Equine Laboratory Testing

Faecal Microbiology in Horses

Several bacterial pathogens are commonly associated with diarrhoea in horses, including:

• Salmonella spp.
• Clostridium perfringens
• Clostridium difficile
• Lawsonia intracellularis

Salmonella spp. infections can occur through contaminated feed or water or contact with carrier animals that shed the bacteria in their faeces. Horses of any age can be affected, presenting symptoms that range from mild to severe, including increased body temperature, diarrhoea, septic shock, and even sudden death. It’s important to note that Salmonella can infect humans, so strict hygiene practices should be followed when handling any horse with diarrhoea.

Clostridium perfringens and Clostridium difficile are anaerobic bacteria commonly found in the environment, particularly in soil, as well as in the intestinal tracts of healthy horses and other animals. In some cases, these bacteria may cause severe diarrhoea in certain horses, though the exact reasons remain unclear. Since these bacteria can also be present in the faeces of healthy horses, culture alone is insufficient for diagnosis; detection of the associated toxins is necessary.

Lawsonia intracellularis is responsible for Equine Proliferative Enteropathy (EPE), primarily affecting weanlings and yearlings. This disease leads to intestinal thickening and protein loss. Affected horses may exhibit dullness, colic, diarrhoea, weight loss, and swelling in the lower legs. Since Lawsonia cannot be cultured in the lab, PCR testing is required to detect its DNA in faeces.

Other bacterial species that may also be involved in diarrhoea, though less frequently, include Campylobacter spp., Aeromonas spp., and Enterococcus durans.

Unlike many laboratories, the IEC conducts comprehensive faecal cultures on diarrhoeal samples to identify all potential pathogens, including these less common species. This approach helps us monitor and detect any emerging novel causes of diarrhoea in horses.

Bacterial and Fungal Culture, and Sensitivity Testing

Bacterial culture and sensitivity testing are essential tools for identifying the bacteria present in a sample and determining which antimicrobial agents are effective against them. The results from bacterial cultures can help diagnose infections, identify potential sources, and assess whether the infection may be contagious to other animals. Sensitivity testing further guides treatment decisions by indicating which antibiotics are likely to be effective.

Fungal culture, on the other hand, is utilized to detect yeasts or moulds in samples to diagnose fungal infections. Antifungal sensitivity testing is also available as a referred service.

The Microbiology Lab, reflecting our commitment to high standards in testing and quality results. Our laboratory team comprises highly experienced microbiologists and is led by an EBVS®-recognized specialist in Veterinary Microbiology. We are equipped with advanced microbiological technology, including a VITEK II system for bacterial identification and susceptibility testing.

Respiratory Microbiology

A healthy respiratory system is essential for the peak performance of equine athletes. Bacterial and fungal agents are often implicated as either primary causes of respiratory diseases or as secondary invaders following viral infections.

Strangles (Streptococcus equi subsp. equi)

Strangles is a highly contagious disease in horses caused by Streptococcus equi subsp. equi. It is characterized by elevated temperature, nasal discharge, and swelling of the lymph nodes in the head and neck. While it is not usually fatal, complications can arise, and even routine infections can result in prolonged downtime for affected horses. Discharges from horses with an active infection are a significant source of contagion, spreading through direct contact or indirectly via equipment, buckets, and tack. Carrier animals, which may appear healthy but harbor the bacteria in their guttural pouch, can also contribute to the spread. The bacterium does not survive in the environment for more than a few days.

Detection of Streptococcus equi subsp. equi is accomplished through bacterial culture or PCR analysis of nasopharyngeal swabs, nasal washes, pus, or guttural pouch washes. Antibody tests can indicate previous exposure to the bacterium.

Rhodococcus equi

Rhodococcus equi is a bacterium known to cause pneumonia with lung abscessation in foals, although it can also infect other sites such as the intestines, bones, and joints. While overt infections in adult horses are rare, Rhodococcus equi is a soil-dwelling organism commonly found on many horse farms. The primary route of infection is inhalation of dust particles containing the bacterium. Some farms experience recurring issues with Rhodococcus equi in foals each year, though the reasons for this phenomenon are not fully understood.

Diagnosis of Rhodococcus equi infection is performed using bacterial culture or PCR analysis of tracheal wash samples or other relevant specimens. Treatment typically requires a combination of two antibiotics over several weeks. However, antibiotic-resistant strains of Rhodococcus equi have emerged, raising concerns due to limited treatment options. The IEC is actively researching these drug-resistant strains.

Aspergillus fumigatus

Aspergillus fumigatus is a fungal organism commonly found in soil, decaying vegetation, and organic debris. While it rarely causes disease in healthy horses, it can quickly exploit any weaknesses in the animal’s immune system. For instance, Aspergillus fumigatus can invade superficial lesions on the eye, leading to severe corneal ulceration. Horses with compromised pulmonary defenses—due to prior infections or corticosteroid treatments—may develop fungal pneumonia or infections in the nasal cavity or sinuses. Diagnosis of Aspergillus fumigatus infection is performed through fungal culture, and susceptibility testing of fungal isolates is available upon request.