Giardia intestinalis (Syn. G. duodenalis or G. lamblia) is a flagellated protozoan parasite that widely infects the intestines of humans and various animals (1). It spreads through direct and indirect contact (via food and water) (2). Globally, G. intestinalis is one of the leading pathogens responsible for parasitic-related diarrhea, with infection rates strongly correlated with regional sanitation conditions. The prevalence in developed countries is significantly lower than in developing countries (3). The World Health Organization (WHO) estimated that approximately 280 million people are infected with this parasite annually, resulting in acute diarrhea (4). Additionally, individuals infected with G. intestinalis may face long-term health risks, including irritable bowel syndrome, childhood malnutrition, and arthritis (5–7). Furthermore, the rise of cross-border animal trade complicates public health control efforts, blurring the lines of parasite transmission and increasing the urgency for effective global surveillance and management strategies.

Molecular biology techniques have been widely applied in the study of G. intestinalis. Common methods include small subunit ribosomal RNA (SSU rRNA) analysis and multilocus genotyping (gdh, tpi, and bg genes) (8). Through molecular analysis, G. intestinalis has been divided into eight assemblages (A–H) (9). Among these, assemblages A and B exhibit strong cross-host transmission capabilities, infecting diverse hosts, including humans, and are typical zoonotic pathogens (10–12). In contrast, assemblages C–H show distinct host specificity. Studies have shown that assemblages C and D primarily infect canines (10, 13), assemblage E mainly infects ungulates such as cattle and sheep (14, 15), assemblages F and H have been detected in marine animals (16, 17), assemblage G was specifically found in rodents (15, 18).

Interestingly, despite assemblages C and D typically being considered exclusive to canines, research has shown some exceptions. Assemblage D was detected in a German traveller, and a study in Egypt identified assemblage C as a zoonotic pathogen (19, 20). These findings suggest that the host range of G. intestinalis may be broader than previously known. Therefore, expanding our understanding of its host adaptability is crucial for effective disease control and prevention strategies.

The fur animal farming industry in northern China is large-scale and is one of the pillars of the local economy. However, with the development of large-scale farming, disease prevention and control face significant challenges. Research has shown that fur animals can be infected with various parasites, including Pentatrichomonas hominis, Sarcocystis spp., and Trichinella spiralis (21–23), indicating that fur animals may be potential hosts for zoonotic pathogens. However, reports on the infection of fur animals (mink, foxes, and raccoon dogs) with G. intestinalis are scarce globally. This study employs tpi, gdh, and bg gene analysis to test samples from mink, foxes, and raccoon dogs, aiming to investigate the infection rates of G. intestinalis and the diversity and distribution of assemblage in these animals as well as to assess the implications for public health and disease prevention in the farming industry.

Foodborne zoonotic diseases are a significant global public health issue, especially in regions with frequent agricultural and livestock activities. These diseases not only threaten animal health but also pose potential risks to human health, particularly when the sources of transmission are complex (28). G. intestinalis, a typical foodborne zoonotic pathogen, has been confirmed to transmit between humans and various animals, and it poses a severe threat to immunocompromised individuals (29). Therefore, studying the epidemiological characteristics of this parasite is of utmost importance. In this study, we tested farmed fur-animals in northern China, and the overall prevalence of G. intestinalis in fur-animals was 1.15% (10/871), which was lower than other animal populations in China, such as cattle in Shanxi province (28.3%, 243/858), dogs in Liaoning province (13.2%, 27/205), black bears in Heilongjiang province (8.3%, 3/36), and donkeys in Jilin, Lioning, and Shandong provinces (15.5%, 28/181) (13, 30–33). The difference may be related to species differences, sample size and living habits. Interestingly, in this study, animals showed different susceptibilities to the disease, raccoon dogs had the highest infection rate (1.72%, 4/233), followed by mink (1.40%, 4/286) and foxes (0.57%, 2/352). although, no significant differences were found among them, which may be related to the small sample size. Future studies could increase the sample size and further investigate the infection mechanisms of G. intestinalis to difference species.

In the present study, the sampling region negatively affected the infection rates of G. intestinalis. The highest infection rate was observed in Hebei province (2.28%, 7/307), followed by Shandong province (0.88%, 1/113) and Liaoning province (0.81%, 2/247). Notably, no positive cases were detected in Jilin (0/73) and Heilongjiang (0/131) provinces, suggesting a lower risk of infection in these regions. However, a report showed that the infection rate of G. intestinalis in diarrhea patients in Heilongjiang was 5.81%, which indicated that the epidemic prevention and control situation was still not optimistic (31). Future studies should aim to expand both the sample size and the range of animal testing. Furthermore, the present study also found that the health status of animals was an important influencing factor affecting the infection rate of G. intestinalis. The infection rate in non-diarrheal animals was 1.16% (9/778) higher than the 1.08% (1/93) observed in diarrheal animals. This contrasts with findings in cattle in Shanxi province and children in Zhejiang province (30, 34). This difference may be related to the stages of G. intestinalis infection and the pathogenic mechanisms that cause diarrhea. Additionally, the host’s age, immune status, and co-infections with other pathogens may also influence the clinical manifestations and transmission patterns of G. intestinalis infection.

