Trypanosomiasis in horse treatment

Equine trypanosomiasis

Equine trypanosomiasis is endemic in many areas of the world with high morbidity and mortality in affected populations. Trypanocides form an essential part of current treatment strategies but evidence regarding efficacy in equines is scarce. In order to inform disease management, the efficacy of three trypanocidal drugs was assessed in horses and donkeys that fulfilled 2/5 clinical inclusion criteria for trypanosomiasis in The Gambia. Selected equines received randomised treatment with either isometamidium, diminazene or melarsomine dihydrochloride and were observed for adverse drug reactions. Follow-up was performed at 1 and 2 weeks. Blood collected at each timepoint was analysed for Trypanosoma spp. using a PCR approach. Within the selected population 66% were PCR positive pre-treatment for Trypanosoma spp.. Trypanosome positive individuals responded favourably to each treatment, but clinical evaluation and PCR status post-treatment supported a superior effect for isometamidium. Melarsomine dihydrochloride had inferior efficacy to isometamidium. Immediate adverse side effects were only documented following isometamidium administration in donkeys (26%) and these were self-limiting. Diminazene had the longest duration of action as judged by PCR status. The data support the continued use of isometamidium and diminazene but not melarsomine dihydrochloride for trypanosomiasis in equines at the doses and routes of administration reported.

African horse sickness (AHS) is a disease caused by the African horse sickness virus (AHSV). The disease affects horses, ponies, and European donkeys most severely; mules are somewhat less affected, and African donkeys and zebra are refractory to the devastating consequences of infection [1–4]. The virus is a non-contagious, vector-borne Orbivirus that is transmitted primarily by female Culicoides midges during a blood meal, which they require for reproduction [4]. In addition to equids, camels, goats, and buffalo can become infected [5]. Additionally, some carnivores such as dogs, can become infected via ingestion of contaminated meat. However, there have been no documented cases of transmission of AHSV in carnivores in the wild, and it is considered that they are a ‘dead-end’ host, rather than a reservoir of infection [6, 7]. Owing to the potential of this virus to cause widespread death and debilitating disease in naïve equid populations, it is listed as a notifiable equine disease by the World Organisation for Animal Health (OIE), which makes outbreaks of the disease compulsorily notifiable to the OIE. Such occurrences can result in serious consequences for international trade of animals and animal products for the affected country [8]. It is currently predicted, that a widespread outbreak of this disease would have a devastating effect on the horse industry of any country affected

African horse sickness is an economically highly important non-contagious but infectious Orbivirus disease that is transmitted by various species of Culicoides midges. The equids most severely affected by the virus are horses, ponies, and European donkeys; mules are somewhat less susceptible, and African donkeys and zebra are refractory to the devastating consequences of infection. In recent years, Bluetongue virus, an Orbivirus similar to African horse sickness, which also utilises Culicoides spp. as its vector, has drastically increased its range into previously unaffected regions in northern Europe, utilising indigenous vector species, and causing widespread economic damage to the agricultural sector. Considering these events, the current review outlines the history of African horse sickness, including information concerning virus structure, transmission, viraemia, overwintering ability, and the potential implications that an outbreak would have for Ireland. While the current risk for the introduction of African horse sickness to Ireland is considered at worst ‘very low’, it is important to note that prior to the 2006 outbreak of Bluetongue in northern Europe, both diseases were considered to be of equal risk to the United Kingdom (‘medium-risk’). It is therefore likely that any outbreak of this disease would have serious socio-economic consequences for Ireland due to the high density of vulnerable equids and the prevalence of Culicoides species, potentially capable of vectoring the virus.

