Summer 2023 Newsletter

In this edition, our newest pathologist, Dr. Carmen Lau, and our two newest technicians, Ellecyn Brimley and Jessica Felts, are introduced. In addition, recent cases of botulism, goiter, Q-fever, and Salmonella abortion in a dog are presented.

Equine Botulism

By Dr. E. Jane Kelly

Type A botulism was recently diagnosed in several young horses in eastern Utah. A horse owner recently lost five of his horses. An older animal died first, then a few days later one of the yearlings died and four other yearlings were recumbent and eventually died or were euthanized. As described by the owner, clinical signs included rapid recumbency in the 4 animals that were not found dead, slow eating, quivering, weakness, teeth grinding, and tremors. The horses that were recumbent did not have the strength to raise their heads. Interestingly, the classic botulism symptom of the tongue hanging out was not seen. The first two horses that died were simply found dead and a period of recumbency before death was not noted. Two of the yearlings were submitted to the UDVL, Spanish Fork Branch for necropsy in February 2023, a few days apart. Other than the two horses that were found dead, the clinical course in the other horses was several days (and probably longer because 3 of them were euthanized). No gross lesions were seen in the horses necropsied. A complete set of tissues (including brain and spinal cord) was taken for histopathology Significant microscopic lesions were not identified. The horses were fed hay and occasionally grain. They were in dry lots so there was no grazing. No new animals had come to the farm recently and none of the horses had moved off the farm for any reason in the past several months. Vaccinations for tetanus and west Nile virus were up to date.

Colon and stomach content from the first horse necropsied were submitted to the National Veterinary Services Laboratory (NVSL) for botulism testing. The Botulism Diagnostic Laboratory at the University of Pennsylvania, where samples have been sent in the past, is no longer offering testing. Clostridium botulinum Toxin A was detected in gastrointestinal samples.

The final diagnosis was botulism and it is likely that the other 4 horses had botulism also. Type A botulism is less common than type B in horses in the US and has been associated with ingestion of toxin in hay or silage (Johnson AL, et al.) and is most common in the western US.

This recent case of botulism highlights some of the important features of the disease in horses. In general, botulism is caused by a potent neurotoxin that is produced by the anaerobic Gram-positive spore-forming bacterium Clostridium botulinum. It affects a wide variety of animals and birds worldwide. There are 9 types of C. botulinum based on toxins produced. Types C and D cause most outbreaks in domestic animals in the United States, but not in horses. Botulism affects human beings too, and is the reason that infants under 1-year of age should not be fed honey. The neurotoxins produced by this bacterium are the most potent biological toxins known. The toxins prevent release of acetylcholine at neuromuscular junctions resulting in flaccid paralysis. Usually, the toxin is ingested preformed (e.g., feed contaminated with rotting carcasses, spoiled food etc.).

Horses are highly susceptible to botulism, only a tiny amount of toxin is enough to cause severe disease. Approximately 85% of cases of equine botulism in the US are type B botulism. Type B is endemic in mid-Atlantic states and Kentucky. Type A occurs more commonly in the western US. The case described here was type A botulism. Most adult horses acquire botulism by ingestion of preformed toxin. Foals with shaker foal syndrome ingest the bacterial spores which germinate in the intestine and then release toxin (toxicoinfectious botulism). There is a third way that horses may acquire botulism: wound contamination with C. botulinum bacteria (less common). Type C botulism in horses has been associated with ingestion of forage contaminated with carcasses of dead animals.

Typical clinical signs appear a few hours to several days after exposure to toxin. Affected horses become weak with decreased tail and tongue tone (will not withdraw tongue into mouth easily), drop food, have difficulty drinking, and have dilated pupils and drooping eyelids. Most progress to recumbency and death due to respiratory failure. Recumbent horses are often alert and continue to want food and drink. Sometimes, treatment with type specific antitoxin (expensive) and supportive care may help horses recover if they are not yet recumbent. Since toxin binding is irreversible, the antitoxin only neutralizes unbound toxin. Antitoxin for horses is available as a monovalent antitoxin against type B and a polyvalent antitoxin against types A to E. The only vaccine licensed for use in horses is a type B botulinum toxoid. The use of type C toxoid that is licensed for mink is not recommended for use in horses.

Unfortunately, there is no equine vaccine against type A botulism. Treatment is expensive and usually only effective in horses that are still standing; in this case, the polyvalent antitoxin would have had to be administered rapidly because the horses’ clinical signs progressed rapidly to recumbency.

References

• Johnson AL, et al. Type A botulism in horses in the United States: a review of the past ten years (1998-2008). J Vet Diagn Invest 22: 165-173, 2010
• Kinde H, et al. Clostridium botulinum type-C intoxication associated with consumption of processed alfalfa hay cubes in horses. JAVMA 199: 742-746, 1991
• Whitlock RH and McAdams S. Equine botulism. Equine Practice: 37-42, 2006
• Whitlock RH. Botulism, type C: experimental and field cases in horses. Equine Practice 18, 1996.

