Molecular characterisation and phylogenetic analysis of Toxoplasma gondii isolates from HIV-positive individuals in Calabar, Nigeria

Toxoplasma gondii is a very successful zoonotic parasite that can infect virtually all warm-blooded animals, including humans. Marked biological differences exist among T. gondii strains in their pathogenicity and geographical distribution, but the relatedness of the prevalent strains in the study area to existing global strains has not been investigated. This study aimed to investigate the molecular prevalence and phylogenetic analysis of T. gondii among HIV-positive individuals in Calabar, Nigeria, to provide information on the relatedness of T. gondii strains in Nigeria to existing global strains in GenBank. In a cross-sectional study, blood samples were randomly collected from 50 confirmed HIV/Toxoplasma gondii seropositive individuals (aged 10-65 years and amplified by Polymerase Chain Reaction (PCR) using the Tox G1 gene. Sequencing of the selected amplicons was performed using the Sanga sequencing method. The molecular prevalence of T. gondii, as determined by PCR, was 70%. Neither age nor sex affected PCR amplification of the Tox G1 gene (P >0.05). Phylogenetic analysis of the sequenced gene using the Basic Local Alignment Tool (BLAST) revealed that 60% of the T. gondii strains (T1–T10) detected in the study area were similar to those in Thailand, 30% (T6, T7, and T8) and Iran, 30% (T1, T2, T3), while 20% (T9, T10) were related to those detected in Norway. This study revealed a high molecular prevalence (70%) of Toxoplasma gondii among HIV-positive individuals in Calabar, Nigeria and demonstrated the genetic relatedness of local strains to those from Thailand, Iran, and Norway, underscoring the importance of PCR-based diagnosis and molecular surveillance in immunocompromised populations.