Seven years since the major outbreak of foot and mouth disease devastated farming here in the UK, another animal health disaster story is unfolding just over a thousand miles to the south, in Morocco. A viral disease, called peste des petit ruminants (PPR), in sheep and goats has broken out in Morocco for the first time. This story may not be reaching the main news channels, but it is having a serious impact on the livelihoods of the many people who rely on these animals to survive, and it could spread to neighbouring countries.
I recently came across a case report of cattle being poisoned by apricot kernels, a reminder of the fact that the seeds (and sometimes leaves) from fruits such as apricots, peaches, and other members of the Prunus genus contain glycosides such as amygdalin that can release the deadly gas hydrogen cyanide. This fact is well known to entomologists who will use a few torn leaves from a cherry tree, in a jar, to kill the specimens that they collect.
The case, reported this week in the Veterinary Record, describes how a farmer in Switzerland obtained a large quantity of soft hulls, separated from the inner part of the apricot kernels. (The report does not link the use of this exotic feedstuff to the rise in world feed and grain prices – a worthy subject of another blog?). The apricot kernels were used for the production of traditional gingerbread cake, and the feedstuff was obtained from a local baker in the Appenzelle region. The farmer did not appear to notice the characteristic smell of bitter almonds in the feed, even though the cows did. They were not keen on the new feed, and showed ‘a strong aversion’ to it. The farmer needed to make it much more acceptable by adding silage to increase the palatability. The result of this misadventure was that 5 of the 12 cows fed the apricot hulls showed quite severe symptoms including tremor, salivation, opisthotonus, tympany, and dyspnoea, and two of them died. The 3 surviving cows refused to feed for another 24 hours, and had reduced milk production, but they recovered without treatment.
The apricot hulls and kernels were found to contain a mean hydrogen cyanide (HCN) level of 110 mg/kg, and an amygdalin content which was the equivalent of another 300 mg/kg of HCN. This meant that the 2 kg of the feed given to the each of the cows would have contained at least 820 mg of HCN equivalents, which is close to the reported lethal dose of 2 mg/kg.
Cyanide poisoning is difficult to diagnose. The volatility and rapid breakdown of HCN, often means that samples from suspected poisonings are negative when tested. This is one of the reasons that cyanide is often the poison of choice in crime novels: easy to disguise in any almond flavoured dish, quick, lethal, and hard to detect. In looking for a better way to detect cyanide poisoning the authors of the case report took blood samples to detect thiocyanate. The blood levels in the three affected cows were 145, 209, and 211 μmol/L compared to normal levels of 50-60 μmol/L. This showed that high serum thiocyanate can be an indicator of cyanide poisoning, although there are other factors that can increase thiocyanate in blood, and these need also to be considered.
Looking into the CAB Abstracts Database for other cases of cyanide poisoning reveals over 30 references. Many of the cases are of goats, whose catholic tastes tempt them to eat leaves of cherry trees if they have access. There are also cases of people being poisoned by apricot kernels by accident (when the kernels were used in making sweets), and in what appears to be attempted suicide.
So, remember, if the feed you are being offered has a distinct smell of bitter almonds then, beware.
The idea that the flap of a butterfly wing in China could cause a tornado in Texas comes from the concept of ‘sensitive dependence on initial conditions’ as part of the chaos theory, and has inspired short stories, poems and films, and the term ‘Butterfly Effect’ has entered the language. Assigning cause and effect in science is notoriously difficult, but there is growing evidence that there is a link between an anti-inflammatory drug for cattle, the demise of the Asian vulture. and the death of children from rabies in India.
The depressing story of the collapse of vulture populations in India began in the 1990s when it was noticed that the numbers of vultures, a common site in rural India, were suddenly in decline. The loss of vultures had a devastating ecological effect, as well as a social impact on the Indian Zoroastrian Parsi community, who traditionally use vultures to dispose of human corpses in "sky burials", and had to find alternative ways to dispose of their dead. The cause of the decline was a puzzle for scientists. New or emerging diseases such as West Nile were considered as a possibility, as bird populations in other parts of the world had been devastated by spreading viral diseases.
