National Geographic : 1994 Jul
Threats in the wild * A knack for hitchhiking in animal hosts makes many viruses that devastate humans hard to control. In northern Brazil a mosquito caught in a vial (below right) may have picked up the yellow fever virus from a mon key that carried it with no ill effects. When a virus-bearing mosquito bites an unvacci nated human, a potentially fatal fever ensues - along with jaundice, which gives the disease its name. Tissue and blood samples from a monkey killed for meat by hunters (below) will help define an area of yellow fever infection so that health workers can target villages for vaccination. A rat trapped with the utmost care in Sierra Leone (left) will provide information about the lethal Lassa fever virus, first identified in 1969. Rats carry the virus, likely transmitting it through their urine and fecal deposits in houses they infest. Do villagers inhale the virus with dried excreta or ingest it with contam inated food? The pathway remains unknown. As Ethleen Lloyd, a public health analyst at the Centers for Disease Control and Preven tion in Atlanta, Georgia, notes with a smile, "We don't have any volunteers for infection." What is known: Blood and other body fluids from victims are highly contagious.