African Horse Sickness (AHS)

MORFAT2023 VIRAL DISEASES July 31, 2024 | 0

African Horse Sickness (AHS) is a severe and often fatal viral disease affecting horses, caused by the African Horse Sickness virus (AHSV), which belongs to the Orbivirus genus within the Reoviridae family. The disease is transmitted by biting midges and is known for its high mortality rate and significant impact on equine health and the equine industry. This guide provides a detailed overview of African Horse Sickness, covering its definition, historical and regional context, species affected, predisposing factors, signs and symptoms, diagnosis, treatment, and prevention strategies.

What It Is

African Horse Sickness (AHS) is an acute viral disease that affects horses, characterized by a range of clinical forms from mild to severe. The disease is caused by the African Horse Sickness virus (AHSV), which is transmitted primarily by Culicoides midges. There are several different serotypes of the virus, and the severity of the disease can vary depending on the strain involved and the immune status of the infected horse.

AHS is known for its high morbidity and mortality rates, with severe forms of the disease often resulting in death within a few days of showing clinical signs. The disease can present in several forms, including:

Peracute Form: Characterized by sudden onset of fever, respiratory distress, and rapid death.
Acute Form: Includes symptoms such as fever, swelling, and respiratory distress, with a high mortality rate.
Subacute and Chronic Forms: Present with less severe symptoms and can result in long-term complications.

AHS is a notifiable disease in many countries, meaning its presence must be reported to veterinary authorities due to its potential to spread and cause significant economic losses in the equine industry.

Historical and Regional Context

African Horse Sickness has a long history, with its first descriptions dating back to the early 20th century. The disease is endemic in sub-Saharan Africa, where it has caused significant losses in horse populations. Historical outbreaks have been associated with the movement of horses and midges, leading to the spread of the virus to new regions.

The disease has also been reported outside of its endemic regions, including in parts of the Mediterranean Basin and the Middle East, due to the movement of infected horses and the migration of vector species. The introduction of AHS to new areas poses a significant risk to equine populations, leading to international efforts to control and prevent the spread of the disease.

Efforts to control AHS include vaccination programs, vector control measures, and international cooperation to manage outbreaks and prevent the disease from spreading to new regions. The disease’s impact on the equine industry and the significant economic losses associated with outbreaks have driven research into better understanding and managing AHS.

Species Affected

African Horse Sickness primarily affects:

Domestic Horses: All breeds and ages of domestic horses are susceptible to AHS. The disease can affect horses used for racing, showing, and recreational riding.
Donkeys and Mules: Donkeys and mules are also susceptible to AHS, although they often exhibit less severe clinical signs compared to horses.
Zebras: Zebras can carry the AHSV and may exhibit mild or subclinical forms of the disease. They can serve as reservoirs for the virus and contribute to its spread.
Humans: AHS does not pose a direct health risk to humans. However, humans can contribute to the spread of the virus through contact with infected animals and contaminated equipment.

Predisposing Factors

Several factors can increase the risk of African Horse Sickness infection:

Vector Presence: The presence of Culicoides midges, which are the primary vectors for AHSV, is a significant predisposing factor. Warm, humid conditions favor the breeding of these midges.
Environmental Conditions: Environments that support the breeding of midges, such as areas with stagnant water and high humidity, increase the risk of AHS outbreaks.
Geographical Location: Horses in regions where AHS is endemic or where the virus has recently been introduced are at higher risk. Movement of horses and vectors between regions can lead to the spread of the disease.
Vaccination Status: Lack of vaccination or incomplete vaccination schedules can increase the risk of AHS. Vaccination is a key component of preventing the disease.
Immune Status: Horses with compromised immune systems or those not previously exposed to the virus are more susceptible to severe forms of AHS.
Importation of Horses: Bringing horses from areas where AHS is prevalent into regions where the disease is not endemic can introduce the virus and lead to outbreaks.

