Common variable immunodeficiency is a rare, but serious disease in adult horses that often leads to hospitalization, said Maria Julia Bevilaqua Felippe Flaminio, DVM, MS, PhD, Dipl. ACVIM, who presented research on the topic at the American College of Veterinary Internal Medicine Forum, held June 3-6 in Montréal, Quebec.

Common variable immunodeficiency (CVID) is a humoral (in the blood) immunodeficiency in the horse in which B cells (cells that produce antibodies) either fail to develop or differentiate into antibody secreting plasma cells.

This condition is characterized by late-onset B cell lymphopenia or depletion, hypo- or agammaglobulinemia (a disorder in which there are very low levels of immunoglobulins), inappropriate response to tetanus toxoid vaccination, recurrent fevers, and bacterial infections. Pneumonia is the most common complaint, and bacteremia and suppurative meningitis are also frequent. Other clinical manifestations include sinusitis, peritonitis, diarrhea, gingivitis, skin abscesses, and hepatitis.

According to Flaminio, humoral deficiency is the most commonly diagnosed primary immunodeficiency in mammals, including the horse. CVID has been diagnosed in horses between 2 and 19 years of life, with no gender, breed, or familial predilection.

It is a progressive disease in which affected horses can appear normal for many years before clinical manifestation of disease. When clinical signs appear, the humoral system is already impaired.

Horses with CVID rarely live beyond six months from the time of diagnosis. The majority of infected horses require hospitalization for appropriate clinical diagnosis and treatment of severe pneumonia and/or meningitis. Euthanasia is often elected by the owner due to clinical complications.

Initially, prolonged parenteral antibiotic therapy seems to control infection and improve the clinical condition of the horse, but clinical signs tend to reoccur with time or when antibiotic therapy is discontinued. Horses with CVID should be monitored closely for signs of infection so that antibiotic therapy can be initiated immediately.

It is apparent that B cells become progressively depleted or reduced to almost undetectable numbers in affected horses, in both primary and secondary lymphoid tissues, which consequently translates to a progressive depletion of circulating immunoglobulins.

Researchers are currently working toward the investigation of both primary (genetic) and secondary (acquired) causes of CVID. Currently, research data suggests that this condition is a primary immunodeficiency, perhaps involving abnormal genetic regulation of B cell differentiation.

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