Exploring the devastating impact of Trypanosoma evansi on camel populations and the scientific fight against surra disease
In the vast, sun-scorched landscapes of Sudan, where camels represent not just wealth but cultural identity and survival, an invisible enemy lurks in the bloodstream of these cherished "ships of the desert." Trypanosoma evansi, a microscopic parasitic protozoan, causes the devastating disease known as surra - a word that strikes concern in the hearts of camel herders across Africa and Asia 3 . This relentless parasite undermines camel health, slashing productivity and market value, while posing a significant threat to food security and local economies in already vulnerable regions 1 .
The economic impact of surra extends far beyond individual animal losses. Infected camels suffer from reduced milk yield, weight loss, infertility, and abortions, creating ripple effects that undermine the livelihoods of pastoral communities 5 8 . In Algeria, surra has been reported to cause over $223 million in losses to the camel industry alone 8 . As we explore this parasitic predator, we'll uncover the risk factors that make certain camels more vulnerable, identify the blood-sucking accomplices that spread the disease, and examine the scientific toolkit researchers use to combat this pervasive threat to camel-rearing communities.
Trypanosoma evansi is a microscopic, single-celled parasite that belongs to the Trypanosomatidae family 3 . What makes this organism particularly remarkable - and dangerous - is its extraordinary ability to evade its host's immune system 7 . It accomplishes this through a sophisticated biological "costume change" mechanism, periodically switching its major Variant Surface Glycoprotein (VSG) 7 .
This constant shifting of its outer surface proteins means that just as the host's immune system recognizes and begins attacking one version of the parasite, a new variant emerges, effectively rendering the immune response useless against subsequent waves of infection 7 .
T. evansi holds the dubious distinction of being the first trypanosome discovered to cause disease in animals 3 . British veterinarian Griffith Evans first identified the parasite in 1880 at Dera Ismail Khan (in what is now Pakistan) while investigating a devastating disease affecting British Army horses 3 .
The name "surra" - meaning "rotten" in Hindi - perfectly captures the progressive deterioration that characterizes the disease in infected animals 3 . From its origins in South Asia, T. evansi has spread across tropical and subtropical regions worldwide, with recent reports indicating its expansion into previously unaffected areas, including the Canary Islands and mainland Europe 3 7 .
Griffith Evans discovers T. evansi in British Army horses in Dera Ismail Khan (now Pakistan) 3
Initial scientific controversy over the connection between the parasite and disease 3
Spread of T. evansi across tropical and subtropical regions worldwide 3
Expansion into new territories including the Canary Islands and mainland Europe 7
To understand how surra silently spreads through camel populations, researchers conducted a cross-sectional study in three Egyptian governorates - a methodological approach that provides a "snapshot" of disease prevalence at a specific point in time 1 . This investigation involved collecting 370 blood samples from camels across different regions, with each animal serving as a living repository of data about parasitic infiltration 1 .
The scientific team employed a multi-layered diagnostic approach to uncover infections, with each method offering different levels of sensitivity.
PCR shows superior detection capability for identifying chronic, low-level infections 1
| Diagnostic Method | Detection Principle | Prevalence Rate | Relative Sensitivity |
|---|---|---|---|
| Thin Blood Smear (TBS) | Direct parasite visualization | 17.3% | Lower |
| CATT/T. evansi | Antibody detection | 18.9% | Moderate |
| PCR | DNA detection | 22.7% | Higher |
The study revealed an alarming prevalence of T. evansi infection, with the highly sensitive PCR method detecting parasites in 22.7% of the camels examined 1 . The CATT test identified 18.9% as positive, while traditional microscopy found 17.3% 1 . These results not only demonstrated the concerning rate of infection but also highlighted the superior detection capability of molecular methods over conventional approaches 1 .
Through meticulous statistical analysis, researchers identified several factors that significantly increase a camel's susceptibility to T. evansi infection 1 . These risk factors create a distinct profile of the most vulnerable animals:
Older camels (>10 years) showed a 9-fold higher infection risk compared to younger animals 1
Camels in poor physical condition had 4 times greater infection odds than those in good condition 1
Female camels faced 2.6 times higher infection risk than males 1
Spring emerged as a higher-risk season, with camels being 2.5 times more likely to be infected 1
Odds ratios for different risk factors associated with T. evansi infection in camels 1
The risk factors identified in the Egyptian study align with findings from research conducted across Africa. In Nigeria, seroprevalence studies using the CATT test revealed infection rates of 41.75% in Borno State and 46.50% in Yobe State 9 . In Algeria, a comprehensive study of 865 camels found an individual seroprevalence of 49.5% and a herd seroprevalence of 73.2% 8 , indicating widespread exposure across the region.
