Occurrence of Gasterophilus spp. in Weanling Foals in Southern Brazil


  • Rebeca Scalco Universidade Federal de Pelotas University of California Davis
  • Carlos Eduardo Wayne Nogueira Universidade Federal de Pelotas https://orcid.org/0000-0002-8555-7953
  • Alice Corrêa Santos Universidade Federal de Pelotas
  • Patrícia Soares Vieira Universidade Federal de Pelotas
  • Nathália Oliveira Ferreira Universidade Federal de Pelotas https://orcid.org/0000-0002-8688-8981
  • Luciana Araujo Borba Universidade Federal de Pelotas
  • Lorena Soares Feijó Universidade Federal de Pelotas
  • Bruna da Rosa Curcio Universidade Federal de Pelotas https://orcid.org/0000-0001-8678-3816




Background: The occurrence of gastrointestinal myiasis caused by Gasterophilus spp. larvae (Diptera: Oestridae) in adult horses has been widely characterized, however data on natural infestation in young foals have been lacking. This observation may be related to the absence of conclusive diagnosis in these individuals, most likely due to logistical or financial constraints. Gastric ulceration is a problem and a significant cause of morbidity in foals, particularly during the weaning stage; therefore, gasterophilosis should be included in the differential diagnosis. The primary purpose of this study was to determine the prevalence of gasterophilosis in 4- to 6-month-old weanling foals.

Material, Methods & Results: Seventy-one healthy weanling foals were enrolled in the study. Physical assessment blood sampling and was completed in all foals before the commencement of the experiment. Gastroscopy examinations were performed under sedation (Detomidine 0.01 - 0.02 mg/kg) with a flexible endoscope inserted through nasogastric via. The lumen of the stomach was examined in order to search for botflies’ larvae. Following gastroscopy, foals were classified into 2 groups based on the presence of Gasterophilus spp. larvae in their stomachs: 1) Infected and 2) Not Infected. Infected foals received a single dose of commercial trichlorfon and albendazole equine oral gel and were stalled for 24 h. The passed feces were thoroughly examined, searching for elimination of larvae. A Total of 64% of the foals (n=45/71) harbored Gasterophilus spp. larvae in the stomach. Mild hyperemia in the gastric mucosa was observed in the attachment sites of the parasites. Physical assessment and hematological parameters’ data were analyzed with Shapiro-Wilk normality test. Comparison between groups for clinical signs, hematological parameters and Gasterophilus spp. infection rates were evaluated using the Kruskal-Wallis test or Student's t-test. Statistical significance was set at P < 0.05. There were no statistically significant variations in physical and hematological parameters between foals that were affected and those that were not infected. The larvae found in the feces were subjected to morphological examination, which confirmed the diagnosis of Gasterophilus intestinalis.

Discussion: No systemic clinical indications compatible with Gasterophilus infestation were seen, as described in previous studies of horses infected with the parasite. No botfly eggs were observed in the hair of evaluated foals. During gastroscopy, mild hyperemic lesions in the gastric mucosa were observed in the larvae fixation sites. Although no changes in clinical or hematological parameters were noted, the confirmation of parasite presence is a cause for concern due to horses' tolerance for low infestation levels and poor diagnosis. Additionally, the presence of this myiasis in foals may be a significant stressor during the weaning period and should be included in the differential diagnosis of recurring abdominal pain. Furthermore, infected foals might be a reservoir for the parasite and, contribute to the elimination and spread of the larvae in the environment. Thus, inclusion of young horses in deworming protocols targeted to botfly larvae is needed. This is the first report of Gasterophilus intestinalis myiasis in foals in Brazil. Further research is necessary to fully understand the epidemiology and prevalence of this condition in young horses in Brazil, based on the findings of this study.


Keywords: Gasterophilus intestinalis, cavity myiasis, gastroscopy, Oestridae.


Download data is not yet available.


Cogley T.P. 1989. Effects of migrating Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) on the mouth of the horse. Veterinary Parasitology. 31(3-4): 317-331. DOI: https://doi.org/10.1016/0304-4017(89)90081-2

Deplazes P., Eckert J., Mathis A., Von Samson-Himmelstjerna G. & Zahner H. 2016. Order Diptera Suborder Brachycera (‘short-horn flyes’) Family Oestridae. In: Parasitology in Veterinary Medicine. 3rd edn. Wageningen: Wageningen Academic Publishers, pp.489-497.

