Final Project Report

Dear all,

It is my pleasure to provide you with this final report about my project on rabies booster vaccination in African wild dogs ( Lycaon pictus ). I would like to express my sincere and deep thanks to you for supporting this work, which also constituted my final thesis for the MSc course in “Wild Animal Health” at the Royal Veterinary College and the Zoological Society of London.

Project summary

The aim of this project was to examine the effects of a rabies booster vaccination on antibody levels in African wild dogs. Rabies is threatening these endangered canids, and field studies have shown that while vaccinated individuals still succumb to the virus, wild dogs that have received multiple doses of vaccine are more likely to survive an outbreak. If a rabies booster vaccination would indeed lead to higher antibody levels, and by extension, a better protection, this finding could be incorporated into future conservation strategies to better protect the last remaining members of the genus Lycaon against this almost inevitably fatal disease.

To test the hypothesis that booster vaccination would indeed lead to higher antibody levels, I examined blood serum collected from captive African wild dogs with a known vaccination history. Blood was collected for purposes of general health monitoring at the site where animals were held. Samples were analysed using both a gold standard Fluorescent Antibody Virus Neutralisation (FAVN) test, as well as an immunoassay based on Luminex® technology. While the FAVN test provides information on whether any antibodies in the serum are able to neutralise live rabies virus, the Luminex® assay picks up the physical presence of antibodies. This can be an advantage, as some antibodies may not neutralise the virus by themselves but will still bind to it and set other immunological processes into motion. Luminex® assays can differentiate between these binding and neutralising antibodies, allowing a more nuanced view of an individual’s immune response to vaccination. As Luminex® immunoassays make use of microscopic, spectrally distinct bead sets that can each be coated with a different capture antigen (virus protein), several analyses can be performed simultaneously, using very little amounts of sample. On the other hand, the FAVN test is a standardised one, and an antibody titre above 0.5 International Units per millilitre (IU/ml) is generally considered “protective” against rabies, making results easily comparable. The FAVN test was conducted by the Animal and Plant Health agency, a UK governmental institution also testing blood of domestic animals set for export. Meanwhile, I optimised the Luminex® assay for use with canine serum samples during my MSc thesis.

Results

The results of the FAVN test showed a clear association between number of vaccinations received and serum antibody titres, whereby animals that were vaccinated twice also showed higher titres. Additionally, a higher rate of animals that had received a booster vaccination showed a titre above 0.5 IU/ml than those that had only received one vaccination. The results of the Luminex® differed from the FAVN test results, in that higher values were measured in general, and some of the trends seen in the FAVN tests were not apparent in Luminex® results. A likely explanation for this is that as explained, the Luminex® assay is capable of measuring several types of antibodies, i.e. more than the ones that are neutralising. Furthermore, as African wild dog serum samples were limited, assay parameters were largely tested on domestic dog samples. While both species are related, they are genetically distinct, and thus the Luminex® assay may not have been optimal for analysis of African wild dog serum samples. However, I was able to find neutralising, as well as binding antibodies in the wild dog samples, proving that the latter also form part of the immune response to vaccination in this species. Furthermore, there was a marked difference in the different vaccine types used for immunisation, which is something that may be explored in future studies.

Conclusion

Overall, the FAVN test results showed that a booster vaccination does indeed stimulate higher antibody titres and a higher rate of animals showing protective titres. While the Luminex® assay needs to be optimised further, results showed that African wild dogs do produce binding antibodies, and also point to a possible influence of vaccine type on antibody levels measured. Due to the opportunistic nature of sampling (blood samples were taken whenever required for health monitoring purposes), it was not possible to determine schedules regarding booster vaccination. Nevertheless, the results of this study serve as a strong basis for future work looking to optimise vaccination strategies in the African wild dog and illustrate the potential use of a Luminex® immunoassay as a cost- and time-efficient alternative to similar assays, as multiple types of antibodies can be analysed within the same sample.

Closing acknowledgements

This work has been awarded the price for the best research project of the MSc “Wild Animal Health” course 2021-22. Without a doubt, this achievement would not have been possible without your generosity and recognition of the important subject this study addresses. The development of the Luminex® assay during the course of this project did not only allow me to gain valuable new skills in a laboratory setting and grow as a researcher, it also provides an important basis for future work. The thesis is currently being reworked for publication, and it is my sincere belief that its results will positively impact African wild dog conservation. Thank you all again for your contribution to this work! I am looking forward to my next project at the University of Melbourne, which will focus on the susceptibility of Australian bats to White Nose Syndrome. Meanwhile, I will follow other projects on the Experiment.com platform closely and with great interest!