Toxoplasma gondii is a globally distributed intracellular parasite capable of infecting almost all known warm-blooded animals, including giant pandas (Ailuropoda melanoleuca). Felines, especially feral domestic cats, are definitive/intermediate hosts of T. gondii, and contamination of the environment with fecal-containing oocysts from felines, is the main cause of toxoplasmosis transmission (Dubey, 2009). Toxoplasmosis can cause reproductive disorders in captive animals as well as livestock (Zhang et al., 2016), such as infertility, abortion, stillbirth, and weak fetuses, in addition, severe acute infection can even cause the death of the host (Dubey, 2022) with several infections and deaths of wildlife reported worldwide (Hollings et al., 2013; Lv et al., 2021).

The giant panda is considered a Class One protected species in China and is currently categorized as “vulnerable” by the International Union for Conservation of Nature (IUCN). One of the leading causes of death for both captive and wild giant pandas is parasitic diseases (Wang et al., 2018). It was reported that a captive giant panda in Zhengzhou zoo died of acute infection of T. gondii which showed that T. gondii can be an important factor in the health of giant pandas (Ma et al., 2015). However, to date, there are no reports about the prevalence of toxoplasmosis in giant pandas, and the major risk factors for the prevalence of T. gondii are also unknown. Therefore, this study aimed to estimate the seroprevalence and risk factors of T. gondii in captive giant pandas. Additionally, the association among age, season, and seroprevalence of T. gondii was investigated. Understanding the seroprevalence and risk factors associated with T. gondii can broaden our knowledge of the conservation of giant pandas, as well as guide us to formulate an appropriate plan for disease prevention and control within the population of this vulnerable species.

Toxoplasmosis is a disease that results from infection with the Toxoplasma gondii, which can cause death in wildlife (Rouatbi et al., 2019; Wilson et al., 2021). It is also a potentially serious threat to giant pandas, which can cause reproductive disorder and even death. As infected individuals can be asymptomatic further investigation of this disease is necessary. Despite the risk of toxoplasmosis in giant pandas, there is limited data on the seroprevalence of T. gondii in the captive population of this vulnerable species. To the best of our knowledge, this is the first large-scale study to survey the seroprevalence and analyze the risk factors for the presence of T. gondii in the captive panda population. As the detection of the T. gondii infection in host primarily relies on serological assays, the serological methods used in this study were selected from our previous studies by comparing five commercial kits (Yue et al., 2022).

Our results showed the seroprevalence of T. gondii in giant pandas was 35.67%, which was consistent with Loeffler et al. (2007) (31.58%, 6/19), but was higher than Zhong et al. (2014) (1.45%, 1/69), these differences may be due to the different diagnostic methods and study designs. These similar differences were found in other wildlife studies, such as in Ursidae species. In the US, previous studies have often used ELISA or MAT to detect T. gondii antibodies in different Ursidae species, with the seropositivity rates of black bears (Ursus americanus) ranging from 14.2% to 84.5%; the brown bears (Ursus arctos) ranged from 24.7% to 44.0%, and polar bears (Ursus maritimus) ranged from 18.5% to 45.6% (Dubey, 2022).

In the present study, we found that the seropositivity of T. gondii increased with age. Higher infection rates were found in the senior age group, and an age-related seroprevalence was seen in giant pandas, the seropositivity became high with increased age. Moreover, the old individuals may have some underlying diseases which enhanced their susceptibility to T. gondii infection. This result is in agreement with previous studies (Brandon-Mong et al., 2015; Deshmukh et al., 2021). In addition, our findings demonstrated that acquired infection may be the main roution giant panda are infected with T. gondii. These results are consistent with previous findings in ursids (Briscoe et al. (1993), in which the prevalence of T. gondii in American black bears was found to increases with age.

