Equine Influenza

Equine influenza, commonly known as horse flu, is a highly contagious respiratory disease that affects horses, donkeys, and mules. It is caused by the equine influenza virus (influenza virus type A) of the genus Influenzavirus of the family Orthomyxoviddae. The disease has a major impact on the equestrian industry, including horse racing, shows, and other equestrian events. This disease is listed as a notifiable disease by the World Organization for Animal Health (OIE). With our extensive understanding of equine influenza, BioVenic assists customers in developing solutions to diagnose, treat, and control this disease.

Etiology and Epidemiology

Equine influenza is caused by two subtypes of the equine influenza virus: H7N7 and H3N8. The H7N7 subtype was responsible for outbreaks in the mid-20th century, but H7N7 has not been isolated for nearly 20 years, and H7N7 is considered extinct. The H3N8 subtype emerged in the late 1950s and has been the leading cause of equine influenza since then. After decades of evolution, H3N8 has mutated into multiple sublineages, including American lineages and Eurasian lineages. The American lineages can be further subdivided into Newmarket/1/93, Kentucky/94, and Florida. Clades 1 and 2 of the Florida subfamilies are prevalent in Europe and North America. Equine influenza viruses undergo antigenic drift, leading to the emergence of new strains, thus requiring regular updates of vaccine strains.

Fig. 1 Schematic diagram of the structure of equine influenza virus.¹

Equine influenza exists in many horse-raising countries and regions in the world, and humans have been fighting against it for many years. The virus spread rapidly among horse herds, especially in environments where horses come into close contact, such as competitions, training facilities, and boarding stables. Despite the high morbidity, the mortality rate is low, usually below 1%.

Transmission

Transmission of equine influenza primarily occurs through direct contact between infected and susceptible horses. Infected horses can expel respiratory droplets containing the virus when coughing, sneezing, or even through normal respiration. Indirect transmission can also occur through contact with contaminated surfaces, objects, or equipment. The virus can remain viable on surfaces for a limited period, facilitating its spread.

Fig. 2 Schematic diagram of the spread of equine influenza virus.¹

Public Health Risk

Equine influenza is primarily a disease of horses and poses a limited direct public health risk. However, it is essential to recognize the potential for interspecies transmission and the role horses may play as intermediate hosts for influenza viruses. H3N8 has been isolated from animals. However, whether H3N8 can infect humans is still unknown. Monitoring the virus's genetic characteristics and its potential to jump to humans is crucial to assessing the risk to public health.

Signs and Symptoms

Symptoms of the disease vary depending on the type of virus. The disease caused by the H7N7 subtype is relatively mild, while the disease caused by the H3N8 subtype is more severe and prone to secondary bacterial infections.

The clinical symptoms of this disease are:

The disease usually subsides within a few days, but complications such as pneumonia often follow, making the horse long-term debilitated and at risk of death, especially in young foals. Most sick animals recover within two weeks, but the cough will be prolonged and some horses may require a recovery period of up to 6 months.

Diagnosis

The diagnosis should be confirmed through laboratory diagnosis, which usually includes the following.

• Virus isolation: Take the nasopharyngeal secretions of suspected infected horses and inoculate them in the allantoic cavity of chicken embryos, or inoculate them in horse kidneys and chicken embryo cell cultures to isolate viruses.
• Serological tests: Equine influenza virus can be detected by hemagglutination inhibition assay on serum samples, and ELISA can be used to detect virus subtypes.
• qPCR: qPCR can determine the virus subtype or strain.

Based on our rich experience and successful cases, we provide customers with a variety of immunodiagnostics and molecular diagnostics development services.

Treatment and Prognosis

Treatment for equine influenza primarily involves supportive care to alleviate symptoms and promote recovery. Rest, appropriate nutrition, and hydration are crucial for affected horses. Medications such as anti-inflammatory drugs may be administered to control fever and reduce respiratory inflammation. Antibiotics are sometimes used to prevent or treat secondary bacterial infections. The prognosis for equine influenza is generally favorable, with most affected horses recovering fully within a few weeks.

Prevention and Control

• Vaccination

Regular vaccination of horses is strongly recommended, especially for those at high risk or participating in activities with a high potential for exposure.

In addition, we recommend the following biosecurity measures,

• Do not directly or indirectly import equine animals and their products from countries and regions where equine influenza epidemics are endemic.
• Do not post or carry equine animals and their products from epidemic-affected countries and regions into the country.
• It is important to improve the breeding environment of horses as well as the nutrition of their feed.
• Disinfect regularly to provide a clean and hygienic breeding environment.
• Report suspected cases immediately and isolate them.

BioVenic is committed to contributing to the fight against equine influenza. Our team of experts actively collaborates with veterinary researchers. We are committed to helping customers develop diagnostics solutions, treatment options, and prevention strategies for equine influenza. If you also need our technical support, please feel free to contact us.

Reference

1. Singh, Raj K., et al. "A comprehensive review on equine influenza virus: etiology, epidemiology, pathobiology, advances in developing diagnostics, vaccines, and control strategies." Frontiers in Microbiology 9 (2018): 1941.