The heightened awareness results from imminent threats to our own animal populations, concerns about food safety, trade sanctions for animals or animal products and restrictions in travel to chosen destinations. Reports of the personal and financial losses incurred by individual owners and agribusiness are sobering.
Next to humans, horses are the most "frequent flyers" in international travel, with hundreds of horses imported through USDA quarantine centers each week. Concerns about importing foreign equine diseases are real, and recent examples of horses arriving in the US infested with screwworms or infected with contagious equine metritis (CEM) illustrate that we are vulnerable to importation of disease.
Foot-and-mouth disease outbreaks remind us that non-equine diseases can severely impact the equine industry when horses may serve as fomites for the infectious agent.
The plethora of mechanisms by which foreign equine diseases can be transmitted, combined with the economic benefits of international trade, precludes adaptation of isolationist tactics or a "zero risk" philosophy. For example, the infectious source for the initial cases of West Nile encephalitis in the US has not been identified.
Nonetheless, the spread of this agent in US mosquitoes, birds and horses serves as an example of what can happen when a pathogen encounters naive populations.
Science-based efforts are made to ensure that we are not importing diseases along with horses. For example, the length of quarantine for horses arriving from countries known to have Venezuelan equine encephalomyelitis (VEE) is longer than that for VEE-free countries to permit manifestation of signs during quarantine if an infected horse arrives.
All overseas horses are tested at the USDA's National Veterinary Services Laboratories, Ames, Iowa for equine infectious anemia, piroplasmosis, dourine and glanders; quarantine release occurs only after tests are completed and results are negative. Special quarantine stations are used for post-import testing for CEM.
Import procedures are adjusted when indicated to provide additional safeguards. Coping with recent disease situations at home and abroad have actually had some positive outcomes. Veterinary laboratories are upgrading to permit work with agents requiring higher biosafety containment. Communication among professionals in veterinary, public health, wildlife, and vector abatement jurisdictions has been enhanced nationally and the need for cross-sectional disease surveillance activities is recognized.
The most important benefit is the loss of complacency among everyone involved in animal agriculture.
Dr. Eileen N. Ostlund, (515) 663-7551, firstname.lastname@example.org
National Veterinary Services Laboratory, Ames, IA.
Cases of foal morbidity and mortality within 48 hours of birth attributable to Clostridium perfringens type A were diagnosed in central Kentucky during March. Clinical signs included bloody diarrhea and acute colic.
Abortion caused by equine herpes virus type-1 (EHV-1) was reported from Japan, United Kingdom and Kentucky, USA. Between September 2000 and April 2001 there were 25 cases on 21 Thoroughbred farms in central Kentucky. Several foals were born alive but died within 5 days of birth. Respiratory disease attributable to EHV-1 and EHV-4 was diagnosed among Thoroughbred and non-Thoroughbred animals in France and the paralytic form was recognised in a stable of riding and driving horses in Switzerland.
Equine arteritis virus (EAV) was isolated from 7 stallions of unspecified breed in Switzerland. Equine influenza was reported from France and Sweden.
Thirty-four cases on 24 premises of Leptospira abortion were recorded in central Kentucky primarily during November and December. The majority were identified as Leptospira serovar kennewicki.
A number of horses in Victoria, Australia had positive titres for Ross Valley Fever. Strangles cases were reported from Australia, Sweden, Switzerland and Kentucky, USA. A fatal case of Tyzzer's disease caused by Bacillus piliformis was confirmed in a 2-week-old foal in Switzerland.
There were no reports of West Nile virus isolations in the USA during the first quarter of 2001. However, up to June 15, the virus was identified in 12 dead crows and 2 mosquito pools in New Jersey, 3 crows in Maryland, 2 crows in New York and 2 in Connecticut..
Although this virus occurs sporadically in Africa, Asia, Europe, and other parts of the world, it had not been isolated in the United States until the late summer of 1999. The severity of the epizootic, causing deaths in humans, horses and thousands of crows and other bird species launched a national effort to improve surveillance of arthropod-borne diseases.
