Systemic Toxoplasmosis in a Horse, a possible emerging problem.

Another cause of chronic weight loss has to be added to the list of rule-outs: Toxoplasmosis. Also, it begs the consideration of pregnant women around horses.

The life cycle of Toxoplasma gondii is complex and comprises two specific phases, sexual and asexual reproduction. The sexual part of the life cycle starts after infecting its definitive host, the cat, while the asexual cycle can take place in any warm-blooded animal including birds, rodents, humans, and now horses. Generally, toxoplasmosis in humans is without symptoms except in pregnant women where the fetus may be aborted, or experience brain or eye damage.
Toxoplasmosis can be treated with combinations of
sulfamethoxazole and trimethoprim
pyrimethamine and sulfadiazine
pyrimethamine and clindamycin
Usually, folinic acid is added to protect the bone marrow from the toxic effects of long term pyrimethamine.

Here we present a series on Toxo in horses including a case report and an investigation using seroepidemiologic monitoring. The epidemiologic picture is that Toxoplasmosis is more prevalent than previously thought and a concern for cultures that eat horse meat.
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Systemic Toxoplasmosis in a Horse
J Comp Pathol. 2021 Jan;182:27-31. doi: 10.1016/j.jcpa.2020.11.004. Epub 2020 Dec 9.
Authors
Katelyn M Kimble 1 , Gabriel Gomez 2 , Joseph A Szule 1 , Jitender P Dubey 3 , Ben Buchanan 4 , Brian F Porter 5
Affiliations

1 Department of Veterinary Pathobiology, Texas A&M University, Texas, USA.
2 Texas A&M Veterinary Medical Diagnostic Laboratory, College Station, Texas, USA.
3 United States Department of Agriculture, Beltsville, Maryland, USA.
4 Brazos Valley Equine Hospitals, Navasota, Texas, USA.
5 Department of Veterinary Pathobiology, Texas A&M University, Texas, USA. Electronic address: bporter@cvm.tamu.edu.

Abstract

An adult American Quarter Horse gelding with a history of weight loss presented with an acute onset of colic, fever, soft faeces and elevated liver enzymes. At necropsy, there were gastric mucosal masses and evidence of caecal necrosis. Histologically, the masses were lymph nodes with granulomatous inflammation and areas of liquefactive necrosis. Within and surrounding necrotic areas were free and intrahistiocytic clusters of protozoal tachyzoites. Similar but milder inflammation was evident in the spleen, lungs and liver. Necrotizing typhlitis was also evident. Immunolabelling for Toxoplasma gondii was positive and the ultrastructural morphology of the protozoa was compatible with T. gondii. Although studies have shown seropositivity to T. gondii in horses throughout the world, this is the first report of clinical toxoplasmosis in this species.

Keywords: Toxoplasma gondii; horses; lymph node; toxoplasmosis.

Toxoplasma gondii infection in horses. A review
P Tassi 1
Affiliations expand
PMID: 18412038
Abstract
This review updates those written by Dubey and Beattie in 1988 (1988a) and by Tenter et al in 2000, on pathological and epidemiological aspects of Toxoplasma infection in horses. Under natural conditions, seroprevalence may variate from 0% up to 90%. This wide variation may be due to the sensitivity of the serological methods, to the age of animals, to the geographical area, and even to the hygienic condition of the farms and farm management. With few exceptions, horses are considered one of the less sensitive specie to the pathogenic effect of Toxoplasma gondii. In fact, neither under experimental nor under natural condition a genuine pathologic picture related to the toxoplasmic infection has been described. In one occasion the organism has been isolated from an eye condition and in others a connection between a higher frequency of unspecified pathological conditions and a positive response to serological test for Toxoplasma has been speculated. Diaplacental transmission and the following abortion have been only occasionally reported, and at least in one case in a quite trustworthy way, therefore it must be considered possible, though rare. Although infection of humans due to the consumption of horse meat has never been reported, the existence of a possible risk arouses by the demonstration of the presence of parasite stages in either naturally or experimentally infected horses, which resulted to be infective for mice and/or cats.

