Camel husbandry holds significant economic, social, and cultural importance in Kazakhstan, particularly within pastoral communities. Camels provide essential resources, including meat, milk, wool, and transportation, contributing considerably to rural livelihoods and agricultural stability. However, the health and welfare of camels are threatened by a wide range of pathogens, including bacterial, viral, and parasitic agents, which negatively impact productivity and survival. Among these, parasitic infections play a major role, with trypanosomoses recognized as particularly important due to their chronic nature, economic impact, and potential zoonotic relevance (1–3).

Trypanosoma evansi (T. evansi), the causative agent of surra, is a chronic vector-borne parasite that affects various domestic animals, including horses, donkeys, dogs, camels, sheep, and goats, and is also a potential human pathogen, resulting in anemia, progressive weight loss, reproductive failure, reduced productivity, and, in severe cases, mortality (2, 4–7). Surra is widely distributed globally, predominantly across regions of Asia, North Africa, Central, and South America, where environmental conditions favor vector survival and parasite transmission (1, 2).

Despite the large camel population and documented outbreaks of trypanosomiasis in Kazakhstan, the disease is poorly documented and there are few literature sources. To date, no peer-reviewed data exist on camel trypanosomiasis in Kazakhstan, and the only relevant publication is the study by Claes et al. (4), which investigated equine trypanosomosis. This highlights a substantial knowledge gap and underscores the importance of targeted research on T. evansi in camels in Kazakhstan.

Diagnosis of trypanosomiasis can be clinical, parasitological, serological, or molecular (8–10). In most cases, a single diagnostic method does not unequivocally identify the different statuses of infection. These include “non-infected,” “asymptomatic carrier,” “sick infected,” “cured/not cured,” and/or “multi-infected.” Therefore, integrative approaches combining parasite detection, molecular methods, and antibody detection, along with epizootiological information, are needed (11, 12).

Control of surra still relies mainly on the observation of clinical signs and subsequent treatment of sick animals, which is inefficient and results in high morbidity and mortality of undiagnosed animals that in the meantime act as reservoirs. Indirect diagnosis is possible through detection of specific antibodies in the mammalian hosts. Currently available antibody detection tests include the immune trypanolysis assay (13), an enzyme-linked immunosorbent assay for T. evansi (ELISA/T. evansi) (14), card agglutination test for trypanosomiasis (CATT/T. evansi) (1), latex agglutination test, and simpler methods for field mass screening such as the complement fixation test (CFT) and the formol gel test (FGT). Definitive diagnosis of T. evansi infection is achieved by microscopic demonstration of the parasite, which however suffers from low sensitivity due to low parasitemia. The choice of one or several tests is guided by epidemiological requirements, technical feasibility, and cost-effectiveness (15, 16).

Serological tests such as CFT and FGT, despite their limitations in sensitivity and specificity, have been widely used for large-scale surveillance in camels because they are simple, inexpensive, and applicable under field conditions.

Our current study aimed to investigate the seroprevalence of T. evansi infection in camels in Kazakhstan using CFT and FGT. The result of this study will be useful for the surveillance and control of T. evansi infection.

Out of 2,773 camel sera tested, 113 (4.07%) were positive for T. evansi antibodies by CFT, and 276 (9.95%) were positive by FGT (Figure 2).

Thus, the FGT detected more than twice as many seropositive camels as the CFT. The seroprevalence results stratified by age group and sex are summarized in Tables 1, 2.

Age-related differences in seroprevalence were statistically significant (χ², p < 0.0001). Old camels (>12 years) showed the highest proportional prevalence, with 5.93% (95% CI: 2.75–12.32) positive by CFT and 26.27% (95% CI: 18.49–35.78) positive by FGT. Mature adults (6–12 years) recorded 3.95% (95% CI: 3.06–5.09) by CFT and 10.57% (95% CI: 9.08–12.28) by FGT, while young adults (3–6 years) showed 5.02% (95% CI: 3.69–6.79) and 8.04% (95% CI: 6.35–10.13), respectively. Juveniles (<3 years) exhibited the lowest prevalence, with 2.70% (95% CI: 1.78–4.08) in CFT and 9.47% (95% CI: 7.64–11.68) in FGT (Table 1). Despite the smaller sample size in the oldest age group, the high rates observed confirm that older camels are more likely to have been exposed to T. evansi.