Vultures have performed a vital role in clearing up the rotting carcasses of animals. I can remember on my first trip to India in 1983, stopping on the road from Dehli to Agra to take photographs of 50 or more griffon vultures gathered around a stinking pit of bones and carcasses. The driver was surprised at the request to stop to see the vultures – a common sight to him, and didn’t realise that then the time the largest raptor I was used to seeing in southern England was the sparrow hawk.
The culprit responsible for the vulture’s problems seems to be a drug residue in the carcases on which they feed. Diclofenac (2-(2,6-dichloranilino) phenylacetic acid) is a non-steroidal anti-inflammatory agent, which has analgesic as well as anti-inflammatory properties. Looking on the CAB Abstracts Database it can be seen that diclofenac has been used in cattle to treat a number of different conditions including arthritis, mastitis, repeat breeding, babesiosis, theileriosis, parotitis, downer cow, radial paralysis, mastitis, and emphysema. Often it is used in conjunction with other drugs for supportive therapy. Because of the ecological problems that the residues of the drug have caused the manufacture of diclofenac for veterinary purposes has been banned in Nepal, India and Pakistan. It is, however, still available as a human drug, and is still cheaper than a safer substitute meloxicam.
The severe effects are due to a number of factors that have come together. Vultures are more susceptible to the toxic affects of diclofenac, in particular acute kidney failure, than are other species. In India, cattle do not usually go into the human food chain and the dead ones would be left for the scavengers. Another unfortunate factor is that diclofenac has a particularly long elimination half life in cattle (30.5 +/- 9.4 hrs compared with 1.1 hours in humans), and would therefore more likely to form residues in the carcase. Even with restrictions on the use of diclofenac, vulture populations will not recover quickly. Vulture populations have been reduced by more than 99% and several species of Gyps are now on the endangered species list. Gyps vultures take several years to reach sexual maturity, and a pair produces only one or two young every one or two years, so it could take decades before their populations recover. Concern for vultures has also spread to Africa where diclofenac is now being manufactured.
As nature abhors a vacuum, the gap left by the vultures has provided other scavengers with a feast. The opportunity has been exploited by stray and feral dogs, usually the pariah dogs, whose numbers have grown. With the growth in the numbers of dogs the risk of rabies has also grown.. Dogs are the main vector of human rabies in India. It is estimated that about 10,000 people die each year from rabies in India, and most of these are in the rural areas and a large proportion are children. The cost of post exposure treatment for the poor is also a contributing factor to the high death rate.
Scientists working on trying to control the facial tumour disease which threaten to wipe out the Tasmanian devil (Sarcophilus harrisii) have increased their understanding the disease. The Tasmanian devil is the largest carnivorous marsupial remaining and is now found only on the island of Tasmania, having been exterminated from the Australian mainland. The disease that is threatening this endangered species is a transmissible neoplasm that grows on the face leading to death from starvation. These creatures, immortalized by the Looney Tunes cartoon character ‘Taz, are about the size of a small dog and have a predisposition to aggressive behaviour, as well as unearthly screeching and raucous communal feeding that has earned them their name. Their aggressive behaviour is probably the most likely way in which the disease is transmitted, through biting as they fight over food and mates.
Devil facial tumour disease was first seen in 1995 and has caused between 20-50% reduction in the devil population. More than half of the State of Tasmania is affected. Two ‘insurance’ populations of disease-free devils are being established at an urban facility in the Hobart suburb of Taroona and on Maria Island off the east coast of Tasmania. The decline in devil numbers is an ecological problem, since its presence in the Tasmanian forest ecosystem is believed to have prevented the establishment of the Red Fox, illegally introduced to Tasmania in 2001. Foxes are a problematic invasive species in all other Australian States, and the establishment of foxes in Tasmania may hinder the recovery of the Tasmanian Devil.
