Diseases Affecting Horses And Humans

Benefits of NAIS

By Charles Hulsey
©Voice, February 2006


The National Animal Identification System (NAIS) is a tool developed to ensure the health of the national livestock herds by facilitating the traceback and traceforward of animals associated with a significant disease outbreak.

Horses can contract infectious diseases that they can pass on or transmit to humans with examples being Rabies, Salmonella, Ringworm, Leptospirosis, Burcellosis and Anthrax. In addition, there are several diseases that are common to horses and to other livestock species as well as to humans, which are considered multispecies diseases.

• Anthrax – Anthrax is an acute infectious disease that commonly occurs in wild and domestic lower vertebrates (cattle, sheep, goats, horses, camels, antelopes and other herbivores) can also be transmitted to humans exposed to infected animals or tissues from infected animals.

• Borna Disease – Borna disease (BD) is a fatal neurological disease of horses and sheep.

∑ Brucellosis – Horses have been known to contract brucellosis and on occasion, been a source of human infection.

• Encephalomyelidities (West Nile Fever, Eastern, Western) – horses do not play a role in transmission of these diseases to humans. The same infection occurs in horses and in humans. All three diseases occur in the U.S. However, horses do play a role in the transmission of another mosquito-borne disease, Venezuelan Equine Encephalomyelitis (VEE), to humans.

• Glanders – Glanders is one of the oldest known equine diseases that are of important biosecurity concern. It is a disease of horses, mules and donkeys. Glanders is not currently found in the U.S. It is a disease that can be spread from horses to humans and it was used as a biological warfare weapons by the German army in World War I. The disease continues to exist in various parts of the world, including both eastern and western hemispheres. The U.S. requires that all horses imported into the U.S., including those temporarily exported for competition purposes be tested negative for Glanders before being permitted entry (or re-entry as the case may be).

•∑ Hendra Virus Disease – This is a relatively new and emerging disease. It causes a severe respiratory illness in horses which is very frequently fatal. Humans having direct contact with blood or saliva of an infected horse are in danger of contracting the disease.

∑ Japanese Encephalititis – Japanese encephalitis (JE) is capable of causing serious infection of the central nervous system (CNS) of humans. Swine are very susceptible to the infection and are also amplifiers of the virus. Less frequently, horses become infected with the disease. Under experimental conditions, however, horse-to-horse transmission has been demonstrated.

•∑ Leptospirosis – Leptospirosis is a disease that affects humans and many animal species. Outbreaks usually result from exposure to water contaminated with the urine of infected animals. Organisms have been found in cattle, pigs, horses, dogs, rodents and wildlife.

•∑ Rabies – like other mammals, horses can be infected with rabies virus and be
a source of infection for humans.

•∑ Ringworm – Ringworm is a skin disease and numerous species of animals can transmit ringworm to people including horses.

•∑ Salmonellosis – This disease is frequently associated with poultry. However, strains of salmonella can infect horses and they constitute a risk for humans. There are strains that exhibit resistance to multiple antibiotics. These represent a significant health risk to horses as well as to humans.

•∑ Screwworm - Although Screwworm infestation in humans is rare, it can, and does occur. Horses infested with Screwworm, like other livestock, could be a source of infection for humans.

•∑ Tetanus – Tetanus is an uncommon but often fatal disease that affects the central nervous system. The bacteria gain entry to the body, through a wound or cut exposed to contaminated soil, dust, or manure. Horses and humans are the most susceptible of all the animal species to tetanus.

•∑ Venezuelan Equine Encephalomyelitis – VEE is a fatal to both horses and humans and horses do play a role in its transmission. The last outbreak occurred in 1971 when the disease spread from South American up through Central America and Mexico into Brown County, Texas, killing tens of thousands of horses and humans during that epidemic. VEE is considered a very serious biosecurity threat because of its highly infectious nature and its significant human health impact.

•∑ Vesicular Stomatitis (VSV) – This is another disease that is common to cattle, sheep, swine and horses as well as humans. It requires laboratory confirmation to distinguish VSV from Foot and Mouth Disease. Direct contact with VS lesions reportedly can spread the virus from animals to humans.

Important Diseases

Import quarantine and post-entry testing are important components in thwarting the introduction of foreign animal diseases, such as Glanders, but it does not entirely guarantee that these diseases won’t appear here, either through natural or intentional introduction. Vector borne diseases such as VEE and VSV can be introduced without necessarily importing infected animals.

Emerging Diseases

Emerging diseases are always a concern. Although it is rare for viruses to jump from one species to another, it does happen. Recently, equine influenza virus was isolated from greyhound racing dogs in Florida after the animals began to show signs of respiratory illness.


Undoubtedly, this list is not fully inclusive of all diseases that may be common between humans or that can be passed from horses to humans. Clearly, some equine diseases do have public health impact. Horse owners must be knowledgeable and aware of the diseases that are common to horses and other livestock species and to humans. A severe outbreak of any of these diseases would have a substantial veterinary and economic impact on the U.S., and on the horse industry. It is for this reason that the horse industry must be included in the National Animal Identification System.

We wish to acknowledge the kind of assistance of Dr. Peter J. Timoney, Chairman and Director of the Department of Veterinary Science at the University of Kentucky, in the development of this paper.

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