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

PATHOGENESIS

• The accidental (incidental) hosts are infected by direct transmission through infected urine, placental or fetal tissues or indirectly through contact with a contaminated environment.
• Venereal transmission plays a major role in pigs. Vertical transmission from the mother to the foetus may also occur in cattle.
• Leptospires gain entry through mucous membrane (nasal, genital, ocular, intestinal) or through abraded or water-softened skin.
• After epithelial penetration there is haematogenous spread (Leptospires able to invade the blood stream more rapidly than other bacteria), with localization and proliferation in parenchymatous organs, particularly the liver, kidneys, spleen and sometimes meninges for upto 16 days.
• It causes damage to endothelium of small blood vessels, leading to extravasion of blood and secondary ischaemia result in damage to liver, kidney and adrenals.
• In the kidneys, the organism reaches and localize in the lumen of proximal convoluted tubules.
• Penetration and multiplication in the fetus leads to fetal death and resorption, abortion or weak-off spring. (In foetus, if infection occur at 3rd trimester, can produce specific antibodies and may overcome the infection).
• The leptospires tend to persist in sites such as renal tubules, eyes and uterus where antibody activity is minimal.
• Leptospira causes following disease syndromes in domestic animals.

Host	Disease syndrome
Cattle	Subclinical with leptospiruria (Hardjo) Milk drop syndrome (Hardjo) Abortion and neonatal mortality (Pomona and Hardjo) Infertlity (Hardjo) Haemoglobinuria, jaundice and fever in calves (Pomona, Grippotyphosa and Icterohaemorrhagiae)
Pigs	Subclinical with leptospiruria (Pomona) Fever and non-suppurative mastitis (Pomona) Infertility, abortion and still birth (Canicola, Pomona, Icterohaemorrhagiae) Haemoglobinuria, jaundice and fever (Icterohaemorrhagiae)
Dogs	Subclinical with leptospiruria (Pomona) Acute haemorrhagic type characterized with fever, vomiting, prostration and death (Icterohaemorrhagiae) Less acute icterus type (Canicola and Icterohaemorrhagiae) Ureamic type (Canicola)
Horse	Recurrent iridocyclitis/periodic opthalmia / moon blindness (Pomona) Abortion at 6 month of gestation
Sheep	Subclinical infection with leptospiruria (Hardjo)