African Horse Sickness: Potential Threat for Disease-free Countries

It is a dreaded, non-contagious, vector-borne disease with the potential to kill 50% to 95% of affected horses. The etiological agent of AHS is an RNA virus belonging to the family Reoviridae, genus Orbivirus, that is transmitted naturally by species of Culicoides or midges.

There are nine antigenically distinct serotypes of the virus. While the primary host species are members of the family, Equidae, evidence of infection has also been found in African elephants, black and white rhinoceroses, camels and dogs, none of which are considered epidemiologically significant.

Historically, AHS was considered restricted to tropical and subtropical regions of sub-Saharan Africa, where it had been known to occur regularly for over 200 years. Although infrequent, the disease has spread from west and north Africa to various southern European or Middle Eastern countries.

The most significant such event occurred between 1959 and 1963 when serotype 9 of AHS virus spread out of Africa into and throughout the Middle East, as far north as Turkey, and extended as far east as Afghanistan, Pakistan, and India. Concern over the risk that AHS poses for horse industries in Europe has been keenly felt for some time. Southern European countries are faced with the potential threat of disease introduction from migration of the virus northwards from regions in Africa, where the disease is endemic.

Spread of the virus could result from the movement of nomads and their animals, passive wind-borne carriage of infected Culicoides over long distances, and legal or illegal trade in zebra from countries where the disease is currently active. A similar if not greater risk exists for the Middle East which experienced incursions of AHS more frequently than any other region or country. As the most recent occurrence of AHS in Thailand has shown, distance is no guarantee of safety from the risk of introduction of this disease. Thailand is approximately 6,000 miles distant from where the virus responsible for this event probably originated, and the furthest east in Asia where AHS has ever been recorded.

The most plausible explanation as to the source of virus lies in the fact that a shipment of zebra arrived in Thailand three to four weeks before the first AHS outbreak of the disease was discovered. Zebra are considered the natural reservoir of the virus, developing viremias lasting up to 40 days. This would not be the first occasion that importation of zebra from a country in which AHS is a seasonal occurrence has been implicated in the introduction of disease into a disease-free country. A shipment of zebra was the confirmed source of this virus for a major disease event that occurred in Spain in 1987 and subsequently involved Portugal and Morocco. International trade in wildlife, both legal and illegal, is believed to have increased significantly in recent years. What happened in the Iberian Peninsula in 1987 and Thailand in 2020 highlights the inherent risks of introducing a disease, such as AHS, into previously disease-free countries.

The influence of climate change and global warming on the epidemiology of AHS must also be considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures and reduced rainfall over a period of years has resulted in more widespread geographic distribution of some of the major vectors of AHS, especially C. imicola, in southern Europe. An increase in ambient temperature can influence not only the life cycle of the Culicoides vector but also replication of the virus in the vector. As temperatures rise, the infection rate in Culicoides midges increases and transmission of the virus can occur sooner, however there is a concomitant decrease in the survival rate of the adult Culicoides.

The overall result of these changes is a higher transmission rate of the virus in a country possibly at risk of the introduction of AHS. The occurrence in Thailand and the very recent confirmation of AHS in Malaysia underscore the importance of increasing awareness and familiarity with this dreaded disease among animal health officials, veterinarians and members of the equine industry around the world. The potential consequences of AHS for the health of a country’s equine population and economy highlight the need for an adequate level of national preparedness in a) minimizing the risk of introduction of this disease, b) maintaining a program of active surveillance for the disease and c) having a response plan in place in the remote event of the introduction of the disease.

The take-home message from past and recent occurrences of AHS is that there is no room for complacency over the potential threat it represents for disease free-countries. CONTACT: Peter Timoney, MVB, MS, PhD, FRCVS ptimoney@uky.edu (859) 218-1094 Maxwell H. Gluck Equine Research Center University of Kentucky Lexington, Kentucky Consequences of Wildfires on the Health of Horses efforts may need to be postponed, and horses with massive smoke exposure may need four to six weeks to recover completely from lower airway inflammation.

