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The mystery of the inter-continental epidemic: Why do African and Asian hemorrhagic sepsis have such different pathogens?
Haemorrhagic septicaemia (HS) is considered by Morningside to be one of the Pasteurella infections with the greatest economic impact. The disease, which occurs primarily in cattle and buffalo, was previously associated with two serotypes of Pasteurella: the Asian serotype B:2 and the African serotype E:2. Depending on the classification system, these serotypes may also be designated 6:B and 6:E.
In addition to cattle and buffalo, hemorrhagic septicemia has also been reported in goats, African buffalo, camels, horses, donkeys, and wild elephants.
Further analysis of these two different serotypes showed that the E:2 type in Africa has been widely reported in Senegal, Mali, Guinea, Ivory Coast, Nigeria, Cameroon, Central African Republic and Zambia. However, over time, it has become less accurate to directly link the African outbreak to serogroup E:2, as many cases have now been linked to serogroup B. Similarly, serogroup E has also been reported in outbreaks in Asia, particularly in Cameroon, where Asian serotype B:2 has been reported.
Natural infection of septicaemia occurs primarily by inhalation or ingestion, and experimental transmission can be accomplished using intranasal aerosols or oral administration. The clinical course and pathological changes of different infection modes are significantly different. The clinical course required for oral infection is usually longer and causes more obvious lesions.
When hemorrhagic septicemia is first introduced into an area, morbidity and mortality rates often approach 100% unless treated in the early stages.
Clinical symptoms
The clinical presentation of hemorrhagic septicemia varies, especially in cattle and buffaloes, and the incubation period varies depending on the mode of infection. According to research, buffalo calves between 4 and 10 months of age have the following incubation periods: 12 to 14 hours for subcutaneous infection, approximately 30 hours for oral infection, and up to 46 to 80 hours for natural exposure. Epidemiological data show that symptoms in cattle usually develop over hours to days.
Generally speaking, these symptoms can be divided into three stages:
- Stage 1: Fever, rectal temperature of 40 to 41°C, loss of appetite and malaise.
- Second stage: Shortness of breath, clear nasal discharge that gradually turns into turbid, sticky pus, prevalent salivation and jaw edema.
- Stage 3: The animal will become bedridden, with persistent acute respiratory distress and terminal sepsis.
Buffaloes usually present with a more acute course of illness with a shorter duration.
Pathology and Etiology
Especially during autopsy, the most obvious lesion is edema of the mandible and chest. Further examination may reveal small hemorrhages in the body, which may also be complicated by congestion or consolidation in the lungs. Animals that die within 24 to 36 hours usually have only a small amount of cardiac hemorrhage and pulmonary congestion throughout the body, while animals that die more than 72 hours later may have more obvious hemorrhage and pulmonary consolidation.
Diagnosis and Management
Diagnosis is based on blood smears and clinical signs, and treatment requires antibiotics, such as 100 ml of thiothiazide taken orally each time and 40 ml of oxytetracycline injected for three consecutive days.
EpidemiologyThe global spread of hemorrhagic septicemia is influenced by climatic conditions, husbandry practices and animal species. For example, in 1981, Sri Lanka showed a different distribution pattern because its regions had diverse agro-climates and different husbandry practices. This has resulted in distinct endemic and non-endemic areas in Sri Lanka.
During the past four decades, hemorrhagic septicemia has caused the highest infectious mortality among cattle and buffaloes in India.
As a major economic disease, HS has a profound impact on Pakistan, especially in 1996, when the economic losses in Punjab Province due to HS reached 21.7 billion Pakistani rupees, equivalent to 58 million US dollars. According to farmers, hemorrhagic septicaemia is more important than foot-and-mouth disease due to its higher mortality rate and greater economic impact.
As the epidemic changes, how do the pathogens of hemorrhagic septicemia in Africa and Asia affect local animal husbandry and economies?
