Antigenic differences between stocks of Cowdria ruminantium

Area of Science:

• Veterinary Microbiology
• Infectious Diseases
• Rickettsial Pathogenesis

Background:

• Cowdria ruminantium causes heartwater, a severe tick-borne disease in ruminants.
• Geographical variation in C. ruminantium strains can impact disease severity and vaccine efficacy.
• Understanding strain diversity is crucial for effective disease control strategies.

Purpose of the Study:

• To compare the virulence and cross-immunity of Cowdria ruminantium stocks from Senegal, Zambia, and South Africa.
• To evaluate the efficacy of the South African reference stock (Ball 3) against other geographical isolates.
• To investigate the potential of the Senegalese stock as a distinct virulent strain.

Main Methods:

• Cross-immunity tests were conducted in goats using C. ruminantium stocks from Senegal, Zambia, and South Africa (Ball 3).
• Goats were challenged with different stocks to assess febrile reactions and mortality.
• The Senegalese stock was passaged in mice to assess its virulence and detectability.

Main Results:

• The Senegalese stock caused fatal heartwater in goats immune to the South African Ball 3 stock.
• Goats immune to the Senegalese stock were fully protected against the Ball 3 stock.
• The Zambian stock showed full cross-protection with Ball 3, but goats immune to both were still susceptible to the Senegalese stock.
• The Senegalese stock was highly virulent in Dutch goats, with high rickettsial loads in brain capillaries.
• Passaging the Senegalese stock in mice did not induce disease but allowed for organism detection via goat subinoculation.

Conclusions:

• The Senegalese stock of Cowdria ruminantium represents a distinct virulent strain.
• The South African reference stock Ball 3 does not provide complete cross-protection against the Senegalese stock.
• Geographical variation in C. ruminantium necessitates further investigation for vaccine development and disease management.