Horses with elevated respiratory rates or persistent cough may require veterinary intervention, including bronchial dilators, airway hydration, and further testing. Smoke inhalation from immediate association with fire can produce thermal injury to the lungs from hot gases and the toxic effects of the smoke components. Often these horses also show evidence of thermal skin injuries. Thermal injury burns to the skin, eyes, limbs, and hoofs can be seen in horses exposed to excessive heat and flames. Horses can incur first-, second-, and third-degree burns. The extent of affected body surface area and the degree of burns can determine prognosis. Equine burn victims may require daily treatments lasting several weeks. Flight-related injuries may be diverse and occur when horses are fleeing the loud noises associated with rapidly approaching wildfires and related responses of emergency personnel and fire suppression vehicles.

Horses left behind during evacuation may remain uninjured by the fire. However, they can be without food and water for extended periods, because owners are often prevented from returning to the affected area for several days. Horses are frequently evacuated from areas at risk. Evacuation carries many risks to horses associated with trailer loading mishaps and injuries, exposure to infectious diseases due to housing in new areas with high densities of horses, and Swelling of the supraorbital fossa, eyelids and facial tissues, and bilateral tearing of a horse affected with the cardiac form of African horse sickness. COURTESY DR. M. RODRIGUEZ 2 3 Correspondence should be addressed to the editors, Department of Veterinary Science, Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, Kentucky USA, 40546-0099 Telephone (859) 257-4757 Fax (859) 257-8542 Internet address: http://gluck.ca.uky.edu/ equine-disease-quarterly Material published in the Quarterly is not subject to copyright. Permission is therefore granted to reproduce articles, although acknowledgment of the source and author is requested.

The University of Kentucky is an Equal Opportunity Organization. Printed on recycled paper Equine Disease Quarterly Editors Peter Timoney Alan Loynachan Rebecca Ruby Staff Diane Furry Tawana Brown Dennis Duross 4 INTERNATIONA L N ATIONA L African Horse Sickness: Potential Threat for Disease-free Countries Second Quarter 2020 Wildfires have become the new normal for many areas of the world, and subsequent health consequences have emerged as an important problem affecting large numbers of horses. For those of us in California with a Mediterranean climate, large areas are affected by unrelenting fires, which produce a particular challenge to horse owners and those providing veterinary care.

There is a paucity of education and training in disaster and emergency response in veterinary curricula, including the health consequences of wildfires. Wildfires can create health problems in horses by direct and indirect exposure to flames and smoke, injury during flight or evacuation, and/or disruption of the horse’s food and water sources.

Wildfire-smoke health effects include primary smoke exposure with direct smoke inhalation and secondary smoke-related air quality issues in areas adjacent to fires where smoke has permeated the environment. Wildfire smoke reduces air quality. It contains small amounts of the toxic gases within the smoke and particulate matter, soot, and other substances depending on what has burned.

Particulate matter within smoke is microscopic and quickly descends into the lower airways of horses producing bronchial and pulmonary inflammation. Eye and nasal irritation, coughing, and increased respiratory efforts may be observed primarily in horses with a history of heaves or recurrent airway obstruction disorders. Published daily reports of air quality indexes that guide humans should be considered for determining horse-related activities. Events that induce increased respiratory The International Collating Centre, Newmarket, United Kingdom, and other sources reported the following disease outbreaks.

The Republic of South Africa (RSA), the Kingdom of Eswatini (SZ), and Thailand reported outbreaks of African horse sickness (AHS). AHS was confirmed in all nine provinces in the RSA, with the majority of cases in Gauteng Province. A single case was recorded in SZ. Outbreaks of AHS continued in Thailand, with multiple cases confirmed in 11 provinces. Estonia, France, Germany, the Netherlands, the UK, and the USA reported outbreaks of equine influenza ranging from one (Estonia), two (Germany), three (UK), four (France and the Netherlands), to at least five in many states (USA), where the disease is endemic. Although diagnosed primarily in unvaccinated or partially vaccinated horses, isolated cases were also seen in vaccinated animals.

