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Equine Infectious Anemia Jeske Noordergraaf, VMD January 2006 |
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In the December issue of Horse & Family, there was a question regarding Equine Infectious Anemia and its prevalence. I would like to take this opportunity to explain the disease and its risk factors. Equine Infectious Anemia (EIA) is a serious disease that affects only horses. It is caused by a lentivirus, the type of virus that causes slowly progressive, often fatal diseases. The virus is a close relative to HIV, which causes AIDS in people, and everyone knows how serious that is. Unfortunately, there is no current treatment for EIA, no vaccine to prevent it, and no cure. Thus, we are trying to prevent the spread of the disease by identifying the horses that carry the virus. Transmission EIA is considered a classic blood borne infection. People have played an important role in EIA transmission over the years when using an item that is contaminated with blood (such as a needle) on several different horses. Now EIA is most frequently transmitted between horses in close proximity by large biting insects such as horseflies and deerflies. The bites from these flies make the horse move, which may result in the interruption of blood feeding. The fly is motivated to complete the feeding, and attacks a second host. In this manner, any infective material from the blood of the first host that is present on the mouthparts of the insect can be mechanically transmitted to the second host. Insect transmission of EIA is dependent on the number and habits of the insects, the density of the horse population, the number of times the insect bites the same and other horses, the amount of blood transferred between horses, and the level of the virus in the blood of the affected horse from which the initial blood meal was obtained. The rate of transmission cannot be predicted accurately because of these variables. Diagnosis EIA is challenging to diagnose because the symptoms vary from one horse to the next and can mimic other diseases such as influenza, anthrax and equine encephalitis. When a horse is first exposed to the EIA virus, it may develop a high fever, depression, limb swelling and anemia. One-fifth of a teaspoon of blood from this horse contains enough virus to infect one million horses. If the horse survives this acute stage, it may develop recurring clinical disease with the following signs: spiking temperature, depression, weight loss, dependent edema, and anemia. One-fifth of a teaspoon of blood from a chronic case during a feverish episode contains enough virus to infect 10,000 horses. The majority of horses with the EIA virus are inapparent carriers – they show no signs of disease – and only 1 horsefly out of 6 million is likely to pick up and transmit the disease from this horse. However, these horses remain carriers all their life, and severe stress or illness may make the disease acute once again, with the number of virus in the blood increasing. Prevention How can we prevent this disease?
Control Diagnosis of EIA is done using the Coggins test. Controlling the spread of the disease involves eliminating contact between positive and negative horses. Once the reservoirs of EIA are identified and isolated, the transmission is stopped. However, until all horses are tested, each horse is a potential reservoir of the virus. Prevalence There are currently 12 affected horses in Minnesota as of August 2005, with the total number of cases since 1996 being 160. Most of these horses will die or be euthanized to stop the spread of the disease. Anyone can research these numbers – EIA is a reportable disease and is regulated. The best sources are the United States Department of Agriculture (USDA-APHIS), and the MN Board of Animal Health. Here are their websites: www.aphis.usda.gov/lpa/pubs/eiaumr.pdf www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_aheia.html We, as veterinarians, take this testing seriously. There is a warning on the testing form which states that falsifying information on the form is a felony. The test is also labor intensive, as we need to draw the horse’s markings, fill out personal information on the horse, address for the owner and where the horse is stabled. The blood and form then need to be sent to a certified lab. These labs are tested and inspected every year to ensure they are in compliance with federal laws. So although just drawing blood from most horses is easy, there is much more involved. This is why takes time to get the results back is. Plan ahead for EIA testing to avoid delays and extra fees before show season!! |
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