Rodents as Reservoirs of the Zoonotic Pathogens Coxiella burnetii and Toxoplasma gondii in Corsica (France)

Introduction

C oxiella burnetii, the causative agent of Q fever, is an intracellular bacterium that usually affects livestock and humans. C. burnetii is transmitted to humans by aerosols from animals, especially after contact with parturient females or birth products, which are highly infective. In humans, Q fever is often asymptomatic, but it may manifest as an acute (febrile illness, pneumonia, and hepatitis) or chronic disease (endocarditis) (Maurin and Raoult 1999). This infection is also generally asymptomatic in animals, nevertheless, C. burnetii induces abortion and stillbirth (Agerholm 2013).

It is believed that during the World War II Coxiella burnetii was used as a biological weapon, because of the many outbreaks of Q fever that took place in different countries through the conflict. Specifically in Corsica, two outbreaks were described in the lapse of 3 years (Madariaga et al. 2003). However, the greatest outbreak of Q fever ever reported took place in The Netherlands in 2007–2009, where 3523 human cases were diagnosed (Roest et al. 2011). C. burnetii is a worldwide pathogen and Q fever is being considered as a re-emerging disease in many countries, which may indicate that the pathogen is becoming more virulent (Arricau-Bouvery and Rodolakis 2005).

Toxoplasma gondii is a worldwide pathogen extremely distributed in humans and warm-blooded animals. Its definitive hosts are felids, and humans become accidentally infected by ingestion of sporulated oocysts contaminating water or food, tissue cysts in undercooked meat, and congenitally, when noninfected women become infected during pregnancy (Hill and Dubey 2018). The most severe symptoms appear during the congenital infection, which includes deafness, retinal damage, and mental retardation, among others. Postnatal infection is mostly asymptomatic, although lymphadenopathy and nonspecific symptoms may occur. However, since 1896 microbes have been studied as a cause of mental illnesses (Wise and Babcock 1896), and many studies have linked T. gondii as a trigger of many mental diseases and psychiatric disorders, especially schizophrenia (Torrey and Yolken 2003).

Previous studies has been carried out focusing in the role of rodents on the maintenance and transmission of C. burnetii and T. gondii. The seroprevalence of both pathogens was studied by Foronda et al. (2015), finding a wide distribution of these pathogens in rodents of both archipelagos. Owing to the lack of data available about the role of rodents on the life cycle of C. burnetii and T. gondii in Corsica, as well as the finding of T. gondii in different wild species of animals in this island (Richomme et al. 2009, Aubert et al. 2010), the importance in both public health and veterinarian points of view and the fact that the main sources of income for the island are tourism and agriculture, the aim of the study was to determine the seroprevalence and distribution of these pathogens in reservoirs in Corsica, analyzing the sera of rodents along the island, to study possible focuses of infection.

Materials and Methods

The study was carried out along Corsica island (France). Between February and June 2016, a total of 118 rodents belonging to the species Rattus rattus and Mus musculus domesticus were captured alive using Tomahawk and Sherman traps. Once captured, animals were taken to the Laboratoire Sciences Pour l'Environnement at Corte University where they were euthanized by cervical dislocation or carbon dioxide inhalation. Blood samples were centrifuged, then sera were removed and stored in glycerol 1:1 at −20°C until analyzed.

For C. burnetii antibodies detection, enzyme-linked immunosorbent assay (ELISA) were set with the Monoscreen AbELISA C. burnetii ELISA kit (Bio-X Diagnostics, Belgium). The essays were carried out following the manufacturers’ instructions but modifying that for the sera samples an antibody anti-rat peroxidase conjugate and anti-mouse peroxidase conjugate (Thermo Scientific, USA) replaced the anti-goat provided by the kit, which was used for the controls provided, following Foronda et al. (2015). The plates were read spectrophotometrically at 450 nm with a microplate reader (Model 680; Bio-Rad Laboratories, Hercules, CA). For setting the cutoff value, the manufacturer instructions were followed.

T. gondii was detected by indirect immunofluorescence (IFI) techniques using the Toxo-Spot IFI Kit (Biomerieux, France) and antibodies of rat and mouse (Thermo Scientific), respectively, following the manufacturer's instructions.

For the statistical analysis a chi-squared test was set, with p value <0.05 as statistically significant.

