THE STORY OF A MYSTERIOUS VIRUS

Cache Valley emerges In August 1956, scientists doing routine surveillance collect a pool of Culiseta inornata mosquitoes under a bridge — and are surprised to discover a virus they have never seen before. They name it Cache Valley, after the northern Utah region where it was found.

The animal connection In 1981, Cache Valley virus is isolated from a sick sheep and healthy cow in Texas. Scientists connect the virus to previously unexplained outbreaks of newborn lamb deformities, and a causal link is later confirmed when scientists experimentally infect sheep and cattle.

A cause of human birth defects? Curious about whether Cache Valley can also cause human birth defects, researcher Charles Calisher obtains archived blood samples from 1,000 women from multiple U.S. states who participated in a rubella study between 1959 and 1964. He finds a statistically significant link between Cache Valley antibodies and macrocephaly (larger-than-normal head size).

The first human case Cache Valley virus is confirmed in a human for the first time after the New England Journal of Medicine publishes a paper on a 28-year-old man who fell sick after a deer-hunting trip in North Carolina. The man recalled being bitten several times by mosquitoes. After a long and painful disease — involving a leg ampu- tation and the loss of his ability to speak, eat or walk — the patient died from pulmonary complications in June 1996.

A second victim The second human case of Cache Valley is reported in the journal Emerging Infectious Diseases. The patient, a 41-yearold Wisconsin man, became ill and developed a severe case of meningitis in October 2003. He was discharged after three days and fully recovered.

The latest patient The third and last human case documented so far is reported in the Journal of Clinical Microbiology. In September 2011, a 63-year-old woman shows up at a hospital in upstate New York, complaining of fever, headache and neck stiffness. She develops meningitis but gradually improves and is discharged four days later. The woman suffered from lingering symptoms, however, and a year after being discharged was still struggling with worsening headaches and memory loss.

Cache Valley in Canada In the winter of 2011-12, an outbreak of Cache Valley in sheep is confirmed by laboratory testing for the first time in Canada. It causes lamb deformities in Ontario and Quebec. There have been many prior anecdotal reports of outbreaks, however, and the virus is believed to be widespread. Studies in Saskatchewan, Ontario and Quebec have found that as many as 40 per cent of sheep studied harboured antibodies.