Skip to main content
NCBI home page
Springer logoLink to Springer
. 2025 Mar 5;49(3):129. doi: 10.1007/s11259-025-10695-y

High prevalence of Chorioptes bovis: an important factor in chronic progressive lymphedema in Belgian draft horses

M Brys 1,✉, E Claerebout 2, V Saey 1, K Chiers 1
PMCID: PMC11882615  PMID: 40042772

Abstract

A cross-sectional study was conducted to estimate the prevalence of chorioptic mange affecting the distal legs of horses in Belgium, focusing on the association between mange and chronic progressive lymphedema (CPL) in Belgian draft horses. Clinical examinations and skin scrapings were performed on the distal legs of 156 Belgian draft horses and 142 Belgian warmblood horses. In the Belgian draft horse breed, 144 (92.31%) horses were infested with Chorioptes bovis mites, and 126 (80.77%) displayed clinical signs of CPL. CPL prevalence in draft horses aged < 1 year was 17.86%, while mites were detected in 85.71% of this age group, with infestations observed as early as 6 days of age. In a subset of horses aged ≥ 1 year, CPL and mange prevalence amounted to 94.53% and 93.75%, respectively. In contrast, no mites or CPL were detected in the Belgian warmblood horses examined. Statistical analysis revealed a strong association between C. bovis and CPL (prevalence odds ratio: 7.37; p = 0.002). The prevalence of CPL was approximately twice as high in horses with mites compared to non-infested horses (prevalence ratio: 2.02). Furthermore, the prevalence risk difference of 42.36%, indicates a substantial absolute increase in CPL prevalence among infested horses. This study demonstrates the high prevalence of C. bovis and its breed-specific predilection in Belgian draft horses. The strong association between mange and CPL highlights the potential role of C. bovis as a contributing factor in CPL pathogenesis.

Keywords: Chorioptes bovis, Prevalence, Association, Belgian draft horse, Chronic progressive lymphedema

Introduction

In draft horse breeds with extensive feathering on the distal limbs (e.g., Shire, Clydesdale, Gypsy horse, and Belgian draft horse), a high prevalence of mite infestations has been reported (Cremers 1985; Geburek 2002; De Cock et al. 2003; Rüfenacht et al. 2011). The only mite species identified on the lower limbs of these breeds is Chorioptes bovis, which causes clinical signs including pruritus, hyperkeratosis, and scaling of the skin on the distal limbs. Additionally, C. bovis infestations have been linked to the occurrence of chronic progressive lymphedema (CPL) in draft horses (De Cock et al. 2003; Wallraf 2003; Geburek et al. 2005a, Brys et al. 2023b). CPL is a debilitating disorder with a high prevalence in specific breeds, such as the Belgian draft horse, characterized by the progressive development of skin folds and nodules in the distal limbs, often leading to reduced mobility and secondary infections.

Although the etiology and pathogenesis of CPL remain unclear, several studies have suggested C. bovis as a complicating or even a potential causal factor in CPL development (Ferraro 2001; Geburek et al. 2005a, Brys et al. 2023b). Notably, Brys et al. (2023b) demonstrated that targeted treatment of C. bovis infestations using moxidectin pour-on resulted in a significant reduction in CPL lesions, further supporting the hypothesis of a causal relationship between mite infestations and CPL pathogenesis. However, the prevalence of C. bovis in Belgian draft horses remains unknown, and no association between mite infestations and CPL has been established to date. Moreover, it is unclear whether warmblood horses exhibit lower susceptibility to C. bovis or, alternatively, may act as asymptomatic carriers, potentially serving as reservoirs for reinfection in draft horse breeds. Therefore, this study aimed to determine the prevalence of C. bovis mites and to investigate the association between mange and CPL.

Materials and methods

Animals and study design

During the summer of 2024, a cross-sectional study was conducted in randomly selected Belgian draft horses and Belgian warmblood horses. For each horse, a full signalment was recorded, including age, sex, and the presence of CPL-associated skin lesions on the lower limbs. Superficial skin scrapings from the distal limbs of each horse were collected to investigate the presence of mites. Sampling for mange and CPL scoring was performed by a single person. The total number of animals required for the study was calculated based on the formula given by Thrusfield (2005).

graphic file with name d33e266.gif

Where, N = required sample size, Pexp. = expected prevalence, d = desired absolute precision.

