Toxoplasmosis is an important world-wide distributed zoonotic infection of most mammals including humans. It is caused by an obligatory intracellular protozoan, Toxoplasma gondii (T. gondii)^{[1, 2]}. Acquisition is mainly by ingesting raw and undercooked infected meat containing viable Toxoplasma tissue cysts or food or drink contaminated with Toxoplasma oocysts excreted from the feces of infected cats, the only definitive host^{[1, 2]}. Blood transfusion and organ transplantation are also possible means of acquiring the infection in human. Congenital toxoplasmosis occurs through trans-placental transmission of tachyzoites from mother with active infection to the developing foetus^{[1, 2]}.

Globally, it is estimated that approximately 30% of the human population is chronically infected. However, most immunocompetent individuals are asymptomatic during acute infection^{[1, 3]}. But mild to severe clinical manifestations including lymphadenopathy and neuropsychiatric symptoms such as, depression, anxiety, schizophrenia, and suicide have been reported in some so-called asyptomatic persons with acute or chronic infection^{[4, 5, 6, 7]}. It has been observed that infection in rats causes them to be fearless near cats and this increase the chance of being preyed upon by the cats^[8]. Another undesirable consequence is that T. gondii infection acquired during pregnancy may lead to congenital toxoplasmosis which may result in abortion, neonatal death and severe morbidity^{[9, 10, 11]}. In immunocompromised individuals such as AIDs, cancer and organ transplantation patients, primary or reactivation of latent infection can cause life-threatening encephalitis or lethargy^{[12, 13, 14]}. Additionally, infection in animals causes a considerable economic loss to the animal husbandry industry as a result of increased abortion, mortality and medical cost. Hence, T. gondii infection is of public and veterinary importance^{[15, 16]}.

The variation in the clinical manifestations has led to researches on the genetic diversity and/or pathogenicity among T. gondii isolates from healthy and sick hosts from different geographical areas. Recent studies have revealed that T. gondii has a complex genetic structure than was initially recognized^[17]. Isolates of Toxoplasma are categorized into two groups through the use of multi-locus enzyme electrophoresis, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) or microsatellite typing techniques^{[17, 18, 19, 20, 21]}. The identified groups are clonal lineage also known as archetypical or typical strains which are distributed worldwide and atypical strains also known as exotic or non-archetypical strains^{[17, 18, 19, 20, 21]}. The clonal lineage strains are predominant in North America and Europe^[19]. They include type I, the highly virulent strain and types II and III, the intermediate or avirulent strains in mice^[19]. Atypical strains constitute all other genotypes that do not fall into archetypical genotypes. These genotypes may be produced when the definitive host, felids are simultaneously infected with multiple strains^[22]. Atypical strains also range from highly virulent to intermediate or avirulent phenotypes^{[22, 23, 24, 25]}. Atypical strains such as Africa 1 and Africa 3 have been isolated in Africa^{[26, 27]}. In Asia, and particularly in China, Chinese 1 has been reported as the predominant atypical genotype^{[28, 29, 30]}. Several studies in Europe, North and South America have also revealed atypical strains and the atypical strain, type 12 is predominant in wild animals^{[31, 32, 33]}. From the available literature it can be concluded that the genetic diversity of T. gondii population varies in geographical areas.

This paper presents a review of the genetic diversity of T. gondii isolates from Africa revealed by multi-locus PCR-RFLP and microsatellite typing.

Toxoplasma gondii infections are prevalent in both humans and animals worldwide. It is known that the development, progression and severity of disease depend on the immunological status of the infected host. However, recent studies have showed that the genotype of the parasite is also a contributing factor^{[19, 22, 23, 24, 25]}. Therefore understanding the genetic structure of T. gondii population is very crucial in providing information about the relationship between the genotypes and the associated phenotypes. Recent studies using multi-locus enzyme electrophoresis, PCR-RFLP or microsatellite typing to genetically characterized T. gondii isolates have showed that the population structure of this parasite is complex. In Asia, particularly in China and Vietnam, type I and Chinese 1 are the frequently isolated strains from both human and animals^{[28, 44, 45, 46]}. In Europe and North America, the archetypical genotypes, types II and III are reported to be predominant^{[20, 47, 48]}. The atypical strain, type 12 is also common in North America isolated mainly from wildlife^{[31, 32, 33, 49]}. However, the isolates from South America are more genetically diverse with no genotype being clearly dominant^{[50, 51, 52]}. In Africa, T. gondii isolates belonging to the clonal lineages, I, II and III have been frequently isolated in addition to Africa 1 and Africa 3. However, some researches from Africa relied on a single locus which is not appropriate to characterize Toxoplasma genotype.

This study was conducted with the aim of analyzing and highlighting the population genetic structure of T. gondii isolates circulating in Africa revealed by multi-locus PCR-RFLP and microsatellite typing.

Our analysis indicates that, both typical and atypical population of T. gondii occur in Africa. The atypical genotype accounted for 76.5% of the human infection with Africa 1 (I/III) being the most dominant one (69.2%). Less than 20% of the infection was caused by mixed genotype (17.6%) and clonal type 1 was (5.9%). This pattern is not different from what is obtained in Asia mainly in China and Vietnam where atypical strain (Chinese 1) and type I have been frequently isolated from cancer patients^{[45, 46]}. However, types II and III which have been frequently reported in AIDS patients and congential infection from North America and Europe were not identified in this study^{[20, 51, 52]}. With the exception of one study, all the studies involving human population did not investigate the virulence of the isolates in mice. This could be partly due to insufficient resources. However, most of the isolates obtained from animals were type II (42.7%) and type III (32.8%) which have also been frequently isolated from animals in North America and Europe. Atypical genotype group accounted for 19.4% and the least was type I (1.9%). Multiple genotype infection in the same animal hosts constituted the remaining 3.2%. Some of the strains were virulent whiles others were avirulent in mice or cell culture^{[27, 37, 38, 40, 41, 43]}.

Overall, the archetypical genotype predominates in Africa accounting for 73.7%: with types II and III dominating indicating that, types II and III genotypes are not merely predominant in Europe and North American but also predominant in Africa. This is consistent with the study done by Shwab et al. ^[53] who reported the global pattern of Toxoplasma gondii genetic diversity revealed by multilocus PCR-RFLP genotyping only.

Totally, infection caused by archetypical genotype of T. gondii is very high in both human and animal population from Africa. Our result will contribute to the information available on the control of this opportunistic pathogen that mainly cause severe disease among immunocompromised diseased individuals like AIDS patients and also in congenital cases. However, more sampling is required in Africa including southern African countries where no studies about the genetic structure of T. gondii have been reported. More studies on human toxoplasmosis are also very important to help to obtain representative isolates from the various geographical regions of the African continent. Also, it was observed that all the studies on animals were biased toward domesticated animals. More studies are needed to include wild animals for better understanding of the genetic structure of T. gondii population in Africa.

The authors have no competing interests

JLS, FP and LW conceived and designed the study. JLS critically revised the manuscript. FP and LW performed database information search. FP wrote the manuscript. FP, LW, DOY, HC, CWS, XWW, FL and QLL participated in the analysis and interpretation of data. All authors have read and approved the final manuscript.