Foreign equine diseases you need to worry about today (Proceedings)


The clinical signs of VEE are similar to both EEE and VEE with a large variation in mortality ranging from 40-90% depending on the outbreak. In addition to subclinical and overt CNS clinical signs, diarrhea has been observed in VEE horses. Florida, Texas, and Louisiana are the three states ecologically at risk but recent activity in Panama could result in a transported case by air travel.

Major Neurological Syndromes

Venezuelan Equine Encephalitis

The clinical signs of VEE are similar to both EEE and VEE with a large variation in mortality ranging from 40-90% depending on the outbreak. In addition to subclinical and overt CNS clinical signs, diarrhea has been observed in VEE horses. Florida, Texas, and Louisiana are the three states ecologically at risk but recent activity in Panama could result in a transported case by air travel. A form of endemic VEE called Everglades virus (EGV) does occur in south Florida. Horse "disease" has only been identified serologically as subclinical infection. Recently, several north Florida horses have been identified during the Florida season with very high serum neutralization titers (SN) without history of vaccination. The interpretation of these titers is difficult and may indicate that EGV is more widespread as a result of recent weather upheavals. Whether or not EGV actually causes some sort of encephalitic syndrome is an open question. Vaccination against VEE is controversial. Currently, the only marketed vaccine is a killed product. Vaccination of horses with what is essentially considered a foreign animal disease confounds testing for that horse should an outbreak occur. In addition, the use of a killed vaccine against a virulent viral variant is of questionable efficacy. During previous outbreaks, a conditionally available modified live vaccine was released to contain the outbreak in Texas. It is likely that this potent vaccine will be released.

Japanese Encephalitis Virus

Japanese Encephalitis Virus (JEV) is actually the type virus of the Flavivirus in which WNV belongs. Many of the disease features are similar, and this discussion will focus on dissimilarities and expectations should outbreak occur. First, like WNV, JEV is spreading geographically and focal, intense outbreaks are occurring new areas of Eurasia. The Ardeid birds (herons and egrets are believed to be the natural wildlife hosts for JE. Pigs also may be important reservoirs and can amplify JEV. The vector is similar to JEV, which Culex mosquitoes most important arthropod hosts. Cycles of outbreaks occur during rainy seasons and in temperate climates late summer is important. Because there are horses that are not exposed to Flaviviruses, severe sporadic outbreaks do occur in naïve horse populations upon encroachment or transport of horses into endemic areas. Like WNV, horses appear to be dead-end hosts. Horses appear to develop long-term immunity to JE virus infection. When naïve horses are shipped into endemic areas, they generally seroconverted within the year and these antibodies persist for several years. Like WNV, horses and donkeys are equally susceptible to disease. Interestingly case fatality rates are between 5 and 15% in some locales, but in Japan 30-40% has been reported. Diagnosis at time relies on neutralization testing. For JE, there are 3 syndromes described: Transient Type: these horses have moderate to high fevers for 2-3 days. The horses can also have anorexia, slow movement, and congested mucous membranes. Lethargic Type: Horses with these types of signs have higher fevers, lethargy, anorexia, nasal discharge, difficulty swallowing, jaundice and petechial hemorrhages. Neurological signs occur with incoordination, staggering, and spontaneous falling. Neck rigidity, radial paralysis and impaired vision all have been noted. These horses usually recover in 4-5 days. Hyperexcitable Type: In less than 5% of cases JE horses develop hyperexcitability. These horses exhibit bizarre mentation characterized by aimless wandering, shaking, violent reactions, blindness, sweating, teeth grinding, and muscle fasciculations. Although the hyperexcitability can be transient, this group of horses is more likely to die from spontaneous collapse. There are available vaccines in Japan for use in horses. Little is known regarding cross-protective immunity with WNV vaccines.

Borna Disease Virus

Although Borna Disease has been reported only in Germany, seropositive horses have been reported in other European countries, Israel, Japan, Iran, Australia and the U.S. In Germany, Borna is the most important viral cause of encephalitis, and possibly this disease has gone unrecognized elsewhere. In Germany, cases occur in central and southern Germany and have a seasonal occurrence in April, May and June. Many horses are seropositive while actual disease occurrence is relatively rare.