Felines are the definitive host of T. gondii, infected cats can excrete oocysts into the environment, which could become a potential source of infection. Moreover, cats are popular pets in many households in both urban and rural areas, and the problem of disease transmission by stray cats has become increasingly prominent. Therefore, stray cats may be the main threat of T. gondii infection to the giant panda. Furthermore, rodents play an essential role in the life cycle of T. gondii and the epidemiology of toxoplasmosis because they are considered the primary source of infection (food and reservoir) for cats (Galeh et al., 2020). Both stray cats and rats often appear in or around the captive enclosures of giant pandas, and are difficult to control. Unfortunately, we did not collect enough data about T. gondii infection in stray cats and rats, so we cannot assess how serious a threat they pose to the health of captive giant pandas, this is also an important factor that needs to be investigated in the future.

As an iconic flagship species for wildlife conservation, the giant panda is considered a national treasure in China and plays a significant role not only as an umbrella species but also in national diplomacy and cultural communication. For cultural exchange, science popularization, and public education, some giant pandas will be transferred between zoos or breeding centers in different cities for exhibition. Based on our results, transferring the giant pandas between facilities was identified as one of the risk factors for T. gondii infection (OR = 2.69, p < 0.05). This result could be due to the zoos often keeping various species of animals, and as almost all known warm-blooded animals can be the intermediate host of T. gondii, infection rates may be higher. Therefore, managing multi-species in one area, such as in a zoo compared to breeding centers, which only have one species, may likely increase the risk of infection of T. gondii. Furthermore, the act of transferring giant panda or any animal is very stressful (Tang et al., 2019). This stress of moving to a new place, combined with acclimating to a new environment may reduce immune function and make the animal more vulnerable to infection.

Non-statistically significant associations were found between antibodies to T. gondii and sex and season. In addition, many studies showed there is no association between T. gondii and sex (Dubey, 2009; Must et al., 2015). The season was not an associated risk factor affecting the prevalence of T. gondii in giant pandas in this study. We also studied the trend of seroprevalence of T. gondii in giant pandas with month, and the seroprevalence was highest in November. However, other previous studies showed that the prevalence of T. gondii in the rainy season or monsoon associated with mild temperatures seems to be higher (Du et al., 2012), one study also mentioned the prevalence of T. gondii in foxes was lower at higher elevations with the cooler and drier area (Wei et al., 2021). Due to the rarity and particularity of giant pandas, the collection of serum samples is often limited and few samples in some months, such as November (three samples), resulting in the fluctuation of seroprevalence. The trend of the seroprevalence of T. gondii with the month in giant pandas needs further investigation.

The T.gondii antibodies of 203 serum samples in giant pandas from 2007 to 2022 were detected and the distribution patterns of T.gondii infections were determined. The results showed 56 (35.67%) giant pandas were seropositive, age and transfer history between institutions were identified as risk factors for T. gondii infection. It is suggested that age-related seroprevalence was the main factor, and zoo housing, where multiple species are kept, may increase the chance of cross-infection of T. gondii. As an iconic flagship species and an umbrella species, the giant panda plays a vital role in wildlife conservation within China. It is hoped that these data can provide baseline information for developing policies and protecting the health of giant pandas and other wildlife.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The animal study was reviewed and approved by the Institutional Animal Care and Use Committee (CRBGPB) (NO. 2020006).

SL, RH, and CY contributed to conception and design of the study. WY, WH, DZ, KW, and LHL collected samples. JL, XS, HZ, and YYL organized the database. XF, WY, XY, YLL and WZ performed the statistical analysis. CY, LL, and WY wrote the first draft of the manuscript. CY, SL and JA wrote sections of the manuscript. All authors contributed to the article and approved the submitted version.

This research was supported by the Research Project of the Science and Technology Department of Sichuan Province (2020YJ0489), Chengdu Research Base of Giant Panda Breeding (2021CPB-B11, 2021CPB-B08) and National Forestry and Grassland Administration and Sichuan Province Finance Department (project title: study on main epidemiological investigation and prevention of giant panda).

We sincerely thank the veterinary staff and keepers of the Chengdu Research Base of Giant Panda Breeding and Zoos for their participation in the sample collection work, and James Edward Ayala for reviewing the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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