Chapare virus is a virus from the family Arenaviridae that causes a hemorrhagic fever in humans known as Chapare hemorrhagic fever. It was first described after an outbreak of a novel zoonotic mammarenavirus infection occurred in the village of Samuzabeti, Chapare Province, Bolivia, in January 2003. A small number of people were infected and one person died.[2][3][4]
In 2019, nine people became infected with the virus in the La Paz regional area, four of whom died. Nosocomial and human-to-human transmission of the virus occurred in at least three of the cases which resulted in the death of a medical intern and a gastroenterologist. Like other members in the Arenavirus family, the specific zoonotic reservoir and primary transmission vector is suspected to be a rodent, probably the small-eared pygmy rice rat.[5][6][2]
Like other arenaviruses that can cause hemorrhagic fever, the Chapare Virus is considered a very dangerous pathogen. Because of it's highly fatal symptoms and lack of a current treatment, the virus is considered a Biosafety Level 4 (BSL4) agent[7]. Highly fatal progression of disease that leads to the virus's 60% fatality rate, the stability and transmissibility are all reasons that the Chapare Virus is labeled as a BSL4 agent. It is noted that the pathogen can remain infectious in aerosols for greater than 48 hours, meaning significant safety measures are needed to prevent infection of this disease[8].
The high risk of this pathogen, as well as the lack of BSL4 labs in the region, have led to the struggle in understanding more about this disease[7]. In the June 2019 outbreak, three samples of those who were suspected to have hemorrhagic fever were sent to the Center for Disease Control in the United States, whose technology and lab safety were able to identify the cause as the Chapare Virus[7]. Further outlook on the virus is important due to the risk it poses. Currently, the main source of the Chapare Virus is the pygmy rice rat who transmits the disease to other hosts. Climate change is an important factor on the spread of the disease as global temperatures rise, Andean glaciers in South America melt, increasing the habitat of the pygmy rice rats. Further human intervention such as deforesting efforts in South America have led to the displacement of pygmy rice rats, increasing the risk of disease spread[8].
Virology
The Chapare Virus belongs to the Arenaviridae family. Arenaviruses are typically derived from rodents and tend to target macrophages and dendritic cells early on[9]. They are split into Old World (OW) and New World (NW) complexes [2]. These complexes each have their own distinctions and are both considered to have some very pathogenic members, with one well known OW complex member being the Lassa Virus, or LASV. LASV suppresses immune signals, specifically slowing the production of interferons, which serve as a warning signal, and proinflammatory cytokines, which helps recruit cells to fight infection [9].
One strongly studied NW complex member is the Junin Virus, or JUNV, which is associated with an opposite response; high interferon and cytokine levels. Intense immune responses aren't necessarily a good thing and can cause high levels of inflammation or possible tissue damage [2]. Along with this, the Junin virus as well as other viruses belonging to the NW complex are associated with hemorrhagic fever (HF) outbreaks. NW viruses are divided into three clades, which include clades A, B, and C [9]. The Chapare Virus is consistent with being a member of Clade B of the NW complex, but should not be assumed to follow the same patterns and virology as the Junin Virus. For a time, the Chapare was believed to be a close relative of the Sabia Virus, another member of the Clade B NW complex, but it proved to have its own distinctions following genetic sequencing of the two strains [9][2][5]. Sequencing showed that the S and L sequences in each virus had noticeable differences, with the nucleotides in the L segment differing by about 30% and the S segment differing by about 26%. The Chapare virus still belongs to the New World arenavirus family, but is viewed independently across different strains [9].
The Chapare has an RNA genome, similar to other arenaviruses. It is also bisegmented into two RNA segments; the s segment (small) and the l segment (large).[10] The Chapare Virus uses an ambisense polarity coding method, meaning these segments are facing opposite directions while being separated by an intergenic region, forming a hairpin-like structure. The s segment encodes both a nucleoprotein and a glycoprotein precursor while the l segment encodes the RNA polymerase as well as a Z protein[10].
Diagnoses
Chapare virus is not easily diagnosed, and is often mistaken for other regional endemic diseases such as dengue fever or yellow fever. Diagnoses are often limited by the rarity of the disease and the high-containment laboratories required. A diagnosis of Chapare Virus requires a laboratory capable of molecular diagnostics to confirm infection.[11] To determine the presence of the virus, a laboratory can run a PCR test. No other test is available to determine the presence of the pathogen as of September 2026.[12]
Symptoms
After an incubation period of around 9–19 days, initial symptoms include fever, malaise, headache, myalgia, back pain, dizziness, nausea, vomiting and diarrhoea. The disease often progresses to include hemorrhagic and neurological symptoms, such as gingival hemorrhage, anaemia, leukopaenia, confusion, seizures, ecchymoses, bleeding from mucous membranes, hemorrhagic shock and multi-organ failure.[2][5]
Chapare virus RNA was detected in the blood, urine, conjunctiva, semen and in broncho-alveolar and nasopharyngeal samples of the infected patients. Those who survived often had prolonged residual neurological symptoms. Viral RNA was detected in survivors up to 170 days after infection and infectious Chapare virus was obtained in a semen sample of one patient 86 days after symptom onset.[5]
Treatment
Treatment relies mostly on supportive care and early diagnosis. Specific antiviral therapy for Chapare virus infection has yet to be properly investigated.[5]
Currently, there is no established for the treatment of Chapare hemorrhagic fever due to its rarity and severity. Some off-label uses for anti-viral drugs have been to see effectiveness in other arenaviruses similar to Chapare, but must need to be given early in the disease progression. Additionally, these drugs have yet to show any efficacy towards the Chapare virus and the hemorrhagic fever it causes[13]. Certain animal models such as guinea pigs lacking the signal transducer and activator of transcription 1 protein, are susceptible to arenaviruses such as Chapare have been studied to identify the workings of the virus, but show signs of struggle due to their lack of availability[13]. Though further testing is needed, studies using these guinea pigs were able to induce the Chapare Virus into guinea pigs that showed similar signs of infection found in humans[13]. These models are promising in the development of a drug or vaccine for the Chapare Virus, though the rarity and safety of the virus still plays a major challenge in discovery.
References
↑Buchmeier, Michael J.; etal. (2 July 2014). "Rename one (1) genus and twenty-five (25) species in the family Arenaviridae"(PDF). International Committee on Taxonomy of Viruses (ICTV). Retrieved 14 June 2019. in the family Arenaviridae change the name of genus Arenavirus to Mammarenavirus and convert the names of its constituent species to a binomial format, by appending the name Mammarenavirus to each existing name
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