Experimental infection of mares with Haemophilus equigenitalis.

This study investigated the effects of infecting horses with a bacterium Haemophilus equigenitalis, which caused symptoms similar to a common equine disease, and found the infection lasted from a few weeks to several months depending on the horse.

Objectives and Process of the Study

• The study aimed at analyzing the impact of Haemophilus equigenitalis on mares by inoculating it into the uterus.
• Seven mares were used as test subjects in the study.
• The scientists paid close attention to the onset of the disease which was similar to contagious equine metritis, a common horse disease.

Observations Made in the Course of the Study

• The clinical signs or symptoms of infection varied from horse to horse, with some mares showing signs for four days, while others showed symptoms for up to eleven days.
• The bacterium stayed in the system of most horses for about 2 to 10 weeks. However, in two other horses, the organism managed to establish a ‘carrier status’ and lasted until their death after six and ten months.
• The scientists were able to recover the bacterium from the vestibule of the vagina and combined swab of the clitoral fossa and sinuses throughout the infection period. There were, however, periods (as long as two weeks) during which the bacterium could not be reisolated.

Immunological Response in the Mares

• Upon being infected, all mares showed a transient serological response which is an immune response measurable in the blood.
• The complement fixation test which is used to measure the antibodies level in the blood, generally turned negative after 12 weeks of infection.
• Conversely, antibodies detected through passive haemagglutination test (PHT) and serum agglutination test (SAT) were more stable and existed for a longer period.
• Interestingly, in some animals, the PHT and SAT titers increased during the breeding season following the infection.
• The study found that the serological response did not appear to be reliant on the duration of infection.