Evidence of Person-to-Person Transmission of Mysterious and Deadly Virus in Bolivia

Microscopic image of the Chapare virus, an arenavirus that killed three of the five people it infected in a 2019 outbreak in Bolivia.

(CN) — A deadly virus that has surfaced twice in Bolivia can spread from person to person in health care settings, raising concerns of future outbreaks, according to the U.S. Centers for Disease Control and Prevention.

CDC researchers determined that a 2019 outbreak of the Chapare virus, a hemorrhagic fever syndrome first discovered in 2004, was spread through human transmission from victims to health care workers who treated them. The 2004 outbreak killed one person, while the 2019 outbreak killed a farmworker and two of the three medical professionals involved in his case. 

“Our work confirmed that a young medical resident, an ambulance medic and gastroenterologist all contracted the virus after encounters with infected patients — and two of these health care workers later died,” epidemiologist Caitlin Cossaboom, with the CDC’s Division of High-Consequence Pathogens and Pathology, said in a statement. “We now believe many bodily fluids can potentially carry the virus.”

Confirming human-to-human transmission demonstrates the importance of avoiding contact with items contaminated with blood, urine, saliva or semen, Cossaboom explained. Her investigation found evidence that the doctor who died may have been infected while suctioning saliva from a patient and that the ambulance medic was likely infected while resuscitating the doctor during transport to the hospital.

Cossaboom and CDC colleague Maria Morales-Betoulle presented their findings at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH).

The Chapare virus could have been circulating in Bolivia for years because infected patients may have been wrongly diagnosed as suffering from dengue fever, a common regional disease that can produce similar symptoms. Symptoms of the Chapare virus include fevers, abdominal pain, vomiting, bleeding gums, skin rash and pain behind the eyes. Since there is no specific treatment, patients are treated mainly with intravenous fluids and other supportive care.

The number of confirmed cases in both outbreaks was small. In 2003, only the one fatal case was confirmed, and there were five known infections in 2019. But with symptoms similar to Ebola, the 2019 outbreak in Bolivia’s capital city of La Paz surprised health authorities, who mobilized infectious disease experts from Bolivia’s Ministry of Health, the CDC and the Pan-American Health Organization to investigate the origins of the disease.

Bolivian authorities worked closely with the CDC to control the outbreak. After ruling out dengue as the cause of the outbreak, patient samples were rushed to a high security biosafety level 4 laboratory operated by the CDC. Next generation genome sequencing technology showed the samples matched data from the patient who died in 2004.

“We isolated the virus, and we were expecting to find a more common disease, but the sequence data pointed to Chapare virus,” Morales-Betoulle said. “We were really surprised because the 2019 outbreak in La Paz occurred long after the first case was identified in 2004.”

Scientists don’t know where the Chapare virus originated or how it infects humans. But new evidence of Chapare viral RNA was detected in rodents collected from an area around the home and nearby farmlands of the first patient identified in the 2019 outbreak. The pigmy rice rats that tested positive for the virus are found across Bolivia and several neighboring countries. Rodents are a prominent source of similar viruses, including Lassa virus, which kills thousands of people annually in West Africa.

“The genome sequence of the RNA we isolated in rodent specimens matches quite well with what we have seen in human cases,” Cossaboom said.

However, the evidence doesn’t prove the rodents were the source of the infection, she cautioned.

Morales-Betoulle and Cossaboom said future work will focus on using diagnostic tests to identify additional human infections and field work to determine whether rodents spread the disease.

“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 ASTMH president Dr. Joel Breman. “It’s a valuable lesson that international scientific teams, equipped with the latest tools and freely sharing their insights, are our best front-line defense against the disruptive threats of deadly infectious diseases.”

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