Analysis of the Cause of Acute Death in a Sow

Clinically, the most common diseases that can cause acute death in sows include African swine fever, classical swine fever, severe gastric ulcers (perforation), acute bacterial septicemia (such as B-type Clostridium novyi, erysipelas), and exceeding the limit of mold toxins in feed. Additionally, urinary tract infections in sows caused by Streptococcus suis can also lead to acute death.

The spleen is an important peripheral immune organ involved in immune responses and blood filtration, serving as a main battleground in the body's fight against pathogens. Therefore, during systemic infection by pathogens, the spleen shows severe reactions. Acute splenitis, where the spleen is several times larger than normal, can be caused by diseases such as African swine fever, classical swine fever, and acute bacterial septicemia (which can involve various bacteria like streptococci and Clostridium novyi). Based on gross pathological changes in the spleen, our focus is on African swine fever, classical swine fever, and bacterial septicemia in pigs. Porcine circovirus and porcine reproductive and respiratory syndrome virus typically do not produce convincing gross pathological changes in the spleen; circovirus usually causes granulomatous splenitis, which is observable only under a microscope.

Gastric ulcer refers to acute indigestion and gastric bleeding leading to local tissue erosion, necrosis, or autodigestion of gastric mucosa, resulting in round ulcerative lesions or even gastric perforation. Prior to the arrival of African swine fever, gastric ulcers were the leading cause of death in Chinese sows. It is noteworthy that gastric ulcers near the esophagus or pylorus have diagnostic significance, whereas ulcers in other parts of the stomach do not. In the figure, no ulcerative lesions are seen in the stomach, hence gastric ulcer can be ruled out as the cause of acute death in sows.

The lower left image shows liver tissue. The liver appears lobulated, filled with various small pores resembling a foamy structure. Foamy liver lesions are characteristic anatomical changes caused by Clostridium novyi infection in pigs. It is difficult to analyze how Clostridium novyi retrogrades to reach the liver and cause liver damage.

Through molecular biology, we can exclude African swine fever and classical swine fever. Bacterial diseases that can cause acute death in sows include erysipelas, Actinobacillus pleuropneumoniae, and Clostridium novyi. However, bacterial diseases also exhibit different invasion sites and damage characteristics; for instance, Actinobacillus pleuropneumoniae not only causes acute splenitis but more importantly, necrotizing hemorrhagic pneumonia. Streptococcus suis causes extensive skin lesions. The gross pathology of the liver indicates a specific direction; foamy liver is typically a characteristic lesion of Clostridium novyi in pigs. Further microscopic examination confirms Clostridium novyi as the cause of acute death in sows. Bacterial culture identification results confirm Clostridium novyi.

In this case, various methods can be flexibly applied, such as liver smears. Normally, no bacteria should be visible in the liver. Once bacteria are observed, and anatomical lesions such as foamy liver-like changes are seen, it can be inferred to be a clostridial disease. Further verification can be done through HE staining of liver tissue, revealing numerous rod-shaped bacteria. Bacterial culture is not necessary because Clostridium novyi is one of the most difficult bacteria to culture.

Understanding the specific damage characteristics and sites of each disease is crucial. For example, porcine epidemic diarrhea virus primarily attacks epithelial cells of the small intestine, and damages in other organs such as the lungs, heart, or liver are not within its scope. Bacterial invasion depends strictly on specific pathways; for instance, Clostridium tetani can only infect through deeply contaminated wounds with necrotic or suppurative changes, while other routes do not lead to infection. Actinobacillus pleuropneumoniae infections are more likely to occur in pig farms with influenza and pseudo-rabies, as these viruses more easily damage the tracheal epithelial cells, making it easier for Actinobacillus pleuropneumoniae to penetrate and settle in the alveoli. Veterinarians must understand the organ-specific damage characteristics of each disease and then combine laboratory testing methods such as molecular biology and microbiology for accurate disease diagnosis.