Preliminary investigation on the seroprevalence and co-exposure of Brucella spp. and Mycobacterium avium subsp. paratuberculosis in dromedary camels from the Eastern Province of Saudi Arabia

Abstract

Background

Brucellosis and paratuberculosis are zoonotic pathogens that affect animal and human health worldwide. Although both diseases are endemic in Saudi Arabia, little is known about their concurrent and potential epidemiological or immunological interactions in dromedary camels. This study investigated the serological evidence and associated risk factors of single and mixed infections with Brucella spp. and Mycobacterium avium subspecies paratuberculosis (MAP) in camels from the Eastern Province of Saudi Arabia. A total of 320 serum samples were collected from 253 female and 67 male camels and screened for Brucella antibodies using the Rose Bengal Test and competitive ELISA, and for MAP antibodies using indirect ELISA.

Results

The overall seroprevalence of brucellosis and paratuberculosis was 12.5% and 15.3%, respectively, with 2.2% of camels showing serological evidence of co-infection. Brucellosis was most prevalent in Hamra camels (15.4%), while Sawahli camels had the highest MAP seropositivity (20.0%). Although female (11.5%) camels showed numerically higher brucellosis seroprevalence than males (6.0%), this difference was not statistically significant. On the other hand, mixed infection was significantly more frequent in males (6.0%) than females (1.2%) (p = 0.04). Older camels (≥ 6 years) were at higher risk of brucellosis seropositivity (12.4%) than younger animals (< 6 years, 5.8%) (p = 0.03). Pregnant females had a significant (p = 0.02) increase in MAP prevalence (22.2%) compared to non-pregnant females (10.6%).

Conclusions

These findings highlight a notable overlap in the serological profiles of Brucella and MAP infections, suggesting shared risk factors or possible immune cross-modulation in camels. The coexistence of anti-Brucella antibodies in approximately 15% of MAP-seropositive camels underscores the need to reconsider diagnostic and control strategies under a One Health framework. Understanding such interactions could improve surveillance programs and inform targeted interventions for the camel industry in Saudi Arabia and other endemic regions.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12917-026-05635-0.

Introduction

Camels are essential livestock species in arid and semi-arid ecosystems, supporting food security, cultural heritage, and economic sustainability in many parts of the world [1]. The global camel population is estimated at more than 38.6 million, of which approximately 2.2 million are found in Saudi Arabia and distributed across nearly 80,000 camel holdings/farms, mainly concentrated in Riyadh, Makkah, and the Eastern Province (Ministry of Environment, Water and Agriculture, 2024). Due to their remarkable thermotolerance and physiological adaptability, camels can survive, reproduce, and produce milk and meat under extreme environmental conditions with limited feed and water availability [2].

Among infectious diseases affecting camels, brucellosis and paratuberculosis are two of the most significant causes of reproductive and productive losses, posing dual challenges to livestock health and public health in Saudi Arabia [3–11]. Both diseases remain endemic in the Kingdom, with regional variation in prevalence and limited integrated surveillance [12–14].

Brucellosis, caused by Brucella spp., primarily results in abortions, infertility, and reduced milk yield in infected animals [15, 16]. Camels are susceptible to several Brucella species circulating in other ruminants [17], with infection risk heightened by mixed grazing or contact with infected cattle, sheep, or goats [3, 18]. Since its first report in 1931, camel brucellosis has been detected in most camel-rearing countries [13, 17, 19–24]. The disease also represents an important zoonotic threat, particularly in the Middle East, where Brucella melitensis is endemic and human infection frequently occurs through consumption of unpasteurized camel milk [13, 23]. A seroprevalence between 5 and 10% was reported for camel Brucellosis in Saudi Arabia, depending on the diagnostic method and region. A recent study in the Al-Qassim region reported a seroprevalence of 9.72% in camels, identifying the biovar 3 of Brucella melitensis as the predominant etiological agent [4]. This seems in alignment with a broader meta-analysis study estimating a pooled national prevalence of approximately 4%, with uneven distribution across provinces [25].