Epidemiology A map of African horse sickness outbreaks that have occurred worldwide during the last century AHS virus was first recorded south of the Sahara Desert in the mid-1600s, with the introduction of horses to southern Africa. The virus is considered endemic to the equatorial, eastern, and southern regions of Africa. Several outbreaks have occurred in the Equidae throughout Africa and elsewhere.[2] AHS is known to be endemic in sub-Saharan Africa, and has spread to Morocco, the Middle East, India, and Pakistan. More recently, outbreaks have been reported in the Iberian Peninsula and Thailand. AHS has never been reported in the Americas, eastern Asia, or Australasia. Epidemiology is dependent on host-vector interaction, where cyclic disease outbreaks coincide with high numbers of competent vectors. The most important vector for AHS in endemic areas is the biting midge Culicoides imicola, which prefers warm, humid conditions. Larvae do not carry the virus, and long, cold winters are sufficient to break epidemics in nonendemic areas.[citation needed] Host The common hosts of this disease are horses, mules, donkeys, and zebras. However, elephants, camels, and dogs can be infected, as well, but often show no signs of the disease. Dogs usually contract the disease by eating infected horse meat, although a recent report has been made of the disease occurring in dogs with no known horse-meat ingestion.[3] Transmission Transmission of African horse sickness virus by insect vector This disease is spread by insect vectors. The biological vector of the virus is the Culicoides (midges) species. However, this disease can also be transmitted by species of mosquitoes including Culex, Anopheles, and Aedes, and species of ticks such as Hyalomma and Rhipicephalus. Clinical signs Horses are the most susceptible host with close to 90%[4][5] mortality of those affected, followed by mules (50%) and donkeys (10%). African donkeys and zebras very rarely display clinical symptoms

Epidemiology A map of African horse sickness outbreaks that have occurred worldwide during the last century AHS virus was first recorded south of the Sahara Desert in the mid-1600s, with the introduction of horses to southern Africa. The virus is considered endemic to the equatorial, eastern, and southern regions of Africa. Several outbreaks have occurred in the Equidae throughout Africa and elsewhere.[2] AHS is known to be endemic in sub-Saharan Africa, and has spread to Morocco, the Middle East, India, and Pakistan. More recently, outbreaks have been reported in the Iberian Peninsula and Thailand. AHS has never been reported in the Americas, eastern Asia, or Australasia. Epidemiology is dependent on host-vector interaction, where cyclic disease outbreaks coincide with high numbers of competent vectors. The most important vector for AHS in endemic areas is the biting midge Culicoides imicola, which prefers warm, humid conditions. Larvae do not carry the virus, and long, cold winters are sufficient to break epidemics in nonendemic areas.[citation needed] Host The common hosts of this disease are horses, mules, donkeys, and zebras. However, elephants, camels, and dogs can be infected, as well, but often show no signs of the disease. Dogs usually contract the disease by eating infected horse meat, although a recent report has been made of the disease occurring in dogs with no known horse-meat ingestion.[3] Transmission Transmission of African horse sickness virus by insect vector This disease is spread by insect vectors. The biological vector of the virus is the Culicoides (midges) species. However, this disease can also be transmitted by species of mosquitoes including Culex, Anopheles, and Aedes, and species of ticks such as Hyalomma and Rhipicephalus. Clinical signs Horses are the most susceptible host with close to 90%[4][5] mortality of those affected, followed by mules (50%) and donkeys (10%). African donkeys and zebras very rarely display clinical symptoms

KNOWLEDGE GAPS AND FUTURE STUDIES OF AFRICAN HORSE SICKNESS VIRUS Overarching Areas of Research The development of cross-protective AHSV vaccines that have a long shelf life and that can provide rapid protection and be differentiated from natural infections during outbreaks is rightly seen as the major priority for research (118). Even if these become available, however, a key lesson from both historical and current emergences of Culicoides-borne orbiviruses is that the time elapsing from incursion to vaccination can be significant in determining the impact of outbreaks (29). This is particularly the case in regions such as northwest Europe, which have no prior experience with AHS incursion or any licensed vaccine banks with which to respond. Under this scenario, the only measures available to owners to protect horses are based on reducing vector-host contact. These measures have not been effective in preventing BTV transmission in this region (29, 70), but owing to limited host density and greater financial or emotional incentives to conduct multiple integrated measures (e.g., stabling, larval habitat clearance, application of repellent or insecticidal products), they may have a greater impact on AHSV. Another almost entirely unexplored area of research is in understanding how hosts present on farm holdings influence Culicoides populations. Mathematical simulation has already identified host preference between equine and ruminant hosts as a key factor influencing AHSV persistence (55). More broadly, however, the Culicoides communities associated with equine hosts in Europe in particular are poorly defined, despite substantial light-suction trapping networks for holdings containing ruminant hosts (1, 32). Though global data demonstrate that species assemblages of Culicoides are likely to be similar on holdings containing equine and ruminant hosts, variation in abundance according to both the number and type of hosts and husbandry regimes employed (e.g., the degree

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