The scientists from the University of Sydney School of Veterinary Science working on the disease are saying that the tumour probably arose from a single individual and has spread on to other devils. The immune system of the original animal probably did not recognize the tumours as foreign, and because Tasmanian devil population is now so genetically similar, their bodies do not recognize that the tumours are foreign cells and so do not attack them. Tasmanian devils have lost genetic diversity in the most important gene region for the immune system, the Major Histocompatibility Complex (MHC). The devils all had a similar MHC type to the tumour. There appears to be some similarities with a transmissible cancer of dogs (canine transmissible venereal tumour).
There is a pilot program on the Tasman Peninsular where all the diseased devils captured are killed. There is currently no test for infected animals that do not yet show the neoplasm, so it is only those showing visible signs of the disease that are removed. There seems to be some evidence that this is working to protect the overall population, because, over time, the average age of the animals they capture has become older, suggesting that more animals are avoiding the cancer and surviving longer. But the program is expensive, and it is not clear how effective the programme will be in stopping the disease.
The problem seems, then, to be a result of the lack of genetic diversity in a small population. There are many other endangered species of wildlife that have populations as small or smaller and could suffer the same fate, falling to new or emerging diseases. Looking through the CAB Abstracts Database to see if there was any other information on biodiversity threatened by disease, I came across a paper by Maillard and Gonzalez entitled Biodiversity. The problems caused by lack of genetic diversity in making the population open to infectious organisms are described. The disease in the Tasmanian devil shows that certain neoplasms can also exploit the restricted gene pool.
Maillard, J. C.; Gonzalez, J. P. 2006. Biodiversity and emerging diseases. Annals of the New York Academy of Sciences, 2006, Vol. 1081, pp. 1-16 Record No: 20073114695
Twenty years ago, a paper appeared in the Veterinary Record recording a new disease in dairy cattle. The syndrome had been seen in cattle in England for a couple of years but with the publication of the paper by Wells and others, the disease was described and named, and the new term bovine spongiform encephalopathy (BSE) entered the English language. This official name soon gave way, in the media, to the more catchy term mad cow disease.
Few people reading that original paper back in October 1987 could have imagined the full consequences of the outbreak as it grew to a peak of more than 30,000 cases in cattle in 1992. Public distrust of the government and scientists also grew, as original claims for the safety of beef were shaken by the arrival of a new form of Creutzfeldt-Jakob disease (v-CJD) in humans. The prospect of an epidemic of v-CDJ in humans on the scale of the BSE outbreak in cattle was truly terrifying to consider. The annual number of v-CJD cases in the UK rose to a peak of 28 in the year 2000, after which it has gradually decreased. Thankfully the epidemic of new-variant CJD did not reach the levels of BSE in cattle, although this was of little consolation to the families of the victims of that terrible disease. To restore public confidence in British beef and to recapture export markets, which had been closed, cattle over 30 months old were excluded from the food chain and stringent regulations on ruminant protein in cattle feed were enacted. The epidemic in the UK became the most expensive peace-time crisis for the Government.
The arrival of BSE and v-CJD prompted an upsurge of research on the causes and pathogenesis of these diseases, and their relationship to other similar diseases such as scrapie and chronic wasting disease of deer. The theory most widely accepted is that the disease is caused by an abnormal form of a protein, the prion protein, which is resistant to both heat and protease enzymes. The abnormal prion accumulates in the cells of the nervous system, causing nervous symptoms and finally death. The affected brain tissue takes on a spongy appearance. The abnormal prion protein appears to act like an organism, being able to replicate itself. The disease appears to be transmitted to cattle (and other species) from the practice of including ruminant protein in feed.
Although there is a substantial body of evidence to support this theory (not least the decline of the UK epidemic following the removal of ruminant protein from cattle feed) there have been several other possible causes suggested, including viruses, bacteria, and chemicals. For example, one suggested cause of the disease was organophosphates, as UK farmers were obliged to use these pesticides to combat warble fly. Although the organophosphate theory sounded plausible, attempts to create BSE experimentally using the pesticides failed in tests on cattle, so there has been no clear experimental evidence to support that theory. Another theory suggested that the infectious protein originated from human remains (rendered protein imported from India) included in cattle feed.