Strangles is considered endemic in most countries with outbreaks reported from Belgium (one), France (seven), the Netherlands (16), Switzerland (four), and the USA (38 outbreaks in 17 states). Equine herpesvirus 1 (EHV-1) related diseases are believed endemic in most countries and were confirmed by Belgium, Canada, France, Germany, Ireland, Japan, the Netherlands, the UK and the USA.

Respiratory disease outbreaks were recorded by Belgium (two), France (two), Ireland (eight), Japan (one), the Netherlands (one), the UK (two) and the USA (one). EHV-1 abortion was reported by France (two outbreaks, single cases), Germany (one case), Japan (three outbreaks, one or two cases apiece), the Netherlands (two outbreaks, one involving two cases and a case of neonatal mortality, and another, a single case), the UK (three outbreaks, one involving multiple cases of respiratory disease, one neonatal mortality and three of neurologic disease; a second, involving three cases of neonatal mortality; and a third, a case of neonatal mortality). EHV-1 neurologic disease was confirmed by Canada (three outbreaks, one involved three cases; another, a single case; and a third, five cases with three having to be euthanized), and the USA (11 outbreaks in eight states, the majority were single cases).

Numerous countries reported equine herpesvirus 4 (EHV-4) respiratory disease; outbreaks ranged from one (Belgium, Switzerland), four (Ireland), five (the Netherlands), to eight (France). France also reported a case of EHV-4 abortion. Single cases of equine infectious anemia were recorded by Canada, Germany, and Hungary. The USA recorded three outbreaks, each involved one or two cases. Equine piroplasmosis cases were reported by the RSA (where the disease is endemic) and New Zealand (a single case in an imported mare). The USA recorded four cases of Tyzzer’s disease caused by Clostridium piliforme and also two cases of equine parvovirus associated hepatitis.

The UK detected Taylorella equigenitalis in an imported stallion. Equine coital exanthema (equine herpesvirus 3 infection) was diagnosed by France (one case) and the USA (three cases). Belgium reported a case of leptospiral abortion and two cases of abortion caused by Streptococcus zooepidemicus. Nocardioform placentitis/abortion was diagnosed by the USA, with 24 cases confirmed in Kentucky and 27 in Pennsylvania.

Amycolatopsis spp. were implicated in the majority of cases. The USA reported 13 cases of salmonellosis, the majority involving Serogroup B isolates. Rotavirus diarrhea in foals was diagnosed by France (14 outbreaks, mostly single cases of infection) and the USA (78 cases, most involving 60-90 day old foals). A subset of 67 cases comprised 31 of the G3 genotype, 21 of the G14 genotype and 15 involving both genotypes.

Clostridium perfringens was reported in 12 foals and Clostridium difficile in seven foals by the USA. The USA confirmed two fatal cases of Eastern equine encephalomyelitis in Florida and two cases of West Nile encephalitis, one in California and the other in Florida; one was euthanized. A total of 71 cases of equine encephalosis were confirmed in seven provinces of the RSA. The USA confirmed re-emergence of vesicular stomatitis in New Mexico in mid-April. The disease was subsequently confirmed in Arizona, Texas, Kansas, and Nebraska. Of 107 affected premises, 103 were equine only premises and four cattle premises. The Indiana serotype was involved in all but seven premises in Texas where the New Jersey serotype was implicated.

Outbreaks of Rhodococcus equi associated diseases were reported by the USA. The number of recorded outbreaks is not considered reflective of the true incidence of the disease. A major outbreak of African horse sickness (AHS) in Thailand earlier this year was a timely reminder for animal health officials, veterinarians, and members of the horse industry of the vulnerability of equine populations to this disease. Of all known equine infectious diseases, AHS is the single most important in terms of devastating losses in naïve horses and economic impact on international trade. It is a dreaded, non-contagious, vector-borne disease with the potential to kill 50% to 95% of affected horses.