Signs and Symptoms

The clinical signs of African Horse Sickness can vary depending on the kind of the disease and the degree of the infection. Common signs and symptoms include:

Fever: A sudden and high fever is often one of the first signs of AHS. The fever can be quite high and persistent.
Respiratory Distress: Severe respiratory symptoms, including coughing, nasal discharge, and labored breathing, are common. This can progress to severe respiratory distress and pulmonary edema.
Swelling: Swelling of the head, neck, and limbs is characteristic of the disease. The swelling is often associated with fluid accumulation and can be severe.
Conjunctivitis: Inflammation of the eyes, leading to redness, discharge, and sensitivity to light, can occur.
Cyanosis: Bluish discoloration of the mucous membranes, particularly around the mouth and nose, may be observed in severe cases.
Depression and Lethargy: Affected horses may exhibit signs of depression, lethargy, and reduced appetite. They may become increasingly weak and unresponsive.
Abortion: Pregnant mares may abort their foals if infected with AHS, leading to significant reproductive losses.
Edema: Severe swelling, particularly around the eyes and mouth, may occur in the acute form of the disease.
Death: In severe cases, horses may die suddenly, often within a few days of the onset of clinical signs.

Diagnosis

Diagnosing African Horse Sickness involves several methods:

Clinical Examination: Observing clinical signs such as fever, respiratory distress, and swelling provides initial diagnostic clues. The characteristic appearance of the disease may suggest AHS.
Laboratory Testing: Diagnostic tests include:
Polymerase Chain Reaction (PCR): PCR testing can detect AHSV RNA in blood samples, tissues, or fluids. This method is highly sensitive and specific.
Virus Isolation: Culturing the virus from blood or tissue samples in cell cultures can confirm the presence of AHSV.
Serology: Testing for antibodies against AHSV in blood samples can help identify past or recent infections. This includes enzyme-linked immunosorbent assay (ELISA) and other serological tests.
Histopathology: Examining tissue samples for characteristic lesions associated with AHS can aid in diagnosis. Histopathological findings may include inflammation and edema in affected tissues.
Differential Diagnosis: Differentiating AHS from other diseases with similar symptoms, such as Equine Influenza, Equine Herpesvirus, and bacterial infections, is crucial for accurate diagnosis and management.

Treatment and Management

Managing African Horse Sickness involves several strategies:

Supportive Care: Providing supportive care, including hydration, nutrition, and a comfortable environment, is essential for affected horses. Ensuring that horses are kept in a clean, well-ventilated area is important.
Veterinary Care: Regular veterinary care and monitoring are crucial for managing AHS and addressing any complications. Veterinarians can provide guidance on supportive treatments and managing secondary infections.
Anti-inflammatory Medications: Anti-inflammatory medications, such as corticosteroids, may be used to reduce inflammation and swelling in affected horses.
Antibiotics: Antibiotics may be prescribed to treat or prevent secondary bacterial infections that can complicate AHS.
Isolation: Isolating affected horses from healthy animals helps prevent the spread of the virus. Implementing strict biosecurity measures is essential to minimize transmission.
Environmental Management: Improving sanitation and disinfection practices in horse housing and facilities can help control the spread of AHS and reduce environmental contamination.
Record Keeping: Maintaining detailed records of health management, vaccination, and biosecurity practices supports effective disease control and management.

Prevention Strategies

Preventing African Horse Sickness involves a comprehensive approach:

Vaccination: Vaccination is the most effective way to prevent AHS. Several vaccines are available, and vaccination programs should be implemented according to recommended schedules. Consult with a veterinarian to determine the appropriate vaccination protocol for your horses.
Vector Control: Implementing vector control measures, such as using insect repellents, eliminating standing water, and using fly screens, helps reduce the risk of midge bites and transmission of AHSV.
Biosecurity Measures: Implementing strict biosecurity measures, such as controlling access to horse facilities, practicing good hygiene, and managing environmental conditions, helps reduce the risk of AHS.
Surveillance and Monitoring: Regular surveillance and monitoring of equine populations for signs of AHS can help detect and address outbreaks early.
Quarantine Protocols: Implementing quarantine protocols for new or returning horses helps prevent the introduction and spread of AHS within a facility.
Education and Training: Educating horse owners, trainers, and caretakers on best practices for preventing and managing AHS can improve overall disease management and reduce the risk of outbreaks.
Environmental Management: Improving ventilation, sanitation, and general environmental conditions in horse housing areas can help reduce the risk of disease transmission.

LivestockWellness.com is committed to providing valuable information and support for managing African Horse Sickness. Understanding the disease, implementing effective prevention strategies, and responding promptly to outbreaks are essential for maintaining equine health and ensuring the productivity and profitability of equine operations.

African Horse Sickness (AHS)