Detection and genetic characterisation of Toxoplasma gondii circulating in free-range chickens, pigs and seropositive pregnant women in Benue state, Nigeria

Nzelu, IN; Kwaga, JKP; Kabir, J; Lawal, IA; Beazley, C; Evans, L; Blake, DP

Abstract

Toxoplasma gondii parasites present strong but geographically varied signatures of population structure. Populations sampled from Europe and North America have commonly been defined by over-representation of a small number of clonal types, in contrast to greater diversity in South America. The occurrence and extent of genetic diversity in African T. gondii populations remains understudied, undermining assessments of risk and transmission. The present study was designed to establish the occurrence, genotype and phylogeny of T. gondii in meat samples collected from livestock produced for human consumption (free-range chickens, n = 173; pigs, n = 211), comparing with T. gondii detected in blood samples collected from seropositive pregnant women (n = 91) in Benue state, Nigeria. The presence of T. gondii DNA was determined using a published nested polymerase chain reaction, targeting the 529 bp multicopy gene element. Samples with the highest parasite load (assessed using quantitative PCR) were selected for PCR-restriction fragment length polymorphism (PCR-RFLP) targeting the surface antigen 3 (SAG3), SAG2 (5' and 3'), beta-tubulin (BTUB) and dense granule protein 6 (GRA6) loci, and the apicoplast genome (Apico). Toxoplasma gondii DNA was detected in all three of the populations sampled, presenting 30.6, 31.3 and 25.3% occurrence in free-range chickens, pigs and seropositive pregnant women, respectively. Quantitative-PCR indicated low parasite occurrence in most positive samples, limiting some further molecular analyses. PCR-RFLP results suggested that T. gondii circulating in the sampled populations presented with a type II genetic background, although all included a hybrid type I/II or II/III haplotype. Concatenation of aligned RFLP amplicon sequences revealed limited diversity with nine haplotypes and little indication of host species-specific or spatially distributed sub-populations. Samples collected from humans shared haplotypes with free-range chickens and/or pigs. Africa remains under-explored for T. gondii genetic diversity and this study provides the first detailed definition of haplotypes circulating in human and animal populations in Nigeria. Author summaryToxoplasma gondii is a parasite that infects most warm-blooded animals and can be transmitted from animals to humans. Three dominant genetic types have been described from a larger pool of around 16, and it has been suggested that the severity of disease may be influenced by genetic type. Little is known of T. gondii in Africa. The burden of disease is unclear, while lack of knowledge around genetic diversity and population structure undermines effective risk assessment and control. We sought to determine if T. gondii was prevalent in pigs and poultry produced for human consumption in Nigeria, comparing with genetic types detected in the overlapping human population. Using meat samples from free-range chickens and pigs, and blood samples from seropositive pregnant women in Benue state, Nigeria, we found that T. gondii with a type II genetic background were most common with limited genetic diversity. Detection of comparable genetic types in the free-range chicken, pig and human populations indicate an overlapping parasite population and can be used to inform assessments of risk to human health, most notably pregnant women. The information reported here informs on the occurrence and population structure of T. gondii in Nigeria, contributing to improved understanding in Africa.

Citation

Nzelu, I., Kwaga, J., Kabir, J., Lawal, I., Beazley, C., Evans, L., & Blake, D. (2021). Detection and genetic characterisation of Toxoplasma gondii circulating in free-range chickens, pigs and seropositive pregnant women in Benue state, Nigeria. PLoS Neglected Tropical Diseases, 15(6), https://doi.org/10.1371/journal.pntd.0009458

• Journal Article Type: Article
• Acceptance Date: May 10, 2021
• Publication Date: 2021
• Deposit Date: Dec 13, 2021
• Publicly Available Date: Dec 13, 2021
• Print ISSN: 1935-2727
• Publisher: Public Library of Science
• Peer Reviewed: Peer Reviewed
• Volume: 15
• Issue: 6
• DOI: https://doi.org/10.1371/journal.pntd.0009458
• Keywords: PCR; IDENTIFICATION; GENOTYPES; ANIMALS; DNA; INFECTIONS; PARASITE; FOOD
• Public URL: https://rvc-repository.worktribe.com/output/1553105