Besnoitiosis in Ox: Skin Thickening, Cysts, and Reproductive Impact

Besnoitiosis is a parasitic disease caused by Besnoitia besnoiti, a tissue-forming protozoan that affects cattle. In oxen and bulls, the disease often starts with a short acute phase that may include fever and body swelling, then progresses to a chronic phase marked by skin thickening, wrinkling, and cyst formation in connective tissues. Affected animals can remain infected for life.

One of the most recognizable findings is the presence of tiny white cysts in the scleral conjunctiva, the white tissue around the eye. Your vet may also see cysts in the genital mucosa, along with thickened skin over the neck, perineum, udder, or scrotum. These changes can interfere with comfort, movement, body condition, and breeding performance.

This disease matters at both the individual and herd level. Many cattle stay subclinically infected, but some develop obvious skin disease or reproductive damage. In breeding animals, especially males, chronic inflammation and vascular injury in the testes and scrotum can reduce fertility or lead to sterility, so early herd-level planning is important.

Besnoitiosis in cattle is caused by infection with Besnoitia besnoiti. The parasite has an acute stage, when rapidly multiplying forms invade blood vessel lining and trigger fever, edema, and inflammation, followed by a chronic stage in which thick-walled tissue cysts develop in the skin, mucous membranes, and reproductive tissues.

Transmission is not fully settled in every setting, but current evidence supports spread through close contact between infected and noninfected cattle, especially when tissue cysts are present in genital mucosa. Natural breeding is considered a risk because cysts can occur in the penis, scrotal tissues, and vaginal vestibule. Mechanical spread by blood-feeding insects has also been demonstrated experimentally and is supported by seasonal patterns in outbreaks.

New herd introductions are a major practical risk. An apparently healthy carrier can bring the parasite into a herd, and many infected cattle never show dramatic signs. That is why your vet may recommend testing purchased animals, reviewing breeding practices, and separating infected from noninfected groups when besnoitiosis is suspected.

Diagnosis starts with a careful physical exam and herd history. Your vet will look for chronic skin thickening, scrotal changes, poor body condition, and the small white cysts in the scleral conjunctiva that are considered highly characteristic of chronic disease. In breeding males, a reproductive exam may be important because testicular and scrotal damage can have lasting fertility effects.

Clinical findings alone are not enough for herd control. Serologic testing is used to detect antibodies in both sick and subclinically infected cattle. Published veterinary references describe ELISA, IFAT, immunoblot, and Western blot as useful tools, with confirmatory testing often recommended because cross-reactions with related parasites can occur.

In some cases, your vet may confirm the diagnosis with a skin biopsy and microscopic identification of tissue cysts. PCR may also be used in some laboratories. For breeding bulls or oxen used for reproduction, semen evaluation and breeding soundness testing can help measure the practical reproductive impact and guide management decisions.

Prevention focuses on keeping infected cattle from introducing or spreading the parasite within the herd. Your vet may recommend testing incoming animals, especially replacements older than 6 months and breeding bulls, before they join the main group. Avoid sharing breeding bulls, and be cautious with natural service if besnoitiosis is known or suspected in the area.

Because many infected cattle look normal, herd surveillance matters. Regular clinical checks for eye cysts, skin thickening, genital lesions, and body condition changes can help catch cases earlier. Serologic monitoring is especially useful for detecting subclinical carriers and guiding separation, breeding, and culling decisions.

Vector control is also part of prevention. Use fly repellents, ectoparasiticides, manure management, and environmental control measures that fit your farm. In herds with confirmed infection, your vet may advise keeping seropositive and seronegative groups apart, using careful reproductive management, and removing clinically affected or reproductively compromised animals from the breeding program.

There is no widely available licensed vaccine for routine cattle use in the US, and no reliably effective curative treatment has been established. That makes biosecurity, testing, and breeding management the core tools for prevention.