Other theories have included infectious agents as the cause. One such theory is that the disease is caused by bacteria and that prions are involved in the pathogenesis but are not the cause. A paper recently published in the Journal of Medical Microbiology (DOI 10.1099/jmm.0.47159-0) claims that Spiroplasma, small wall-less bacteria, can induce spongiform encephalopathy in ruminants.
The paper reports on experimental work carried out in Baton Rouge, Louisiana, where Spiroplasma mirum isolated from rabbit tick was inoculated into the brains of deer, sheep and goats. The deer developed nervous system symptoms and showed post-mortem signs of spongiform encephalopathy. Sheep and goats did not show nervous symptoms but post-mortem examination of their brains showed clear signs of progressive spongiform encephalopathy. Spongiform encephalopathy was also induced in deer and sheep inoculated with Spiroplasma isolated from brains of sheep and goats with the disease.
The idea that bacteria are behind transmissible spongiform encephalopathies (tSE) is also suggested in another recent paper, by another author. H. Peter Schmitt of Heidelberg University (Germany). He suggests that rather than the bacteria themselves, it is the bacterial toxic proteins (BTPs) that cause tSEs and diseases such as Alzheimer’s disease. His theory is that BTPs can meet the key-proteins of Alzheimer’s disease (AD) and tSEs in the lipid-rich domains of the plasma membrane called rafts. This then could enable them to start a large variety of unfavourable molecular events, eventually resulting in pathogenic cascades as in AD and the tSEs. The reasoning involves some pretty complicated biochemistry which would be out of place in a blog like this, but the reference is listed below for those who are not deterred by biochemical detail.
So are tSEs caused by prions, bacteria, bacterial proteins, organophosphates or some combination of these? Even looking through the published evidence (there are nearly 5000 references on BSE, scrapie and the other tSEs on the CAB Abstracts Database) one is always left with the feeling that there is some vital part of the story missing. The 20 years of research has certainly increased the understanding of these strange and terrifying diseases, but there is still much more to learn about them. I suspect that in 20 years time (unless the BTPs have got me) I will still be seeing new theories trying to explain BSE, CJD and the other tSEs.
Wells, G. A.; Scott, A. C.; Johnson, C. T.; Gunning, R. f.; Hancock, R. D.; Jeffrey, M; Dawson, M.; Bradley, R., 1987. A novel progressive spongiform encephalopathy in cattle. Veterinary Record, Oct 1987; 121(18), 419 – 420.
Schmitt, H. P. 2007. Profiling the culprit in Alzheimer’s disease (AD): Bacterial toxic proteins – Will they be significant for the aetio-pathogenesis of AD and the transmissible spongiform encephalopathies? Medical Hypotheses 69 (3), 596-609. DOI:10.1016/j.mehy.2007.01.022
Bastian, F.O.Sanders, D. E.; Forbes, W. A.; Hagius, S.; Walker, J. V.; Henk, W. G.; Enright, F. M.; Elzer, P. H. Sproplasma spp. 2007. From transmissible spongiform encephalopathy brains or ticks induce spongiform encephalopathy in ruminants. Journal of Medical Microbiology, 56, 1235-1242. DOI 10.1099/jmm.0.47159-0
The big animal health story in the newspapers in the UK this summer has been the return, after 6 years, of foot and mouth disease. The outbreak was almost certainly caused by the escape of the virus from the virology research laboratory in Pirbright, Surrey. It seemed as if the outbreak had been contained quickly and the disease controlled, but initial claims that the outbreak was dead were subsequently shown to be premature as more farms became infected in September, emphasising the highly infectious nature of the disease.
