Cross-protection between Trypanosoma congolense strains of low and high virulence

J Masumu,T Marcotty,S Geerts,J Vercruysse,P Van Den Bossche

doi:10.1016/j.vetpar.2009.04.006

Abstract

The aim of this study was to assess the existence of possible cross-protection between Trypanosoma congolense strains of low and extreme virulence circulating in the same trypanosomiasis focus. Groups of six mice were infected using one of three strains of low virulence and challenged with one of three strains of extreme virulence. A group of six mice was used as control for each strain of low and extreme virulence. The results showed that mice infected with one of the strains of extreme virulence developed high parasitaemia and a significant drop of the PCV compared to mice infected with a strain of low virulence and challenged with one of the strains of extreme virulence. With an exception of one strain of extreme virulence (strain F), the survival time of mice infected with the strains of extreme virulence was shorter compared to mice infected with strains of low virulence and subsequently challenged with a strain of extreme virulence. These results suggest that in an area where trypanosomes of various virulence profiles circulate, livestock infected with T. congolense strains of low virulence can be protected against the adverse effects of extremely virulent T. congolense strains.

Highlights

Trypanosomiasis is an important constraint to livestock and rural development in extensive areas of sub-Saharan Africa
The data presented in these studies revealed that challenge of animals infected with a trypanosome strain of low virulence, and subsequently challenged with an extremely virulent heterologous strain, did not prevent the establishment of this strain and its development as a mixed T. congolense infection
Despite the establishment of a secondary infection with a strain of extreme virulence, the virulent strain's parasitaemia, its effect on the Packed Cell Volume (PCV) and the mortality rate of infected animals were significantly reduced in the experimental animals previously infected with a strain of low virulence

Summary

Introduction

Trypanosomiasis is an important constraint to livestock and rural development in extensive areas of sub-Saharan Africa. In a study conducted in a bovine trypanosomiasis endemic area of eastern Zambia, almost 20% of the T. congolense strains circulating in the cattle population were highly pathogenic whereas the remaining trypanosome strains (80%) were of moderate or low virulence (Masumu et al, 2006a). Notwithstanding this proportion of extremely virulent strains and the low trypanocidal drug treatment frequency (Van den Bossche et al, 2000), the disease in livestock in the area has an endemic character (Doran and Van den Bossche, 1999). To investigate the role of cross-protection between trypanosome strains on the expression of the virulence of circulating trypanosome strains and the persistence of virulent strains in a susceptible host population, the cross-protection between strains of various levels of virulence isolated from cattle in a trypanosomiasis endemic area of eastern Zambia was investigated

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