Paratuberculosis (Johne’s disease), caused by Mycobacterium avium subspecies paratuberculosis (MAP), is a chronic granulomatous enteritis of ruminants, including camels [14, 26]. The disease causes severe weight loss, diarrhea, reduced fertility, and substantial economic losses in livestock production systems [26–28]. Transmission occurs primarily via the fecal–oral route through contaminated feed, water, or milk [28]. Recent studies from eastern Saudi Arabia reported apparent herd-level MAP seroprevalence rates exceeding 40%, with apparent individual camel-level prevalence reaching 16% based on ELISA testing [29]. A comprehensive 2025 study in camels from the Eastern Province found an overall MAP seroprevalence of 8.11% using ELISA [30].

While both Brucella and MAP infections have been studied independently in Saudi camels, their potential co-existence and epidemiological interactions remain poorly understood. Given that both pathogens are intracellular bacteria capable of modulating host immune responses, simultaneous exposure could influence disease expression, diagnostic accuracy, and transmission dynamics. Despite several national surveys, there is a critical knowledge gap regarding co-infection patterns among dromedary camels in the Eastern Province—one of the country’s most important camel-rearing areas.

Therefore, this study aimed to investigate the serological evidence of single and mixed infections with Brucella spp. and MAP in dromedary camels from Eastern Province of Saudi Arabia, and to identify associated host- and management-related risk factors. The findings provide new insight into the epidemiology of dual infections in camels and their implications for disease control under a One Health framework.

Materials and methods

Study area and population

A total of 320 dromedary camels were sampled from the Eastern Province of Saudi Arabia, which borders several Arabian Gulf countries including Qatar, Kuwait, and the United Arab Emirates. The study population comprised 213 camels (66.6%) from 11 smallholder herds, 69 camels (21.6%) presented to the Veterinary Clinic of King Faisal University, and 38 camels (11.9%) from the Al-Omran slaughterhouse. Slaughterhouse-derived camels represented a heterogeneous population that included culled animals, older animals at the end of productive life, and animals slaughtered for meat production according to local management practices. Detailed farm-of-origin records were not consistently available for all slaughterhouse animals. To be eligible for inclusion, animals were required to be of one of the main Saudi camel breeds (Magateer, Majaheem, Hamra, or Sawahli breeds), encompassing both males and females with no prior vaccination history against brucellosis or paratuberculosis. Except for the camels presented to the Veterinary Clinic of King Faisal University, which exhibited reproductive or general clinical complaints including metritis, mastitis, or repeat breeding at the time of examination, all sampled camels were clinically healthy without any signs of disease. These clinical conditions were recorded as presenting findings only and were not considered specific indicators of brucellosis or paratuberculosis. The present study was designed primarily as an exploratory animal-level serological investigation of Brucella spp. and Mycobacterium avium subsp. paratuberculosis (MAP) in dromedary camels from the Eastern Province of Saudi Arabia. Herd selection was based on accessibility and owner willingness to participate rather than stratified random sampling across all camel holdings in the region. Therefore, the study was not intended to provide province-wide herd-level prevalence estimates.

The demographic characteristics of the sampled camels including sex, breed distribution, and sampling source are summarized in supplementary Table 1 (Table S1). The majority were female (n = 253; 79.1%), while males accounted for 20.9% (n = 67). The animals represented four major local breeds: Magateer (n = 150; 46.9%), Majaheem (n = 134; 41.9%), Hamra (n = 26; 8.1%), and Sawahli (n = 10; 3.1%). Herd sizes ranged from 12 to 63 animals (mean ± SD = 31.6 ± 15.6). The required sample size was calculated according to [31] based on an estimated camel population of 100,000 in the Eastern Province, an expected prevalence of 10% [3, 4], a 95% confidence level, and a 5% absolute precision. The calculated minimum sample size was 139 camels; however, a total of 320 samples were collected to enhance statistical robustness and representativeness.

Table 1.

