Vascular malformations and angiomatous lesions in horses: a review of 10 cases

Vascular malformations and angiomas are rather uncommon in horses and the literature concerning these lesions is reviewed. The pathology is described in 10 additional cases. These lesions were classified as arteriovenous malformation (one case), haemangiomas (six cases), 'proliferative angiomas' (two cases) and lymphangioma (one case). The haemangiomas and lymphangioma were probably hamartomatous in origin. Both cases of 'proliferative angioma' developed in aged animals and their pathogenesis was uncertain. More information is needed on the natural history and behaviour of lesions of this type.

Alimentary lymphomas in the horse

A series of 9 cases of primary diffuse alimentary lymphoma of the equine small intestine is described. Clinically, the principal effects were attributable to malabsorption and disordered alimentary function and several cases had severe anaemia; in four this was of the haemolytic type. Hypoalbuminaemia and elevated gamma globulin levels were often present. The neoplasms were confined mainly to the small intestine and mesenteric lymph nodes, sometimes with some involvement of other lymph nodes as well. The large bowel was affected in one horse, but none of the cases showed detectable invasion of parenchymatous organs. Evidence is presented that some of these lymphomas were of follicle centre cell origin and it is suggested that they had probably arisen from B lymphocytes in gut-associated lymphoid tissue.

Chronic inflammatory and lymphoproliferative lesions of the equine small intestine

A retrospective study was made of 20 horses with severe and extensive chronic disease of the small intestine. Many of the animals had clinical evidence of malabsorption, with progressive loss of weight, hypoalbuminaemia and sometimes anaemia. All but two of the horses were Thoroughbreds. The pathology was diverse. Nine of the cases were alimentary lymphomas (Platt, 1986) and five had lymphocytic and eosinophilic infiltrations in the bowel wall which were considered to be probable reactions to parasitic invasion. One had acute thrombosis associated with partial occlusion of the anterior mesenteric artery by a verminous thrombus, superimposed on granulomatous lesions resulting from earlier ischaemic episodes. Two animals, from one stud, had dense mononuclear infiltration of the intestinal mucosa with villous atropy accompanying an unidentified acid-fast bacillary infection in the mesenteric lymph nodes and other sites. Three horses had granulomatous or lymphogranulomatous infiltration of the small intestine accompanied by marked mucosal and villous atrophy. One of these had multiple abscessation in part of the affected bowel. Only the three latter cases had lesions resembling those of equine granulomatous enteritis and the results of this study indicate the rarity of this condition in Thoroughbreds in Britain. The different types of lesion were only distinguishable by histological examination, since their clinical effects and gross pathology were not characteristic.

Pathological observations on an outbreak of paralysis in broodmares

A description is given of the pathological changes present in 8 mares which died or were euthanased in the course of an outbreak of paralysis on a Thoroughbred studfarm. In all cases the principal changes were in the central nervous system (CNS) and consisted of a severe and widespread vaculitis in the brain, cord, sheaths of nerves, capsules of ganglia and occasionally elsewhere in the body. Associated with the damage to vessel walls there was haemorrhage and exudation of plasma into the perivascular tissues. Involvement of neurones was minimal and no neuronophagia was present. Six cases had malacic foci in the brain, related to thrombosis of local arteries. Acinar necrosis in the mammary gland was present in one case. Examinations of the CNS and cerebrospinal fluid (CSF) for the presence of equid herpesvirus 1 (EHV1) or other microbial agents proved negative but EHV1 was isolated from the spleen of one mare and from the pharyngeal mucos membrane in another. The pathogenesis of this type of paralysis is discussed.

Observations on vaccine and post-infection immunity in contagious equine metritis

The vaccination of four ponies on two occasions with a formolised culture of Haemophilus equigenitalis produced a high circulating antibody titre to the organism in each pony. Three out of four vaccinated and all of three unvaccinated ponies developed typical symptoms of contagious equine metritis (CEM) when subsequently challenged with a vaginal exudate containing H equigenitalis. Similarly, three ponies which had previously been infected with H equigenitalis and which had recovered spontaneously also developed contagious equine metritis when rechallenged with the organism. The clinical and bacteriological symptoms in the vaccinated ponies and in the rechallenged ponies were less severe than those observed in the unvaccinated ponies but H equigenitalis was still recovered 17 days after challenge from the three vaccinated ponies which had developed CEM. The vaccinated pony which remained free from infection did not exhibit the highest circulating antibody titre of the vaccinates before challenge.

Yersiniosis in a free-living fallow deer

A case of yersiniosis in a free-living fallow deer is described. Pathological examination revealed an emaciated carcase with numerous abscesses of various sizes throughout the abdominal and thoracic cavities. Staining of material from the abscesses showed a small Gram-negative coccobacillus which was identified as Yersinia pseudotuberculosis type 1A.

The experimental infection of ponies with contagious equine metritis

Four pony mares were readily infected with the organism of contagious equine metritis by intracervical inoculation and one by coitus with an infected stallion. Infected mares developed an acute endometritis with local destruction of the endometrial epithelium. In 2 experimentally infected mares, infection appeared to have been spontaneously eliminated from the genital tract within 3 to 4 weeks. A third mare however remained persistently infected in the clitoral fossa over a long period and was a symptomless carrier. Four pony stallions were readily infected in the urethral fossa and the organism survived for varying periods without giving rise to any signs of infection. From 2 of these animals it appeared eventually to have been eliminated spontaneously. An experimentally infected stallion transmitted infection to a healthy mare by coitus. Bacteriological examination of infected pony stallions may occassionally give false negative results and fail to reveal the organism in the external genitalia. Repeated bacteriological examinations need to be undertaken before it can be concluded that a stallion is free of infection.

Joint-ill and other bacterial infections on thoroughbred studs

From a perinatal survey carried out on Thoroughbred studs, information was obtained on the incidence, mortality and long-term effects of joint-ill and other bacterial infections. Many of these infections occurred in foals with a history of other perinatal abnormalities, and in foals in which receipt of colostrum was delayed. There was no direct relationship between the incidence of infection and maternal age, but prenatal lactation and loss of colostrum were more frequent in older mares. There was a significant reduction in the incidence of infections in foals given neomycin and framomycin during the first 30 days of life.

Klebsiella and Enterobacter organisms isolated from horses

An account is given of K. pneumoniae capsule types occurring in horses, with particular reference to strains originating from the genital tract in the mare and the external genitalia of the stallion. A survey of the prevalence of K. pneumoniae and E. aerogenes strains in the preputial flora of healthy stallions is described. The majority of horses were found to be carriers of these organisms. The cultural characteristics of these preputial strains are described and compared with those of K. pneumoniae strains associated with epidemic metritis in mares. The epidemiological significance of certain K. pneumoniae capsule types is discussed.

Infection of the horse fetus

Many infections of the equine placenta and fetus result from ascending spread along the cervical canal. Most abortions due to infection occur during the later stages of pregnancy and the possible effects of intrauterine infection on the developing fetus and young foal are discussed.