The National Farmers Union has claimed that the outbreak of foot and mouth has cost the British farmers tens of millions of pounds, but it seems unlikely that it will get to the serious levels of the epidemic in 2001. While this outbreak has been capturing the attention of the farmers, veterinarians and ministry officials working to control it, the spectre of another animal disease has been hovering just across the English Channel in the form of bluetongue disease. The discovery on 23rd September of cattle in Suffolk with bluetongue shows that the disease is no longer just knocking on the door of the UK, but has found a way in. An epidemic of bluetongue is currently gripping the Netherlands, Luxembourg, Belgium, and parts of France and Germany. The strain identified in the UK is the same serotype (serotype 8) as that in the European outbreak.
Veterinary authorities have been worried for some time that climate change could extend the range of the bluetongue vector from the tropical and sub-tropical regions of Africa and Asia to southern Europe. The threat that P.S. Mellor identified in his review article in 1996
(Culicoides, vectors, climate change, and disease risk. Veterinary
Bulletin, 1996, vol. 66 no.4) was that climate change could bring the virus into contact with new vector species of midge that could transmit the disease and survive the northern winters, thus establishing the disease much further north.
Bluetongue first appeared in Northern Europe 2006 and its resurgence in 2007 showed that it had survived the northern winter and was established in the local midge population. The 2007 outbreak has resulted in more cases and a wider range than in 2006. Sheep and deer are severely affected by the disease whereas cattle tend to act as reservoirs of infection.
Bluetongue is a haemorrhagic disease caused by an Orbivirus genus of the family Reorvirades. At present, 24 distinct serotypes have been identified by serum neutralization tests. The virus is transmitted by a small number of species of biting midges of the genus
Culicoides. These vectors prefer to feed on large animals such as cattle. The main transmission cycle is between the
Culicoides midge and cattle, with sheep or deer being infected when cattle are not present or the midge population is high. Thus, cattle can be used to detect the presence of the virus, and can be used as sentinel animals. Culicoides populations peak in the late summer and autumn and this is the time when bluetongue is most prevalent. When the disease becomes established it takes on a seasonal cycle with peaks in the autumn.
Only about 20 of the more than 1,400 Culicoides species worldwide are actual or possible vectors of bluetongue virus. Continued cycling of the virus among competent
Culicoides vectors and susceptible ruminants is critical to the viral ecology. In Europe, Middle East and Africa, the main vector is
C. imicola. In the USA, the principal biological vector is C. variipennis sonorensis, which is mainly distributed in southern and western regions (although there are recent reports of bluetongue causing the death of deer and antelope in Montana) . In Australia the principal vector is
The fear in recent years is that climate change would extend the range of the main European vector,
C. imicola, and spread the disease up through Europe. What seems to have happened in Northern Europe is that the virus has become established in other species of midge such as
C. obsoletus, and that these are transmitting the disease. Also in the Netherlands it appears that
C. dewulfi is also infected with the virus. C. obsoletus can over-winter in the Northern European climate, unlike
C. imicola, so that the disease can return each autumn when midge numbers increase.
A number of serotypes (including 4, 1, 2, 15, and 16) of bluetongue have appeared in southern Europe, and their progression has been tracked from North Africa and the Middle East. However, the serotype 8 that is now established in northern Europe, and now in the UK, appears to be related to strains of the virus from sub-Saharan Africa. The question of how the virus came to northern Europe is not an easy one to answer with certainty. Movement of infected midges or, more likely, of infected livestock seems to be the most probable way. The rapid movement of livestock across the globe as part of the globalized economy provides a huge boost to virus mobility.
Currently the Belgian authorities are applying to the European authorities for permission to vaccinate against the disease to prevent its resurgence next year. The disease is causing large numbers of deaths among sheep and economic hardship for farmers coping with the restrictions. As the UK is the largest producer of sheep in the European Union with more than 30% of total production, the spread of the disease here would be particularly damaging. There is, as any visitor to the highlands of Scotland will testify, no shortage of midges in the UK.
Bluetongue is a serious infectious disease like FMD but is transmitted in a different way, and is particularly difficult to control because of its transmission by midges and its silent presence in cattle, as reservoirs. Control of bluetongue in Europe will probably require strategic vaccination, along with large scale testing and slaughter. The experiences in Europe show that when the disease becomes established in the local midge population it is very difficult to control.
