VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

PATHOGENESIS

Salmonella

• Ingestion
• Gastroenteritis form Enteric fever form
• Colonize intestine Colonize intestine
• Penetrate epithelial cells of intestinal villi Penetrate epithelial cells of intestinal villi
• Produce enterotoxins Enter blood stream
• Gastroenteritis Endotoxaemia

Abortion

• Following adherence with fimbriae to the surface of the intestinal mucousal cells, the bacteria induce ruffling of cell membranes.
• The ruffles facilitate uptake of the bacteria in membrane bound-vesicles, which often coalesce.
• The org. replicate in these cells and eventually released from the cells.
• The virulence of salmonellae relates to their ability to invade host cells and replicate in them.
• The O-antigen chains of LPS resist phagocytosis and long chains of LPS prevent complement action, which will facilitate the spread of organisms.
• The LPS is also responsible for endotoxin activity.
• Salmonellae often localize in the mucosae of the ileum, caecum and colon, and in the mesenteric lymphnodes of infected animals. Subclinical infection may persist with small numbers of salmonellae in the faeces. Latent infections, in which salmonellae are present in the gall bladder but are not excreted, also occur.
• Stress factors such as inter-current infections, transportation, overcrowding, pregnancy, extreme ambient temperature, sudden changes in rations etc may activate latent or sub clinical salmonellosis.

Diseases caused by Salmonella

Host	Salmonella serotypes	Disease
Cattle	S.dublin S.typhimurium	Enteritis, septicaemia, meningitis in calves, abortion, osteomyelitis, joint ill, terminal dry gangrene in calves. Enteritis or septicaemia
Pigs	S.cholera suis S. typhisuis S.typhimurium	Outbreaks clinically similar to swine fever Chronic enteritis in young pigs Enteritis or septicaemia
Sheep	S.abortus ovis S.typhimurium S. brandenburg	Abortion Enteritis or septicaemia Abortion
Horse	S.abortus equi S.typhimurium	Abortion in mares Enteritis or septicaemia
Poultry	S.pullorum S.gallinarum S.arizonae S.enteritidis, S.typhimurium and many other serotypes	Pullorum disease (bacillary white diarrhoea) in chicks Fowl typhoid in all ages. Mainly adults. Severe enteritis and septicaemia in chicks, turkey poults ( Arizona ). Fowl paratyphoid
Human	S.typhi S.paratyphi (S.paratyphi A) S.schottmuelleri (S.paratyphi B) S.hirschfeldri (S.paratyphi C) S.enteritidis S.typhimurium	Typhoid fever Paratyphoid fever Food poisoning