The expected prevalence of mange in Belgian draft horses and Belgian warmblood horses was estimated at 90% and 10%, respectively. These estimates were based on preliminary findings from our own research in Belgian draft and warmblood horses (data not shown) and smaller sample sizes of draft horse breeds reported in earlier studies (Cremers 1985; Geburek 2002; De Cock et al. 2003; Rüfenacht et al. 2011). The required sample size for each breed was calculated using a 95% confidence interval and a desired margin of error of 0.05, resulting in a minimum sample size of N = 139 for both breeds.

Sample collection and parasitological investigation

Superficial skin scrapings were collected by use of a sharp scalpel blade from three distinct sites on each leg (palmar/plantar in the pastern region, palmar/plantar of the fetlock, and palmar/plantar on the cannon bone) each covering an area of 3 × 3 cm. The individual samples were pooled per leg and examined immediately after collection for the presence of live mites using a stereomicroscope (Olympus, SZX7) with overhead lighting (25× magnification). Identification of mange mite species was done based on the morphological characteristics described by Wall and Shearer (2001).

CPL scoring

CPL-associated skin lesions on the lower legs of each horse were evaluated through palpation and visual inspection of all four limbs. The scoring system used to assess lesions was adapted from Brys et al. (2023a). The presence of skinfolds and nodules was scored on a scale from 0 to 4 (0 = No skinfolds/nodules, 1 = Skinfolds/nodules present in the pastern region, 2 = Skinfolds/nodules present up to the fetlock region, 3 = Skinfolds/nodules present up to the cannon bone, 4 = Skinfolds/nodules present on the palmar/plantar side up to the cannon bone, as well as on the dorsal aspect of the leg). By summing the individual scores for each leg, a total score ranging from 0 to 16 was obtained for each horse.

Data analysis and prevalence calculation

The collected data were entered in a Microsoft Excel spread sheet and coded appropriately. Statistical analyses were conducted using GraphPad Prism software (version 8.4.3). The association between mange mite infestation and the presence of CPL was analyzed by a Chi-square (χ2) test. The prevalence odds ratio (POR) was used to measure the relative strength of the association between the presence of mites and CPL. Statistical significance was assessed using a threshold P-value of < 0.05. The prevalence ratio (PR) was determined to estimate the proportional increase in the probability of the condition at a given point in time, while the prevalence risk difference (PRD) quantified the absolute difference in CPL prevalence between mite-infested and non-infested horses. These metrics were derived from a 2 × 2 contingency table based on the presence or absence of mites and CPL in the study population.

The prevalence of mites and CPL was recorded following the modified formula described by Thrusfield (1986).

graphic file with name d33e315.gif

Results

Animals

A total of 156 Belgian draft horses were included in this study, comprising 47 horses presented to the Faculty of Veterinary Medicine at Ghent University, Belgium, for reasons unrelated to this study, and 109 privately owned horses residing in their home stables. A maximum of four horses per owner was included in the sampling, representing a total of 100 owners. The sampled population comprised 88 males and 68 females. The median age was 6 years, with ages ranging from 2 days old to 23 years of age. Additionally, 142 Belgian warmblood horses were sampled, belonging to 92 different owners, with a maximum of four horses per owner. This group included 83 males and 59 females, with a median age of 9.5 years, ranging from 3 days to 24 years. Age groups, CPL prevalence, mean CPL scores and ranges and the number of horses testing positive for C. bovis are summarized in Table 1.

Table 1.

CPL prevalence, median CPL scores and ranges, and mite prevalence in Belgian draft and warmblood horses by age group

Age Group Total number
of horses		 Horses with CPL (%) Median CPL score (range) Horses with mites (%)
Belgian draft horse < 1 year 28 5 (17.86%) 0/16 (0/16–4/16) 24 (85.71%)
≥ 1 year 128 121 (94.53%) 8/16 (0/16–16/16) 120 (93.75%)
Total 156 126 (80.77%) 6/16 (0/16–16/16) 144 (92.31%)
Belgian warmblood horse < 1 year 8 0 (0%) 0/16 (0/16–0/16) 0 (0%)
≥ 1 year 136 0 (0%) 0/16 (0/16–0/16) 0 (0%)
Total 144 0 (0%) 0/16 (0/16–0/16) 0 (0%)
Open in a new tab

Prevalence of mites

Of the 156 Belgian draft horses, 144 (92.31%) tested positive for mites. The only encountered mite species was Chorioptes bovis (100%). Among the 28 horses aged < 1 year, mites were detected in 24 individuals (85.71%), with infestations observed as early as 6 days old. In the subset of 128 horses aged ≥ 1 year, 120 (93.75%) horses tested positive for the presence of mites. No mites were detected in any of the 142 Belgian warmblood horses included in the study.

