Animals to Human Transmission of Intestinal Diseases: A Review of the Mechanism and Factors Involved

Abstract

Many intestinal diseases in animals either in pets or livestock animals have the potential to transmit to humans and cause disease. These diseases include bacterial (campylobacteriosis, salmonellosis, yersiniosis, plesiomonas and Aeromonas, clostridial disease, shigellosis, colibacillosis), protozoal (coccidiosis, giardiasis, amoebiasis, balantidiasis, trichomonas), helminthic (strongyloidiasis, echinococcosis, echinococcus multilocularis, taeniasis, coenurosis, dipylidium caninum, cutaneous larva migrans) and even viral (parvovirus infection). The mechanism of transmission, clinical features and intermediate vectors vary with disease to disease. The most common route for transmission of these diseases is the fecal-oral route. Many of the causative agents for these diseases are the normal inhabitants of the intestinal tract of the animals. The widespread presence of these reservoir hosts determines the prevalence of these diseases. Other factors such as the persistence of causative agent in the environment, effective fecal shedding and efficient use of transmission vectors also determine the prevalence of a zoonotic disease. Transmission of campylobacter to humans principally occurs through contaminated animal-origin food, water and direct contact with infected animals specially pets. Salmonella transmission primarily occurs through close contact with the infected animals, contaminated food, contaminated raw poultry and meat, aerosols and oropharyngeal secretions. The primary source of Yersinia serotypes 0.3 and 0.9 are swine. Cryptosporidial transmission happen in two ways: direct or indirect transmission. Direct transmission occurs through oral exposure to oocytes and indirect transmission occurs through crosscontamination. Transmission of giardia occurs through cysts that are very resistant to harsh environmental conditions. Helminthic diseases are transmitted by ingestion of either larvae (Strongyloidiasis), eggs (Echinococcosis) or meat of infected animal (Taeniasis).