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April 2000

Outbreak

Rabies/Cattle - Mexico, Chiapas District

A severe outbreak of paralytic rabies in cattle has killed, as of April 4, at least 2300 animals on 92 ranches in southern Mexico, Chiapas District, bordering Guatemala. The outbreak began in January, although the disease first appeared in the central part of the district in 1987. Autopsies on some of the dead cattle have shown that 90% of the cases were transmitted by common vampire bats (Desmodus rotundus), who feed on animals.

Rabies in cattle can be prevented through vaccination. However, given that most of the cattle in Chiapas are owned by impoverished farmers -- many of whom are generally opposed to vaccinating their cattle -- the percentage of animals protected before the outbreak was small. In late March, the Ministry of Agriculture for the district provided 60,000 units of vaccine at a cost of one peso (about US 11 cents) per dose. However, it is estimated that the need is for an additional 500,000 units to control the outbreak. Of that number 400 thousand units were on order as of March 21. Private clinics also have vaccine available, but at a cost of 8 pesos per dose, a cost out of reach for most of the farmers in the outbreak area.

The severity of the current outbreak in cattle may also be due to a scarcity of other animals on which the vampire bats more ordinarily prey. Such a scarcity could be caused by drought, flooding or the disruption of small animal habitats through logging or land-clearing.

Controlling vampire bat populations range from large capture-and-kill operations to the deployment of anticoagulants, in ointment or injectable solution form. As an ointment, it is used in two ways. One is to smear the ointment on captured bats and then release them to return to their roosts, where they spread the anticoagulant through their practice of grooming each other with their tongues. The other way is to put the ointment on the cattle wounds, since the bats return to feed through wounds they have already created. In solution, the anticoagulant is injected intramuscularly into the cattle, doing no harm to the animals but proving lethal to the bats who take up the anticoagulant through their feeding. (Obviously, it is more cost effective to vaccinate the cattle than to employ any of these control mechanisms in bats in large numbers.)

Sources: Associated Press Worldstream and ProMED/AHEAD-mail, 21 March through 4 April 2000

Outbreak

Foot and Mouth Disease/Cattle & Pigs - South Korea

By April 4, an outbreak of foot and mouth disease in South Korean cattle that began on March 21 had spread so widely that livestock markets were closed in six provinces (Kyonggi, Kyongbuk, Kyongnam, Chonnam, Chungnam and Kangwon), roughly 85% of all such markets in the entire country. Further, import bans on beef, and in some instances pork, and associated animals were imposed by Australia, China, Taiwan, Hong Kong, Singapore and Japan, which has its own outbreak of the disease.

In South Korea, the outbreak is not now confined to the provinces listed above, but has spread rapidly, with symptoms seen in pigs as well as cattle. A national epidemic is seen as a real threat that could wipe out livestock production in the country. An initial report from the South Korean government dated 27 March to of the Office International des Epizooties in Paris on 31 March prompted the following detailed OIE report:

Report Date - 27 Mar 2000

Date of initial incident: 20 Mar 2000

Location: Papyung county, Paju city, Kyunggi province, about 5 km from the Demilitarized Zone, in a basin, well isolated by a wall of mountains

Population affected: 1 dairy farm of 12 milking cows and 3 calves. All cattle were destroyed.

Clinical signs and history: clinical signs observed were: depression, anorexia, excessive salivation, lameness, vesicles and ulcers on feet,mouth, tongue and teats, and a sudden drop in milk production. Disease started with one milking cow on 20 Mar 2000, spread to 10 animals on 22 Mar 2000 and rest of herd on 24 Mar 2000. Owner notified officials on 24 March.

Diagnostic results:

• RT-PCR(1) (3D polymerase, IRES(2) and 1D common regions): positive;
• DNA sequencing (3D polymerase region): partial;
• Viral antigen typing by ELISA(3): positive;
• Antibody detection using liquid-phase blocking ELISA: positive;
• Indirect ELISA using recombinant 3D polymerase: positive;
• Transmission electron microscopy: virus particles in vesicular fluid;
• Virus isolation: in progress.

Causal agent: FMD virus type O is suspected by ELISA for antibody detection and viral antigen typing (using diagnostic reagent and kit made by Pirbright Laboratory, United Kingdom), and by RT-PCR.

Control Measures: stamping out (26 March 2000); setting up of protection and surveillance zones. [Also, the government of South Korea is preparing to inoculate all 11 million cattle and pigs in the country.]

Sources: OIE Weekly Disease Status Report, London Financial Times, Agence France Presse, AFX News, 27 March through 6 April

Alert

Infectious Salmon Anemia/Salmon - Scotland

There is a disputed report that the first case of the deadly infectious salmon anemia virus (ISA) has been found in a salmon that "appeared to be a farmed fish which escaped into the wild" last year. As announced by Friends of the Earth in Scotland as a confirmed finding, a single fish was netted in June 1999 by the Lochaber and District Fisheries Trust, after which tests were conducted. Owners of fish farms in the area where the fish was caught question the finding, although ISA has been present in some of the farms in the recent past, and are asking why the test results were not released for almost nine months.

For many years, those who are charged with, or involved in, protecting the wild salmon in Scotland have feared that salmon farming operations would lead to disease in the wild species. Fish farming, which has increased to enormous proportions worldwide in the last decade, provides most of the trout, salmon and catfish, and much of the shellfish, that is sold for consumption by the public. The farming operations use netting to confine the fish in both salt and fresh water, separating them from wild species in the same locations. The fish are bred, fed and harvested as in any other farming operation. Because of the numbers contained in any one netted "corral", diseases are a big problem. Consequently, the farm owners monitor and test the fish. In recent years, salmon farms in Scotland have been forced to destroy substantial stock. At the same time, Scottish fish farms are not regulated by an independent agency.