Goiter in Neonatal Cattle

By Dr. E. Jane Kelly

Over the years, I have seen enlarged thyroid glands (goiter) mostly in aborted goats. However, this year I have seen it in stillborn and neonatal beef calves. This is something we rarely see in calves in Utah. In fact, iodine deficiency causing goiter is rare in modern production due to fortification of salt (Arthington, JD). The most severe case seen this spring was a 3-day-old female Angus calf that was submitted for necropsy in March of 2023. She had a history of coughing and dyspnea, and respiratory disease was suspected as cause of death. Several disease processes were identified and contributed to death. There was omphalitis (navel ill) with secondary septicemia and meningitis, myodegeneration of skeletal muscle likely due to white muscle disease (liver selenium levels were within normal levels; however, vitamin E testing was not done), and congenital goiter. Thyroid glands were enlarged bilaterally (at least 4 times normal size, 3 x 3 x 5 cm) and compressed the proximal trachea, which explains the coughing and dyspnea. Histologically, goiter was confirmed as thyroid glands were hyperplastic. Thyroid tissue was submitted to the Michigan State University Veterinary Diagnostic Laboratory for testing of iodine levels. The result was 117.8 ug/g with normal values between 1,100- 1,800 ug/g. Thyroid iodine concentrations are the most accurate determination of iodine nutritional status.

Goiter occurs for 2 reasons: iodine deficiency (most common) or iodine excess. In congenital goiter, deficiency in the dam is usually the problem. The deficiency can be primary (lack of iodine) or secondary (iodine uptake blocking e.g., by brassica plants: kale, rape, cabbage, soybeans, peas, turnips). Occasionally, it is hereditary. Iodine is required to synthesize thyroid hormones that regulate energy metabolism. Dietary requirement for iodine is influenced by efficiency of the thyroid gland and the extent of iodine recycling. Nutrients and toxins that affect iodine metabolism include high arsenic, fluorine, and calcium, deficient or high cobalt, and low manganese. The recommended level of supplementation of iodine in beef cattle is 0.5 ppm. Mineral supplements for cattle usually contain iodine in the form of calcium iodide, sodium iodide, or potassium iodide. Commonly, an organic complex EDDI (ethylenediamine dihydroiodide) is the source of iodine in salt and trace mineral supplements. In this case, the dam did not have access to sufficient iodine in her diet either due to lack of or inadequate trace mineral supplementation.

References

• Current Veterinary Therapy 4: Food Animal Practice edited by Howard & Smith, W.B. Saunders Co. Wither SE. Congenital goiter in cattle. Can Vet J, 1997, Vol 38, page 178
• Homerosky ER, et al. An outbreak of congenital goiter and chondrodystrophy among calves born to spring-calving beef cows. Can Vet J, 2019, Vol 60, pages 981-983
• Arthington JD, Ranches J. Trace Mineral Nutrition of Grazing Beef Cattle. Animals, 2021, Vol 11, 2767. https://doi.org/10.3390/ani11102767

Abortion due to Salmonella spp. Infection in a Dog

By Dr. E. Jane Kelly

An aborted puppy wrapped in placenta was necropsied at UVDL, Spanish Fork Branch in September 2022. No significant gross lesions were identified. Histopathologic findings included acute multifocal amnionitis. Aerobic and Brucella spp. cultures were set up on fetal liver and placenta and Salmonella spp. was detected in pure culture from the liver and placenta. Heaviest growth was from the placenta. The isolate was submitted to the National Veterinary Services Laboratory (NVSL) in Ames, Iowa for serotyping and the reported serotype was III_50:z36:- (Salmonella enterica subspecies arizonae). The source for this subspecies of Salmonella enterica is usually cold-blooded animals and the environment.

The dam is a 2-year-old bernedoodle dog and this was her first litter. She presented at the veterinary clinic with a history of aborting a litter of puppies. Five fetuses total had been aborted over the previous several days (at 52-53 days of gestation). The 5^th puppy aborted was necropsied. A vaginal discharge was observed by the owners starting just before puppies were aborted. At the time of physical exam, the discharge was brown and moderate to severe. Other than the vaginal discharge, no significant abnormalities were noted. The diet consisted mostly of dry kibble with occasional raw hamburger or raw egg when the owner was cooking. She was artificially inseminated and, up to 52 days of gestation, had a normal, active pregnancy. The owners opted for ovariohysterectomy when another dead puppy was seen in the uterus by ultrasound.

Salmonella spp. is an unusual cause of abortion in dogs. It is a more common in other domestic animals such as cattle, small ruminants, and horses. In these species, infection is thought to occur via ingestion with subsequent colonization of the placenta. Some Salmonella spp. associated with abortion are zoonotic. The source of the Salmonella spp. in this case was not determined. It is possible that the dog ingested or was in contact with a reptile or an amphibian that was carrying Salmonella spp.

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