Snake Bite in Horses

From Equine Disease Quarterly, Univ. Of KY.

Snakebite in Horses

With warm weather comes the increased risk of snakebite. The major venomous snakes in the United States are the pit vipers, including rattlesnakes, water moccasins, and copperheads. Pit vipers are named after the heat-detecting holes, or pits, on each side of the head that help the snake locate prey. Pit vipers can be differentiated from other snakes by their triangle-shaped heads, narrowed necks, and tail rattles (rattlesnakes only). Coral snakes, another type of poisonous snake in the U.S., do not pose much risk to horses because of their small mouth size.Venom components vary tremendously by snake species, but most venoms contain substances that cause breakdown of tissues and blood vessels, impair blood clotting, and damage the heart. Venoms from some species of snake also contain neurotoxins. Snakebite severity depends on multiple factors such as snake species, size, recent feeding, and number of bites. Some bites are “dry bites,” where little venom is injected. Other bites, such as when a snake is stepped on and releases all of its venom agonally, can be very severe. Victim factors such as horse size, age, disease conditions, medications, and bite location also influence bite severity.Clinical signs of snakebite in horses vary widely but generally include pain and swelling at the bite site, and often sloughing of tissues near the bite. Bite wounds may not be readily apparent. Dry bites with little venom injected or bites from copperhead snakes often cause only mild signs. Bites from dangerous species of snakes and large doses of venom can cause marked pain and swelling, coagulopathy, hemorrhage, cardiac arrhythmias, shock, collapse, and even death. With neurotoxic venoms, paralysis can occur. Horses bitten on the nose can develop nasal swelling and respiratory distress. Signs of envenomation can occur within minutes or be delayed for many hours.The best first aid is to keep the horse calm and arrange for immediate veterinary care. No first-aid treatments performed by owners in the field have proven particularly helpful, and many folk remedies can even be harmful. Suction devices have not been shown to be beneficial in animal models of snakebite.Treatment varies with the severity of the bite, but may include fluids, pain medications, wound care, antibiotics, tetanus prophylaxis, and antivenin. Antivenin can decrease the amount of tissue damage and hasten recovery times, and can be especially helpful in cases of severe envenomation. Antivenin is dosed according to the estimated amount of venom injected, not the patient size, so even one vial of antivenin can have beneficial effects. Cardiac arrhythmias occur in many horses and may require treatment. Horses with severe nasal passage swelling may need treatment to maintain a patent airway; nutritional support may be required if swelling impairs the horse’s ability to eat and drink.Even after horses have recovered from the immediate effects of snakebite, subsequent complications such as heart failure or kidney damage are possible. Cardiac failure can occur weeks to months after the bite incident, necessitating continued evaluation and monitoring.A vaccine is now available for use in horses to help prevent complications of snakebite, but efficacy in horses is not yet well documented. Contact your veterinarian for more information about snakebite in your region.

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“Differential Virulence and Pathogenesis of West Nile Viruses.”

Pathogenesis of West Nile Viruses.
pubmed: pubmed horse / by Donadieu E, Bahuon C, Lowenski S, Zientara S, Coulpier M, Lecollinet S / 18 hours ago
Differential Virulence and Pathogenesis of West Nile Viruses.

Viruses. 2013;5(11):2856-2880

Authors: Donadieu E, Bahuon C, Lowenski S, Zientara S, Coulpier M, Lecollinet S

Abstract
West Nile virus (WNV) is a neurotropic flavivirus that cycles between mosquitoes and birds but that can also infect humans, horses, and other vertebrate animals. In most humans, WNV infection remains subclinical. However, 20%-40% of those infected may develop WNV disease, with symptoms ranging from fever to meningoencephalitis. A large variety of WNV strains have been described worldwide. Based on their genetic differences, they have been classified into eight lineages; the pathogenic strains belong to lineages 1 and 2. Ten years ago, Beasley et al. (2002) found that dramatic differences exist in the virulence and neuroinvasion properties of lineage 1 and lineage 2 WNV strains. Further insights on how WNV interacts with its hosts have recently been gained; the virus acts either at the periphery or on the central nervous system (CNS), and these observed differences could help explain the differential virulence and neurovirulence of WNV strains. This review aims to summarize the current state of knowledge on factors that trigger WNV dissemination and CNS invasion as well as on the inflammatory response and CNS damage induced by WNV. Moreover, we will discuss how WNV strains differentially interact with the innate immune system and CNS cells, thus influencing WNV pathogenesis.
PMID: 24284878 [PubMed – as supplied by publisher]