Brucellosis and paratuberculosis seropositivity in serum samples collected from 320 dromedary camels from the Eastern Province of Saudi Arabia according to sample source

Sample source	Animals tested	Animals positive n (%)
		Brucellosis	Paratuberculosis	Co-infectionb
Local herdsa	213	24 (11.3%)	36 (16.9%)	6 (2.8%)
Vet clinicc	69	9 (13.0%)	5 (7.2%)	1 (1.4%)
Slaughterhoused	38	0 (0%)	1 (2.6%)	0 (0%)
Total	320	33 (10.3%)	42 (13.1%)	7 (2.2%)

^a: Local camel herds distributed around Al-Hofuf city

^b: Antibodies to Brucella sp. and Mycobacterium avium subsp. Paratuberculosis

^c: Veterinary clinic of King Faisal University, Al-Ahsa, Saudi Arabia

^d: Alomran Slaughterhouse in Al-Ahsa, Saudi Arabia

Animal ethics and consent to participate

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of King Faisal University, Saudi Arabia (KFU-REC-2023-SEP-ETHICS1372). Informed consent was also obtained from the owners to use their animals in the study.

Sample collection and preparation

Blood samples (5 mL per animal) were collected via jugular venipuncture (vena jugularis externa) into plain serum tubes between October 2023 and September 2024. Samples were maintained in a cool box and transported to the laboratory within 4 h of collection. Sera were separated by centrifugation at 1000 × g for 15 min and stored at − 80 °C until serological testing.

Serological testing for brucellosis

Each serum sample was tested using the Rose Bengal Test (RBT) and a competitive enzyme-linked immunosorbent assay (cELISA) [21].

Rose Bengal Test (RBT): A commercial kit (BENGATEST®, SYNBIOTICS, France) was used following the manufacturer’s protocol. Briefly, 30 µL of Rose Bengal-stained, heat-inactivated Brucella abortus strain 99 antigen was mixed with 30 µL of serum on a glass slide, agitated for 4 min at room temperature, and examined visually for agglutination, which indicated a positive reaction.

Competitive ELISA (cELISA): A multi-species competitive ELISA kit (SVANOVIR® Brucella-Ab c-ELISA; Svanova Biotech AB, Uppsala, Sweden) was used according to manufacturer instructions. Camel sera were diluted 1:5 in the supplied buffer and incubated on antigen-coated microplates (smooth B. abortus LPS antigen) for 30 min at room temperature. Plates were washed four times and incubated with anti-mouse IgG conjugated with horseradish peroxidase (HRP) for 30 min. Following a second wash, substrate solution was added and the reaction stopped after 10 min with stop solution. Optical density (OD) was read at 450 nm using an ELISA reader (MR 5000, Dynatech, Germany). Samples showing inhibition ≥ 30% were interpreted as positive.

Detection of Mycobacterium avium subsp. paratuberculosis (MAP) antibodies

Antibodies to MAP were detected using an indirect ELISA kit (IDEXX MAP Ab Test, IDEXX Laboratories) following the manufacturer’s instructions with minor modifications. To eliminate nonspecific reactivity, 11 µL of serum was pre-incubated with 99 µL of dilution buffer containing Mycobacterium phlei antigens for 15 min at room temperature. Diluted sera (100 µL) were then transferred to MAP antigen-coated wells and incubated for 60 min at room temperature. After four washes, bound antibodies were detected with HRP-conjugated Protein A/G (Thermo Fisher Scientific, Germany) diluted 1:25,000 in wash buffer and incubated for 60 min. Following additional washes, wells were developed with TMB substrate for 20 min in the dark, and the reaction stopped with 50 µL of 0.5 M H₂SO₄. Absorbance was measured at 450 nm (MR 5000, Dynatech). The sample-to-positive (S/P %) ratio was calculated as:

Samples with S/P ≥ 55% were considered positive.

According to the manufacturer, the IDEXX MAP Ab Test has been developed and validated primarily for ruminant species, with reported diagnostic sensitivity and specificity values of 68% and 99%, respectively. Although formal validation data for camelids remain limited, some studies employed this ELISA test in the detection of anti-MAP antibodies in camels vaccinated or infected with MAP after replacing the kit conjugate with either Protein A or the goat anti-camel IgG conjugates [32].

