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Medical Discovery: Some Peruvian Amazon Natives Survive Rabies Without Treatment

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Since ancient times, the specter of rabies has struck fear in people’s hearts, minds and souls. Now, a new study turns the notion that an untreated bite by an infected animal means a certain frenzied death sentence on its head.

Scientists from the U.S. Centers for Disease Control and Prevention (CDC) surveyed two Peruvian Amazon jungle communities regularly affected by rabies outbreaks over the past two decades, and discovered that some victims had developed antibodies to the rabies virus without medical treatment.

The collaborative research with the Peruvian Ministry of Health studied the knowledge, attitudes and practices among Peruvians exposed to vampire bats. “These are very small villages and, when they witness ten people dying from what is a horrible disease, it is incredibly traumatic," lead study author Dr. Amy Gilbert said. “The Peruvian Ministry of Health is considering pre-exposure rabies immunization campaigns among high-risk communities in the Amazon, which could benefit many peoples in and near the study area.”

Rabies is transmitted to humans through animal bites or scratches and produces a neurological disease that is—with few exceptions—prevented only by rapid follow-up immunization. And while that firmly remains the recommended course of action to prevent developing the disease, the results of the new study could change the way we treat rabies in the future.

“Despite finding rabies virus neutralizing antibodies among some persons, we do not consider such antibody-positive persons to be protected against rabies,” Gilbert said. Even those previously immunized must seek post-exposure treatment after a bite or non-bite exposure to rabies virus, and any future vaccination campaigns in this region should target all persons in the community, and should not exclude antibody positive persons.

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Bats may be important reservoirs and/or vectors of several emerging infectious diseases in the Americas, not just the recent reports of rabies outbreaks, particularly in the Amazon region but as well reported detection of coronaviruses, dengue virus, flu viruses and bartonella bacteria in certain bat species. The scientists sought to understand whether exposure of these populations to bats was associated with exposure to rabies virus or other potential pathogens associated with bats. They collected information on exposure history, suspected illness and measured the levels of rabies antibodies in blood samples from 63 villagers, none of who had received a rabies vaccine or reported previous disease symptoms.

Their report, in this month’s issue of the American Journal of Tropical Medicine and Hygiene describes evidence of exposure to rabies virus based upon laboratory results demonstrating rabies virus neutralizing antibodies in the blood of some respondents. Their protocol, approved by the CDC, and the Hospital Nacional Dos de Mayo (Peru) Institutional Review Boards complied with regulations governing the protection of human subjects.

Worldwide rabies kills 55,000 people a year. In the United States, effective vaccines, and animal control and vaccination programs that eliminated domestic dogs as virus reservoirs reduced deaths in this century to an average of two or three each year. Vampire bats live in South America and have not been found in the U.S. The vast majority of cases in this country occur in wild rabies reservoir animals like raccoons, skunks, bats and foxes—though rabies in dogs is more virulent, and causes 99 percent of rabies deaths worldwide.

A 2008 report from the U.S. National Library of Medicine National Institute of Health cited dog vaccination rates on Indian reservations may be as low as five to 20 percent. CDC Public Health Advisor and Indian Health Service (IHS) Immunization Program Manager Amy V. Groom, MPH told ICTMN she agrees the reported low dog rabies vaccination rate is alarming, but in the context of what we know about rabies in the U.S., “someone is more likely to get rabies from bats or livestock.”

Domestic animals make up a small proportion of the total animal rabies cases in the U.S. at ~8 percent in 2010, Groom said. That exposure to rabid dogs is responsible for the majority of human deaths worldwide, largely owed to dogs remaining a reservoir in other countries. In the U.S., dogs are a much smaller proportion of the animal rabies cases, and are not the main source of human infection. Cats make up the largest proportion of rabies cases in domestic animals.

Gilbert said people who may have had a bite or mucous membrane contamination with saliva of bats, or other rabies reservoir animals should immediately cleanse the wound with soap and water, and then seek medical advice. Exposures should be promptly reported to local public health authorities. “Any person that has had a potential exposure to rabies virus should receive post-exposure prophylaxis,” Gilbert said. “For persons never immunized previously, prophylaxis typically includes an injection of rabies immune globulin and five injections of rabies vaccine (although in the U.S., four vaccine injections are recommended for most persons). For persons immunized previously, rabies post-exposure prophylaxis consists of two doses of vaccine only.”