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Human transmission confirmed in deadly outbreak of Chapare virus

Researchers from the CDC have found evidence of human transmission in the deadly outbreak of a mysterious virus in Bolivia. The study suggests that Chapare virus, an emerging hemorrhagic fever, can spread from person to person in healthcare settings.

The research raises concerns about the potential for future Chapare outbreaks, and also provides preliminary information about the species of rodent that carries the virus.

The Chapare virus caused at least five infections near Bolivia’s capital city of La Paz in 2019, and three of the individuals did not survive. Prior to this incident, the only record of the disease was a single confirmed case in 2004 in Chapare Province, about 370 miles east of La Paz. 

All that was initially known about the Chapare virus was that it may produce symptoms similar to diseases such as Ebola.

The recent outbreak sparked a rapid mobilization of infectious disease experts from Bolivia’s Ministry of Health, the CDC, and the Pan-American Health Organization (PAHO). The team explored the origins of the disease by securing samples from patients and developing a new diagnostic test.

“Our work confirmed that a young medical resident, an ambulance medic and a gastroenterologist all contracted the virus after encounters with infected patients – and two of these healthcare workers later died,” said Dr. Caitlin Cossaboom. “We now believe many bodily fluids can potentially carry the virus.”

Dr. Cossaboom said the confirmation of human-to-human transmission shows healthcare providers and anyone else dealing with suspected cases must take extreme care to avoid contact with items that may be contaminated with blood, urine, saliva, or semen. 

The medical resident who died from the disease may have been infected while suctioning saliva from a patient, while the ambulance medic who survived was likely infected when he resuscitated the same medical resident as she was being transported to the hospital.

Furthermore, the team detected viral RNA in the semen of one survivor 168 days after infection, which indicates the potential for sexual transmission. Further investigation is needed to identify other possible routes of transmission.

The Chapare virus belongs to a group called arenaviruses. This group includes extremely dangerous pathogens such as Lassa virus, which causes thousands of deaths every year in West Africa. These pathogens can cause hemorrhagic fevers – a condition that triggers severe problems across multiple organs. 

Dr. Cossaboom said that patients in the 2019 Chapare outbreak suffered fevers, abdominal pain, vomiting, bleeding gums, skin rash, and pain behind the eyes. There is still much that remains unknown about the Chapare virus, such as where it originated, how it infects humans, and the likelihood of larger outbreaks.

The researchers did come up with a few new clues about the mysterious disease, however. They detected Chapare viral RNA in rodents collected from an area around the home and nearby farmlands of the first patient identified in the 2019 outbreak. While it has not yet been determined that rodents transmitted the disease to humans, the rodents that tested positive are found across Bolivia and several neighboring countries. 

Scientists believe the Chapare virus may have been circulating in Bolivia for several years, and that infected patients could have been misdiagnosed as suffering from Dengue, which is common in this region and produces similar symptoms.

Dr. Maria Morales-Betoulle said that when it became clear the illness was not caused by Dengue, patient samples collected by Bolivian authorities were quickly moved to a highly secure biosafety level 4 (BSL-4) CDC laboratory. 

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

According to Dr. Morales-Betoulle, the availability of new sequencing tools allowed CDC experts to rapidly develop a test for Chapare, which is the same type of test often used to diagnose COVID-19 and is considered the gold standard.

The experts said that future work will focus on conducting surveillance with the diagnostics test to identify additional human infections and using field studies to determine whether rodents are involved in spreading the disease. 

“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 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.”

The research was presented at the American Society of Tropical Medicine and Hygiene 68th Annual Meeting.

By Chrissy Sexton, Staff Writer

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