Prevalence and scoring of CPL

CPL lesions were observed in 126 of the 156 Belgian draft horses (80.77%), with a median CPL score of 6/16 (range: 0/16 to 16/16). Among horses aged < 1 year, CPL-associated lesions were present in 5 of 28 individuals (17.86%), with a median CPL score of 0/16 (range: 0/16 to 4/16). The prevalence of CPL lesions increased markedly in horses aged ≥ 1 year, affecting 121 of 128 horses (94.53%). In this group, the median CPL score was 8/16 (range: 0/16 to 16/16). No CPL-associated lesions were detected in any of the 142 Belgian warmblood horses included in the study.

Association between mites and CPL

In the total population of Belgian draft horses (n = 156), 30 horses displayed no signs of CPL, and 12 horses were found to have no mites. Among the 30 horses without CPL, 23 (76.67%) were still found to harbor mites, however, 19 of these 23 (82.60%) being less than 1 year old.

A Chi-square test revealed a statistically significant association (p = 0.002) between the presence of C. bovis and CPL in Belgian draft horses. The POR was calculated as 7.37, indicating a strong association between mite infestations and CPL. The PR was 2.02, demonstrating that the prevalence of CPL was approximately twice as high in horses infested with C. bovis compared to non-infested horses. Furthermore, the PRD between infested and non-infested horses was 42.36%, highlighting a substantial absolute increase in CPL prevalence associated with mite infestations.

Discussion

A very high prevalence of Chorioptes bovis infestations was observed in Belgian draft horses, in contrast to the complete absence of mites in the examined population of Belgian warmblood horses. This disparity may be attributed to morphological variations in the distal limbs, particularly the dense feathering characteristic of draft horses. Feathering could provide an ideal microenvironment for mites by retaining warmth, moisture, and skin debris, all of which promote mite proliferation. However, C. bovis is also commonly found in other animals, such as certain cattle breeds (Rehbein and Visser 2024), which lack the heavy feathering seen in draft horses. This observation suggests that additional environmental or physiological factors, such as skin composition, may predispose Belgian draft horses to mange infestations. Indeed, Sweatman (1957) has demonstrated that certain Chorioptes mite populations may exhibit adaptations specific to draft horse breeds, including the ability to complete their life cycle solely on draft horse skin scales, potentially highlighting breed-specific differences in skin physiology.

The early detection of mite infestations, with some foals affected within days of birth, suggests direct transmission from the mare to the foal immediately postpartum. Indirect transmission from contaminated environments is also plausible, particularly in stabling systems that promote close contact and shared bedding. This early infection seems to correspond in time with the initial development of CPL, where subclinical processes may begin at a young age, even though chronic lesions only become macroscopically apparent later in life.

This study also confirmed a high prevalence of CPL in Belgian draft horses. Previous research by De Keyser et al. (2014) reported a CPL prevalence of 60.66% in the Belgian draft horse population, increasing to 85.86% in horses aged 3 years and older. The prevalence observed in our study suggests that no improvement in CPL prevalence has occurred over the years, despite increased awareness, selection based on phenotype, and management efforts. The discrepancy between the demonstrated CPL prevalence in foals (< 1 year, 17.86%) and older horses (≥ 1 year, 94.53%) in this study suggests that lesions of CPL take time to manifest, aligning with previous studies that reported delayed onset of clinical signs (De Keyser et al. 2014). However, our findings suggest that onset-stage CPL may be detectable earlier than the previously assumed threshold of three years (De Keyser et al. 2014), emphasizing the importance of early detection and intervention to mitigate disease progression.

Statistical analyses demonstrated a significant and strong association between C. bovis infestations and CPL in Belgian draft horses. The difference between the POR and PR in this study can be attributed to the high prevalence of CPL in the study population. While the POR of 7.37 reflects the strength of the association between C. bovis infestations and CPL, it tends to overestimate the relative prevalence, particularly when the outcome is common in the population. In contrast, the PR of 2.02 provides a more intuitive measure of the proportional increase in prevalence, indicating that mite-infested horses are approximately twice as likely to exhibit CPL compared to non-infested horses. The PRD of 42.36% quantifies the absolute increase in CPL prevalence associated with C. bovis infestations.