Statistical analysis

Data were compiled in Microsoft Excel (Microsoft Corp., Redmond, WA, USA) and analyzed using GraphPad Prism v10 (GraphPad Software, San Diego, CA, USA). Seroprevalence and 95% confidence intervals (CIs) were computed using the Fraction-of-Total function. Associations between seropositivity and categorical variables (breed, sex, age group, and sampling source) were evaluated using Chi-square or Fisher’s exact tests.

Correlation coefficients (R²) were computed to assess relationships between seropositivity and continuous variables such as animal age or herd size. An area-proportional Euler diagram illustrating the overlap between infections was generated using the Euler Package [33].

Results

Performance of serological tests for detection of anti-Brucella spp. antibodies

Serological screening using the Rose Bengal test (RBT) and competitive ELISA (c-ELISA) revealed that 40 of 320 samples (12.5%) were positive in both assays. Seven samples (2.2%) were positive only by RBT and three (0.9%) only by c-ELISA. For the subsequent analyses, a camel was considered seropositive for brucellosis only if both tests yielded positive results.

Seroprevalence of Brucella spp. and Mycobacterium avium subsp. paratuberculosis (MAP) antibodies

Antibodies to Brucella spp. were detected in 40 samples (12.5%), whereas 49 samples (15.3%) were seropositive for MAP (Fig. 1A). Co-existence of antibodies to both pathogens was observed in seven samples (2.2%) (Fig. 1B). At the herd level, 11 of 13 investigated camel holdings/flocks (84.6%) had at least one seropositive animal for either disease for either Brucella spp. or MAP. However, because herd selection was opportunistic rather than based on stratified random sampling, these findings should not be interpreted as representative estimates of province-wide herd-level prevalence. Flock sizes ranged from 12 to 63 animals (mean ± SD = 31.6 ± 15.6). No significant correlation was detected between flock size and seroprevalence of either brucellosis (r² = 0.02, p = 0.6) or paratuberculosis (r² = 0.06, p = 0.4).

Fig. 1.

A Pie chart displaying the seroprevalence of and co-exposure to Brucella spp. and MAP in camels from the Eastern Province of Saudi Arabia. B Euler diagram shows the number of camel samples seropositive for brucellosis, paratuberculosis, or both pathogens

Seroprevalence by sampling source

The highest brucellosis seroprevalence was detected among samples from the King Faisal University Veterinary Clinic (9/69; 13.0%), followed by local herds (24/213; 11.3%), while no positive cases were found among slaughterhouse samples (0/38). In contrast, antibodies to MAP were most frequent in local herds (36/213; 16.9%), compared with clinic samples (5/69; 7.2%) and slaughterhouse samples (1/38; 2.6%). Co-existence of antibodies to both pathogens was observed in 6 of 213 local-herd camels (2.8%) and 1 of 69 clinic camels (1.4%) (Table 1).

Seroprevalence by camel breed

Brucellosis seroprevalence was highest in Hamra camels (15.4%), while comparable rates were found in Magateer (10.0%), Majaheem (9.7%), and Sawahli (10.0%) breeds. For MAP, Sawahli camels showed the highest seroprevalence (20.0%), followed by Majaheem (14.2%), Magateer (12.0%), and Hamra (11.5%). Dual seropositivity to Brucella and MAP was detected in one Hamra (3.8%), four Magateer (2.7%), and two Majaheem (1.5%) camels (Table 2).

Table 2.

Brucellosis and paratuberculosis seropositivity in 320 dromedary camels from the Eastern Province of Saudi Arabia according to animal breed

Breed	Animals tested	Animals positive n (%)
		Brucellosisa	Paratuberculosis	Co-infection
Magateer	150	15 (10.0%)	18 (12.0%)	4 (2.7%)
Mojaheem	134	13 (9.7%)	19 (14.2%)	2 (1.5%)
Hamra	26	4 (15.4%)	3 (11.5%)	1 (3.8%)
Sawahli	10	1 (10.0%)	2 (20.0%)	0 (0.0%)
Grand Total	320	33 (10.3%)	42 (13.1%)	7 (2.2%)