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The Aged Horse: Immune System and Nutrition

From the Equine Disease Quarterly, University of KY

The Importance of Nutrition in Enhancing Immunity in the Aging Horse

Over the past century, improvements in health care and advancements in biology, chemistry and medicine have extended the average lifespan of humans and companion animals, including horses. However, we are now facing new challenges with the paradox of an older population with increased longevity, while confronted with the potential for many years of poor health. A better understanding of the mechanisms leading to a decline in physiologic function with age would provide new predictive biomarkers and potential therapeutic targets.It has been well-documented that the aged, including horses, have increased susceptibility to and prolonged recovery from infectious diseases, poor responses to vaccination, and increased incidence of various cancers. Furthermore, it is now accepted that chronic inflammation (inflamm-aging) is a major underlying condition of many age-related diseases, such as atherosclerosis, arthritis, cancer, diabetes, osteoporosis, dementia, vascular diseases, obesity and metabolic syndrome.In anti-aging research, much attention is focused on nutritional interventions as practical, cost-effective approaches to mitigating this agerelated breakdown in immune function. These natural dietary compounds found in a variety of fruits, vegetables, nuts and seeds are promising candidates in helping to combat the effects of aging. They possess broad biological activities: anti-oxidative, anti-inflammatory, detoxification, regulating signaling pathway, and modulation of enzyme activities (see Table 1).Since aged horses (>20 years) have increased levels of inflammation, and treatment with longterm use of non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine and phenylbutazone can pose health problems, we are interested in nutritional interventions to counteract this inflamm-aging process.Flavonoid (quercetin) and polyphenolic compounds (curcuminoids, resveratrol, pterostilbene and hydroxypterostilbene) were compared to phenylbutazone and flunixin meglumine to determine differences in equine cytokine production in cell culture. White blood cells from aged horses were isolated and incubated overnight with each compound or NSAID at multiple concentrations. Inflammation production was measured when cells were stimulated.At varying doses (measured in micromolar units [μM]), each of the compounds and NSAIDs significantly reduced cellular inflammation: curcuminoids (20 μM), hydroxypterostilbene (40 μM), pterostilbene (80 μM), quercetin (160 μM), resveratrol (160 μM), flunixin meglumine (40 μM) and phenylbutazone (>320 μM). Interestingly, curcuminoids at a concentration of 20 μM reduced inflammation to the same level as higher doses of flunixin meglumine (40 μM) and phenylbutazone (>320 μM). All natural compounds outperformed phenylbutazone by being effective at lower doses.This preliminary research has led into two studies using aged horses to determine: 1) if a relationship exists between circulating vitamin and fatty acid levels to systemic inflammation and muscle mass, and 2) if anti-inflammatory supplementation affects immune responses to vaccination. These are preliminary steps to identify effective nutritional intervention regimens to improve function of the immune system in the aged horse.

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Selenium Status in Horses: A review on supplementation

From Equine Disease Quarterly – University of KY.