| Risk Factor | Category | Odds Ratio | Confidence Interval |
|---|---|---|---|
| Age | >10 years | 9.0 | 3.5-23.1 |
| Body Condition | Poor | 4.0 | Not specified |
| Sex | Female | 2.6 | Not specified |
| Season | Spring | 2.5 | 1.1-5.7 |
T. evansi employs an ingenious transmission strategy that relies on blood-sucking insects as its primary accomplices. Unlike some related trypanosomes that require specific tsetse flies for cyclical development, T. evansi utilizes a mechanical transmission method 3 . This means the parasite doesn't need to develop within the insect vector but simply hitches a ride from one host to another, making it capable of utilizing multiple insect species.
When these flies bite an infected camel, their mouthparts become contaminated with parasites, which are then injected into the next camel they feed on 4 . This mechanical transmission makes control particularly challenging, as multiple fly species can spread the disease throughout camel populations.
While insect vectors represent the primary transmission method, research has uncovered additional pathways for T. evansi spread:
The alarming practice of reusing needles or surgical instruments without proper sterilization has been identified as a significant route of transmission in some modern farming operations 7 . A devastating example from a camel farm in the United Arab Emirates demonstrated infection rates approaching 90% in female camels that had undergone extensive reproductive treatments with contaminated equipment 7 .
Evidence suggests the parasite can cross the placental barrier, leading to abortions or infected offspring 4
Carnivores may acquire infection through consumption of infected raw meat 8
The 2024 iatrogenic transmission study revealed particularly concerning consequences, with 61% of all abortions and 82% of all neonatal deaths occurring in trypanosome-infected camels 7 , highlighting the profound economic and welfare impact of this preventable transmission route.
| Reagent/Kit | Primary Function | Specific Application |
|---|---|---|
| CATT/T. evansi | Antibody detection | Field-friendly serological testing for exposure screening |
| Giemsa Stain | Blood smear staining | Visualization of parasites in blood samples via microscopy |
| DNA Extraction Kits | Nucleic acid purification | Isolation of high-quality DNA from blood for molecular studies |
| PCR Master Mix | DNA amplification | Molecular detection of parasite-specific gene targets |
| T. evansi Primers | DNA target selection | Amplification of species-specific genetic markers |
The continuous refinement of these research tools has dramatically improved our ability to detect, monitor, and understand T. evansi infections in the field. Molecular techniques particularly have revolutionized surra surveillance, with PCR assays capable of detecting as little as 1 trypanosome per milliliter of blood 2 , making them indispensable for identifying chronic, low-level infections that would escape detection by traditional microscopy.
Controlling surra requires a multi-pronged strategy that addresses both the parasite and its transmission routes:
Regular insecticide spraying of animal shelters and strategic placement of fly traps can reduce mechanical transmission by biting flies 4
The simplest yet most overlooked prevention method involves using disposable needles and syringes for each animal during veterinary treatments 7
Implementation of routine testing using sensitive diagnostic methods like PCR or CATT to identify and treat infected animals early 1
Restricting the movement of infected animals to prevent introduction into clean herds 7
The pharmaceutical arsenal against T. evansi is limited, with suramin being one of the recommended treatments 3 . However, widespread trypanocide resistance has been reported globally, particularly against diminazene aceturate 3 . This resistance problem is exacerbated by the lack of new drug development for animal trypanosomiasis, creating an urgent need for more sustainable control approaches.
The battle against Trypanosoma evansi represents more than just a veterinary concern - it's a crucial effort to protect livelihoods, food security, and cultural heritage in camel-rearing communities across Sudan and beyond. As research continues to unveil the parasite's secrets, our ability to combat this threat grows stronger. From the pioneering work of Griffith Evans in 1880 to today's molecular diagnostics, scientific progress has steadily shifted the advantage toward disease control.
The path forward requires integrating traditional husbandry wisdom with modern scientific insights, combining vector control, sanitary practices, regular screening, and judicious treatment. Most importantly, it demands collaboration between researchers, veterinarians, and camel herders themselves - those who know these remarkable animals best. Through this united front, we can work toward a future where the silent camel killer no longer threatens the livelihoods of those who depend on these magnificent "ships of the desert."
Primary transmission method
Contaminated equipment
Mother to offspring
Consumption of raw meat