^a: Includes animals that were positive for both Rose Bengal test and competitive ELISA

Influence of animal sex, age, and pregnancy status on seropositivity

Antibodies to Brucella spp. were detected in 29 of 253 females (11.5%; 95% CI = 8.1–19.0) and 4 of 67 males (6.0%; 95% CI = 2.3–14.4). Paratuberculosis seroprevalence was similar between sexes with 13.0% in females (95% CI = 4.9–17.8) and 13.4% in males (95% CI = 7.2–23.6). However, the co-existence of antibodies to both pathogens was significantly higher in males (6.0%; 95% CI = 2.3–14.4) than in females (1.2%; 95% CI = 0.3–3.4; p = 0.03) (Table 3). Age-related analysis showed that camels aged ≥ 6 years (Group II) had significantly higher brucellosis seroprevalence (12.4%; 95% CI = 8.7–17.5) than younger animals (< 6 years; 5.8%; 95% CI = 2.7–12.1; p = 0.03). MAP seropositivity was also higher in older camels (14.7%; 95% CI = 10.6–20.1) than in younger ones (9.7%; 95% CI = 5.4–17.0; p = 0.11). Co-exposure to both pathogens occurred in 2.8% (95% CI = 1.3–5.9) of older camels compared with 1.0% (95% CI = 0.0–5.3) of younger ones.

Table 3.

Brucellosis and paratuberculosis seropositivity in serum samples from 320 dromedary camels according to animal sex, age, and pregnancy status

	Brucellosis		Paratuberculosis			Co-infection
Animal sex	Female	Male	Female		Male	Female		Male
Animals tested	253	67	253		67	253		67
Animals positive n (%)	29 (11.5%)	4 (6.0%)	33 (13.0%)		9 (13.4%)	3 (1.2%)		4 (6.0%)
CI (95%)	8.1—16.0	2.3—14.4	9.4—17.8		7.2—23.6	0.3—3.4		2.3—14.4
Fisher's Exact Test (P value)	0.23		0.29			0.04
Animal age (relative to median)a	Group I	Group II	Group I		Group II	Group I		Group II
Animals tested	103	217	103		217	103		217
Animals positive n (%)	6 (5.8%)	27 (12.4%)	10 (9.7%)		32 (14.7%)	1 (1.0%)		6 (2.8%)
CI (95%)	2.7—12.1	8.7—17.5	5.4—17.0		10.6—20.1	0.0—5.3		1.3—5.9
Fisher's Exact Test (P value)	4.5 (0.03)		2.5 (0.11)			1 (0.31)
Pregnancyb	Preg	Non-preg	Preg		Non-preg	Preg		Non-preg
tested	54	199	54		199	54		199
pos (%)	3 (5.6%)	26 (13.1%)	12 (22.2%)		21 (10.6%)	0 (0.0%)		3 (1.5%)
CI (95%)	15.1—1.5	18.5—9.1	34.9—13.2		15.6—7.0	6.6—0.0		4.3—0.4
Fisher's Exact Test (P value)	2.3 (0.12)		5.1 (0.02)			0.8 (0.36)

P values in boldface indicate significant differences

^a: Age group I includes animals < 6 years, while age group II includes animals ≥ 6 years

^b: preg: pregnant, non-preg.: nonpregnant

As shown in Table 3, the data reveals a trend of lower brucellosis seropositivity in pregnant (5.6%) compared to non-pregnant female camels (13.1%). However, statistical analysis indicates no significant impact (P = 0.12). In contrast to brucellosis, pregnancy was identified as a significant risk factor for paratuberculosis with pregnant females demonstrated a significantly higher prevalence (22.2%) than non-pregnant females (10.6%), (P = 0.02).

Discussion

Brucellosis and paratuberculosis remain major bacterial infections of livestock in Saudi Arabia, exhibiting variable regional prevalence and posing persistent challenges to animal productivity and public health [3–10]. Polymicrobial infections are particularly concerning in areas where multiple pathogens coexist under minimal control measures, as they may exacerbate clinical outcomes and complicate diagnosis [34]. The present study investigated the serological prevalence and co-exposure of dromedary camels to Brucella spp. and Mycobacterium avium subsp. paratuberculosis (MAP) in the Eastern Province, one of the major camel-rearing areas in Saudi Arabia.

