Early recognition of new and re-emergent diseases in horses is crucial if their impact is to be minimized, an expert in equine virology says.
Dr Peter Timoney, with the Maxwell H. Gluck Equine Research Center at the University of Kentucky, says a wide range of factors involving an infectious agent, host, or the environment can contribute to the occurrence of an emergent or re-emergent disease.
These can include microbial change and adaption, host susceptibility to infection, climatic factors, altered ecosystems, population demographics, trends in international trade and land use.
Timoney, writing in the latest issue of Equine Disease Quarterly, says the number of emergent and re-emergent diseases in humans, animals and plants continues to increase as more sophisticated technologies become available that enable detection of previously undiscovered infectious agents.
There are various examples of re-emergent diseases, most of them viral.
He cited the emergence of a strain of equine influenza virus, influenza-A/equine/ Jilin/89 (H3N8), in China in 1989, which gave rise to very high morbidity and associated case-fatality rates in the equine population exposed to this particular strain of virus.
Fortunately, the Jilin/89 strain of H3N8 virus did not spread beyond China.
Other examples that qualify as re-emergent were the outbreaks of Venezuelan equine encephalomyelitis caused by subtype 1E strains of the virus that occurred in Chiapas and Oaxaca states in Mexico in 1993 and 1996.
Both disease events were associated with unprecedented clinical-attack rates and moderate case-fatality rates.
Before these occurrences, subtype 1E strains of the virus were not known to cause significant disease and losses in horses.
The most widely known re-emergent disease of horses is equine herpesvirus-1 myeloencephalopathy, he says.
“The occurrence of more virulent strains of the virus has been responsible for major outbreaks of disease especially over the past 15 years, both in Europe and North America.”
The enhanced ability to affect nerve tissue is largely associated with a single point mutation in the gene.
“Infection with these strains of virus has on occasion resulted in significant clinical disease and a high mortality rate.”
Timoney said diseases can be regarded as re-emergent if they occur in a different epidemiologic setting. Examples of two diseases involving horses include West Nile encephalitis and equine encephalosis.
West Nile virus, first discovered in the United States in 1999, has been responsible for significant annual losses in unvaccinated horses.
“Confirmation of equine encephalosis in Israel in 2008 was the first time this disease was reported outside of the African continent,” he says.
“Undoubtedly, there will be additional new and re-emergent equine diseases in the years to come, some of which may have significant economic consequences for the equine industry in certain countries.
“Early recognition of such diseases is of paramount importance if their impact is to be minimized.”
Equine Disease Quarterly is funded by underwriters at Lloyd’s, London, brokers, and their their Kentucky agents.