Edens L.M. & Murray M.J. 1992. Gastro‐oesophageal reflux in a weanling filly: association with Gasterophilus spp. infestation. Equine Veterinary Journal. 24(S13): 26-28. DOI: https://doi.org/10.1111/j.2042-3306.1992.tb04785.x

Gao D.Z., Liu G.H., Song H.Q, Wang G.L, Wang C.R & Zhu X.Q. 2016. The complete mitochondrial genome of Gasterophilus intestinalis, the first representative of the family Gasterophilidae. Parasitology Research. 115: 2573-2579. DOI: https://doi.org/10.1007/s00436-016-5002-9.

Henneke D.R., Potter G.D., Kreider J.L. & Yeates B.F. 1983. Relationship between condition score, physical measurements, and body fat percentage in mares. Equine Veterinary Journal. 15: 371-372. DOI: https://doi.org/10.1111/j.2042-3306.1983.tb01826.x

Herdt T.H & Sayegh A.I. 2014. Fisiologia do Trato Gastrointestinal In: Cunningham J.G. & Bradley G.K. (Eds). Tratado de Fisiologia Veterinária. 3.ed. Rio de Janeiro: Elsevier, pp.263-356.

Lyons E.T., Tolliver S.C., Collins S.S. & Drudge J.H. 2001. Transmission of endoparasites in horse foals born on the same pasture on a farm in central Kentucky (1996-1999). Veterinary Parasitology. 97: 113-121. DOI: https://doi.org/10.1016/S0304-4017(01)00393-4

Murray M.J. 1999. Gastroduodenal ulceration in foals. Equine Veterinary Education. 11(4): 199-207. DOI: https://doi.org/10.1111/j.2042-3292.1999.tb00948.x

Otranto D., Milillo P., Capelli G. & Colwell D.D. 2005. Species composition of Gasterophilus spp. (Diptera, Oestridae) causing equine gastric myiasis in southern Italy: Parasite biodiversity and risks for extinction. Veterinary Parasitology 133: 111-118. DOI: https://doi.org/10.1016/j.vetpar.2005.05.015

Rodrigues F.S., Silva C.E., Schmidtt E., Nizoli L.Q., Gotze M.M. & Silva S.S. 2007. Presence of Gasterophilus (leach, 1817) (díptera: oestridae) in horses in Rio Grande do Sul state, Brazil. Parasitología Latinoamericana. 62(3-4): 122-126. DOI: http://dx.doi.org/10.4067/S0717-77122007000200004

Rooney J.R. 1964. Gastric ulceration in foals. Pathology Veterinary. 1(6): 497-503.

Sequeira J.L., Tostes R.A. & Oliveira-Sequeira T.C. 2001. Prevalence and macro- and microscopic lesions produced by Gasterophilus nasalis (Diptera: Oestridae) in the Botucatu Region, SP, Brazil. Veterinary Parasitology. 102: 261-266. DOI: https://doi.org/10.1016/S0304-4017(01)00536-2

Sweeney H.J. 1991. Gastroduodenal ulceration in foals. Equine Veterinary Education. 3 (2): 80-85.

Taylor M.A., Coop R.L. & Wall R.L. 2016. Parasites of Horses. In: Veterinary Parasitology. 4th edn. Chichester: Wiley- Blackwell, pp.524-561

Walden H.S., Ness S.A.L., Mittel L.D., Divers T.J., Vaan Laaren K. & Sellon D.C. 2014. Miscellaneous Parasitic Diseases. In: Equine Infectious Diseases. 2nd edn. Saint Louis: Elsevier, pp.505-514.

Weese J.S. 2008. The gastrointestinal system. In: McAuliffe S.B. & Slovis N.M. (Eds). Color Atlas of Diseases and Disorders of the Foal. Saint Louis: Elsevier, pp.79-131.

Zumpt F. 1965. Morphology, Biology and Pathogenesis of Myiasis-producing Flies in Systematic Order - Family: Oestridae. In: Myiasis in man and animals in the Old World: A Textbook for Physicians, Veterinarians, and Zoologists. London: Butterworth, pp. 110-128.



How to Cite

Scalco, R., Nogueira, C. E. W., Santos, A. C., Vieira, P. S., Ferreira, N. O., Borba, L. A., Feijó, L. S., & Curcio, B. da R. (2021). Occurrence of Gasterophilus spp. in Weanling Foals in Southern Brazil. Acta Scientiae Veterinariae, 49. https://doi.org/10.22456/1679-9216.114163




Most read articles by the same author(s)