West Nile is an arthropod-borne virus. Birds are the reservoir hosts and various mosquito species, primarily Culex species, are the vectors. People, horses and other mammals are incidental hosts and not contributory to the spread of infection.
The West Nile virus is capable of causing a fatal neurologic disease in humans and horses. Ongoing research projects may shed new information on the maintenance and transmission of this virus among birds, mammals, other mosquito species and possibly ticks.
Based on available data, 60 equines were diagnosed with clinical West Nile virus in 2000. Thirty-seven (37) survived and 23 (38%) died or were euthanized. These horses were from 7 of the northeastern states listed above. The youngest affected horse was four months of age.
There is no vaccine available for equines at this time. The most important mechanism to prevent a mosquito-borne disease like West Nile virus is source reduction: the elimination of stagnant water sources where mosquitoes may breed.
More aggressive measures, such as insect-proofing stables and individual animal treatment would be prudent once West Nile virus is isolated from mosquitoes, birds, humans or horses in an area.
The Kentucky Department for Public Health (KDPH) is coordinating surveillance efforts statewide in cooperation with the Department of Fish and Wildlife (DFW), the Kentucky Department of Agriculture, the United States Department of Agriculture (USDA), the animal disease diagnostics laboratories, and veterinarians.
Bird mortality surveillance has been the best sentinel for tracking the movement of West Nile virus in the United States and will be the primary focus in 2001. The DFW investigated 170 dead bird reports in 2000, with 23 specimens submitted for West Nile virus testing, all being negative.
Persons who find sick, injured, or dead birds, especially crows or blue jays, are encouraged to report them to the DFW, USDA or KDPH, so a determination can be made on submission of the bird for West Nile testing.
The two animal disease laboratories in Kentucky will be assisting with the dead bird surveillance through federal grant funding. Also, there will be mosquito surveillance in the Louisville and Lexington areas this year, with plans to expand it over the next several years to more areas in the state.
Equine surveillance is essential for economic reasons and for the horse’s potential as a sentinel animal, especially in rural areas. The surveillance case definition for West Nile virus in horses states that the clinical signs in horses must include ataxia or at least two of the following: circling, hind limb weakness, inability to stand, multiple limb paralysis, muscle fasciculation, proprioceptive deficits, blindness, lip droop/paralysis, teeth grinding, or acute death.
The Animal and Plant Health Inspection Service (APHIS) has developed specific guidelines to follow for investigations of equine exhibiting neurological symptoms, and the animal disease diagnostic laboratories in Kentucky are available for pathology and other laboratory services.
West Nile virus activity in 2001: As of June 15, New Jersey has reported 12 dead crows and 2 mosquito pools positive for WNV; Maryland 3 dead birds, New York, 3; Connecticut, 2; and Rhode Island, 2.
Dr. Sue K. Billings, (502) 564-3418, email@example.com
Kentucky Department for Public Health, Frankfort, Kentucky
Wildlife accounted for 91% of the cases, with raccoons remaining the major player, due in part to the continuing epizootic of raccoon rabies on the East Coast and in the southeast US. The geographic hindrances of the Ohio River and the Appalachian Mountains in the south have historically provided a barrier to the spread of raccoon rabies. However, northeastern counties of Ohio have reported cases of rabies in raccoons, resulting in aggressive efforts on rabies vaccine baiting in affected areas in that state.
Bat rabies has occurred in all continental states, and evidence from human cases of rabies due to bat exposure indicates that the bite of a bat is considered almost undetectable, and similar to an insect bite. Due to lack of routine testing of animal brains to detect the specific rabies variant, it is unknown how many cases of equine rabies are due to bats. Documented cases of equine rabies cases due to the bat variant exist in Kentucky and Idaho, both states where skunk rabies predominates.
Of equine rabies cases, 35 of 65 cases were reported from New York, North Dakota, Oklahoma, South Dakota, and Texas. The numbers of cases reported here are the minimum number of cases in 1999; not all neurologic horses are necropsied and tested for rabies.
