( Latest news below)
Link to the African Horse Sickness Trust website in South Africa
AFRICAN HORSE SICKNESS
Expert advice from world authority Dr Rudy Meiswinkel: received 21 April 2008
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Dear Mary,
In most respects it is correct say that AHS is a re-invention of the BT wheel i.e. all the same epidemiological principles apply. But with a mortality rate of close to 100% you can be sure that if AHS was to strike it would cause a kind of mayhem that the veterinary authorities might well not be prepared for.
With BTV-8 in northern Europe we are seeing how difficult it is to anticipate the spread of the virus because of the movement of infected animals and the random dispersal of infected midges; both these avenues of virus movement are impossible to control effectively. Once this was realised (with realisation coming only through experience!) the competent authorities opted for widespread vaccination, but only after 15 months had passed. If AHS was to arrive in northern Europe there is NO WAY that a wait of 15 months could be allowed. In all probability the EU would opt for the live-attenuated vaccine currently being produced and used in South Africa and where it gives adequate protection. While 9 serotypes of African horse sickness virus (AHSV) exist large outbreaks invariably involve only one of the serotypes. The serotypes circulate at random but each seems to be as devastating as the next. Where instituted the culling of infected animals did little to halt the spread of BTV-8. There is NO chance that the culling of horses for the control of AHS would be tolerated by the equine industry.
High-lying areas.
There is some merit to the long-held belief that horses removed from low-lying disease ridden areas to high-lying mountainous retreats will escape the ravages of AHS. Its an old strategy that was used to apparent great effect 150 and more years ago in the Cape colony of South Africa. But already in the 1890's Edington noted that if there were flat areas at altitude then the disease was able to establish itself also at higher elevations. He did not know it at the time but this is because C. imicola is able to breed in flat areas wherever the required levels of moisture in the soil do not drain away too rapidly. Thus we still have devastating outbreaks of AHS in South Africa at altitudes in excess of 5,000ft (such as in the high grass plains around Johannesburg and Pretoria) and where C. imicola always becomes superabundant after heavy rains have fallen. For mountainous terrain to be safe it must be steep to ensure rapid water runoff (which leads to desiccation of the muddy surface layer in which C. imicola breeds). BUT - UNFORTUNATELY - there is a second vector of AHS in South Africa, namely C. bolitinos and which breeds exclusively in cattle dung (just like C. dewulfi and C. chiopterus do in Europe). In 1998 100 horses died from AHS in the most mountainous area of central South Africa and where C. imicola is rare. Wild horses, which had roamed the hills unfettered for decades, were found dead along the slopes. It was discovered eventually that an increase in cattle numbers in the valleys led to farmers grazing cattle at ever higher altitudes to get at the sweet grass. In the process dung accumulates widely, which C. bolitinos invades, thereby enabling it to penetrate into all corners of the landscape. Thus when the virus of AHS entered the valley below it was spread by C. bolitinos from the low to the higher-lying areas with the result that horses succumbed everywhere (and were safe nowhere!). The exact same scenario repeated itself 2 or 3 years later about 300km south along the eastern side of the Drakensberg. And was followed in 2001 by the deaths of an estimated 3,000 horses in the former Transkei, which consists of strongly undulate terrain and where C. bolitinios holds rein also. The point to all this is that the introduction of cattle into mountainous terrain can lead to the local establishment of dung-breeding Culicoides, thereby increasing the risk of viruses being transmitted at any unknown point in time. In this regard the situation in Europe is dire firstly because there is a 'shortage' of mountainous terrain (e.g. Holland!) and secondly, because high animal densities are very much the norm. Therefore, the risk of AHS virus establishment and movement is high everywhere (at least below 55 degrees of latitude north). This latter piece in brackets gives you a clue as to what I think would be more effective: the northward latitudinal displacement of horses rather than altitudinal displacement. Yes, I realise its impractical!While it is not known which European species of Culicoides will be able to transmit AHSV it seems safest to assume that at least one or more of the six potential vectors of BTV will also transmit African horse sickness. In Africa both Culicoides vectors of bluetongue act as vectors of AHSV.