Results

Both C. burnetii and T. gondii were found in the two rodent species analyzed, R. rattus and M. m. domesticus, with an overall seroprevalence of 9.32% and 12.76%, respectively (Table 1). With regard to C. burnetii, 8.73% of the rats and 13.33% of mice analyzed were found positive. In contrast, 12.76% of rats and 14.29% of mice had antibodies against T. gondii, no significant differences were found when the seroprevalence of both pathogens was compared for each host.

These pathogens were in different areas of the island, as C. burnetii was restricted mainly to the Northern regions of the island, which are precisely the drier areas, and T. gondii was widely spread along the island (Fig. 1). Coinfection was only found in 1 of the 118 rodents analyzed (0.85%).

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FIG. 1.

Map of Corsica showing the sampled locations (), as well as the seropositive rodents for Toxoplasma gondii (), Coxiella burnetii () or both pathogens () (1. Rizzanese, 2. Taravo, 3. Porticcio, 4. Ajaccio, 5. Liamone, 6. Calacuccia, 7. Corte, 8. Ostriconi, 9. Padula, 10. Saint Florent, 11. Tettola, 12. Biguglia, 13. Golu, 14. Chiatra, 15. Matra, 16. Canale di Verde, 17. Terrenzana, 18. Diane, 19. Urbino, 20. Prunelli-di-Fiumorbu. 21. Palo, 22. Gradugine, 23. Pinarellu, and 24. Saint Cyprien.).

Discussion

Considering the wide distribution of both C. burnetii and T. gondii in Corsica and the serious diseases these pathogens can cause, the results of this study are relevant from a public health and veterinary point of view. On the one hand, the finding of C. burnetii in animals should not be taken for granted, even when there are not human cases reported, as animals act as reservoirs and facilitate the transmission of the disease, as occurred in the Netherlands outbreak, in which several regulations related to seropositive animals were applied, including the culling of pregnant goats and sheep, to control the transmission of Q fever (Roest et al. 2011). On the other hand, T. gondii is linked to several mental diseases and psychiatric disorders, which have considerable economic repercussions, as they can affect the working capacities of the individual, as well as its social life, especially those diseases related to suicide attempts, such as depression and schizophrenia.

C. burnetii in rodents from Corsica is focused on warm dry areas of the island (Rome and Giorgett 2007), which may imply that ticks, which act as vectors for C. burnetii, are adapting to a certain kind of climate conditions.

In addition, Corsica is well known for its cheese manufacturing, although the role of unpasteurized dairy products in the transmission of C. burnetii is still not well defined, some studies show the presence of C. burnetii in handicraft cheeses (Galiero et al. 2016). That is why, the results of this study should be taken into consideration by the sanitary entities, as Corsican cheeses play a main role in the gastronomy of the island and are tasted by many tourists every year, which may imply not only the possibility of an outbreak of Q fever in the island, but in any country.

On the contrary, T. gondii was found in some of the biggest cities of Corsica, Corte, and Sartène, as well as in touristic locations, Ostriconi and Aléria. This distribution makes sense taking into consideration that the highly populated areas of the island may also be the ones with more domestic animals, such as cats, which close the life cycle of T. gondii.

A comparative analysis with the Atlantic archipelagos of Canary Islands and Cape Verde (Foronda et al. 2015) showed similar seroprevalence in rodents of the archipelagos regarding T. gondii or C. burnetii, which may indicate that the transmission rate of this pathogens may not be influenced by many factors, such as climate and socioeconomical status.

Conclusions

Both C. burnetii and T. gondii are of public health interest because of the serious symptoms and diseases they can cause. These pathogens are also important from an economic point of view, as they cause abortions and stillbirths in livestock, which translates into high economic losses. The finding of these pathogens widely distributed in the island of Corsica should be considered by the competent veterinary authorities, to prevent a possible outbreak of Q fever or toxoplasmosis in Corsica.

C. burnetii was found in cheesemaking regions of Corsica, although this bacterium is mainly transmitted through aerosols, dairy products may be a source of contamination. Therefore, strict sanitary controls should be applied to Corsican cheeses, as they have great importance in the gastronomy of the island and are considered a tourist attraction.

The finding of T. gondii in highly populated and touristic areas implies a great chance of transmission to humans. This pathogen has traditionally been considered dangerous only for pregnant women with acute infection; however, its importance as a trigger of mental illnesses and psychiatric disorders has been increasing since the past century (Torrey et al. 2007). That is why, the existence of this parasite cohabiting in close contact with humans should not be ignored by the proficient sanitary authorities.