Mite infestations have long been identified as complicating factors in horses suffering from CPL (Cremers 1985; Geburek 2002; Geburek et al. 2005a; De Cock et al. 2003; Wallraf 2003; Rüfenacht et al. 2011; Brys et al. 2023b). While the exact etiology and pathogenesis of CPL remain unclear, it is hypothesized that a chronic inflammatory response in the distal limbs may trigger the characteristic proliferative skin lesions observed in CPL (Wallraf 2003; De Cock et al. 2003, 2006, 2009; Geburek et al. 2005b; Mömke and Distl 2007; Mittmann 2009; Mittmann et al. 2010; François 2018, Brys et al. 2023b). Chronic C. bovis infestation could present a plausible initiating factor for this inflammatory response. Indeed, mite infestations were detected before the manifestation of clinical CPL, including in very young foals. This temporal relationship supports the hypothesis that C. bovis infestations may precede and potentially contribute to CPL development, rather than CPL predisposing horses to mite infestations. However, early subclinical changes at the cellular or inflammatory level in CPL-affected horses cannot be ruled out as contributing factors to susceptibility.

Although this cross-sectional study demonstrates a strong association between C. bovis infestations and CPL in Belgian draft horses, causality cannot be inferred due to the study design. However, previous findings by Brys et al. (2023b) provide further evidence, showing that treatment with moxidectin pour-on significantly reduced mite infestations, which was associated with a decreased severity of CPL lesions. These results suggest that C. bovis infestations may play a causal role in CPL pathogenesis, as reducing mite burden appeared to alleviate clinical signs. Longitudinal studies are necessary to confirm a potential causal relationship between mites and CPL, determine whether chronic infestations directly contribute to CPL development or merely exacerbate pre-existing conditions, and elucidate underlying mechanisms.

Conclusion

This study demonstrates a high prevalence of mange caused by C. bovis mites in Belgian draft horses, contrasted with the complete absence of the parasite in Belgian warmblood horses. Belgian draft horses infested with C. bovis are significantly more likely to exhibit CPL, with prevalence nearly twice as high as in non-infested horses. This is further reflected in a substantial absolute increase in CPL prevalence among mite-infested horses. These findings highlight the importance of effective mite management strategies to reduce the burden of CPL in Belgian draft horses and improve animal welfare.

Acknowledgements

The authors would like to express their sincere gratitude to Leen Claeys, Geert and Yana Brys for their invaluable assistance in the collection of samples during the course of this study. In addition, we would like to thank all the horse owners to voluntarily participate in this study.

Author contributions

Marieke Brys: Writing – original draft, Visualization, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Edwin Claerebout: Writing – review & editing, Supervision, Methodology, Conceptualization. Veronique Saey: Writing – review & editing, Supervision, Methodology, Conceptualization. Koen Chiers: Writing – review & editing, Supervision, Methodology, Conceptualization.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data availability