Selenium Status in Horses

Selenium (Se) plays a role in the antioxidant mechanism of the body, and has also been shown to affect the immune system in many species. Additionally, Se is incorporated into at least 25 different selenoproteins. The synthesis of these selenoproteins depends on the availability of Se within the body. Herbivores rely on plants to meet their Se requirements, while plants obtain Se from the soil. However, soil Se concentration varies geographically, resulting in inconsistent dietary Se intakes across regions in grazing animals.Areas that tend to be low or marginal in Se include parts of the Eastern United States, New Zealand, Northeastern China, Europe, Egypt and South Africa. Horses kept in low Se areas, or exclusively fed forage and unsupplemented grains produced in low Se areas, may become Se deficient over time.Central Kentucky is known to be marginal in Se. Therefore, the long term effects of dietary Se intake on the Se status, immune function and exercise response of the horse was studied at the University of Kentucky in collaboration with the Alltech–UK Nutrigenomics Alliance.Horses grazing low Se pastures were fed a Se-free supplement for 28 weeks. Then, over the next 28 weeks, a third of these horses was supplemented with 0.3 mg Se/kg dry matter and a third received the same amount of Se, but as sodium selenite. The remaining horses stayed on the unsupplemented diet. Throughout the study a fourth group of horses was given a supplement providing the National Research Council’s recommended Se intake of 1 mg Se/day for a 500 kg horse (approximately 0.1 mg Se/kg dry matter).The study results demonstrated that the Se status of horses kept in a low Se area, without additional Se supplementation, declined over time. At the end of the initial 28 week depletion, blood Se concentration was 165 ng/mL and glutathione peroxidase (GPx) activity was 43.1 enzymatic units/g hemoglobin (EU/g hb), compared to reference values for horses of adequate Se status of 180- 240 ng Se/mL and 40-160 EU/g hb, respectively. A selenoprotein, GPx is regarded as a hallmark indicator of Se status.Following Se supplementation, low Se status was corrected within 60 days. In unsupplemented horses, both blood Se and GPx continued to decrease to 125 ng Se/mL and 33.8 EU/g hb, respectively. Immune function assessment of the horses indicated that low Se status was detrimental to the immune system.Also, following exercise the horses of low Se status experienced a decrease in GPx activity which did not recover within 24 h post-exercise. This decrease occurred even though the exercise was mild, designed with the recreational riding horse in mind. GPx activity increased post-exercise in horses supplemented with Se-yeast, but decreased in the inorganic Se group. Because of its antioxidant role, a decrease in GPx post-exercise could leave horses vulnerable to oxidative stress.Overall, dietary Se intake should receive special consideration for horses kept in low Se areas, especially if they are kept on pasture with minimal supplementation. Commercial feeds and supplements often contain additional Se, so all feeds (pasture, hay, concentrates and supplements) should be considered when estimating dietary Se. Although Se deficiency may pose risks for horses, Se toxicity can also occur, so over-supplementation should be avoided.

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Potomac Horse Fever – A Review

From Equine Disease Quarterly – University of KY.

Equine Monocytic Ehrlichiosis: Kentucky Case Series, January 2008-August 2013

Equine monocytic ehrlichiosis (EME) is also known as Potomac Horse Fever (PHF) and equine ehrlichial colitis. The disease has since been reported in most states in the US, at least three Canadian provinces and also in parts of South America, Europe and India. The disease usually occurs near rivers, lakes and wet pastures from mid- to late-summer.The cause of EME is Neorickettsia risticii, formerly Ehrlichia risticii. The reservoir for the causal agent is not clear but it has been isolated from ticks, aquatic insects, flukes and other helminths. Snails act as an intermediate host in the fluke cycle. Horses are thought to be infected through the ingestion of insects, often mayflies, which may land in drinking water. Experimentally, the incubation period ranged from 1-3 weeks in horses.In the early stage of the infection, horses may become anorexic, depressed, pyrexic and have decreased gut sounds. This is usually followed by loose stools or watery diarrhea and colic. In the late stages of the disease, affected animals may have severe dehydration, ventral abdominal edema, and laminitis. Death is the consequence of cardiovascular compromise and toxemia. Case fatality rates range from 5-30%. Transplacental transmission is reported often leading to fetal resorption, abortion, or weak foals. Horse-to-horse transmission is not thought to occur.Horses that recover from the disease may have protective immunity for up to two years. Available vaccines appear to have variable efficacy. Limiting proximity of horses to rivers, ponds, lakes and low-lying pastures during the peak EME season and eliminating lighting at night in horse stables to minimize attraction of insects may reduce the risk of infection.A provisional clinical diagnosis of EME needs to be confirmed by a veterinary laboratory competent in diagnosing the disease. A single positive indirect fluorescent antibody (IFA) test result for EME on serum only indicates exposure to the agent. Paired blood samples collected two weeks apart demonstrating a four-fold or greater rise in titer is evidence of an active infection. In clinical cases, a polymerase chain reaction (PCR) assay should be performed on an EDTA blood sample as well as on a fecal sample, as presence of the causal organism in blood and feces may not temporally coincide. At necropsy, a scraping of the colonic mucosa is the specimen of choice for PCR testing for EME.From January 2008 through August 2013, the University of Kentucky Veterinary Diagnostic Laboratory had 123 equine samples submitted that tested positive for EME by PCR. Included in this number were 26 horses submitted for necropsy that were diagnosed with EME. Of the necropsy cases, the sex distribution was 53% female and 47% male. The mean age distribution was 8.7 years (range 0.3-34 years). The breeds involved were mostly Thoroughbred.

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