It is called Chapare, and until some time ago it was an unknown virus, but now it is a cause for concern.
In particular, experts are trying to figure out where it has come from and what its characteristics are, because it has killed four people.
It was discussed at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH) by researchers from the Centers for Disease Control and Prevention (CDC) in Atlanta, who reported what is happening in Bolivia. They also provided preliminary theories on two types of rodents – pygmy rice rats and small-eared pygmy rice rats – that carry the virus and could spread it to humans through direct contact with excrement or urine.
The virus was first identified in the province of Chapare (from which it took its name) in 2003, where one infected person had died from it. Then, all traces of it disappeared until 2019, when five people near La Paz, the Bolivian capital, showed signs of the disease.
Initially it was thought that they had dengue fever, which has very similar symptoms. However, the researchers from the CDC, along with those from the Bolivian Ministry of Health and the Pan-American Health Organization discovered, instead, by investigating with sophisticated techniques, that the five people had in fact contracted Chapare (two patients transmitted the virus to three health workers who had helped them). Three out of these five people died.
The Bolivian authorities then dispatched blood and tissue samples to a high biosafety level 4 laboratory in the United States (BSL-4, the same type of facility where the coronavirus is treated). The genetic mapping of the virus showed that it was the same type that had infected the first patient in 2003: Chapare.
Experts believe that infection among human beings can occur through contact with any biological fluid, such as blood, urine, saliva and sperm.
Chapare has also proven to be very resistant: the virus was found in the sperm of one of the survivors 168 days after the initial diagnosis. According to the experts, the spread of the virus in Bolivia could be higher than estimated after the first cases.
The disease presents itself as a haemorrhagic fever and produces symptoms that overlap, at least in part, with those of Ebola. Those affected suffer from fever, abdominal pain, vomiting, bleeding gums, rashes and pain behind the eyes. For now, there is no specific treatment, but only supportive care to try to alleviate at least some of the most serious symptoms.
Chapare belongs to the “family” of arenaviruses that also includes other dangerous viruses, such as the one known as Lassa or as Machupo. Survivors can suffer extensive organ damage.
The researchers have focused their attention on pygmy rice rats as possible vectors of the virus. Because viral genetic material was found in several of these animals, which live in the vicinity of the house of one of the victims (a farmer): this is not proof in itself, but is still a strong indication.
Pygmy rice rats are found across Bolivia and in several neighbouring countries. These rodents, among other things, are a natural reservoir of other similar viruses, such as Lassa.
“While there is still much that remains unknown about Chapare virus, it’s commendable how quickly this team was able to develop a diagnostic test, confirm human-to-human transmission and uncover preliminary evidence of the virus in rodents,” said the ASTMH president, Dr Joel Breman.
Analysis and monitoring will now be intensified. The Bolivian Center for Tropical Diseases has identified another three suspicious cases, including that of a child. Fortunately, however, these three people have survived.