The etiological agent of AHS is an RNA virus belonging to the family Reoviridae, genus Orbivirus, that is transmitted naturally by species of Culicoides or midges. There are nine antigenically distinct serotypes of the virus. While the primary host species are members of the family, Equidae, evidence of infection has also been found in African elephants, black and white rhinoceroses, camels and dogs, none of which are considered epidemiologically significant. Historically, AHS was considered restricted to tropical and subtropical regions of sub-Saharan Africa, where it had been known to occur regularly for over 200 years.

Although infrequent, the disease has spread from west and north Africa to various southern European or Middle Eastern countries. The most significant such event occurred between 1959 and 1963 when serotype 9 of AHS virus spread out of Africa into and throughout the Middle East, as far north as Turkey, and extended as far east as Afghanistan, Pakistan, and India. Concern over the risk that AHS poses for horse industries in Europe has been keenly felt for some time. Southern European countries are faced with the potential threat of disease introduction from migration of the virus northwards from regions in Africa, where the disease is endemic. Spread of the virus could result from the movement of nomads and their animals, passive wind-borne carriage of infected

Culicoides over long distances, and legal or illegal trade in zebra from countries where the disease is currently active. A similar if not greater risk exists for the Middle East which experienced incursions of AHS more frequently than any other region or country. As the most recent occurrence of AHS in Thailand has shown, distance is no guarantee of safety from the risk of introduction of this disease. Thailand is approximately 6,000 miles distant from where the virus responsible for this event probably originated, and the furthest east in Asia where AHS has ever been recorded. The most plausible explanation as to the source of virus lies in the fact that a shipment of zebra arrived in Thailand three to four weeks before the first AHS outbreak of the disease was discovered.

Zebra are considered the natural reservoir of the virus, developing viremias lasting up to 40 days. This would not be the first occasion that importation of zebra from a country in which AHS is a seasonal occurrence has been implicated in the introduction of disease into a disease-free country. A shipment of zebra was the confirmed source of this virus for a major disease event that occurred in Spain in 1987 and subsequently involved Portugal and Morocco. International trade in wildlife, both legal and illegal, is believed to have increased significantly in recent years. What happened in the Iberian Peninsula in 1987 and Thailand in 2020 highlights the inherent risks of introducing a disease, such as AHS, into previously disease-free countries.

The influence of climate change and global warming on the epidemiology of AHS must also be considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures and reduced rainfall over a period of years has resulted in more widespread geographic distribution of some of the major vectors of AHS, especially C. imicola, in southern Europe.

An increase in ambient temperature can influence not only the life cycle of the Culicoides vector but also replication of the virus in the vector. As temperatures rise, the infection rate in Culicoides midges increases and transmission of the virus can occur sooner, however there is a concomitant decrease in the survival rate of the adult Culicoides. The overall result of these changes is a higher transmission rate of the virus in a country possibly at risk of the introduction of AHS.

The occurrence in Thailand and the very recent confirmation of AHS in Malaysia underscore the importance of increasing awareness and familiarity with this dreaded disease among animal health officials, veterinarians and members of the equine industry around the world.

The potential consequences of AHS for the health of a country’s equine population and economy highlight the need for an adequate level of national preparedness in a) minimizing the risk of introduction of this disease, b) maintaining a program of active surveillance for the disease and c) having a response plan in place in the remote event of the introduction of the disease. The take-home message from past and recent occurrences of AHS is that there is no room for complacency over the potential threat it represents for disease free-countries.

CONTACT: Peter Timoney, MVB, MS, PhD, FRCVS ptimoney@uky.edu (859) 218-1094 Maxwell H. Gluck Equine Research Center University of Kentucky Lexington, Kentucky

Extract from EQUINE DISEASE QUARTERLY  (October 2020)