**6. Conclusion: consequences for the management of zoonotic transmission**

20 Toxoplasmosis – Recent Advances

countries [169, 170, 171].

true complexity of less disturbed ecosystems. The relative richness of potential hosts that exists within the tropics may have resulted in a correspondingly more diverse range of genotypes of the parasite that can co-exist in such an environment. Under this hypothesis, *T. gondii* would have developed a plurality of alleles to increase its colonization potential [160, 162]. In addition, the larger home ranges of wild felids compared to domestic cats can also strongly influence hybridization patterns and gene flow of the parasite and thus the genetic structure of pathogen populations. The high prevalence in IHs, added to wild felid ecology (diet and home range), could suggest that DHs are more frequently infected by multiple *T. gondii* genotypes, which then cross and recombine before transmission to a new IH. The possibility of reinfection by different strains is known for humans [166]. It has never been explored for felids, but may be hypothesized as another source of increasing diversity.

Most tropical countries are also characterized by an ongoing anthropization with development of farming and settlement in deforested areas. At the confluence between the two environments, wild animals may penetrate in anthropized areas and domestic animals come in contact with the wild through wild game, soil or running water. The increasing pressure of anthropization reduces the hunting area of wild carnivores, including felids and favours their penetration in domestic area. The predatory activity of wild felines or stray cats around these disturbed environments (consumption of chickens, dogs, cats…) would ensure gene flow between the two populations of strains. The consequences of this interpenetration in terms of *T. gondii* genotypes are diverse: (i) detection of *T. gondii* strains with "hybrid" genotypes between the "wild" population and the anthropized population reflecting genetic exchanges, (ii) strains from the wild environment found in domestic animals, such as stray dogs, or (iii), on the opposite, strains from the anthropized environment found in wild animals [165]. In parallel, the influence of human activities with urbanization, fragmentation of landscape, deforested areas, farming, domestication of cats and other animals, modifies *T. gondii* ecology reducing the number of ecological niches. This process favours an impoverishment of *T. gondii* genetic diversity with the selection of a few strains well adapted to a small number of domestic species [167, 168]. Transportation of these strains through large distances by human trade exchange and transportation of animals lead to introduction of domestic strains in the wild environment and occasionally to expansion of clonal lineages. In tropical countries, this is evidenced by the so-called *Caribbean* genotypes found in the anthropized areas of French Guiana and in several Caribbean Islands, or in Africa, where the same African lineages were found in different

Finally, the dynamics of *T. gondii* in wildlife and its interaction with domestic areas show a contrasted pattern. In most European countries, due to the large anthropization, any wildliving individual lives relatively close to domestic areas. Farming and cat domestication occurred long time ago. Farms constitute the reservoir of infection, from which a few genotypes adapted to farm species irradiate in the surrounding environment [72]. This could explain the widespread occurrence of only a few well adapted clonal lineages (types II Like other IHs, humans can be infected either by cysts containing bradyzoits, or by oocysts of *T. gondii*. Tissue cysts are responsible for meat-borne infection (pork, lamb, beef or poultry are possible source of contamination), while sporulated oocysts lead to infection by ingesting particles of soil (after gardening for example) or by consuming unwashed raw fruits or vegetables, or untreated water [2, 145, 173, 174, 175]. However, the crucial question of the relative part of risk related to bradyzoits versus oocysts remains open. Different approaches have been used to estimate the relative importance of sources of contamination, using risk-factor analyses or estimation of the fraction of attributable risk, either in the general population (chronic infection) or in cases of seroconversion in pregnant women. These studies clearly identified the ingestion of undercooked meat as a risk factor [7, 13, 173, 176]. However, this result is probably partly due to this risk being easier to characterize than the risk due to oocysts. Another way to get an idea of the relative part of risk related to cysts or oocysts is to undertake a quantitative assessment of the risk of toxoplasmosis [177]. Recently, in the Netherlands, Opsteegh *et al.* performed a quantitative microbial risk assessment (QMRA) for meat-borne toxoplasmosis, which predicted high numbers of infections per year. The study also demonstrated that, even with a low prevalence of infection in cattle, consumption of beef constitutes an important source of infection [178]. However, the risk assessment remains limited by the lack of detailed information on which fraction of meat is more contaminated in carcass: although seroprevalences are available for farm animals from many countries [2], the correlation between seropositivity and detection of parasites in meat is weak. In terms of veterinary medicine, there is no surveillance system for animal toxoplasmosis and only cases of abortions (due to *T. gondii* or other causes) have to be declared. The meat-borne risk analysis is also limited by the low level of information on the food cooking practices, and on the contamination of species consumed less often, such as game [90, 91, 78].

Up to now, the risk analyses essentially used information on, and produced estimates about, meat-borne toxoplasmosis. These studies permitted to identify control points for the

management of meat-producing animals. For example, in intensively managed swine farms, modern biosecure management practices have resulted in reduced levels of infection in swine raised in confinement [96, 179, 180]. In organic livestock production systems, farmmanagement factors including feeding are thought to play an important role in the on-farm prevalence of *T. gondii* [181]. To limit *T. gondii* infection in such farms, recommended practices include exclusion of cats or other wildlife, strict rodent control and restriction of human entry in pig barns [182]. These measures could be effective in other species to reduce the level of contamination of meat. On the contrary, organic pork meat may pose a specific risk of transmitting T*. gondii* to humans [183]. However, due to the capacity of dissemination of *T. gondii*, the objective of a completely *T. gondii*-free meat seems difficult, but feasible using pre-harvest measures for prevention of T. gondii infection [184].

