small fat droplets inside the cells), and infiltration of large numbers of inflammatory cells called morula cells, comprised mainly by macrophages containing HDV antigens.

In the 1987 Boca do Acre study, scientists did an epidemiological survey and reported delta virus infection in 24% of asymptomatic hepatitis B virus carriers, 29% of acute nonfulminant hepatitis B cases, 74% of fulminant hepatitis B cases, and 100% of chronic hepatitis B cases. The delta virus seems to be endemic in the Amazon region.

Treatment and prevention

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Treatment is similar to hepatitis B, but due to its high letality, more aggressive therapeutic approaches are recommended in the acute phase. In absence of a specific vaccine against HDV, the vaccine against hepatitis B (HBV) must be given soon after birth in risk groups.

References

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Eponymous diseases | Infectious diseases | Tropical disease | Hepatology