The recent outbreak of foot and mouth disease in UK, possibly from a neighbouring laboratory working on vaccines for the disease, has raised the question of biosecurity in micro-organism research and the risks to the health of people, animals and plants.
The Initial report on potential breaches of biosecurity at the Pirbright site 2007, by the UK Health and Safety Executive states that there is a strong possibility that the FMDV strain involved in the outbreak of foot and mouth disease at a farm in Surrey in August 2007 originated from the Institute of Animal Health or Merial sites. The strain of virus isolated from the infected farm was also being worked on in both organizations (IAH and Merial) between 14-25 July 2007. There was large scale production (10,000 litres) at the Merial site and a series of small scale experiments (less than 10 millilitres) at the IAH. The examination found that there was little likelihood of an airborne release of the virus from the site, but there was potentially the possibility of waterborne release. However the possibility that surface water from flooding (southern England experienced unusually high rainfall in July causing flooding in many areas) at the site could have reached the infected farm is considered to be small due to distance, topography, and direction of flow of the water. The report goes on to say that human movement of materials, either deliberate or accidental from the site remains a distinct possibility. As a result a number of ‘lines of enquiry’ are being ‘urgently pursued’. The report provides the basis for a review of biosecurity that will be carried out by Professor Spratt of Imperial College, London.
If the further evidence emerges of the disease originating from the laboratories then the threat of legal action by farmers against them is a distinct possibility, particularly if the commercial company Merial is involved. As Peter Kendall of the National Farmers Union said "It is important to understand that farmers who have lost livestock at the moment are only being compensated for the value of that stock, there’s no [compensation for] consequential loss," he said. "If this turns out to be a commercial company, that has been and can be shown to have been careless in any way, my members are already very loudly saying, ‘We’ve lost money, our businesses are no longer able to function, we’ve got animals, extra feed costs, problems with capacity being squeezed on farms’. There are many, many costs that have been incurred by farmers through no fault of their own."
I heard a discussion on BBC radio yesterday on the question of whether it is right to allow production of vaccines in a country such as UK for disease that do not occur here. The spokesman for the farmers suggested that this was unfair because the risks of biosecurity lapses were being borne by the farmers and not the company producing the vaccines. That sounded like a reasonable point, except that if there was to be another outbreak of foot and mouth like the one in 2001, which did not originate in a laboratory, then vaccination could be a useful way of containing the disease. It would then be important for the country to source large quantities of the vaccine at very short notice, which might be difficult if could not be sourced locally.
The risks and benefits of working with micro-organisms are complex and it is easy to ignore the great benefits society gain from microorganisms, and to only focus on the problems caused by them. This issue is dealt with in a forthcoming paper by David Smith and Christine Rohde, Microorganisms: good or evil. The authors (David Smith is a CABI scientist and has extensive knowledge of the biosecurity issues involved in working with microorganisms, and maintaining a large culture collection) see the need for secure and safe system for access and distribution but one that does not restrict legitimate use of the organisms. They also suggest that rules should distinguish between dangerous organisms and those that present little risk. They point out the benefits that we gain from microorganisms including pest control, soil fertility, diagnostics, and vaccines, and also the need to understand microorganisms to enable authorities to protect society from the threats of bioterrorism.
The paper refers to the recently published OECD Best Practice Guidelines for Biological Resource Centres 2007, (published by OECD publications, 2, rue André-Pascal, 75775 Paris Cedex 16, France) which covers the development of biological resource centres, best practice for receiving, handling and preserving samples, as well as documentation and staff training. The guidelines cover all biological collections so would be relevant to laboratories handling viruses. As yet there is no way of ensuring that the guidelines will be followed by all relevant laboratories.
Without jumping to premature conclusions about the Surrey FMD outbreak, the biosecurity systems are only as good as the people implementing them. Even with the best systems in place, in the end humans (by accident or malicious intent) are likely to be the weakest link.