Epidemiology

The viruses causing SAHF are clade B New World arenaviruses (family Arenaviridae; genus Mammarenavirus) found in specific geographical locations within the countries after which they are named. This geographical restriction of the virus is due to the presence of different rodent vectors in specified locations within each country. The viruses are spread mainly through aerosolisation of infected rodent secretions and excreta,​​​​​ and there is a direct correlation between rodent numbers and annual case incidence.[2][3][4][5][6][11] There are 5 SAHFs, each caused by a different New World arenavirus:

  • Argentine haemorrhagic fever is caused by infection with Junin virus, and is found in the Pampas region in the eastern part of Argentina.[3][4][5] Junin virus was first discovered in 1958.[12]​​

  • Venezuelan haemorrhagic fever is caused by infection with Guanarito virus, and is found in Portuguesa state and Barinas state in northern Venezuela.[6] Guanarito virus was first discovered in 1989.[13]​​

  • Bolivian haemorrhagic fever is caused by infection with Machupo virus, and is found in Beni district in northeastern Bolivia.[2] Machupo virus was first discovered in 1963.[14]​​

  • Chapare virus infection is caused by infection with Chapare virus, and is found in Cochabamba district in central Bolivia.[8] Chapare virus was first discovered in 2004.[8]​​

  • Brazilian haemorrhagic fever is caused by infection with Sabia virus, and is found near Sao Paolo, Brazil.[9] Sabia virus was first discovered in 1993.[15]​​

SAHF tends to occur in epidemics in rural areas with seasonal fluctuation, with a predominance of cases during harvest season.[2][3][4][5][6]​ Agricultural workers are at highest risk as the rodent vectors often live in the long grasses at the edge of fields. However, in the 1950s and '60s there were clusters of cases of Bolivian haemorrhagic fever in small towns when infection by the rodent vector Calomys callosus occurred.[16]

The diseases are most commonly found in adult males (approximately 60% to 70% of cases).[2][3][4][5][6][11] This is likely due to the demographic of more men working as agricultural labourers when compared with women, who culturally are more likely to be homemakers. The disease has, however, been described in women, particularly those working in fields (e.g., cotton pickers). Children are relatively spared and few cases have been described in children under 5 years of age.[2][3][4][5][6]

Imported cases of disease outside of the relevant South American countries are unlikely; however, with increasing international travel and changing patterns of adventure and working holidays, these diseases should still be considered in the differential of a returning febrile traveller from an endemic location.

While rare, nosocomial, laboratory, and person-to-person transmission from symptomatic individuals have been described,​​​​​ and appear most common in Bolivian haemorrhagic fever.[2][3][4][5][6]​ Laboratory exposure has been described for several of these viruses.[9][10]

Few cases have been described of Chapare virus infection and Brazilian haemorrhagic fever, so little is known about the specific epidemiology of these two diseases. Brazilian haemorrhagic fever has only been identified in 3 cases, two of which were as a result of laboratory exposure.[9] One confirmed case of Chapare virus infection was identified in 2004; a cluster of 5 cases (with 3 confirmed) occurred in Bolivia in mid-2019.[8][17] Large epidemics have been described for Argentine, Venezuelan, and Bolivian haemorrhagic fever.[2][4][5][6] The geographical region where Venezuelan haemorrhagic fever and Bolivian haemorrhagic fever have been found is relatively static;​​ however, the geographical region where Argentine haemorrhagic fever is found has been steadily expanding and it is now estimated that approximately 5 million people are at risk of the disease.[2][3][4][5][6]​​ The incidence of Argentine haemorrhagic fever is estimated at 140 to 355 per 100,000 adult males in affected rural areas.[5] Incidence figures have not been estimated for Venezuelan and Bolivian haemorrhagic fever, but there has been significant fluctuation in annual case numbers with prolonged periods of very few cases followed by a resurgence of disease for a number of years.[2][6]

[Figure caption and citation for the preceding image starts]: Regions of the world at risk of South American haemorrhagic feverCreated by BMJ Evidence Centre [Citation ends].com.bmj.content.model.Caption@1dfba03d

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