Immunological insights and vaccine advances against apicomplexan parasites: Emerging concepts and innovations.

The apicomplexan parasites are globally considered as the major cause of numerous infectious diseases in humans and animals. Apicomplexan parasites include Plasmodium, Toxoplasma gondii, Cryptosporidium, Eimeria and Babesia. The rise in the drug resistance have made the traditional control measures, such as chemotherapy and vector management, inadequate against them. These are the intracellular infectious agent and possess complex life cycles, antigenic variability, and immune evasion abilities. These different abilities hinder the development of vaccines against them. Hence, there is urgent need for development of effective vaccines by novel measures. However, notable progress has been made in past years due to the advancements in immunology, molecular biology, and biotechnology. Different types of vaccines including subunit vaccines have been developed and have demonstrated favorable efficiency. In the meantime, live-attenuated vaccines (LAV) continue to provide protection in animals. Apart from that, there are different innovations like CRISPR/Cas9 gene editing that have enabled the creation of genetically attenuated strains for T. gondii and Eimeria. These attenuated strains are used for the development of vaccines. Furthermore, mRNA vaccine technology, which was successfully utilized during the COVID-19 pandemic, is now being used against parasitic infections. It is now offering fast and rapid development along with vigorous cellular immunity. The use of nanoparticles and novel adjuvants such as TLR agonists and saponins has improved the stability and effectiveness of vaccines. Approaches like mucosal delivery, especially for enteric parasites such as Cryptosporidium and Eimeria, is achieving attention for their ability to provide the localized protection. In spite of these advancements some challenges still persist. Antigenic diversity, short-lived immunity, regulatory barriers, and limited funding need to be addressed. Some of the emerging technologies including systems vaccinology, reverse vaccinology, and vectored delivery platforms, are paving the way for more targeted and effective vaccination. There is need for concerted effort incorporating multidisciplinary research, One Health integration, and scalable manufacturing methodologies for effective translation of these scientific innovations into solutions. By harnessing these emerging technologies within a One Health framework, the next generation of vaccines has the potential to transform the management of apicomplexan diseases worldwide.