The Life Cycle of *Toxoplasma gondii* in the Natural Environment 23

case, prevention measures should focus on specific aspects depending on the exposure of people. These elements should help to reduce the burden of toxoplasmosis in human and

Emmanuelle Gilot-Fromont1,2,\*, Maud Lélu3, Marie-Laure Dardé4, Céline Richomme5, Dominique Aubert6, Eve Afonso7, Aurélien Mercier4, Cécile Gotteland1,6, Isabelle Villena6 *1UMR CNRS 5558 Laboratoire de Biométrie et Biologie Evolutive, Université Lyon 1, Villeurbanne,* 

*Neuroepidemiology and Tropical Neurology, CNRS FR 3503 GEIST, University of Limoges,* 

*5ANSES, Nancy laboratory for rabies and wildlife, Technopole agricole et vétérinaire, Malzéville,* 

*6Laboratoire de Parasitologie-Mycologie, EA 3800, UFR de Médecine, SFR Cap Santé, FED 4231,* 

*7Department Chrono-environnement, UMR CNRS 6249 USC INRA, University of Franche-Comté,* 

The authors thank Aurélien Dumètre, René Ecochard, Michel Langlais, Dominique Pontier, Philippe Thulliez and Stéphane Romand for their help in elaborating the 10-year research period that produced part of the results presented here. This project has been supported by the Agence Française de Sécurité Sanitaire de L'Environnement et du Travail (AFSSET) and by the Agence De l'Environnement et de la Maitrise de l'Energie (ADEME), with additional grants from Grünenthal France Laboratory (EA), Institut National de la Recherche Agronomique (INRA, CR), Région Champagne-Ardenne (EA, ML and CG), Département des Ardennes (ML), Communauté de Communes de l'Argonne Ardennaise (ML) and the National Institute for Mathematical and Biological Synthesis (NIMBioS, sponsored by the National Science Foundation, the U.S. Department of Homeland Security, and the U.S.

[1] Dubey JP (2010) Toxoplasmosis of animals and humans, second edition. Boca Raton:

*2VetAgro-Sup Campus Vétérinaire, Université de Lyon, Marcy l'Etoile, France,* 

*4INSERM UMR1094, Tropical Neuroepidemiology, School of Medicine, Institute of* 

*3NIMBioS, University of Tennessee, Knoxville, Tennessee, USA,* 

*University of Reims Champagne-Ardenne, Reims, France,* 

animal populations.

**Author details** 

*Limoges, France,* 

*Besançon, France* 

**Acknowledgement** 

Department of Agriculture, ML).

CRC Press. 313 p.

**7. References** 

Corresponding Author

 \*

*France.* 

*France,* 

On the other hand, working to reduce the level of infection in meat does not act on the risk of toxoplasmosis due to direct contact with oocysts, which stays largely unknown and unmanaged. Limiting the level of contamination in meat may even result in the increase of the relative risk due to oocysts. The importance of oocysts in the overall contamination rate remains difficult to assess, due to the lack of information on the level of environmental contamination and to the difficulty to characterize the level of contact of people with contaminated areas. In this framework, a better knowledge of the life cycle of *T. gondii* in its natural environment should help to characterize the risk due to oocysts. For example, the estimates provided in Table 1 give an order of magnitude of the expected differences between environments. Moreover, two recent methodological advances should improve our knowledge of environmental contamination. First, new methods to detect oocysts in soil [185] and water [186, 187, 188] have been proposed, based on molecular detection or immunocapture. Being highly sensitive, these methods should allow researchers to better characterize areas and periods at risk of contamination. A few studies have already measured the level of soil and water contamination [50, 68, 189]. These studies confirmed that the risk in urban areas is spatially structured at the very local scale, and they should help to identify areas most contaminated in other environments. The second useful tool that should bring relevant information is the development of methods to detect antibodies specifically linked to infection by oocysts [190]. This test, based on western blot assay detecting for IgG positive serums antibodies to sporozoites, allowed the authors to determine the proportion of cases that had contacts with oocysts in Chile, both in humans [191] and in swine [192]. In North America, a survey using this method shows that a high proportion of mothers of congenitally infected infants had primary infection with oocysts [193].

These new analytical tools should help to identify the origin of contamination, and thus solve several fundamental and practical questions regarding *T. gondii* life cycle. For example, estimating the frequency of infection from oocysts in cats of urban and rural area should help to estimate the part of the DH-environment life cycle in different environments. In people, these tools should help to assess if the relative role of oocyst and meat-born infection varies according to the area (urban versus rural populations for example). In such case, prevention measures should focus on specific aspects depending on the exposure of people. These elements should help to reduce the burden of toxoplasmosis in human and animal populations.
