Equine Disease Quarterly

From University of Kentucky,  www.uky.edu

 

“Nature doesn’t break, it only bends.” This quote was recently uttered on a television drama, which depicted an infectious disease clinician fighting a catastrophic epidemic that developed following a genetic mutation of a forgotten infectious disease agent. As a pathologist and former microbiologist, this reference to the constant evolution of microbes made me ponder, once again, how such relatively simple organisms rapidly and continually adapt to their environments to survive and replicate. It is unfortunate, at least for the host, when the intricate balance between host, environment, and microbe becomes offset and results in infectious disease.

 

This theme was exemplified in April 2016 when equine infectious disease experts from around the world gathered for the 10th International Equine Infectious Diseases Conference in Buenos Aires, Argentina. The conference, which is held every four years, provides excellent continuing education for equine clinicians and brings together equine infectious disease researchers who share recent developments and breakthroughs. The five-day event addressed infectious diseases of continued and historical concern, newly recognized and emerging diseases, and important reemerging infectious diseases of the horse. These motifs were addressed in 11 separate sessions on biosecurity, diagnostics, diseases of working equids, emerging and reemerging diseases, gastroenterology, international equine movement, neurology, parasitology, theriogenology (reproduction), respiratory diseases, and infectious diseases of other systems.

 

Although I enjoyed all of the presentations, I was particularly taken with the talks on emerging and reemerging diseases. Emerging viral agents that were discussed included: equine enteric coronavirus (a potential cause of necrotizing enteritis), Theiler’s disease associated virus (the newly identified cause of equine serum sickness), and other viral causes of hepatitis (equine hepacivirus and equine pegivirus), Bunyamwera virus in Argentina (a cause of nervous disease and/or abortion), and Hendra virus (an acute fatal and zoonotic disease that frequently affects the respiratory and neurologic systems). Other interesting and noteworthy disease conditions comprised anthelmintic resistance (resistance of parasitic worms to treatment), the potential role of microbes in equine polyneuropathy, and strangles-like disease caused by Streptococcus zooepidemicus. The reemergence of West Nile virus (a cause of neurologic disease) in France and Salmonella Abortusequi (a cause of abortion and septicemia) in Argentina were also addressed. Although many of these diseases are emerging or reemerging in specific locations, one must be globally aware of them due to the increasing frequency with which equine athletes and breeding stock are transported around the world.

 

We may never break nature, but rest assured that clinicians and infectious disease researchers will continually attempt to challenge nature and develop new modalities to quickly detect, track, diagnose, treat, and hopefully learn to prevent and control infectious diseases as they occur.

 

CONTACT: 

Alan T. Loynachan, DVM, PhD, DACVP 

alan.loynachan@uky.edu

(859) 257-8283 

Veterinary Diagnostic Laboratory 

University of Kentucky 

Lexington, Kentucky

 

 

The International Collating Centeer, Newmarket, United Kingdom, and other sources reported the following disease outbreaks.

 

Three outbreaks of vesicular stomatitis in Colorado in February brought to a conclusion the 2015 occurrence of the disease in the USA. Of the eight affected states—Arizona, Colorado, Nebraska, New Mexico, South Dakota, Texas, Utah, and Wyoming—the greatest number of outbreaks was recorded in Colorado. The 823 reported outbreaks comprised 329 that were confirmed positive for the New Jersey serotype of the virus and 494 that were diagnosed based on clinical signs of the disease but not virologically verified.

 

Influenza was reported by the UK and the USA; in the latter country, the disease was considered to be endemic. Outbreaks were confirmed in California and Florida.

 

Equine herpesvirus 1 and 4 (EHV-1, -4) related diseases were recorded in Argentina, Australia, France, Germany, Ireland, Japan, South Africa, UK, and the USA. Respiratory disease caused by EHV-1 was recorded in France (two outbreaks), Germany (12 cases involving 11 premises), South Africa (two cases also with intercurrent equine piroplasmosis), and the UK (one case). Abortion due to EHV-1 was reported by Argentina (one vaccinated mare), Australia (one), France (four), Germany (three), Ireland (13 involving nine counties), Japan (51 vaccinated Thoroughbred mares on 19 premises), the UK (14), and the USA (three). Additionally, single cases of fulminant neonatal disease due to EHV-1 were diagnosed in the UK. Outbreaks of EHV-1 myeloencephalopathy were recorded in France (one 7-year-old mare with intercurrent signs of respiratory infection) and the USA (eight outbreaks at various premises). Affected states included Arizona (one), California (two), Florida (one), Georgia (one), Illinois (one), New Mexico (two), and Pennsylvania (one).

 

France, Germany, and the USA confirmed outbreaks of EHV-4 respiratory disease. Twelve outbreaks were recorded in France; the majority involved single cases of the disease. The latter was observed primarily in weanling foals in the USA. Limited evidence of EHV-2 and EHV-5 infection was recorded in the USA.