Brucellosis remains one of the most significant zoonoses globally, including in Saudi Arabia, where Brucella melitensis is endemic and transmission to humans frequently occurs through consumption of unpasteurized camel milk [12, 13, 35]. Although brucellosis in camels has received less attention than in small ruminants, this study confirms its continued presence in the Eastern Province of Saudi Arabia, with an overall seroprevalence of 12.5% using both the Rose Bengal Test (RBT) and competitive ELISA (cELISA). The slightly higher RBT positivity (14.7%) compared to cELISA (13.4%) likely reflects the lower specificity of RBT due to potential cross-reactivity with antibodies to smooth lipopolysaccharide (S-LPS) antigens of other Gram-negative bacteria [17, 22]. Consistent with previous reports, cELISA provides a more specific and confirmatory method for camel brucellosis screening [22].

The observed animal-level seroprevalence aligns with previous Saudi studies reporting individual camel-level brucellosis seroprevalence rates between 5 and 10% in central and northern regions [3, 4, 18], but remains lower than the individual animal-level prevalence of approximately 20% reported in neighboring Qatar [21]. These findings confirm that camel brucellosis remains an important endemic infection in eastern Saudi Arabia, with implications for both livestock management and zoonotic risk. The relatively highest seroprevalence of brucellosis among camels presented to the Veterinary Clinic may suggest a possible association between Brucella exposure and reproductive disorders in camels. However, because reproductive disorders are multifactorial conditions, causality cannot be inferred from the present serological findings alone. No direct bacteriological or molecular confirmation of Brucella infection was performed using vaginal or preputial swabs, and complete reproductive histories, including recent or previous abortion records, were not consistently available for all clinic-admitted animals.

Brucellosis prevalence increased significantly with age, consistent with previous studies indicating that older camels experience cumulative exposure to infection sources through prolonged contact with contaminated materials or infected animals [19–21]. Although female camels showed numerically higher brucellosis seroprevalence than males, this difference was not statistically significant. Therefore, sex should not be interpreted as an independent risk factor for brucellosis seropositivity in the present dataset. The observed numerical difference may partly reflect the uneven sex distribution in the sampled population, with females representing the majority of sampled animals. Similar patterns have been reported in several studies across the Arabian Peninsula [21]. However, a few exceptions exist—for instance, higher male prevalence was observed in Egyptian camels [17]—underscoring the influence of management and demographic variations. Although not statistically significant in the present study, the lower prevalence in pregnant females seems in agreement with the known pathogenesis of brucellosis as an abortion-causing disease in camels. As infected camels are more likely to lose their fetus, a randomly sampled "pregnant" cohort may naturally exclude active brucellosis cases.

Breed-specific differences were also noted, with the Hamra breed showing the highest seroprevalence (15.4%). This observation agrees with previous reports suggesting possible genetic or husbandry-related susceptibility of Hamra camels [4], though breed-related risk remains underexplored and warrants further genomic and immunological investigation.

Serological evidence of MAP infection was detected in 15.3% of sampled camels at the individual animal level. This is broadly consistent with previous ELISA-based apparent individual camel-level MAP seroprevalence estimates of approximately 16.1% in the Eastern Province [29] and apparent animal-level seroprevalence estimates of 10–13% reported in small ruminants in the same region [8]. Where previous studies reported herd-level estimates, these have now been explicitly described as herd- or farm-level prevalence to avoid ambiguity. The results reaffirm the endemicity of paratuberculosis across multiple livestock species in the region. Variations among studies may arise from differences in diagnostic methods, sampling strategies, herd management, and farm-level environmental conditions influencing MAP persistence. Although MAP can persist for prolonged periods in contaminated environments, its survival may be affected by direct sunlight exposure, shelter structure, humidity, flooring, and accumulation of organic material. These environmental variables were not systematically assessed in the present study and should be incorporated into future farm-level investigations. Only a limited number of camel holdings were included in the present study relative to the large number of camel farms operating in the Eastern Province and Saudi Arabia overall. Therefore, caution is required when extrapolating these findings to the wider regional camel population.