Seroepidemiological study of Toxoplasma gondii in equids in different European countries
Zoonoses Public Health. 2023 Jan 23.
Authors
David Cano-Terriza 1 2 , Juan J Franco 3 , Eduard Jose-Cunilleras 4 , Francesco Buono 5 , Sonia Almería 6 , Vincenzo Veneziano 5 , Eduardo Alguacil 7 , Jesús García 8 , Isabelle Villena 9 , Jitender P Dubey 10 , Débora Jiménez-Martín 1 , Ignacio García-Bocanegra 1 2
Affiliations

1 Departamento de Sanidad Animal, Grupo de Investigación GISAZ, UIC Zoonosis y Enfermedades Emergentes ENZOEM, Universidad de Córdoba, Córdoba, Spain.
2 CIBERINFEC, ISCIII – CIBER de Enfermedades Infecciosas, Instituto de Salud Carlos III, Madrid, Spain.
3 Inmunología y Genética Aplicada, S.A. (EUROFINS – INGENASA), Madrid, Spain.
4 Servei de Medicina Interna Equina, Departament de Medicina Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona, Barcelona, Spain.
5 Department of Veterinary Medicine and Animal Productions, Università degli Studi di Napoli Federico II, Naples, Italy.
6 Division of Virulence Assessment, Department of Health and Human Services, Food and Drug Administration, Center for Food Safety and Nutrition (CFSAN), Office of Applied Research and Safety Assessment (OARSA), Laurel, Maryland, USA.
7 Uplands Way Vets, Diss, UK.
8 Fethard Equine Hospital, Tipperary, Ireland.
9 University of Reims Champagne-Ardenne, EA 7510, National Reference Centre for Toxoplasmosis, Laboratory of Parasitology, Reims Hospital, Reims, France.
10 Animal Parasitic Disease Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, Maryland, USA.

Abstract

Toxoplasmosis, caused by the obligate intracellular protozoan Toxoplasma gondii, is a worldwide parasitic zoonosis. A cross-sectional study was carried out to determine the exposure to T. gondii in equids in Europe. Serum samples from 1399 equids (1085 horses, 238 donkeys, and 76 mules/hinnies) bred in four European countries (Italy, Spain, United Kingdom [UK], and Ireland) were collected during the period of 2013-2021. The overall seroprevalence of T. gondii was 18.9% (95% Confidence Interval [CI]: 16.9-21.0) by using the modified agglutination test (MAT) at a cut-off of 1:25. Seropositivity by country was 27.1% in Italy, 16.6% in Spain, 12.0% in UK and 7.0% in Ireland. Anti-T. gondii antibodies were detected in 12.8% of the horses, 43.7% of the donkeys, and in 28.9% of the mules/hinnies. A Generalized Estimating Equation (GEE) analysis was carried out to study the associations between seropositivity and explanatory variables related to individuals, herds, and management measures on these herds, selected based on the bivariate analysis. The risk for being seropositive for T. gondii was 5.3 and 2.7 times higher in donkeys and mules/hinnies than in horses, respectively. In addition, significantly higher seropositivity was observed in horses from herds that used disinfectants less than once a week (13.9%; p = 0.038, odds ratio [OR] = 1.6; 95% CI: 1.03-2.62) compared with those from herds that performed weekly disinfection of the facilities (9.4%). This is the first large-scale seroepidemiological study on T. gondii comprising horses, donkeys, and mules/hinnies in Europe and the first report of T. gondii exposure in horses from Ireland and UK. We found a widespread distribution of T. gondii among equid populations in different European countries. The seroprevalence found in these species, especially in donkeys and mules/hinnies, highlights the potential risk of human infection through the consumption of their raw/undercooked milk or meat.

Keywords: equids; food-borne pathogens; toxoplasmosis; zoonosis.
© 2023 The Authors. Zoonoses and Public Health published by Wiley-VCH GmbH.