During his doctoral research, Stephen Kaba made two vaccines based on a protein found on the surface of the parasite. In total, 72 percent of the animals that were injected with the new protein vaccines and subsequently infected with the parasite, were found to be protected. This protection was achieved with a low vaccine dosage and with just two injections. Previous protein vaccines could only protect half of the animals.
Up until now, veterinary surgeons have injected the entire parasite instead of one of its proteins. The cattle were also simultaneously treated with a cure of antibiotics. This method, which requires considerable skill and the culturing of large quantities of parasites, is a time-consuming and expensive process. An associated problem is that the parasites must be stored at a very low temperature, which is difficult in tropical areas. Furthermore, with this method there is always the chance that the animal could become ill as a result of the vaccination. The new vaccines do not have these problems.
The researchers developed two methods to make a stable form of the parasite protein, in large quantities in insect cells. They used modified baculovirusses for this. In one method the researchers linked the parasite protein to the carrier protein (Green Fluorescent Protein or GFP). In the other method the protein was attached to the outside of the baculovirus particles. Both products provided vaccines with a good level of effectiveness.
The protein used, p67, ensures that the parasite can penetrate white blood cells. The immune system of the cattle recognises this protein and makes antibodies against it. After the injection with the protein vaccine, the cattle's body knows how to attack this part of the parasite. The attack of the antibodies on the protein eventually kills the parasite and prevents the animal from becoming ill after it has been infected.
The parasite is transmitted via ticks. Upon entering the cattle's body the parasite settles in the white blood cells. Once inside, the parasite enters a following life stage. In this stage it induces the white blood cells to reproduce uncontrollably just as in a tumour. This leads, for example, to weight loss, high fever and respiratory distress. If treatment does not follow, the infected animal dies within three weeks. The reduced productivity of the cattle as a result of this disease leads to a lot of poverty in the area affected.
For further information please contact Dr Stephen Kaba (Laboratory for Virology, Wageningen University and Research Centre), e-mail: stephen.kaba@wur.nl or his assistant supervisor Dr Monique van Oers, tel. 31-317-485-082, e-mail: monique.vanoers@wur.nl. The doctoral thesis was defended on 17 October 2003. Dr Kaba's supervisor was Prof. J.M. Vlak.
The research was funded by the Netherlands Organisation for Scientific Research.