Dealing with Emerging Infectious Diseases

Scientists are becoming increasingly concerned about the marked and persistent development of emerging infectious diseases--infections that are new to a population or geographic area, have appeared more frequently, or have become more virulent (able to cause disease).

Within the past two decades, the list of emerging infectious diseases and pathogens of clinical relevance to the equine industry has expanded and now includes: the equine herpesvirus-1 neuropathogenic mutant; equine multi-nodular pulmonary fibrosis; Clostridium difficile; equine protozoal myeloencephalopathy (EPM), and; methicillin-resistant Staphylococcus aureus (MRSA), among others.

Within the North American equine populations, likely the best example of an emerging infectious disease is West Nile virus (WNV).

"Prior to 1999, WNV was not recognized in the United States," explained Josie Traub-Dargatz, DVM, MS, Dipl. ACVIM, professor of equine medicine at Colorado State University, "Now, the WNV equine vaccine is the most commonly administered vaccine among equine operations that vaccinate against one or more diseases, which illustrates a rapid and broad response by veterinarians and equine owners that were faced with an emerging disease."

Infectious diseases are on the rise, and horse owners and veterinarians are responding to this challenge by becoming increasingly cognizant of abnormal behaviors in horses. Owners, with the assistance of their veterinarians, possess the ability to recognize new diseases.

What has caused this surge in emerging infectious diseases?

According to Barbara Bischoff, DVM, veterinary analyst from the Centers for Emerging Issues at the USDA's Animal and Plant Health Inspection Service, a variety of factors are thought to contribute to the development of an emerging disease.

"In general, shifts in the environment-host-agent triad result in the opportunity for an emerging disease to develop," said Bischoff.

The most common causes of emerging infectious diseases include:

  • Climate change or other environmental changes that can potentially impact the life cycle of the vectors (e.g., insects and other animals);
  • Urban sprawl of humans and horses into geographic areas that are home to animals or insects that can transmit viruses, bacteria, or parasites;
  • Alterations in host factors such as immune capabilities of horses (perhaps via changes in management practices);
  • Globalization of humans and animals that provides unique opportunities to potentially spread disease; and
  • Changes in the agent (virus, bacterium, parasite) itself at a cellular level such as the shifting or drifting of genetic material.

"Because it is challenging to predict what the next emerging diseases might be, the best way to protect horses is to contain potentially contagious diseases via hygiene and isolation measures, until targeted intervention strategies (such as vaccination) are available," suggested Traub-Dargatz. "Other control measures could include insect or rodent management to control spread of infection, depending on the mode of transmission."

While it may not be possible to predict the next "big" infectious disease in horses, recent technological advances permit the relatively rapid development of diagnostic tests as well as vaccines, as evidenced by the rapid vaccine development subsequent to the WNV outbreak.

Emerging infectious diseases also have an obvious economic impact on the horse industry. For example, in 2002 WNV-associated costs in Colorado and Nebraska alone were $4 million; these included such factors as cost of treatment, loss of use, loss of horse, and cost of vaccinations.

"Nonetheless, beneficial impacts to the equine industry include an increased awareness of emerging diseases, increased biosecurity measures on the owner's part, an increased co-operation between owners and veterinarians in the face of new or abnormal clinical signs of disease, and an impressively rapid rate of developing diagnostic tests and safe, effective vaccines as we saw following the emergence of WNV," concluded Bischoff.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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