Sex-related differences were also observed (Table 2). Seroprevalence was significantly higher in females compared to males, both in CFT (4.69%; 95% CI: 3.78–5.80 vs. 3.06%; 95% CI: 2.17–4.30) and in FGT (10.47%; 95% CI: 9.10–12.03 vs. 9.09%; 95% CI: 7.48–11.00). This sex-related difference in infection rate was statistically significant (p = 0.046). In absolute numbers, 81 females versus 32 males were CFT-positive, and 181 females versus 95 males were FGT-positive. The higher infection rate in females could be associated with factors such as greater exposure to vectors (for example, around watering or feeding sites), physiological stress from reproduction, or sex-based differences in immune response. Overall, the FGT identified substantially more positive cases than the CFT across all age groups and in both sexes. In every category, some camels that tested negative by CFT were positive by FGT. This discrepancy suggests that the FGT has higher analytical sensitivity, potentially detecting low-level or older infections that the CFT might miss. However, it also raises the possibility that FGT-positive/CFT-negative results could include animals with residual antibodies from earlier infections or non-specific reactions. No camels were found CFT-positive while FGT-negative in this study.

Seroprevalence varied significantly across the three surveyed regions (Table 3). In Mangystau, the proportion of seropositive camels was 5.0% (95% CI: 2.15–11.18) by CFT and 65.0% (95% CI: 55.13–73.76) by FGT. In Kyzylorda, prevalence was 4.01% (95% CI: 3.33–4.82) by CFT and 7.83% (95% CI: 6.86–8.91) by FGT, while in Turkestan prevalence reached 7.14% (95% CI: 1.98–22.65) by CFT and 14.29% (95% CI: 5.70–31.49) by FGT. These findings indicate marked regional heterogeneity in the distribution of surra in Kazakhstan.

A more detailed district-level breakdown is provided in Supplementary Table S1. In Kyzylorda, the highest prevalence by FGT was observed in Karmakshy (19.06%; 95% CI: 15.14–23.72) and Aral (13.43%; 95% CI: 11.06–16.24) districts, while very low levels were recorded in Syrdarya (2.64%; 95% CI: 1.29–5.35) and Kyzylorda (0.55%; 95% CI: 0.19–1.59) districts. In Mangystau, extremely high prevalence was detected in Munaily (90.0%; 95% CI: 74.38–96.54) and Mangystau (72.5%; 95% CI: 57.19–83.89) districts. In Turkestan, Shardara district showed moderate prevalence (14.3%; 95% CI: 5.70–31.49), although the sample size was small (n = 28). These district-level findings underscore strong local variation, which may reflect ecological conditions, herd management practices, and vector abundance.

Agreement between the two serological assays was further evaluated (Table 4). Overall, 92.4% of samples showed concordant results between CFT and FGT. The Cohen’s kappa statistic was 0.41, indicating moderate agreement. As expected, FGT detected additional positive samples that were negative in CFT, reflecting its higher sensitivity but lower specificity.

This study provides the first seroepidemiological evidence of T. evansi infection in camels from Kazakhstan, filling a major knowledge gap in Central Asia. The overall prevalence detected in our survey (4.07% by CFT; 9.95% by FGT) indicates that surra is present at endemic levels, although with strong local variation. These results are broadly comparable with reports from ecologically similar regions such as Iran (7.5–12.3%) (2) and Algeria (8.7%) (16, 18), but considerably lower than in some African countries where prevalence may exceed 20–30% (1). Such comparisons highlight that the epidemiology of surra is strongly influenced by ecological conditions, management practices, and vector abundance.

As expected, the FGT identified more positive samples than the CFT across all categories. This finding is consistent with earlier reports that the FGT, although less specific, is more sensitive in detecting residual or cross-reacting antibodies (9). The CFT is considered more specific but may miss chronic or low-level infections due to waning antibody titers. Importantly, the possibility of cross-reactivity with other trypanosome species and lingering antibodies post-treatment cannot be excluded. In endemic areas, animals may retain detectable antibodies for months or years, which inflates seroprevalence without necessarily indicating active infection. This underlines the need for cautious interpretation of serological results and the complementary use of molecular tests in future studies.

The agreement analysis between the two serological tests indicated an overall concordance of 92.4% but only moderate agreement (κ = 0.41). This finding reflects the different diagnostic properties of the assays: while CFT is more specific, FGT identifies a higher number of positive cases due to its greater sensitivity. Similar patterns have been reported in other endemic regions, where FGT tends to overestimate prevalence compared to CFT or ELISA. These results emphasize the importance of carefully selecting the appropriate serological tool depending on whether the priority is screening (sensitivity) or confirmation (specificity).

