Cause and Frequency

B virus infections in people are usually caused by macaque monkeys. These kinds of monkeys are commonly infected with B virus, but they usually do not have symptoms, or have just mild disease. Other primates, such as chimpanzees and capuchin monkeys, can become infected with B virus and will frequently die from these infections. There have not been documented cases of such primates spreading B virus except to macaques.

B virus infections in people are rare. Since B virus was identified in 1932, only 50 people have been documented to have infections; 21 of them died. Most of these people got infected after they were bitten or scratched by a monkey, or when tissue or fluids from a monkey got on their broken skin, such as by needle stick or cut. In 1997, a researcher died from B virus infection after bodily fluid from an infected monkey splashed into her eye.

Hundreds of bites and scratches occur every year in monkey facilities in the United States, but people rarely get infected with B virus. A study of more than 300 animal care workers showed that none had B virus infection, including the 166 workers who had possible exposures to monkeys.