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A strain of Babesia divergens, attenuated after long term culture
C M Winger1, E U Canning, J D Culverhouse
1Department of Pure and Applied Biology, Imperial College of Science and Technology, London.
Abstract:
The Weybridge strain of Babesia divergens became less virulent after 18 months in culture and was believed to be attenuated. Inoculations with the attenuated line using as many as 5 x 10(8) infected erythrocytes failed to raise a normal infection in Mongolian gerbils (Meriones unguiculatus) whereas, with the line that had been passaged from culture through gerbils at bimonthly intervals, inoculations of 10(7) infected erythrocytes gave rise to fatal infections. Gerbils were immunised with the attenuated line using doses ranging from 5 x 10(5) to 5 x 10(7) infected erythrocytes. Parasitaemias in the infected gerbils did not exceed 0.7 per cent after immunisation. All animals were protected when challenged with the virulent line four weeks later. Control animals died four days after challenge infection.
Insights
An attenuated Babesia divergens strain, weakened after prolonged culture, successfully immunized gerbils against virulent Babesia infections. This highlights the potential of attenuated Babesia strains for developing effective vaccines.
Area of Science:
- Veterinary Parasitology
- Immunology
- Microbiology
Background:
- The Weybridge strain of Babesia divergens, a significant cattle pathogen, was observed to decrease in virulence after extended in vitro culture.
- This attenuation raised questions about its potential use in immunological studies or vaccine development.
Purpose of the Study:
- To investigate the virulence of an attenuated Babesia divergens strain compared to a virulent counterpart.
- To evaluate the efficacy of the attenuated strain in inducing protective immunity against Babesia divergens infection in a susceptible host model.
Main Methods:
- Comparison of virulent and attenuated Babesia divergens strains in Mongolian gerbils (Meriones unguiculatus).
- Assessment of infection parameters following inoculation with varying doses of attenuated and virulent strains.
- Immunization of gerbils with different doses of the attenuated strain followed by challenge with the virulent strain.
Main Results:
- Inoculation with up to 5 x 10(8) infected erythrocytes of the attenuated strain failed to establish a significant infection in gerbils.
- A virulent line, passaged through gerbils, caused fatal infections with as few as 10(7) infected erythrocytes.
- Gerbils immunized with the attenuated strain (5 x 10(5) to 5 x 10(7) infected erythrocytes) showed controlled parasitemia (≤0.7%) and were fully protected against a subsequent challenge with the virulent strain.
Conclusions:
- The attenuated Babesia divergens strain, despite its reduced virulence, is capable of inducing robust protective immunity in gerbils.
- This study demonstrates the potential of using attenuated Babesia divergens strains as a vaccine candidate to prevent babesiosis.