 

Strangles was reported by France, Germany, Ireland, Singapore, Switzerland, and the USA. Thirteen outbreaks, most involving single cases, were recorded in France, one in Germany, 11 in Ireland, one in Singapore, and one in Switzerland. The disease was stated to be endemic in the USA, with 42 outbreaks confirmed in 14 states, in eight of which multiple outbreaks were reported.

 

Infection with equine arteritis virus was confirmed in two stallions in Germany, each on a different premises.

 

Canada and the USA reported outbreaks of equine infectious anemia. Isolated cases on two farms in Saskatchewan were diagnosed in Canada. Infection was identified in five of 10 horses on a premises in New York, USA.

 

Equine piroplasmosis was reported as endemic by France; Switzerland recorded a single case of dual infection with Babesia caballi and Theileria equi, and the USA identified one case of T. equi infection in a Quarter Horse in New Mexico.

 

Germany confirmed the presence of Taylorella equigenitalis in four stallions and one mare. A single case of infection with equine herpesvirus-3 was diagnosed in Kentucky, USA.

 

The USA reported 11 cases of abortion due to Leptospira pomona var kennewicki and several cases of nocardioform placentitis associated with Amycolatopsis spp or Crossiella spp.

 

Outbreaks of salmonellosis were recorded by Germany (single case) and the USA (six cases associated with Salmonella Group B and six with untyped Salmonella spp). There was a single report of rotavirus infection in a foal from Germany. Three cases of infection with Lawsonia intracellularis were recorded in foals in Kentucky, USA. The USA also reported several outbreaks of clostridial enteritis in foals associated with Clostridium perfringens Toxin Type A.

 

Rabies was recorded in two horses in the USA, one each in Florida and South Carolina.

 

Rhodococcal related disease was reported as endemic in the USA, with numerous outbreaks diagnosed.

 

 

Vector-borne diseases represent a singularly serious threat to the health of humans and domestic livestock species in countries or regions of the world in which they occur. Historically, many such diseases were frequently regarded as geographically restricted in their global distribution and not considered a risk to human and animal populations in far-distant countries in other continents or possibly other hemispheres. Major disease migrations in the last 20 years, however, have undermined that sense of security. No longer can the future distribution of specific infectious agents be predicted with confidence. This was most recently exemplified by the explosive and unexpected spread of Chikungunya and Zika viruses, both human pathogens, from where they were originally identified in Africa many years ago. Concerns are further highlighted by the risk of spreading yellow fever from Angola, Republic of Congo, and Uganda to European Union member states and even further afield to inter-tropical zones in the Americas and Asia.

 

The most significant group of emerging human and animal diseases is caused by arboviruses such as West Nile, Chikungunya, and Zika; they are single stranded RNA viruses which have spontaneous mutation rates as high as one base per 1,000 bases for each replication cycle. Arboviruses are transmitted in nature by arthropod vectors. With the exception of African swine fever virus, all arboviruses of medical or veterinary medical importance belong to one of the following four families: Bunyaviridae, Flaviviridae, Reoviridae, and Togaviridae. They are maintained in nature by cycling between a host (mammal, bird, reptile, amphibian) that is infected with a particular virus and a vector (mosquito, tick, sandfly, midge) that is a carrier and transmits the virus to other hosts.

 

Some of the most important viral diseases of humans are caused by arboviruses, many belonging to the Flaviviridae and Togaviridae families. These include the following notable examples: yellow fever, dengue fever, Japanese encephalitis (JE), West Nile encephalitis (WNE), Zika virus infection, Eastern and Western equine encephalomyelitis (EEE and WEE), Venezuelan equine encephalomyelitis (VEE), and Chikungunya virus infection. Arboviruses are also the cause of a number of highly significant equine diseases, the most important of which are African horse sickness (Reoviridae), VEE, EEE, and WEE (Togaviridae), JE, WNE, and Murray Valley encephalitis (Flaviviridae). It is evident from the foregoing that many of the listed equine diseases are caused by zoonotic pathogens.

 

Of major concern in assessing the health impact of arboviral diseases is the potential of the causal agents to evolve, giving rise to strains of enhanced pathogenicity for humans or animals. This is well exemplified by the emergence of variants of West Nile virus (lineage 2) in Europe that are highly pathogenic for horses. The same phenomenon has also been observed with respect to human infection with Chikungunya virus and most recently, also, with Zika virus. There is mounting evidence that strains of Zika virus have acquired marked neurotropic tendencies, being implicated as a cause of neurologic defects in unborn infants and an increased incidence of Guillain-Barre syndrome in people.

 

It is highly likely we will face future threats from the emergence of other arboviruses with epidemic potential. If we are to be successful in preventing such a threat becoming a reality, we need to identify those viruses with the potential for emergence and gain a greater understanding of their biology and epidemiology, complemented by development of more effective vector control strategies, active surveillance, and enhanced ability to diagnose such infections.

 

CONTACT: 

Peter Timoney, MVB, MS, PhD, FRCVS 

ptimoney@uky.edu

(859) 218-1094 

Maxwell H.Gluck Equine Research Center 

University of Kentucky 

Lexington, Kentucky

 

 

Source: University of Kentucky