Sexual Development in Non-Human Parasitic Apicomplexa: Just Biology or Targets for Control?

Abstract

The phylum Apicomplexa is a major group of protozoan parasites including gregarines, coccidia, haemogregarines, haemosporidia and piroplasms, with more than 6000 named species. Three of these subgroups, the coccidia, hemosporidia, and piroplasms, contain parasites that cause important diseases of humans and animals worldwide. All of them have complex life cycles involving a switch between asexual and sexual reproduction, which is key to their development. Fertilization (i.e., fusion of female and male cells) results in the formation of a zygote that undergoes meiosis, forming a new generation of asexual stages. In eukaryotes, sexual reproduction is the predominant mode of recombination and segregation of DNA. Sex is well documented in many protist groups, and together with meiosis, is frequently linked with transmission to new hosts. Apicomplexan sexual stages constitute a bottleneck in the life cycle of these parasites, as they are obligatory for the development of new transmissible stages. Consequently, the sexual stages represent attractive targets for vaccination. Detailed understanding of apicomplexan sexual biology will pave the way for the design and implementation of effective transmission-blocking strategies for parasite control. This article reviews the current knowledge on the sexual development of Apicomplexa and the progress in transmission-blocking vaccines for their control, their advantages and limitations and outstanding questions for the future.

The transcriptome from asexual to sexual in vitro development of Cystoisospora suis (Apicomplexa: Coccidia)

“…Based on the motile nature of the male sexual stages and the lack of invasion machinery genes in sexual stages, it is obvious that the fertilization process takes place extracellularly, rather than intracellularly as previously assumed 40 , 107 , 108 . The transmission blocking potential of proteins specific to sexual stage as candidates for vaccination or drug targets has been suggested in related Coccidia and other Apicomplexa 2 . Oral application of sera containing E. tenella gamont-specific monoclonal antibodies significantly reduced oocyst output and cecal lesions in chicken 109 .…”

“…Isospora suis 1 ) is a protozoan parasite of the phylum Apicomplexa (Class Conoidasida, subclass Coccidiasina, order Eucoccidiorida, family Sarcocystidae). This phylum contains almost exclusively obligate endoparasites of animals, including species of great medical and veterinary relevance such as Plasmodium spp., Eimeria spp., Cryptosporidium spp., and Toxoplasma gondii 2 . Cystoisospora suis is the causative agent of neonatal porcine cystoisosporosis (coccidiosis).…”

The Tubulin Superfamily in Apicomplexan Parasites

“…We specifically consider the potential redundancy or specialization of α- and β-tubulin isotypes, the presence, absence, or divergence of δ- or ε-tubulins, and the stage-specific expression of tubulin family members. Ultimately, the properties of the tubulin superfamily inform proposed strategies to control apicomplexan parasites via tubulin-targeting antimitotic agents, or through transmission-blocking strategies that disrupt microgamete flagella [ 46 , 47 , 48 , 49 , 50 , 51 ].…”

Sex in protists: A new perspective on the reproduction mechanisms of trypanosomatids

“…In Apicomplexa parasites, addressed in this review, obligate sexual reproduction with the presence of haploid gametes is fundamental for parasite transmission, as observed in Plasmodium and Toxoplasma . Such a characteristic may be targeted by epidemiological strategies to contain the spread of malaria and toxoplasmosis ( Cruz‐Bustos et al, 2021 ). Understanding if and how meiotic recombination events occur in trypanosomatids such as T. cruzi and Leishmania can guide the development of different research methods for these organisms.…”