In the present study, the serological evidence for the presence of T. gondii infection in pet dogs and cats, and their owners in Shandong province, eastern China is reported. We demonstrated that T. gondii seroprevalence in pets and pet owners was 18.61% and 18.04%, respectively. Seroprevalence of T. gondii in cats was 21.67%, being slightly lower than the 24.5% seroprevalence detected in cats in mainland China, from 1991 to 2015 [20]. Seroprevalence T. gondii in dogs was 15.56% - higher than the 11.1% seroprevalence previously reported in pet dogs in China [19].
The association between cat ownership and increased seropositivity of T. gondii is to be anticipated, because cats - serving as the definitive host of this parasite - play a key role in the transmission of T. gondii to humans [21]. In the studied regions, cats are used mainly to control rats and mice, or as a pet. Cats become infected with T. gondii when they prey on infected rodents or birds. This is followed by excretion of millions of environmentally-resistant oocysts in cat feces, causing health risks to animals and humans [3, 22]. The presence of cats at home increases the risk of exposure to T. gondii, as reported previously [23].
Dogs, on the other hand, are a dead-end intermediate host and do not produce T. gondii T. gondii oocysts; and might be considered less important to the zoonotic transmission of T. gondii. However, dogs can ingest oocysts from cat feces, by coprophagia, which pass intact [24] and even viable [25] through their gut into the feces. Some dogs have a tendency to roll in pungent substances, such as cat feces. This behaviour means that dogs can mechanically spread T. gondii oocysts, contaminating the environment [24] and infecting humans - accidentally through ingestion of oocysts from dog fur while petting them [26]. The ingestion of improperly-cooked infected meat, can be a source of transmission to people in areas where selling dog meat for human consumption is permitted [27].
Our study also found that female pet owners (24.39%, 60/246) had a significantly higher seroprevalence than male pet owners (10.75%, 23/214; P < 0.001) (Table 2). This may be due to various factors. In China, women are responsible for taking care of pet animals at home, handling raw meat and vegetables, and performing household cleaning tasks. These factors can increase their contact with cats and dogs, and their feces, thus increasing opportunities of acquiring the infection compared with men. With this in mind, women should follow basic hygienic measures to limit exposure to zoonotic agents; including wearing gloves and masks when handling cat feces, together with hygienic disposal of cat feces and frequent hand-washing - particularly before preparing food.
There is increasing evidence for the importance of waterborne transmission of T. gondii to humans, via the dissemination of oocysts through surface water [28]. Therefore, proper disposal of cat litter can reduce environmental contamination with oocysts excreted in cat feces [29]. Although pet owners who used their hands to dispose pet feces (18.97%) had a higher seroprevalence compared with those who used gloves (12.86%), the difference was not statistically significant (P > 0.05). This may be due to a large difference in the sample-size between people who disposed pet feces using gloves, and those using bare hands. Regardless, cat feces must be hygienically disposed of, in order to reduce the environmental contamination with T. gondii oocysts.
In China, approximately 1 in 5 pet cats is T. gondii-seropositive, and this may impose a significant risk as the number of owners, and their interactions with cats, is increasing [20]. Cats and dogs are known to harbor other protozoal species [17], helminthes [30], and many other types of pathogens, such as fungal, viral, and bacterial agents [31], and may constitute potential reservoirs to their owners. Therefore, the epidemiological and public health importance of zoonotic infections, in pet dogs and cats in China, should be investigated in future studies. In the interim, we advocate the implementation of better measures to improve personal hygiene; and to maintain good pet-keeping management practice, which will ultimately help in reducing the risk of T. gondii infection, and other zoonoses, in humans.