Bolivian Hemorrhagic Fever: Transmission And Pathways Explained

Bolivian Hemorrhagic Fever (BHF) is a zoonotic infectious disease originating in Bolivia, caused by the Machupo mammarenavirus. The disease was first identified in 1959, and is transmitted to humans through exposure to the excreta and secretions of infected rodents. The large vesper mouse (Calomys callosus), a rodent indigenous to northern Bolivia, is the primary vector and reservoir for the virus. While infected animals are asymptomatic, they shed the virus in their excreta, thereby infecting humans. Person-to-person transmission of BHF is believed to be rare but possible, and has been reported in hospital settings.

Person-to-person transmission is rare but possible

Person-to-person transmission of Bolivian Hemorrhagic Fever (BHF) is believed to be rare. However, it is possible, and there is evidence to support this.

In 1971, four secondary cases of BHF were identified in hospital workers following close contact with a patient suffering from the disease. In 1994, a farm worker transmitted BHF to six of their eight family members, sadly resulting in fatalities. Transmission by intimate contact during convalescence is also possible.

In the first instance, the patient suffering from BHF was the index case, and in the second, the farm worker was the index case. This demonstrates that transmission is possible from both patients and asymptomatic carriers.

The exact method of person-to-person transmission is not yet known, but it is likely to be via direct contact with infectious body fluids.

The primary transmission route is through the inhalation of aerosolized excreta from infected rodents

Bolivian Hemorrhagic Fever (BHF) is a highly fatal disease with a mortality rate of 5-35%. The disease was first identified in 1959 in Bolivia and is caused by the Machupo mammarenavirus, an infectious agent of the Arenaviridae family. The primary transmission route of BHF is through the inhalation of aerosolized excreta from infected rodents. The large vesper mouse (Calomys callosus), a rodent indigenous to northern Bolivia, is the primary vector and reservoir for the virus. Infected mice are asymptomatic and shed the virus in their excreta, including saliva, urine, and faeces, thereby infecting humans.

The inhalation of aerosolized excreta from infected rodents is the most common route of BHF transmission. This typically occurs when there is an increase in rodent populations, causing them to invade human habitations. Inhalation of the virus-laden aerosols within confined spaces, such as houses and outbuildings, poses a significant risk of infection. The risk of inhalation transmission is heightened during the dry season, when agricultural activity is at its peak, and in areas where grassland intergrades into forest, which is the natural habitat of the Calomys callosus rodent.

In addition to inhalation, direct contact with infected rodent excreta can also lead to BHF transmission. This can occur through broken skin or mucous membranes coming into contact with the excreta, or by consuming contaminated food or water. Person-to-person transmission of BHF is uncommon but possible, especially in familial or nosocomial settings. However, the overall risk of person-to-person transmission is low, and BHF is primarily considered a zoonotic disease.

To prevent BHF outbreaks, rodent control measures such as trapping and poisoning have been implemented with success in the past. These measures aim to reduce the population of Calomys callosus rodents and limit their contact with humans. During BHF epidemics in the 1960s, aggressive rodent control efforts led by survivors of past epidemics resulted in a rapid decrease in rodent numbers and a subsequent decline in BHF cases.

Contaminated food can also cause infection

The risk of contracting Bolivian hemorrhagic fever through contaminated food is heightened in rural and agricultural areas where humans come into closer contact with infected rodents. The initial outbreaks of the disease in the 1950s and 1960s were linked to farming and rural work. The disease was first identified in the Bolivian village of San Joaquín in 1962, and subsequent cases have been associated with rural and agricultural exposures.

The prevention and control of Bolivian hemorrhagic fever primarily focus on reducing contact between humans and the vesper mouse. This includes implementing rodent control measures and eliminating rodents from towns and homes. These measures have proven effective in reducing the number of outbreaks and limiting the spread of the disease.

In addition to contaminated food, the Machupo virus can also be transmitted through inhalation of aerosolized excreta or direct contact with infectious particles. Person-to-person transmission is believed to be rare but has been documented in some cases.

Bolivian hemorrhagic fever is a severe and potentially fatal disease, with a mortality rate estimated at 5 to 35%. The disease has three phases: prodromal, hemorrhagic, and convalescent. The incubation period is variable, ranging from 5 to 19 days, and the onset of symptoms is slow. Early symptoms include fever, malaise, headache, and myalgia, similar to malaria. As the disease progresses, patients may experience bleeding from the nose and gums, along with severe hemorrhagic and neurological symptoms.

Direct mucus membrane contact with infectious particles can cause infection

BHF is a severe disease with a high mortality rate, and while it was first identified in 1959, outbreaks continue to occur. The disease has three phases: prodromal, hemorrhagic, and convalescent. The first phase is characterised by unspecific symptoms such as fever, headache, and fatigue. In the second phase, patients develop severe hemorrhagic manifestations, including bleeding from the oral and nasal mucosa. The final phase is a slow convalescent period.

Control measures such as rodent population eradication have been effective in reducing BHF cases. However, with increasing tourism and travel to Bolivia, there is a risk of travellers becoming infected and spreading the disease to non-endemic countries.

The large vesper mouse (Calomys callosus) is the primary vector

The large vesper mouse, or Calomys callosus, is a rodent indigenous to northern Bolivia. It is the primary vector and reservoir for the Machupo virus, which causes Bolivian hemorrhagic fever. The Calomys callosus has a wide natural geographical range, including portions of Bolivia, Brazil, Paraguay, and Argentina. This rodent thrives in villages and near human habitations, which are found on high ground in seasonally inundated areas of the Beni Department in Bolivia.

The Machupo virus infects the Calomys callosus, resulting in asymptomatic infection. The infected rodents then shed the virus in their saliva, urine, and faeces. About 50% of experimentally infected Calomys callosus are chronically viremic and shed the virus in their bodily excretions or secretions.

Humans can contract the Machupo virus by inhaling virus-laden aerosols or breathing in aerosolized excreta or secreta from infected rodents. Consumption of contaminated food or direct mucus membrane contact with infectious particles from the rodent reservoir can also lead to infection. For example, in 1994, a farm worker transmitted fatal Bolivian hemorrhagic fever to six of eight family members.

Bolivian hemorrhagic fever tends to be a seasonal disease, with more cases occurring during the dry season, coinciding with the peak of agricultural activity. Epidemics in towns may occur when rodent densities reach unusually high levels, causing rodents to invade human settlements. Transmission to humans is likely from the inhalation of infectious aerosols within confined spaces of houses and outbuildings. However, direct contact of broken skin or mucous membranes with rodent excreta or contaminated fomites, such as food, is also a possible mode of transmission.

During the initial outbreaks of Bolivian hemorrhagic fever in the 1960s, rodent control was recognized as the primary method for preventing the spread of the Machupo virus. Trapping and poisoning resulted in a rapid reduction in the Calomys callosus population, helping to control the outbreaks.

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