Equine Encephalosis Virus

This is a South African virus that is often confused with African Horse Sickness virus. This is a virus that is transmitted by Culicoides also. After an incubation of 3-6 days, horses develop fairly mild clinical signs which included a high fever, depression, and inappetence. A reddish-brown discoloration of the mucous membranes also occurs. There is occasionally varying degrees of selling of the eyelids and supraorbital fossae. The central nervous system, respiratory distress, acute heart familiar

Major Hemolymphatic Diseases

Piroplasmosis or Equine Babesiosis

Equine Babesiosis is endemic Worldwide EXCEPT United States, Canada, Australia, Japan, England and Ireland. U.S. high at risk from lack of regulation of events, shipping of sport horses, variable clinical signs, carrier status, and test inefficiency. Multiple vectors include Dermacentor, Rhipicephalus, Hyalomma spp. B. caballi and B. equi are the causative agents resulting in fever, depression, pale mucous membranes, anorexia, petechia, ecchymoses, hemorrhages, edema, hemoglobinuria. Death loss can be as high as 20% of naïve, infected animals. Many outbreaks occurred in the 1960's in Florida and horses, mules, donkeys and zebra are equally susceptible. Zebra's are reservoirs in Africa. This disease has a long incubation of 10-30 days. The disease is characterized by anemia, thrombocytopenia, and leukocytosis. Diagnosis is by visualization of parasites. Serology: has become controversial, nonetheless the CI-is the best test but IFA distinguishes B. equi and caballi. The CF test is inappropriate. Treatment to avoid testing positive is unethical and puts US population at risk.

UPDATE: The USDA Animal Plant Health Inspection Service (APHIS) and individual State Departments of Agriculture continue to conduct comprehensive epidemiological investigation of this event.

Update as of 5 July 2010

Kleberg County, Texas outbreak

Over 2,300 horses have been tested for equine piroplasmosis as part of the epidemiological investigation. The NVSL has confirmed equine piroplpasmosis (Theileria equi) in 406 horses directly linked to the index premises.

The epidemiologically linked T. equi positive horses are currently in seven States: Texas, Alabama, Colorado, Louisiana, Indiana, North Carolina, and Tennessee.

The T. equi positive horses either currently live or previously lived on the index premises, or live on a premises immediately adjacent to the index premises, or are dangerous contacts (positive foal born to an infected mare, or temporarily boarded on index premises), or are from high risk premises (located in close proximity to the index ranch and have similar terrain and tick populations).

Trypanosomiasis is a complex of diseases caused by various Trypanosomes found worldwide.

Clinical signs vary slight depending on species but Surra is the hemolymphatic form. This principally infects horses and camels of North Africa, Middle East, South America. Incubation is 5-60 days and it is caused by T. evansi. Transmssion is by Tabanids and Stomoxys. Clinical signs include fever, weakness, lethargy, petechial hemorrhages, edema: legs, thorax, abdomen, urticarial eruption of skin, progressive weight loss, anemia, icterus. This is eventually fatal with death in 2 weeks to 4 months. Diagnosis is by Blood Smear of the deep vessels, examination for parasites, and antigen ELISA. Serology consists of ELISA followed by card agglutination test.

Exotically Named Virus That Are Floating Around!

African Horse Sickness

African Horse Sickness is a disease of horses, donkeys and mules which is endemic dz Central Africa. South African outbreaks occur regularly. This disease is transmitted by Culicoides primarily and transmission by mosquitoes and ticks occur also. Disease is weather cycle associated and the virus will travel in wind-blown arthropods. The clinical manifestations can be subclinical. In subacute disease there is swelling of supraorbital fossa, eyelids, facial tissues, neck, thorax, chest, shoulders. A painful death from colic in 1 week usually occurs. In the respiratory form, dyspnea, coughing, frothy fluid streams from dilated nostrils with death from anoxia occurs. In the mixed form: mild pulmonary, death from cardiac failure occurs. Diagnosis is based on serology, viral Isolation, and PCR.

NOTABLE Disease Outbreak Reports for 2010

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