Also questioned are the numbers of farmed fish that are said to have escaped from the "corrals", and from which farms they escaped. An agency known as the Scottish Executive has said that 400 thousand fish have escaped since August 1997, including 6000 in the Loch Eil, where the ISA infected salmon was caught last year.

Whether or not this report is accurate in all respects - that it was an escaped farm salmon rather than a wild salmon and that ISA was isolated by acceptable testing methods, the implications appear rather clear: the deadly virus may indeed be present in wild, or non-farmed, waters, and may present a threat to wild salmon in Scotland.

Sources: Aberdeen Press and Journal and The (Glasgow) Herald, 3 April 2000, and AHEAD project resources

Outbreak

Rabbit hemorrhagic disease - United States - Iowa

Rabbit hemorrhagic disease, caused by the rabbit calicivirus first diagnosed in Northern Europe, is highly virulent - rapidly spreading through rabbit populations and leaving the countryside littered with their bodies. Vaccination against the virus is generally effective, although there have been situations in which vaccinated rabbits have died.

In 1995, the virus escaped from an Australian experimental rabbit control program on an island just south of Adelaide. Within weeks many thousands of wild rabbits had been exterminated. While there the release was unintentional, farmers in Australia who battle rabbit destruction of crops were pleased with the results.

This event led farmers on New Zealand's south island to release illicitly obtained virus in their own country in the late summer of 1997. There, the results were not as significant.

One of the criticisms at the time was that farmers spread the illicitly imported virus by whipping up batches of serum in kitchen blenders and dropping tonnes of bait dosed with the virus. Because the serum was left out in sunlight, ultraviolet rays broke down some of the virus to the point where it vaccinated rabbits against virulent forms of the disease.

In September 1998 an outbreak was reported in the UK, mostly southern England and Wales. It killed hundreds of wild rabbits.

In the current US outbreak, the disease has affected only domesticated rabbits not derived from European breeds. Wild American cottontail and jack rabbits are not susceptible. [In Australia and New Zealand the virus affects wild rabbits because they are European breeds imported years before.] The virus is not known to harm humans or other animals. The disease was identified in Iowa after 25 rabbits died in March at the Crawford County farm, which is not being identified. The source of the infection has not been determined, partly because no new animals have been introduced into the colony in two years and the rabbits haven't left the farm since being taken to a 4-H show in August.

How the virus transmitted onto the Iowa is, as of now, a mystery. Research, however, has suggested that arthropods, such as fleas, may act as vectors.

US authorities promptly reported the outbreak to the OIE:

Text of a fax received on 12 April 2000 from Dr Alfonso Torres, DeputyAdministrator, Veterinary Services, United States Department of Agriculture (USDA), Washington, DC:

Report date: 10 Apr 2000.

Nature of diagnosis: clinical, postmortem and laboratory.

Date of initial detection of animal health incident: 31 Mar 2000.

Estimated date of first infection: 7 Mar 2000.

Description of affected population: all rabbits on the affected premises, which is in a rural location, were being raised for the purposes of exhibition. They were all Palominos or California Whites.

Total number of animals in the outbreak:

susceptible 27 cases 25 deaths 25 destroyed 2 slaughtered 0

• The first rabbit, one allowed to roam near the house, died on 9 Mar 2000.- Rabbits housed in hutches started dying on 16 March.
• On 22 March, a private veterinarian forwarded samples to Iowa State University Veterinary Diagnostic Laboratory. Rabbit haemorrhagic disease (RHD) or toxic hepatopathy was suspected based on the clinical history and microscopic lesions in the liver.
• On 24 March, a second rabbit was submitted with similar lesions.
• The State and Federal offices were notified on 27 March and a foreign animal disease investigation began immediately. Epidemiological informationwas collected and samples were sent to the USDA's Foreign Animal Disease Diagnostic Laboratory (FADDL), Orient Point, State of New York.
• On 31 March FADDL tentatively diagnosed RHD based on haemagglutination test on liver homogenate from inoculated rabbits and electron microscopy.
• FADDL forwarded samples to the National Institute for Agrarian Research(INIA), Madrid, Spain, for confirmation.
• Confirmation of RHD was received from INIA on 7 April, based on polymerase chain reaction tests.

Epidemiology:

1. Source of agent / origin of infection: despite extensive investigations, the source of the introduction of the virus onto the site has not yet been identified.
2. Mode of spread: spread has been confined to one premises. Spread on that premises has been by close contact with infected rabbits and indirect spread by materials contaminated with virus is also suspected.
3. Other epidemiological details:
   • There have been no introductions of rabbits onto the premises for the last two years.
   • The first week of August 1999 was the last time rabbits left the farm and returned.
   • In January 2000, six rabbits, all healthy and over two months old, were sold.
4. Control measures during reporting period:
   • - The affected premises are quarantined by the State authority.
   • - The State authority destroyed the remaining two rabbits on 8 Apr 2000.
   • - Cleaning and disinfection will be controlled by the State authority.
   • - Premises with rabbits in the near vicinity are being located, and owners are being contacted to determine whether similar circumstances have occurred elsewhere.

Sources: Omaha World Herald, 14 April 2000; OIE Disease Status Report, 19 April; Wellington Dominion 11 Feb 2000 and AHEAD project archives

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