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

Declarations

Ethics approval

This is an observational study. The Ethical Committee of the Faculties of Veterinary Medicine and Bioscience Engineering of Ghent University, Belgium has confirmed that no ethical approval is required.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. Brys M, Claerebout E, Chiers K (2023a) Chronic progressive lymphedema in Belgian draft horses: understanding and managing a challenging disease. Vet Sci 10(5):347. 10.3390/vetsci10050347 [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Brys M, Claerebout E, Chiers K (2023b) Alleviating lesions of chronic progressive lymphedema in Belgian draft horses by successfully treating Chorioptes bovis infestation with moxidectin 0.5% pour-on. Vet Parasitol 324. 10.1016/j.vetpar.2023.110074 [DOI] [PubMed] [Google Scholar]
  3. Cremers HJ (1985) The incidence of Chorioptes bovis (Acarina: Psoroptidae) on the feet of horses, sheep, and goats in the Netherlands. Vet Q 7:283–289 [DOI] [PubMed] [Google Scholar]
  4. De Cock HE, Affolter VK, Wisner ER, Ferraro GL, MacLachlan NJ (2003) Progressive swelling, hyperkeratosis, and fibrosis of distal limbs in Clydesdales, Shires, and Belgian Draft horses, suggestive of primary lymphedema. Lymphat Res Biol 1(3):191–199. 10.1089/153968503768330238 [DOI] [PubMed] [Google Scholar]
  5. De Cock HE, Affolter VK, Farver TB, Van Brantegem L, Scheuch B, Ferraro GL (2006) Measurement of skin desmosine as an indicator of altered cutaneous elastin in draft horses with chronic progressive lymphedema. Lymphat Res Biol 4:67–72. 10.1089/lrb.2006.4.67 [DOI] [PubMed] [Google Scholar]
  6. De Cock HE, Van Brantegem L, Affolter VK, Oosterlinck M, Ferraro GL, Ducatelle R (2009) Quantitative and qualitative evaluation of dermal elastin of draft horses with chronic progressive lymphedema. J Comp Pathol 140:132–139. 10.1016/j.jcpa.2008.10.009 [DOI] [PubMed] [Google Scholar]
  7. De Keyser K, Janssens S, Peeters L, Gasthuys F, Oosterlinck M, Buys N (2014) Chronic progressive lymphedema in the Belgian draft horse in Belgium: Clinical phenotyping, prevalence and risk factor analysis. Vlaams Diergeneeskd Tijdschr 83:119–124. 10.21825/vdt.v83i3.16651
  8. Ferraro GL (2001) Pastern dermatitis in Shires and Clydesdales. J Equine Vet Sci 21:524–526. 10.1016/S0737-0806(01)70153-0 [Google Scholar]
  9. François L (2018) Conservation genomics of living heritage breeds. (Inaugural Dissertation). Catholic University of Leuven, Leuven [Google Scholar]
  10. Geburek F (2002) Zur entstehung des Warzenmauke-syndroms der kaltblutpferde, klinische und histomorphologische untersuchungen. (Inaugural dissertation). Tierärztliche Hochschule, Hannover [Google Scholar]
  11. Geburek F, Deegen E, Hewicker-Trautwein M (2005a) Verrucous pastern dermatitis syndrome in heavy draught horses. Part II: clinical findings. Dtsch Tierärztl Wochenschr 112:243–251 [PubMed] [Google Scholar]
  12. Geburek F, Ohnesorge B, Deegen E, Doeleke R, Hewicker-Trautwein M (2005b) Alterations of epidermal proliferation and cytokeratin expression in skin biopsies from heavy draft horses with chronic pastern dermatitis. Vet Dermatol 16:373–384. 10.1111/j.1365-3164.2005.00482.x [DOI] [PubMed] [Google Scholar]
  13. Mittmann EH (2009) Application of horse genomics to identify quantitative trait loci (QTL) for chronic pastern dermatitis in German draft horses. (Inaugural Dissertation). Hannover, Tierarztliche Hochschule [Google Scholar]
  14. Mittmann EH, Mömke S, Distl O (2010) Whole-genome scan identifies quantitative trait loci for chronic pastern dermatitis in German draft horses. Mamm Genome 21:95–103. 10.1007/s00335-009-9244-z [DOI] [PubMed] [Google Scholar]
  15. Mömke S, Distl O (2007) Molecular genetic analysis of the ATP2A2 gene as candidate for chronic pastern dermatitis in German draft horses. J Hered 98:267–271. 10.1093/jhered/esm004 [DOI] [PubMed] [Google Scholar]
  16. Rehbein S, Visser M (2024) Is chorioptes texanus to displace chorioptes bovis? Notes on the mites causing bovine chorioptic mange in Central Europe. Diversity 16(4):199. 10.3390/d16040199 [Google Scholar]
  17. Rüfenacht S, Roosje PJ, Sager H, Doherr MG, Straub R, Goldinger-Muller P, Gerber V (2011) Combined moxidectin and environmental therapy do not eliminate Chorioptes bovis infestation in heavily feathered horses. Vet Dermatol 22:17–23. 10.1111/j.1365-3164.2010.00892.x [DOI] [PubMed] [Google Scholar]
  18. Sweatman GK (1957) Life history, non-specificity, and revision of the genus Chorioptes, a parasitic mite of herbivores. Can J Zool 35:641–689. 10.1139/z57-058 [Google Scholar]
  19. Thrusfield MV (1986) Veterinary disease information systems. In: 4. International symposium on veterinary epidemiology and economics, Singapore
  20. Thrusfield MV (2005) The control and eradication of diseases. Veterinary epidemiology, 3rd edn. Blackwell Science, Ltd., Oxford, pp 384–402 [Google Scholar]
  21. Wall R, Shearer D (2001) Veterinary ectoparasites: biology, pathology, and control, 2nd edn. Blackwell Science Ltd., Oxford [Google Scholar]
  22. Wallraf A (2003) Populationsgenetische untersuchung zum auftreten von Mauke bei den deutschen kaltblutpferderassen. (Inaugural dissertation). Tierärztliche Hochschule, Hannover [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

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

Articles from Veterinary Research Communications are provided here courtesy of Springer

RESOURCES