The World Health Organization (WHO) reported on June 5 the first-ever case of a human infection with H5N2, a different strain of avian influenza. What is avian flu?
Avian influenza is an infectious viral disease of birds. Avian flu viruses do not normally infect humans. However, there have been instances of certain highly pathogenic strains causing severe respiratory disease in humans. Most infected people had been in close contact with infected poultry or with objects contaminated by their feces. Nevertheless, there is concern that the virus could mutate to become more easily transmissible between humans, raising the possibility of an influenza pandemic.
Influenza viruses are normally highly species-specific, meaning that viruses that infect an individual species stay “true” to that species, and only rarely spill over to cause infection in other species. Of the hundreds of strains of avian influenza A viruses, only four are known to have caused human infections. In general, human infection with these viruses has resulted in mild symptoms and very little severe illness, with one notable exception: the highly pathogenic H5N1 virus.
How does it spread?
All evidence to date indicates that close contact with dead or sick birds is the principal source of human infection. Especially risky behaviors identified include plucking, slaughtering and preparation for consumption of infected birds. In a few cases, exposure to chicken feces is thought to have been the source of infection. Swimming in waters where carcasses of dead infected birds have been discarded or which may have been contaminated by feces from infected birds might be another source of exposure.
Research is urgently needed to better define the exposure circumstances, behaviors, and possible genetic or immunological factors that might enhance the likelihood of human infection.
What are the symptoms?
Current data for H5N1 infection indicates an incubation period ranging from two to eight days and possibly as long as 17 days; however, the possibility of multiple exposures to the virus makes it difficult to define the incubation period precisely.
Initial symptoms include high fever and influenza-like symptoms. Diarrhea, vomiting, abdominal pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some patients. On present evidence, difficulty in breathing develops around five days following the first symptoms. Respiratory distress, a hoarse voice, and a crackling sound when inhaling are commonly seen. Almost all patients develop pneumonia.
What is the cure?
Limited evidence suggests that some antiviral drugs; notably oseltamivir, commercially known as Tamiflu; can reduce the duration of viral replication and improve prospects of survival, provided they are administered within 48 hours following symptom onset. However, such antiviral drugs were developed for the treatment and prevention of seasonal influenza, which is a less severe disease associated with less prolonged viral replication.
What is the situation?
H5N1 avian influenza in humans is still a rare disease, but a severe one that must be closely watched and studied, particularly because of the potential of this virus to evolve in ways that could start a pandemic.
References
Adapted from the official website of the World Health Organization (WHO)
http://www.who.int/topics/influenza/en/
Image source. Getty Images.