Equine Influenza

Equine influenza is a highly contagious infectious disease of horses caused by equine influenza viruses. Except for Australia, Iceland, and New Zealand, these pathogens are distributed worldwide. Transmission occurs primarily via aerosolised respiratory droplets, for example, during coughing or snorting of infected horses. Indirect transmission is also possible through virus-containing secretions on hands, contaminated clothing, or shared equipment such as grooming tools or transport vehicles.

The incubation period typically ranges from one to three days. Common clinical signs include high fever (39–41 °C), a painful, non-productive cough, enlargement of the regional lymph nodes, and, in some cases, oedema of the limbs. Some horses may remain subclinically infected while still shedding the virus and contributing to its spread.

Definitive diagnosis can be achieved either by detecting the virus with a nasopharyngeal swab or by demonstrating a rising antibody titre in paired serum samples. As equine influenza is a viral infection, treatment is primarily symptomatic and supportive. This includes strict stall rest, isolation from the remainder of the herd, and the administration of anti-inflammatory and antipyretic medications. Depending on the clinical course, antimicrobial therapy may be indicated to prevent or treat secondary bacterial infections.

Regular vaccination represents the most effective preventive measure. Based on current scientific evidence, vaccination remains the only reliable method to protect against equine influenza virus infection and to limit its spread within equine populations.

Equine Herpesvirus Infection

Equine herpesvirus infection is a viral disease of horses that occurs worldwide, with primary infection often taking place during foalhood or early in life. Following initial infection, the virus persists in the host in a latent state for life and may reactivate during periods of stress or immunosuppression.

Among the known types, equine herpesvirus types 1 (EHV-1) and 4 (EHV-4) are the most commonly encountered. Viral shedding occurs via the mucosal surfaces of infected horses, including those that remain clinically inapparent. Transmission occurs through direct horse-to-horse contact or indirectly via contaminated fomites, such as grooming equipment, feed and water buckets, or clothing. EHV-1 may cause not only respiratory disease but also a neurological form, whereas EHV-4 predominantly induces respiratory clinical signs. Both virus types can also result in abortion in pregnant mares.

Diagnosis is based on direct pathogen detection from nasopharyngeal or uterine swabs, which are typically analysed by polymerase chain reaction (PCR) in the laboratory. As causal treatment is not available, therapy is directed at clinical signs and disease severity.

Vaccination does not provide complete protection against infection or clinical disease; however, it reduces viral shedding and mitigates disease severity. To maintain effective herd immunity, all horses should be vaccinated regularly.

Strangles (Streptococcus equi subsp. equi Infection)

Strangles is a highly contagious bacterial disease that most often affects young horses. It is caused by Streptococcus equi subsp. Equi is distributed worldwide. Transmission occurs via purulent secretions from affected lymph nodes and the respiratory tract, either through direct contact or indirectly via contaminated fomites such as feed and water buckets, grooming equipment, or clothing. Strangles is a highly contagious bacterial disease that most often affects young horses. It is caused by Streptococcus equi subsp. Equi is distributed worldwide. Transmission occurs via purulent secretions from affected lymph nodes and the respiratory tract, either through direct contact or indirectly via contaminated fomites such as feed and water buckets, grooming equipment, or clothing. ssp. equi and is spread worldwide. Infection occurs via secretions from the lymph nodes and respiratory tract, either through direct contact or indirectly via objects such as feeding troughs, grooming utensils or clothing.

The disease typically begins with high fever, often reaching approximately 40 °C. As the condition progresses, marked swelling of the submandibular and retropharyngeal lymph nodes develops, with subsequent abscess formation. These abscesses may rupture externally or internally. If the guttural pouches become involved, purulent exudate frequently accumulates within these structures.

Diagnosis is based on examination of abscess material, nasopharyngeal lavage samples, or guttural pouch washings. In the laboratory, the bacteria are identified either by culture or by polymerase chain reaction (PCR). Treatment depends on the severity and clinical course of the disease.

In the majority of cases, strangles follows an uncomplicated course, and the prognosis is favourable. Severe or complicated disease courses occur only rarely.

West Nile Fever

West Nile virus originated in Africa and is transmitted by mosquitoes. It can cause a febrile systemic illness in both horses and humans, and birds may also be affected. Direct transmission from human to human, horse to horse, or between humans and horses does not occur.

Approximately two-thirds of infected horses develop mild, influenza-like clinical signs such as fever, lethargy, and reduced appetite. However, in about one-third of cases, a severe neurological form develops, characterised by inflammation of the brain and spinal cord. Affected horses may exhibit clinical signs including an unsteady, uncoordinated gait (ataxia), swaying, recumbency, muscle tremors, facial asymmetry, or behavioural changes.

Diagnosis is established by detecting the virus or virus-specific antibodies in blood samples. Depending on the severity of the disease, affected horses often require intensive veterinary care. While the febrile form usually resolves without complications, the neurological form may be fatal or result in permanent neurological deficits.

Vaccination is recommended to protect against infection, particularly for horses kept in or near affected areas. Ideally, vaccination should be completed before the onset of mosquito season.