More people, more cats, more parasites: Human population density and temperature variation predict prevalence of Toxoplasma gondii oocyst shedding in free-ranging domestic and wild felids

Toxoplasma gondii exposure in wildlife in Spain: Is there any predictable threat for humans and domestic animals?

Toxoplasmosis is a parasitic zoonosis of key importance in veterinary and public health. This article summarizes the available data (from 2000 to 2023) of exposition to Toxoplasma gondii in wildlife species in Spain based on a systematic bibliographic search, as well as further analysis of its potential relationship with environmental variables, biodiversity, anthropogenic impact on the habitat, and the reported human cases of toxoplasmosis. The overall seroprevalence of T. gondii in carnivorous mammals, birds, ungulate and lagomorph species in Spain was estimated at 69.3 %, 36.4 %, 18.4 %, and 16.2 %, respectively. Among the studies considered, great heterogeneity was observed both between and within taxonomic groups [Cohen's d > 0.8; X2 = 1039.10, df = 4 (p < 0.01) I2 = 97 %, r2 = 1.88, (p < 0.001)] and between and within bioregions [Cohen's d > 0.5; X2 = 368.59, df = 4 (p < 0.01)]. The results of a generalized linear model explaining T. gondii seroprevalence in wild animals suggest the influence of abiotic variables [wetland (p < 0.001), unvegetated (p < 0.001), isothermality (p < 0.001), and mean temperature during wettest quarter (p < 0.05)] and number of intermediate host species as positively associated with increased exposure of wildlife to T. gondii (p < 0.01). Toxoplasma gondii DNA was detected in both wild birds and wild mammals (range: 0.0-51.2 %) mainly from north-centre, northeast, and central-west of Spain. Regarding hospitalisation rates due to toxoplasmosis in humans, some abiotic variables [permanent crops (p < 0.05) and mean temperature during wettest quarter (p < 0.05)] showed a positive association. Despite certain limitations, this research evidences a substantial gap of knowledge on the implication of wildlife in the life cycle of T. gondii in Spain. This lack of knowledge is particularly evident in areas where the human-livestock-wildlife interface overlaps, preventing us from accurately determining its true distribution in different habitats, as well as its potential direct or indirect implications on public and veterinary health.

Parasites of Stray Cats in Iran: A Parasitological and Histopathological Study

Many zoonotic parasitic diseases, including Toxocara cati, may be spread by stray cat populations. This study aimed to determine the prevalence of parasites by performing parasitological and histopathological examinations on stray cats in Shiraz, Iran. A total of 106 stray cats from different geographical areas of Shiraz, southern Iran, were examined for the presence of parasites. The overall prevalence was found to be 83.02% (88/106), and eight parasites were found. The parasites included three genera of cestodes [Joyeuxiella echinorhynoides (52.83%), Taenia taeniaeformis (21.70%), and Dipylidium caninum (1.89%)], three nematodes [Physaloptera praeputialis (23.59%), Toxocara cati (15.09%), and Rictularia sp. (1.89%)], one protozoa [Isospora spp. (6.60%)], and one arthropod [Ctenocephalides felis (5.66%)]. The prevalence did not significantly differ between males and females. It did appear, nevertheless, that the age of cats may be regarded as a risk factor for these parasitic infections. Histopathological examination revealed some parasite-induced lesions in the intestine and stomach, including hyperemia, hemorrhage, mucosal destruction and inflammation. The lung tissues showed some histopathological lesions such as hemorrhage, edema, emphysema and mild inflammation, and dormant larvae were found in one tongue sample. The results of the present study showed that parasitic infections and, more importantly, T. cati are relatively prevalent in stray cats, and the people living in this area are at serious risk of this zoonotic disease. The cats in this region need to be monitored, and specific preventive measures should be developed by public health officials.

The role of species ecology in predicting Toxoplasma gondii prevalence in wild and domesticated mammals globally

Macroecological approaches can provide valuable insight into the epidemiology of globally distributed, multi-host pathogens. Toxoplasma gondii is a protozoan that infects any warm-blooded animal, including humans, in almost every habitat worldwide. Toxoplasma gondii infects its hosts through oocysts in the environment, carnivory of tissue cysts within intermediate host prey and vertical transmission. These routes of infection enable specific predictions regarding the ecological and life history traits that should predispose specific taxa to higher exposure and, thus infection rates of T. gondii. Using T. gondii prevalence data compiled from 485 studies representing 533 free-ranging wild mammalian species, we examined how ecological (habitat type, trophic level) and life history (longevity, vagility, gestation duration and torpor) traits influence T. gondii infection globally. We also compared T. gondii prevalence between wild and domesticated species from the same taxonomic families using data compiled from 540 studies of domestic cattle, sheep, and pigs. Across free-ranging wildlife, we found the average T. gondii prevalence was 22%, which is comparable to the global human estimate. Among ecological guilds, terrestrial species had lower T. gondii prevalence than aquatic species, with freshwater aquatic taxa having an increased prevalence compared to marine aquatic species. Dietary niches were also influential, with carnivores having an increased risk compared to other trophic feeding groups that have reduced tissue cyst exposure in their diet. With respect to influential life history traits, we found that more vagile wildlife species had higher T. gondii infection rates, perhaps because of the higher cumulative risk of infection during movement through areas with varying T. gondii environmental loads. Domestic farmed species had a higher T. gondii prevalence compared to free-ranging confamilial wildlife species. Through a macroecological approach, we determined the relative significance of transmission routes of a generalist pathogen, demonstrating an increased infection risk for aquatic and carnivorous species and highlighting the importance of preventing pathogen pollution into aquatic environments. Toxoplasma gondii is increasingly understood to be primarily an anthropogenically-associated pathogen whose dissemination is enhanced by ecosystem degradation and human subsidisation of free-roaming domestic cats. Adopting an ecosystem restoration approach to reduce one of the world's most common parasites would synergistically contribute to other initiatives in conservation, feline and wildlife welfare, climate change, food security and public health.