Darde, M.-L. | bioRxiv Science

bioRxiv2021

A unique Toxoplasma gondii haplotype under strong selection has accompanied domestic cats in their global expansion

Toxoplasma gondii is a cyst-forming apicomplexan parasite of virtually all warm-blooded species, with all true cats (Felidae) as definitive hosts. It is the etiologic agent of toxoplasmosis, a disease causing substantial public health burden worldwide. Its wide range of host species and its global occurrence probably complicate the study of its evolutionary history, and conflicting scenarios have been proposed to explain its current global distribution. In this study, we analyse a global set of 156 genomes (including 105 new genomes) and we provide the first direct estimate of T. gondii mutation rate and the first estimate of its generation time. We elucidate how the evolution of T. gondii populations is intimately linked to the major events that have punctuated the recent history of cats. We show that a unique haplotype --whose length represents only 0.16% of the whole T. gondii genome-- is common to all domestic T. gondii strains worldwide and has accompanied wild cats (Felis silvestris) during their emergence from the wild to domestic settlements, their dispersal in the Old World and their recent expansion to the Americas in the last six centuries. By combining environmental and functional data to selection inference tools, we show that selection of this domestic haplotype is most parsimoniously explained by its role in initiation of sexual reproduction of T. gondii in domestic cats.

genomics↗

bioRxiv2019

Toxoplasma gondii in house mice Mus musculus domesticus from Dakar, Senegal: clues for oral rather than vertical mode of infection

Toxoplasma gondii is an ubiquitous highly prevalent zoonotic protozoan. Cats are the definitive hosts, while all other warm-blooded animals are intermediate hosts for this parasite. Commensal rodents, being the main preys of cats, are probably the major reservoir for T. gondii. Rodents often develop dormant tissue cysts after ingestion of oocysts shed in the environment by cats in the form of contaminated feces. Experimental evidence that vertical transmission can be sufficient to the perpetuation of transmission between generations of mice has also been found. In natural settings, the relative epidemiological importance of vertical transmission over oral transmission is a matter of debate and raises the question of the possibility of a T. gondii cycle in the absence of cats. In the present study, we took advantage of an extensive survey of commensal rodents in Dakar, Senegal, where the house mouse Mus musculus domesticus is the predominant putative reservoir of T. gondii. Host genotype and spatial location through GPS referencing of all trapping localizations were investigated in relation to T. gondii infection in 12 sites of the city of Dakar and on Goree Island. In each sampled site, the occurrence of over-prevalence zones of T. gondii infection was investigated through Kulldorfs statistic using SaTScan software. For the sites where a possible over-prevalence zone was identified, mice family lines were inferred from Discriminant Analysis of Principal Components (DAPC). In 3 of the 4 identified possible over-prevalence zones, T. gondii infection was not confined to a single family line, which suggested no association between kinship and infection occurrence. This finding rather suggests an environmental source of infection for mice associated with localized putative foci of environmental contamination and supports an oral route of infection for mice from Dakar rather than a cycle based on vertical transmission.

epidemiology↗