An overview of calf diarrhea - infectious etiology, diagnosis, and intervention

Cho, Yong-il; Yoon, Kyoung-Jin

Salmonella enterica colonizes the gastrointestinal tract of a wide range of hosts. S. enterica serovar Typhimurium (S. typhimurium) and serovar Dublin (S. dublin) are the most common etiologic agents that cause salmonellosis in cattle [60, 127] . S. typhimurium is the most common serotype that affects calves in the USA [120] . Salmonella infection has a wide variety of clinical symptoms ranging from asymptomatic to clinical salmonellosis. Acute diarrheal disease is most common with S. typhimurium and systemic disease is associated with S. dublin. Calves less than 3 weeks of age are commonly infected by Salmonella. The lesions frequently observed in affected calves involve the pseudomembrane on the mucosa of the small intestine as well as enlargement of the mesenteric lymph nodes. Infected cattle can serve as a source of zoonosis through food-borne routes or direct contact [87] . The basic mechanism underlying Salmonella virulence includes the ability to invade the intestinal mucosa, multiply in lymphoid tissues, and evade host defense systems, leading to systemic disease. For Salmonella pathogenesis, the organism should be capable of invading intestinal epithelial cells, surviving within macrophages, and causing enteropathogenicity [132] . Salmonella colonizes M-cells, enterocytes, and tonsilar tissues [115] . Following lymphoid tissue (e.g., tonsilar tissue) infection, Salmonella easily spreads throughout the whole body by invading mononuclear cells and phagocytes [58] . Salmonella pathogenicity island 1 (SPI-1) and SPI-5 are known to influence the type III secretion system, and are mainly responsible for Salmonella-induced diarrhea in calves [21, 132] . SPI-2 is involved in the second type III secretion system and is responsible for intracellular survival of the organism [97] . Clinical presentation of salmonellosis is characterized by watery and mucoid diarrhea with the presence of fibrin and blood [41] . Even though Salmonella can cause diarrhea in both adult cattle and calves, infection is much more common and often causes severe symptoms in 10-day to 3-month old calves [41] . Calves can shed the organism for variable periods of time and intermittently depending on the degree of infection (e.g., clinical or subclinical infection).