The comparable seroprevalence between male and female camels observed in this study supports earlier findings suggesting that sex does not significantly influence MAP exposure [14, 36]. Although the higher prevalence in older camels was not statistically significant, it is biologically plausible given the chronic nature of MAP infection and cumulative environmental exposure over time. Such age-associated trends have been reported in other ruminant species (Khol et al., 2012; Tigani-Asil et al., 2023). The higher prevalence rates in pregnant compared to nonpregnant animals suggests a role for the pregnancy-associated physiological stress or immunological modulation in higher susceptibility to MAP in camels. Alternatively, since paratuberculosis is a chronic disease with a long incubation period, this association might be confounded by age, as older females are more likely to be recruited for breeding. In contrast to brucellosis, antibodies against MAP were most prevalent in local small flocks, rather than in the clinical cohort, reflecting the subclinical nature of Johne’s disease.

Approximately 15% of MAP-seropositive camels were also positive for Brucella antibodies, demonstrating potential co-exposure and overlapping epidemiological niches. Notably, co-exposure was significantly higher in male camels than females, which may reflect differences in sample composition, behavior, or management practices rather than true biological susceptibility.

Reports of concurrent Brucella and MAP infections in other species, such as goats [37] and buffaloes [38], suggest that shared risk factors or immune interactions may facilitate co-infection. Both pathogens are facultative intracellular bacteria that stimulate Th1-type immune responses, potentially leading to immune modulation or diagnostic cross-interference. The observed coexistence may therefore reflect either true dual infection or overlapping serological responses, emphasizing the need for molecular and culture-based confirmation in future studies.

The present study has several epidemiological limitations that should be considered when interpreting the statistical associations. First, herd selection was opportunistic rather than based on stratified random sampling across camel farms in the Eastern Province. Consequently, the findings primarily reflect animal-level serological evidence and should not be interpreted as representative estimates of province-wide herd-level prevalence. Second, complete farm-level traceability and management information were not consistently available for clinic-admitted and slaughterhouse-derived animals. Third, the study relied on serological evidence without molecular or bacteriological confirmation of infection. Therefore, the observed statistical associations should be interpreted as exploratory rather than causal. Despite these limitations, the study provides useful preliminary insight into the circulation and co-exposure patterns of Brucella spp. and MAP among dromedary camels in eastern Saudi Arabia.

Conclusion

In summary, this study provides animal-level serological evidence for the co-circulation of Brucella spp. and Mycobacterium avium subsp. paratuberculosis among dromedary camels sampled from the Eastern Province of Saudi Arabia. The findings indicate distinct but partially overlapping serological profiles, with age associated with brucellosis seropositivity and limited evidence of dual seropositivity in a small proportion of animals. However, because the study was cross-sectional and based on serological testing, it cannot establish active infection, transmission pathways, or causal interactions between the two pathogens.

Future research should incorporate structured herd-level sampling, molecular confirmation, culture isolation, longitudinal follow-up, and immunological profiling to determine whether exposure or infection with one intracellular pathogen influences susceptibility, immune responses, diagnostic performance, or disease outcome associated with the other. Integrating camel health surveillance within a One Health framework linking animal, human, and environmental monitoring would support improved detection and control of zoonotic and production-limiting infections in camel-rearing regions.

Supplementary Information

Supplementary Material 1. ^{(18.9KB, docx)}

Authors’ contributions

Jamal Hussen, Hind Althagafi, and Baraa Falemban designed the study, collected and analyzed the samples. Jamal Hussen, Mayyadah Alkuwayti, Najla K Al Abdulsalam, Bashir Salim, and Salma Al Adwani prepared the first draft. All authors read and approved the final manuscript.

Funding

This work was supported by the Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi Arabia (Project number KFU263075). This study was also supported through Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2026R460), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Data availability

The datasets generated during the current study are available from the corresponding author on reasonable request.

Declarations

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.