I hope my thoughts are not too garbled. And I am not into scaremongering. But AHS demands that we look directly into its eye - because this is a no-nonsense disease.
Email from Dr Rudy Meiswinkel to warmwell.com received April 21 2008.
Advice received from Dr Ruth Watkins
After Rudi Meiswinkels excellent letter you can see that what we need are killed vaccines at the ready should an outbreak occur in a non-endemic area like Northern Europe including the UK. The objection to using live vaccines would be fairly similar to BTV8 in that the live vaccine could be transmitted to midges, would therefore infect non-vaccinated horses and could proove to be only partially attenuated, back mutation with partial reversion to virulence would be a matter for concern. Killed vaccine would be safe for use in non-endemic areas where the goal would be virus elimination.
AHSV is an orbivirus like Bluetongue (BTV ) and therefore it is reasonable to think that effective killed vaccines could be made to AHS as in the case of BTV. Not all viruses can be killed and yet remain capable of producing protective antibodies; examples where this failed are measles and respiratory syncytial virus infection of humans, both enveloped viruses where the crucial virus surface protein is damaged by the chemical process of killing the virus. This does not apply to orbiviruses, nor to FMD. It would be possible to make killed vaccines for all the serotypes (9) of AHSV just as in FMD.
These could be kept, as they are with FMD, ready to thaw and make up into aliquots in a matter of days - the correct serotype selected for the outbreak virus; as Rudi Meiswinkel says, we would expect there to be just one serotype causing an outbreak.
After the experience with BTV-8 in N Europe one cannot assume that any AHS outbreak would be small and easily controlled by culling a few worthless horses. However because of the lethality of AHS there would not be such wide spread infection as in BTV-8 before the outbreak was documented. The extent of the outbreak in horses would be clearly apparent.
I see that it is reported it cost the Australians $100 million to get on top of equine influenza with vaccination and not culling, and I am not sure if they have eliminated it yet. India is contemplating producing 200 million doses of FMD vaccine a year to eliminate FMD from India by vaccination and not culling. Once there is a serious problem with widespread infection it is very expensive to control the epidemic. Culling horses in large numbers in order to control and eliminate an outbreak of AHS could be very expensive, very unpopular indeed and in my view would be totally unnecessary if we have a vaccine.
Who will develop, license and manufacture this suite of killed AHS vaccines covering all 9 serotypes? I am sure a drug company such as Fort Dodge would do it if commissioned and the vaccine paid for, including storage. Who will pay for it? Certainly Europe and DEFRA will not. Will the horse industry pay for it? I would have thought this is possible- and if they do, they would be in a powerful position to negociate sensible and humane terms for the use of the vaccine with the authorities.
The essence of success and economy in epidemic control is preparation. The best preparation is to have a vaccine waiting and ready for use should it ever be required in the case of an arbovirus outbreak, such as AHS which like BTV will not be confined or eliminated by movement controls.
(From the email received from Ruth Watkins BSc Hons, BFA Oxon, MBBS, MSc, MRCP, MRCPath, April 2008 )
Latest News
Monday 28 April ~" it is now believed that, contrary to previous thinking, AHS could also spread if it arrived in the UK."
- New Zealand's www.horsetalk.co.nz
".....AHS has yet to be seen in Britain, but because sheep and cattle have been infected with bluetongue it is now believed that, contrary to previous thinking, AHS could also spread if it arrived in the UK.
There is no vaccine available to control AHS at present. If a case occurred in the UK, current control regulations would mean a total shut-down of the £4 billion equestrian industry, affecting racing, eventing, show-jumping, pony club and leisure riders.
The other emerging threat is West Nile Virus, an encephalitis disease of horses spread by mosquitoes...." The article also mentions the seminar mentioned below.
Friday 25th April 2008 ~ seminar discussing African Horse Sickness (AHS) and West Nile Virus
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Horse and Hound say that all interested owners are invited and it is to be
- "hosted by the Thoroughbred Breeders' Association (TBA) and The Horse Trust.
