Infection is the condition in which a pathogenic microorganism has established itself in the tissues of a host, evaded or overwhelmed the initial innate defenses, and begun to replicate and cause measurable tissue damage or systemic physiological disruption. It is distinguished from mere exposure or contamination by the element of establishment: an organism that contacts the skin surface without penetrating it does not constitute infection. Clinically, infection is recognized by the cardinal signs of cardinal signs of local tissue response—heat, swelling, redness, pain, and loss of function—at the affected site, and by systemic signs including elevated temperature (see hyperthermia), elevated heart and respiratory rate, and depression when the infection spreads beyond its initial focus.
Infections in horses are classified by the causative agent and anatomical location. Bacterial infections range from locally contained abscesses—the most common cause of severe acute lameness (see hoof abscess)—to systemic septicemia in neonatal foals lacking adequate passive passive immunity in neonatal septicemia. Viral infections such as equine influenza, equine herpesvirus, and equine arteritis virus spread rapidly through respiratory secretions and can move through an entire barn population within days. Fungal infections (dermatomycosis, guttural pouch mycosis, aspergillosis) tend to affect immunocompromised horses or specific anatomical niches. Internal parasitic infection, while technically an infestation in precise terminology, produces pathological changes indistinguishable in clinical appearance from tissue-invasive bacterial and protozoal infections.
Diagnosis requires identification of the causative organism through culture and sensitivity testing for bacteria, PCR for viruses, and cytological or histological examination for fungi. Treatment is agent-specific: antibiotics for susceptible bacteria, antifungals for mycotic infections, and supportive care for viral infections where no specific antivirals are licensed for equine use. The route and duration of antibiotic therapy must be guided by culture results to avoid treatment failure and minimize selection pressure for resistance. Hygienic biosecurity measures at the facility level—quarantine, disinfection, foot baths, and equipment isolation—remain the primary tools for preventing infectious disease from entering or spreading within a herd, because prevention is substantially less costly than treatment and the disruption to training or showing schedules from an outbreak can be severe.
Further Reading
- infection (Wikipedia)
- For disease-specific guidance: infectious diseases of horses — MSD Veterinary Manual