In this study, no significant differences in infection rates were observed between farms with different farming sizes. Notably, the infection rate of farms with less than 2,000 animals (1.41%, 7/498) was higher than that of farms with 2,000–5,000 animals (0.75%, 2/266) and ≥5,000 animals (0.93%, 1/107). These small-scale farms are usually family-run, and the technical level of feeding management, disease prevention and control is relatively low. Additionally, some farms have the phenomenon of raising dogs together, which may be a factor leading to the high infection rate.

Researchers have classified G. intestinalis into eight genotype assemblages (A–H), based on common genetic markers such as the SSU rRNA gene, and the gdh, bg, and tpi loci (9). In the present study, G. intestinalis in fur-animals were identified primarily as assemblages A (n = 3) and D (n = 3) through the analysis of bg and gdh genes. Among them, assemblage A was the dominant assemblage in mink, consistent with studies on ferrets in Europe and Japan, confirming that assemblage A was common in mustelids (35–37). Assemblage A is distributed globally across mammals and poultry and is recognised as an important pathogen responsible for human infections (3, 9, 33, 38). The discovery of assemblage A in mink in this study indicates that mink may be a potential host for human infections. Notably, pathological reports indicate that both person-to-person and person-to-animal transmission can occur through direct contact (49). Therefore, it is recommended to further investigate the infection rates among farmers and industry workers to prevent the spread to other animal populations or human communities.

Assemblages C and D were the most common genotypes in canids globally (9). They were widely reported in dogs (13, 39, 40). In China, these assemblages have also been detected in dogs from Xinjiang and raccoon dogs from Jilin (41). In the present study, assemblage D was found in foxes and raccoon dogs, consistent with studies on foxes in Australia and raccoon dogs in Poland (42, 43). However, assemblage C was not detected in this study, which may be related to sample size, sampling time, and geographic regional differences. Notably, although assemblage D was considered host-specific to canids, existing research shows that it can infect other species, including humans (9). For instance, assemblage D has been detected in German travellers, Australian kangaroos, British cattle, and American chinchillas (19, 37, 43, 44). These findings suggest that assemblage D may cross-infection between wildlife and livestock, posing a potential zoonotic risk.

In this study, the amplification success rates for the bg and gdh genes were relatively high, whereas the tpi gene sequences were not successfully obtained. This suggests that the amplification success rates for bg, gdh, and tpi genes may be associated with different assemblage types, which is consistent with previous studies. For example, Chen et al. (31) successfully obtained 20 bg, 19 gdh, and 9 tpi sequences from 22 positive samples of black bears, while Xiao et al. (45) obtained 70 bg, 32 gdh, and 7 tpi sequences from 90 positive samples of goats. These results indicate that more accurate and sensitive molecular diagnostic techniques are urgently needed to achieve a more precise genetic characterization of G. intestinalis.

G. intestinalis exists as cysts in vegetables, meat and other foods (29). The food source of fur-animals in mainly poultry meat, which may be one of their infection routes. Additionally, G. intestinalis is also wildly present in the environment, particularly in surface water sources (46). In 2013, a waterborne outbreak of G. intestinalis infection was reported in South Korea, highlighting its potential for waterborne transmission (47). In addition to known hosts, there are many unknown hosts that could serve as potential sources of human infection. These potential transmission routes pose a threat to public health security. Therefore, it is essential to strengthen the quarantine of foods such as vegetables and meat, while expanding the sampling scope to include more species for detection. At the same time, treatment of the disease is also crucial. Although metronidazole is the drug of choice for treating giardiasis, its issues with resistance and potential side effects such as abdominal pain and nausea limit its use. Therefore, there is an urgent need to develop new treatment formulations, such as phytochemicals, to address this challenge (48).

The present study investigated the prevalence of G. intestinalis in fur-animals in northern China, first reporting the occurrence of assemblage A in mink, indicating that mink may be a potential zoonotic source of G. intestinalis, while also contributing to the epidemiological data on this parasite. Additionally, the detection of assemblage D in foxes and raccoon dogs suggests a similar zoonotic risk. Therefore, attention should be given to the prevalence of G. intestinalis among fur industry workers and their surrounding environments to effectively control and prevent potential transmission risks. However, this study has some limitations. For instance, the tpi gene sequence was not successfully obtained, and the effect of seasonality on prevalence was not investigated. Therefore, future studies should aim to expand the sample size and incorporate seasonal sampling to better understand the infection dynamics of G. intestinalis in fur-animals.