African Swine Fever in Pigs: Causes, Signs & Prevention

Introduction

African swine fever (ASF) and swine erysipelas are significant diseases affecting pigs worldwide. This article will discuss the causes, transmission, clinical signs, and control measures for both diseases.

African Swine Fever

African swine fever is a highly contagious and often fatal disease characterized by high mortality rates, especially in its acute form. The clinical signs and postmortem findings closely resemble those of hog cholera, but the severity of the signs is more pronounced.

Warthogs and bush pigs act as reservoirs of the infection. While the disease was initially confined to Africa, it has now spread to other regions, including Portugal, Spain, France, Italy, Bulgaria, and the former Union of Soviet Socialist Republics (USSR).

Causes of African Swine Fever:

The disease is caused by a large Iridovirus that can be found in blood, tissue fluids, internal organs, and all excretions and secretions of infected animals. The virus is resistant to heat, drying, and putrefaction. It can survive in partly cooked or smoked sausages and other related products.

Transmission of African Swine Fever:

Natural infection primarily occurs through direct contact with infected pigs, feces, and body fluids. However, exposure to infected premises and ingestion of contaminated food and water can also result in transmission. Ticks, such as Ornithodourus moubata, as well as pig lice, have been implicated in the field as vectors for the disease.

Clinical Signs of African Swine Fever:

Following an incubation period of one week, affected pigs experience a sudden onset of high fever (40-42°C), which persists for up to 48 hours. Despite the fever, the animals continue to eat and remain alert. The fever eventually subsides, and the pigs develop marked cyanosis of the skin.

Other clinical signs include depression, weakness, difficulty in standing, gummed-up eyes, huddling together, and potential reproductive issues such as miscarriage, stillbirths, and abortions in sow barns. Incoordination, red or blue blotches on the ears and snout, dyspnea, diarrhea, vomiting, coughing, and labored breathing may also be observed.

These signs are often followed by vomiting or diarrhea with mucopurulent or bloody ocular and nasal discharge. Death usually occurs within one to two days after the onset of obvious signs, often accompanied by convulsions.

Postmortem Lesions of African Swine Fever:

Gross postmortem changes in African swine fever closely resemble those found in hog cholera, with the difference that lesions are typically more severe. Widespread hemorrhages throughout the body, especially in lymph nodes, epicardium, myocardium, lungs, kidney, bladder, and sometimes the spleen, are common.

Button ulcers in the colon and caecum, splenic infarcts, and petechial hemorrhages in the renal cortex and bladder are less common than in hog cholera.

Diagnosis of African Swine Fever:

The history of a highly contagious infectious syndrome causing high mortality in pigs of all ages, combined with clinical signs such as high fever, occasional vomiting, and diarrhea, strongly suggests African swine fever. Confirmation of the disease can be achieved through tests such as the Enzyme-linked immunosorbent assay (ELISA), demonstration of the virus in tissues, and animal transmission tests.

Control and Prevention of African Swine Fever:

To control and prevent the spread of African swine fever, the following measures are recommended:

1. Restriction on the movement of pigs or pork from infected areas.
2. Culling infected animals on affected farms and implementing strict biosecurity measures.
3. Isolation and slaughter of infected pigs.
4. Thorough disinfection of piggery units.
5. Implementation of effective fencing to separate wild pigs from domestic pigs.
6. Procurement of pigs from disease-free areas.
7. Proper treatment of swill or waste before feeding it to pigs.

Other Viral Diseases in Pigs

In addition to African swine fever, several other viral diseases affect pigs, including Foot and Mouth Disease, Rabies, Pseudo rabies, Transmissible gastroenteritis, and Respiratory diseases, among others. These diseases will be further discussed about cattle diseases and pet diseases (dogs and cats).

Swine Erysipelas

Swine erysipelas is an infectious disease of pigs with a worldwide distribution. It can manifest in both acute and chronic forms, with distinct clinical signs and postmortem findings.

Cause and Transmission of Swine Erysipelas:

Swine erysipelas is caused by the bacterium Erysipelothrix rhusiopathiae. Infected pigs shed the organism in urine, feces, and oronasal secretions, contaminating the environment. Ingestion of contaminated food is the main route of infection, although skin abrasions can also serve as a possible route.

Pathogenesis and Clinical Signs of Swine Erysipelas:

The bacterium invades the bloodstream in all infected animals. The subsequent development of either acute septicemia or bacteremia with localization in organs and joints depends on the virulence of the strain and concurrent viral infections, such as hog cholera, which increase susceptibility.

The acute form is characterized by a sudden onset of high fever, anorexia, thirst, conjunctivitis, and diamond-shaped, urticarial skin lesions. The mortality rate can be significant.

The sub-acute and chronic forms present milder symptoms, including chronic arthritis and cardiac issues.

Postmortem Findings of Swine Erysipelas:

In the acute form of swine erysipelas, postmortem examination reveals diamond-shaped skin lesions, along with diffuse purplish edema on the belly. Minor petechiation may be observed under the kidney capsule, pleura, and peritoneum. The bacterium can be isolated from blood and tissues. In the chronic form, there are enlarged joints with increased synovial fluid and large, crumbly lesions on the heart valves.

Control and Treatment of Swine Erysipelas:

To control swine erysipelas, the following measures are recommended:

1. Immunization using hyperimmune serum, as the bacterium is resistant to harsh environmental conditions.
2. Vaccination of all gilts and young boars before they enter the breeding herd.
3. Prompt disposal of clinically affected animals.
4. Isolation of newly introduced animals.
5. Proper incineration of all animals that die from the disease.

Treatment of swine erysipelas involves the administration of penicillin, with a recommended dose of 50,000 IU/kg body weight of procaine penicillin for three days. However, chronic cases may not respond well to treatment due to structural damage to the joints or the inaccessibility of the bacteria in the endocardial lesions. In such cases, cortisone can be administered subcutaneously at a dose of 75 mg daily to alleviate arthritis symptoms, although complete recovery may not be achieved.

Conclusion

In conclusion, African swine fever and swine erysipelas are significant diseases affecting the pig population worldwide. Understanding their causes, modes of transmission, clinical signs, and appropriate control measures is crucial for preventing their spread and minimizing their impact on pig health and production.

By implementing strict biosecurity measures, such as restricting movement, culling infected animals, ensuring proper hygiene and disinfection protocols, and sourcing pigs from disease-free areas, farmers and authorities can work together to mitigate the risks associated with African swine fever and swine erysipelas.

It is important for pig farmers to stay informed about these diseases and regularly monitor their herds for any signs of illness. Early detection and prompt reporting of suspected cases to veterinary authorities can help prevent further spread and facilitate timely intervention.

Additionally, maintaining overall herd health through vaccination programs, implementing appropriate biosecurity measures, and proper waste management can contribute to disease prevention and control.

Pig farmers should also be aware of other viral diseases that can affect pigs, such as Foot and Mouth Disease, Rabies, Pseudo rabies, Transmissible gastroenteritis, and Respiratory diseases. Understanding the signs, transmission routes, and control strategies for these diseases can aid in the overall management of pig health.