Raccoon rabies continues to push westward into West Virginia, closing in on the borders of Kentucky and Tennessee. From 0 human rabies cases in 1999, 5 cases occurred in 2000 in California, New York, Georgia, Minnesota and Wisconsin, as well as one in Quebec, Canada. One of the six was due to canine rabies likely obtained from a dog bite while the patient was overseas; all other cases were due to bats.
Kentucky rabies cases
Kentucky rabies cases in 2000 are found in Figure
2. As of May 15, 2001, the only equine rabies case was from Breckenridge
Dr. Roberta Dwyer, (859) 257-4285, firstname.lastname@example.org
Maxwell H. Gluck Equine Research Center, or
Dr. Michael Auslander, (502) 564-3418, email@example.com
Kentucky Department for Public Health, Frankfort, Kentucky
During the first two weeks of May, veterinary clinicians reported an increased incidence of separate cases of pericarditis and unilateral panophthalmitis among a wide age range of horses and breeds. Twelve necropsied cases of pericarditis have been examined at the Livestock Disease Diagnostic Center (LDDC). A range of tests has been performed and further tests are underway to identify the cause of these conditions and clarify the link to MRLS.
Cases of MRLS have been widely reported throughout Kentucky among all breeds of horses. Reports received from contiguous and other states north of Kentucky indicate MRLS may also be occurring in those areas. The incidence of LFL was highest during the first two weeks of May, based on submissions to the LDDC. Similarly, the incidence of EFL was highest during the same period among barren and maiden mares bred during February and early March. Subsequently the incidence of LFL and EFL has fallen. It is estimated that 5% of the 2001 Thoroughbred foal crop produced in Kentucky has been lost and approximately 20 of the foal crop for 2002.
All virological tests have proved negative to date. Although Streptococcus and Actinobacillus species have been isolated from a high proportion of LFL cases examined at the LDDC, they are considered secondary invaders following the primary insult. Gross and histopathological lesions indicate a constant pattern in the fetus and amniotic sac of the placenta. Fetal lungs show evidence of intrauterine toxic insult and inflammation, as does the amniotic sac
Necropsy examinations of pericarditis cases reveal the pericardium is completely covered with grape-sized bright yellow fibrinous nodules. The eye condition involves hemorrhage followed by fibrin deposition.
Fetal tissue samples were submitted from the LDDC on May 17 to the toxicology laboratory at the College of Veterinary Medicine, University of Illinois. Results received on May 24 indicated low levels of cyanide or a cyanide-containing compound in fetal heart tissues.
Possible Factors Contributing to MRLS 2001
Weather data provided by the Department of Agricultural Engineering for the month of April confirmed severe frosts on the nights of April 17 and 18. The month overall had experienced low rainfall. Temperatures through the month had been higher than normal providing ideal conditions for pasture growth. This was an exact replica of weather data observed during April 1981 when a similar syndrome was reported in central Kentucky, although the cause was not identified.
The last two weeks of April also saw massive numbers of the Eastern Tent Caterpillar, which feeds on the leaves of the wild black cherry tree. Investigations revealed a considerable number of cherry trees, a source of cyanogenic compounds, in pastures containing mares that had experienced high numbers of EFL and LFL.
Confirmation of the Cause of MRLS 2001
Additional equine tissues are being examined to confirm the presence of cyanide. The possibility that caterpillars may be a source of cyanide exposure to horses is being examined in depth. In addition, the investigation of other possible causes including mycotoxins, fungal endophytes, phytoestrogens, chemical compounds, and infectious agents is still underway, although results to date provide no evidence that they are involved in the cause of MRLS. A detailed epidemiological survey of 150 horse farms was begun May 30 to identify contributing risk factors.
Visit our web site for the most up-to-date information: www.uky.edu/Agriculture/VetScience/mrls/index.
David G. Powell, (859) 257-2756, firstname.lastname@example.org
Maxwell H. Gluck Equine Research Center