Special Veterinary Pathology

BABESIOSIS

Synonym : Piroplasmosis, tick fever

Definition

• Babesia occurs in erythrocytes, destroy them giving rise to fever, anaemia, jaundice and haemoglobinuria

Aetiology

• Babesia sp.

Incidence

• In cattle, severity of infection also depends on the breed. Bos indicus breeds are relatively resistant because of their resistance to heavy infestations with ticks
• The disease may have seasonal incidence if the tick population varies with climate

Transmission

• Ticks are the intermediate host

Cattle (Bovine piroplasmosis, tick fever, texas fever or red water)

• It is a an acute or chronic disease of cattle and buffaloes characterized by fever, haemoglobinuria caused by B.bigemina, B. bovis etc.
• B.bigemina is the most common in India and occurs in the erthrocytes as pear shaped forms in pairs.

Babesia bigemina-Pear shaped forms in pairs

Pathogenesis

• Multiplication is by cell division during which it destroys the host cells and invade another causing haemoglobinaemia, haemoglobinuria
• The vector is : Boophilus annulatus

Clinical signs

• The clinical manifestation are variable. The common signs being fever, anorexia, depression initially and icterus, haemoglobinuria and ascites later
• Haemolytic anaemia is manifested by thin watery blood with a fall in haemoglobin, erythrocytes and packed cell volume

Gross lesions

• Emaciated carcass with oedema, haemorrhages in subcutaneous, subserous and intramuscular regions.
• Spleen and liver are enlarged. Gall bladder distended with dark green bile

Microscopic lesions

• Haemoglobinuric nephrosis also known as lower nephron nephrosis, centrilobular and paracentral necrosis of the liver, oedema, excess fluid in the peritoneal, pericardial and pleural cavities
• Babesia can be demonstrated in capillaries in the brain

Equine babesiosis is caused by B.caballi and B. equi of which the latter is more pathogenic

Canine babesiosis is caused by B.canis and B.gibsoni

• B.canis is larger and haemoglobinuria is constant while B.gibsoni is smaller and chronic form of disease with haemoglobinuria and jaundice are not seen

B.canis-Larger pear shaped	B.gibsoni-Smaller and ring form

Babesiosis in sheep and goats

• B.motasi is longer and virulent
• B. ovis causes a less severe conditon.

Babesia are easily differentiated from Plasmodium sp. by the absence of haemoglobin derived pigment. Babesia completely catabolize haemoglobin whereas plasmodium retain the brownish pigment (Haemozoin)

Immune response in Babesia

• The sporozoites attack red blood cells. This invasion involves activation of the alternate complement pathway. Infected erythrocytes incorporate babesia antigen into their membranes. These, in turn induce antibodies which opsonize the red cells and lead to their removal by the mononuclear phagocyte system. In addition to the humoral response, infected red blood cells may also be destroyed by antibody dependent cell mediated cytotoxicity (ADCC). The babesia antigen-opsonizing antibody complex on the surface of infected erythrocytes can be recognized by macrophages and cytotoxic lymphocytes
• Premunition is a form of immunity that is dependent on the continued presence of parasite in the host. The resistance that is established after the primary infection has become chronic

Diagnosis

• Indentification of babesia in blood smears
• Enzyme immunoassay
• ELISA
• DNA probes are also used to detect specific parasitaemias at very low levels of infection