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Britain Remains Free From West Nile Virus

Samples from nearly 1,000 British horses revealed no presence of West Nile Virus (WNV). Transmitted by mosquitoes, West Nile Virus can cause severe neurological issues in horses; the disease has a fatality rate of about 33 percent in unvaccinated animals.

Drs. Arran Folly, Elisabeth Waller, Fiona McCracken, Lorraine McElhinney, Helen Roberts and Nicholas Johnson note that while this is good news for horse owners, they must remain vigilant in the fight against the disease. WNV is seen in many parts of the world, including the United States, southern Europe and Germany.

The researchers focused their study on southeast England, the area of Britain considered most at risk for virus introduction. The virus is most likely spread geographically by birds that have the virus; horses are a dead-end host for WNV.

Two of the 998 horses tested were positive for WNV antibodies, but upon further review, it was deemed that the antibodies were a result of vaccination for the virus within seven days of the testing.

The scientists concluded that there was no evidence of West Nile Virus transmission in England in 2019; this is in agreeance with the results of a 2019 British bird surveillance, which also found no West Nile Virus RNA in the birds.

Read the short report here.

Study: Omeprazole And Bute Not Necessarily A Good Combination

Omeprazole is often prescribed to horses that are receiving phenylbutazone in an effort to reduce the chances of a horse developing equine gastric ulcer syndrome (EGUS), though it isn't clear how safe or effective this treatment is.

Drs. Megan Ricord, Frank Andrews, Francisco Yñiguez, Michael Keowen, Frank Garza Jr., Linda Paul, Ann Chapman and Heidi Banse created a study to evaluate the effect of omeprazole on adult horses with EGUS caused by phenylbutazone.

The research team used 22 horses that had equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD), each horse had a score of a 2 or higher when tested for the disease. The horses were divided into three groups: one group (eight horses) received 4.4 mg/kg of oral phenylbutazone every 12 hours; the second group (eight horses) received the same phenylbutazone dose plus 4 mg/kg of oral omeprazole every 24 hours. The control group (six horses) received neither phenylbutazone or omeprazole.

The horses were treated for 14 days and had their stomachs scoped at days seven and 14. Blood tests were done at the beginning and end of the study period. Five of the horses did not complete the study because of intestinal issues (two in the phenylbutazone-only group and three in the phenylbutazone/omeprazole group).

The scientists found that the EGGD score increased in the study group that received the phenylbutazone only when compared to the horses that also received omeprazole. They found no difference in the ESGD scores between the two groups. Strikingly, six of the eight horses in the phenylbutazone/omeprazole group developed intestinal complications—two of which were fatal. Only two of the horses in the phenylbutazone-only group had intestinal complications, and neither of them died.

The team concluded that using omeprazole reduced the severity of EGGD, but that caution should be exercized when using the two concurrently, especially when this takes place at the same time as a management change.

Read the study here.

UC Davis Researchers Identify Genetic Variant For Fatal Condition In Thoroughbreds

Researchers at the UC Davis School of Veterinary Medicine have identified a genetic cause for the fatal condition equine familial isolated hypoparathyroidism (EFIH) in Thoroughbreds, marking the first genetic variant for hypoparathyroidism identified in any domestic animal species. Additionally, this is the first widely available genetic test for Thoroughbreds.

The study, led by Drs. Carrie Finno and Gary Magdesian, which was reported in the journal PLoS Genetics. Genetic testing can now be performed at the UC Davis Veterinary Genetics Laboratory to identify horses with the variant and avoid mating carriers that could produce affected foals.

“For Thoroughbred owners and breeders, the loss of a foal has tremendous economic and emotional impacts,” says first author Victor Rivas, who conducted the project as part of his undergraduate training in Finno's laboratory. “It is important to promote safe and strategic breeding habits by actively breeding horses genetically screened not only for EFIH, but for other diseases that may impact quality of life.”

Foals affected with EFIH suffer from low blood calcium concentrations, resulting in involuntary muscle contractions, muscle stiffness that leads to a stiff gait and can progress to an inability to stand, seizures, fevers, and an abnormally fast pulse. Parathyroid hormone is typically produced to increase calcium levels in the body, but in these foals, concentrations are low or “inappropriately” normal (i.e. they should be high due to the low calcium). Affected foals die or are euthanized due to poor prognosis. Necropsy results reveal underdeveloped or absent parathyroid glands.

Previously termed idiopathic hypocalcemia, EFIH has been observed in Thoroughbred foals up to 35 days of age. Disease onset and progression are likely determined by the amount of calcium in the diet early in life. This can vary based on dam milk calcium concentration and the amount of milk ingested.

The current study determined an autosomal recessive mode of inheritance and performed whole genome sequencing of two affected foals. A mutation in the rap guanine nucleotide exchange factor 5 (RAPGEF5) gene was present in two copies (homozygous) in both foals. The variant was further analyzed in a frog developmental model and demonstrated loss-of-function of the RAPGEF5 protein leading to aberrant development. Based on this data, the researchers hypothesize that RAPGEF5 may play a role in the derivation of the parathyroid gland during development.

The variant was not identified in individuals from 12 other breeds. The allele frequency for the RAPGEF5 variant in an expanded set of 82 randomly selected, unaffected Thoroughbreds was 0.018. An unbiased allele frequency study has not been performed, so the allele frequency in the larger Thoroughbred population is currently unknown.

“The next steps are to assess the allele frequency in a large population of randomly selected Thoroughbreds,” says Finno. “Additionally, we have discussed collaborating with Dr. Nathan Slovis at Hagyard Equine Medical Institute in Kentucky to test for the variant in cases of 'sudden death' in Thoroughbred foals.”

The clinical presentation of EFIH is similar to human familial hypoparathyroidism. Since the RAPGEF5 gene is highly conserved across species, it is a potential new candidate gene for primary hypoparathyroidism in humans.

“This type of research discovery requires a unique collaboration between clinicians, pathologists and basic researchers,” says Finno. “We were incredibly fortunate to have samples submitted from Drs. Slovis, Daniella Leuthy (University of Pennsylvania) and Laura Javsicas (Rhinebeck Equine) and the expertise of Drs. Brian Caserto (VetPath services) and Andrew Miller (Cornell University). Additionally, the 'proof' of functional results of this genetic mutation would not have been possible without our collaborator from Yale University, Dr. Mustafa Khohka.”

Support for this study was provided by the UC Davis Center for Equine Health.

African Horse Sickness Outbreak In Malaysia

Five horses in Malaysia have been diagnosed with African Horse Sickness; the disease had never been confirmed in the country until this outbreak. The horses lived in Terengganu, located in the eastern part of the Malay Peninsula. On September 2, Malay authorities reported the outbreak, noting that the horses had been exhibiting signs of the disease since early August. The horses had difficulty breathing, were lame and had a fever.

The source of the virus is not known. There are nine different serotypes of African Horse Sickness, each with a specific geographic distribution. Identifying the serotype may indicate from which region the virus originated. AHS is transmitted by biting midges and the disease tends to be seasonal; it's generally associated with hot and humid weather.

The Malaysian outbreak follows on the heels of an AHS outbreak in Thailand, where 604 horses were affected and 562 died. Malaysia is approximately 550 miles from Thailand, but it is unknown if the occurrence in Malaysia is the from the movement of horses, the movement of infected vectors or is a new occurrence of the disease.

AHS affects all species of Equidae and the severity of clinical signs is dependent upon the virus strain and species affected. The fatality rate in horses can reach up to 90 percent. Though there is a commercial vaccine for AHS, none are approved for use in the European Union.