New virus puzzles scientists

The scientists have been trying to find out how this farmer and another Missouri man contracted a severe viral disease—a new one,never seen before. It put both men in the hospital for more than a week with high fevers,diarrhea,nausea,muscle pain,low blood cell counts and liver abnormalities.

Scientists at the Centers for Disease Control and Prevention think the men were infected by lone star ticks,meaning that there may be a frightening new addition to the list of tick-borne dangers that includes Lyme disease,babesiosis and Rocky Mountain spotted fever.

But despite scouring the countryside,investigators have found neither ticks nor animals carrying the new virus. So far,the two men in Missouri are the only humans known to have been infected. The cases are a stark reminder that new infectious diseases can still emerge,frequently from unknown bacteria and viruses that lurk in animals.

The disease first appeared in Missouri in June 2009,when Robert Wonderly,then 57,a factory worker who lives on a farm,suddenly fell ill. For several days he felt weak,feverish and irritable. Then his chest began to ache. When his wife told a nurse that she had found a tick embedded in his skin the day before he became ill,the nurse called in an infectious diseases expert,Dr. Scott M. Folk.

Folk immediately suspected ehrlichiosis,a bacterial disease that is carried by ticks and is common in the area. So he prescribed the standard treatment,the antibiotic doxycycline. In the meantime,he sent a sample of Wonderly’s blood to Atlanta to be tested at the CDC. Not surprisingly,the test for ehrlichiosis came back negative,and Folk was left puzzled by his patient’s strange illness.

Just a few weeks later,it happened again: A second patient,the owner of the 100-acre farm,seemed to have come down with a severe case of ehrlichiosis. Working outdoors in the weeks before,he had come home day after day with 20 or more ticks embedded in his flesh and had plucked them out. Again,doxycycline did not work,and the test for ehrlichiosis was negative.

But CDC researchers found something else growing in the lab cultures: a virus—a member of a group called phleboviruses,which are carried by sand flies,mosquitoes or ticks. The new virus is closely related to one recently discovered in China that has caused severe illness and even some deaths. They are the only two tick-borne phleboviruses known to cause disease in humans.