"Emerging Equine Diseases" takes place on Monday 23 June at Tattersalls, Park Paddocks, Newmarket, Suffolk. Experts from Defra, Pirbright (the government laboratory) and the Animal Health Trust will discuss subjects including disease prevention, insect vectors, the strategy for containment and the development of an AHS vaccine."
April 20 2008 ~".. as many as 90% of the horse population could be infected and compulsorily slaughtered".
- African Horse Sickness may sound like a far off threat - but the same Culicoides midges that spread bluetongue in Africa also act as vectors of AHS. One remembers the kind of wishful thinking that bluetongue midges "may not be able to survive the British climate" in this BBC report on the first bluetongue case last year - and in which farming leaders were reported as saying they were "confident there would not be a major bluetongue outbreak".
The stark reality, however, is that our island boundaries do not protect us. Nor does the "wait and see rather than prepare" mindset whose only "cure", when the worst happens, is slaughter. The UK reluctance, as always, to commit to vaccine production may lead to disaster for horses and owners, Horse and Hound this week are under no illusions about the seriousness of the danger:
- "Jonathon Shaw has confirmed horse owners would only be given £1 compensation by Defra - no matter how valuable the animal."
An endemic disease in the central tropical regions of Africa, AHS spreads regularly to Southern Africa and occasionally to Northern Africa. A few outbreaks have occurred in the Near and Middle East (1959-63), in Spain (1966, 1987-90) and in Portugal (1989) Viraemia in horses may extend for as long as 18 days, but usually lasts for fewer days - about 4-8 days. In zebras and donkeys viraemia may last up to 28 days
The virus - Viscerotropic virus, family Reoviridae, genus Orbivirus Inactivated by 50°C/3 hours; 60°C/15 min pH: Survives between pH 6.0 and 12.0
Chemicals: - Inactivated by ether and ß-propiolactone 0.4%
Disinfectants: - Inactivated by formalin 0.1%/48 hours. Also phenol and iodophores
Survival: Survives at 37°C/37 days
The mortality rate in horses is 70-95%, in mules about 50%, and in donkeys about 10%
From DEFRA's AHS page
Clinical signs
The clinical signs seen are different depending on what form of the disease is present.- In the most acute form, which has a short incubation period of only three to five days, affected horses have a high fever, severely laboured breathing, coughing and profuse discharge from the nostrils. The mortality rate is very high with up to 95% of horses dying within a week.
- In the cardiac form of the disease, which has an incubation period of from seven to fourteen days, swellings are present over the head and eyelids, lips, cheeks and under the jaw. The mortality rate is around 60 per cent and death results from heart failure.
- The mixed form of the disease is a combination of the above two types. It has an incubation period of from five to seven days and the disease shows itself initially by mild respiratory signs followed by the typical swellings of the cardiac form.
- Horse sickness fever is the mildest form, characterised by a fever with low temperatures in the morning rising to a high peak in the afternoon.
Post mortem
Blood samples from up to five horses showing high temperatures can be taken to diagnose this disease. These vary with the form of the disease. - from severe and extensive fluid in the lungs, including froth in the airway, to petecial haemorrhages in the heart and gut and hydropericardium in the cardiac form.
GB Legislation
African Horse sickness is included in The Specified Diseases (Notification and Slaughter) Order 1992 to implement the slaughter requirements of EU Council Directive 92/35/EEC which lays down control rules and measures to combat African horse sickness.(1) Imported horses from at-risk countries outside the European Union are routinely tested for African horse sickness.
The severity of disease and the controls to monitor and restrict movement of horses could significantly affect the Equine Industry in the United Kingdom, particularly in southern UK, where this disease is most likely to occur.
EU Legislation
Council Directive 92/35 provides for compulsory notification, and the setting up of a protection zone of least 100 kilometres radius around and infected premises. This, together with a surveillance zone of at least a further 50 kilometres, would have to remain in force for at least 12 months.
The risks and dangers of African Horse Sickness (AHS) are spelt out in a new leaflet from The Horse Trust and The British Horse Society. (The pdf file takes some time to load.)