by Kathy Rusniak

Created on: February 10, 2009

A horse with the sniffles? A pig with a sneeze? It's true, humans are not the only animals that can come down with the flu. The influenza virus, which consists of several species and subtypes, can infect a broad range of animals from the familiar horses, pigs, dogs and birds to the exotics such as seals, camels, minks and whales. Some types of influenza are particular in the type of animal they infect, while other viruses have the ability to target multiple species. While most influenza research focuses on human susceptibility and immunity, some other types of animal flu are also of interest because of their potential to occasionally spread to human populations or because of the value of the domesticated host species to humans as pets or farm and ranch stock.

Influenza A is a species with many subtypes that are widely known to be contracted throughout bird populations. Recent occurrences of the specific subtype known as avian influenza, bird flu, or H5N1 have crippled wild and domestic bird populations through both direct infection and culling (to prevent continued transmission) in Southeast Asia. Loss of bird stocks in particular farming areas has put bird farmers out of business. Of course, the possibility of avian influenza infecting human populations is also a great concern and an area of intense research.

Other variants of Influenza A are found in pig populations throughout the world. There is evidence of subtype H1N1 (different than human subtype H1N1) antibody levels in pig populations, which suggests natural exposure to the virus. However, it is increasingly common for livestock farmers to vaccinate their herds, and there is no way to differentiate between acquired and mediated immunity. This complicates estimates of the natural range of this subtype. Another subtype, H3N2, has more recently been discovered and is currently being studied for transferability between swine and human populations.

Incidents of horse flu or equine influenza, also involve subtypes of Influenza A (H7N7 and H3N8). Contracting the flu is a serious matter for horses, with strains being highly contagious and infecting almost 100% of any group where the virus is introduced. Because of the heavy reliance of humans on horses for work and the big business of racing, equine influenza can have significant economic consequences as well. Also, there are documented cases of transmission of this illness from horses to humans. In 2007 a major outbreak of horse flu occurred in Australia and

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