Age-related differences were pronounced. Old camels (>12 years) showed the highest proportional prevalence (26.3% by FGT), followed by mature adults, young adults, and juveniles. This pattern reflects cumulative exposure to T. evansi over time, as older animals are more likely to have been repeatedly exposed to vectors. Similar age-related increases have been reported in Algeria and Ethiopia (19). In contrast, juveniles consistently showed the lowest prevalence, likely reflecting shorter exposure duration and possibly stronger veterinary supervision in younger animals.

Seroprevalence was also higher in females compared to males, a pattern observed in previous studies (20, 21). Possible explanations include physiological stress during pregnancy and lactation, as well as husbandry practices where females are retained longer in herds for breeding and milk production, thus accumulating greater lifetime exposure.

Marked regional heterogeneity was evident, with extremely high prevalence in Mangystau (65% by FGT), moderate levels in Turkestan (14.3%), and relatively low prevalence in Kyzylorda (7.8%). The district-level breakdown (Supplementary Table S1) further highlights this variation. In Kyzylorda, prevalence ranged from as low as 0.55% in Kyzylorda district to as high as 19.1% in Karmakshy. Similarly, in Mangystau, prevalence exceeded 70% in Mangystau and Munaily districts but was only 30% in Tupkaragan. These findings illustrate how local ecological conditions – such as vector density near rivers and pastures – may strongly shape infection risk. Comparable intra-regional variation has been reported in Iran and Pakistan (22).

Transmission of T. evansi in camels is primarily mechanical, mediated by biting flies such as Tabanus spp., Stomoxys spp., and Haematobia spp. Vector ecology is strongly linked to temperature, rainfall, and vegetation cover, which create suitable habitats for fly breeding and activity (2). Our survey was conducted between January and May, prior to the peak summer months when tabanids are most active. Therefore, some seasonal bias cannot be ruled out, as prevalence may differ if sampling is performed later in the year during maximum vector activity. Longitudinal studies across different seasons are needed to capture this dynamic.

Globally, a wide range of diagnostic tools are used for surra surveillance, including ELISA, the card agglutination test (CATT/T. evansi), latex agglutination, and molecular assays such as PCR (2). While serological tests such as CFT and FGT remain practical for large-scale surveys, they cannot distinguish between past and current infections and may be influenced by cross-reactions. The incorporation of molecular tools in future studies would allow confirmation of active infection and a more precise understanding of disease dynamics.

An additional challenge in interpreting serological data is the frequent use of trypanocidal drugs by camel owners. Indeed, the majority of camels in the surveyed farms had a history of treatment with locally produced urea-derivative drugs or with Deminkel (Belgium). Such practices may reduce parasitemia and clinical signs, but antibodies often remain detectable for extended periods. This complicates the distinction between current and past infections. Similar observations were reported by Boushaki D. et al. (23), who emphasized that prior chemotherapeutic intervention can bias prevalence estimates by lowering parasite detection while maintaining serological positivity.

The main limitations of our study include the relatively small sample size in some districts (e.g., Shardara, n = 28), the exclusive reliance on serological tests, and the lack of longitudinal data across different seasons. While molecular methods such as PCR and sequencing were beyond the scope and objectives of this survey, we acknowledge this as a limitation and emphasize that future studies should incorporate molecular confirmation to complement serological data and provide a more comprehensive picture of strain diversity and infection dynamics. Despite these limitations, our findings establish baseline data for surra in Kazakhstan and demonstrate clear patterns of age-, sex-, and region-related risk. These results emphasize the importance of tailored surveillance strategies and the need to integrate serological and molecular diagnostics, as well as vector monitoring, in order to design effective control measures for surra in camels.

In summary, this study provides important surveillance data on T. evansi in Kazakhstan’s camel population and evaluates the practical performance of two serological tests in the field. The notable differences between CFT and FGT outcomes highlight that a one-test strategy may underdetect surra. Field programs might achieve better sensitivity by using the FGT for initial screening, but they should be aware of its limitations and consider confirmatory testing. Our findings also indicate that certain groups (especially adult female camels) have higher infection rates, which could inform targeted interventions.

The surveillance conducted in three regions of Kazakhstan revealed a significant prevalence of T. evansi infection in camels, detected through serological testing. The CFT and FGT proved to be useful tools for large-scale seromonitoring of surra in camels, with the FGT demonstrating a higher overall sensitivity in this setting. These results underline the importance of using both tests in complement: the FGT for broad surveillance and the CFT (or another specific assay) for confirming active cases. Strengthening surra control in Kazakhstan will require continued monitoring of camel herds using reliable diagnostic methods, combined with the development of improved diagnostic assays for greater accuracy. Further, implementing vector control and other preventive measures will be essential to mitigate the impact of surra on camel health and the livelihoods of pastoral communities.