There is a strain of the influenza virus called H5N1 that is highly lethal for wild birds and
domestic fowl (chickens, ducks, etc.). It has caused major outbreaks in domestic chicken flocks
during recent decades. On rare occasions, this virus has infected humans who were in very close
contact with infected chickens. Since 1997, HPAI H5N1 virus infections have infected
approximately 900 people in 22 countries, with about a 50% fatality rate.
In the past few years, this virus has infected mammalian species such as cats, dogs, mink, foxes,
among others. However, during the last week, media have reported the first-ever cattle infections
with this highly pathogenic avian influenza A (HPAI) H5N1 in at least 6 states. The cows likely
contracted the virus from infected wild birds. It appears to be causing only mild illness in cows.

Human Case

Of some concern is the report of a Texas dairy farm worker who tested positive for H5N1 after
exposure to presumably infected cattle. The symptoms were mild and the patient is recovering.
The question is whether or not the virus has mutated to be able to infect and spread among
humans to cause another pandemic. To answer this question the US CDC has examined the
genetic sequences of the Texas virus. There were minor differences between the human specimen
and those collected from cattle, but both maintain primarily avian genetic characteristics.
Overall, this sample lacks changes that would make the virus better adapted to infect mammals.

Summary

As a result of these early studies, the US CDC considers that the risk assessment for the general
public remains low. However, people with close or prolonged, unprotected exposures to infected
birds or other animals, including livestock, or to environments contaminated by infected birds or
animals, are at greater risk of infection. Nevertheless, pasteurized milk is safe to drink, although
raw milk should be avoided.
Given the lack of either mutations or other signs that would favour transmission to humans, the
risk of exposure for the general traveller is nil. However, only time and careful surveillance will
prove that the Texas case is just an isolated event. But I am concerned that the H5N1 strain that
has been around for decades worldwide may be mutating to adapt to humans.

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