Pursuing effective vaccines against cattle diseases caused by apicomplexan protozoa

Authors: FLORIN-CHRISTENSEN, MONICA - Instituto De Clima Y Agua (INTA); SCHNITTGER, LEONHARD - Instituto De Clima Y Agua (INTA); BASTOS, REGINALDO - Washington State University; RATHINASAMY, VIGNESH - James Cook University; COOKE, BRIAN - James Cook University; ALZAN, HEBA - Egypt National Research Center; Suarez, Carlos

Submitted to: CABI Agriculture and Bioscience (CABI A&B)
Publication Type: Review Article
Publication Acceptance Date: 2/16/2021
Publication Date: 3/24/2021
Citation: Florin-Christensen, M., Schnittger, L., Bastos, R.G., Rathinasamy, V.A., Cooke, B.M., Alzan, H.F., Suarez, C.E. 2021. Pursuing effective vaccines against cattle diseases caused by apicomplexan protozoa. CABI Agriculture and Bioscience (CABI A&B). https://doi.org/10.1079/PAVSNNR202116024.
DOI: https://doi.org/10.1079/PAVSNNR202116024

Interpretive Summary: Apicomplexans are a group or protozoan organisms characterized for their ability of invading host cells using their apical complex organelles. Apicomplexan parasites such as Theileria spp., Babesia spp., Toxoplasma gondii, Neospora canis, Eimeria spp., Besnoitia spp., Sarcocystis spp.,are responsible for important livestock diseases that compromise the production of much needed protein resources, and public health. Unfortunately, most of these diseases are neglected and poorly controlled. Vaccines, widely recognized as the most cost-effective method for the prevention of infectious diseases in livestock, can avert losses in food production and decrease the exposure of humans to zoonotic pathogens. This review focuses on the needs and advances on the development of vaccines against this group of apicomplexan parasites. Progress in vaccine development is severely limited by the complexity of the life cycles of the parasites and the complexities in the relationships with their host. In addition, there are large knowledge gaps in the understanding of their biology, and the mechanisms leading to protective immune responses in the hosts. Furthermore, the incidence and impact of these diseases is increasing due to globalization, human interventions, and climate change, among other factors. Increased public awareness on the impact of these diseases should stimulate future research focused on specific vaccine approaches and other important aspects leading to improved control, including the identification of vulnerabilities in these parasites that can be exploited for vaccine targeting. The application of recently developed "omic" research approaches in the areas of molecular biology and vaccinology will be crucial for achieving effective and practical vaccines against the devastating diseases caused by apicomplexan parasites. Novel vaccines will likely help preventing human diseases and the loss of important protein resources required to feed the growing human population in the 21st century, and beyond.

Technical Abstract: Apicomplexan parasites are responsible for important livestock diseases such as theileriosis, babesiosis, cryptosporidiosis, and coccidiosis including toxoplasmosis, neosporosis, besnoitosis, sarcocystiosis, and eimeriosis. These diseases affect the production of much needed protein resources, and those transmissible to humans pose a public health risk. Vaccines, widely recognized as the most cost-effective method for the prevention of infectious diseases in livestock, can avert losses in food production and decrease the exposure of humans to zoonotic pathogens. This review focuses on the needs and advances on the development of vaccines against the apicomplexan parasites Theileria spp., Babesia spp., Toxoplasma gondii, Neospora canis, Eimeria spp., Besnoitia spp., Sarcocystis spp., and Cryptosporidium parvum. Altogether, these parasites affect livestock causing an enormous economic and public health burden, yet they remain poorly controlled and only a few effective and practical vaccines against them are available. Progress in vaccine development is hampered by the complexity of their life cycles and relationships with their host, our scarce knowledge of their biology, and the absence of correlates of host immune protection. Unfortunately, the incidence and thus the impact of these diseases is increasing due to several factors, including globalization, human interventions, and climate change, among others. Increased public awareness on the impact of these diseases should stimulate future research focused on specific vaccine approaches, the study of the biology of these parasites and their interactions with their definitive and intermediate hosts, the correlates of immune protection, and the identification of vulnerabilities in these parasites that can be exploited for vaccine targeting. The application of recently developed “omics” and gene editing approaches is facilitating efforts towards the achievement of effective and practical vaccines against the devastating diseases caused by apicomplexan parasites, which is essential for higher standards in animal health. This, in turn, will help preventing human diseases and will allow producing enough protein to feed the growing human population in the 21st century, and beyond.