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Infection by Besnoitia — Clinical Guidelines

Overview

Besnoitia besnoiti causes bovine besnoitiosis, an economically significant parasitic disease affecting cattle, particularly in Africa and Mediterranean countries. This condition leads to substantial losses due to high morbidity, abortion, and infertility, especially in bulls. Clinical signs include acute phases characterized by fever, weakness, and lymphadenopathy, transitioning to chronic stages marked by extensive cyst formation in subcutaneous tissues, resulting in hyper-sclerodermia, hyperkeratosis, alopecia, and testicular lesions in males. Early recognition and management are crucial for mitigating economic impacts and preventing disease spread within herds. 1

Pathophysiology

Besnoitia besnoiti, an obligate intracellular protozoan parasite within the phylum Apicomplexa, invades host cells, primarily in the acute phase, where it proliferates as tachyzoites. These proliferative forms cause significant tissue damage, particularly in lymph nodes and subcutaneous tissues. As the infection progresses, the parasite transforms into bradyzoites, forming cysts that are resistant to host immune responses. These cysts accumulate extensively in subcutaneous tissues, leading to chronic manifestations such as hyperkeratosis, alopecia, and sclerosis. In bulls, the testicular involvement results in irreversible damage, affecting reproductive capabilities. The non-reversible nature of cyst formation underscores the importance of early intervention to prevent chronic complications. 1

Epidemiology

Bovine besnoitiosis exhibits varying prevalence rates across different regions. In endemic areas, the disease predominantly affects older cattle, with higher seroprevalence noted in beef cattle compared to dairy cattle. For instance, in Israel, approximately 50% of beef cattle tested positive for antibodies against Besnoitia, while over 90% of dairy cattle remained seronegative. Among beef bulls, seropositivity increased with age, suggesting a cumulative exposure risk. The disease's distribution is largely confined to Africa and Mediterranean countries, with sporadic cases reported in other regions due to cattle movement. 4

Clinical Presentation

Clinical signs of bovine besnoitiosis vary from acute to chronic phases. Acute cases often present with fever, lethargy, lymphadenopathy, and generalized weakness. Chronic stages are characterized by visible subcutaneous cysts, leading to clinical signs such as alopecia, hyperkeratosis, and thickened skin (pachydermatitis). In bulls, specific testicular lesions manifest as atrophy, sclerosis, and focal necrosis, significantly impacting fertility. Less commonly, subclinical infections may occur, where animals show no overt clinical signs despite serological evidence of infection, complicating early detection and management. 1 3

Diagnosis

Diagnosing bovine besnoitiosis involves a combination of clinical evaluation and specific diagnostic tests. Initial suspicion arises from clinical signs and epidemiological context. Definitive diagnosis relies on identifying Besnoitia besnoiti stages within tissue samples:

Skin Biopsy Smear: Demonstrates bradyzoites (cystic stages) in affected skin or conjunctival scrapings, with bradyzoites appearing stumpy or banana-shaped.

Serological Tests: ELISA and indirect immunofluorescence tests (IFT) are utilized, though sensitivity can be limited. Positive results in cattle older than 1 year are more reliable, especially when correlated with clinical findings and presence of conjunctival cysts.

Differential Diagnosis: Conditions like sarcocystosis, toxoplasmosis, and other parasitic infections may present similar clinical signs but can be distinguished by specific serological cross-reactivity tests and histopathological examination. 2 3

Specific Diagnostic Criteria

Skin Biopsy: Presence of Besnoitia besnoiti bradyzoites in skin or conjunctival scrapings.

Serology:

- ELISA: Positive threshold not clearly defined but generally indicates exposure; false positives rare. - IFT: Positive threshold similarly indicates exposure; no false positives reported.

Histopathology: Identification of characteristic cysts and host cell encapsulation in tissue samples.

Differential Diagnosis: Rule out sarcocystosis and toxoplasmosis via cross-reactivity tests. 2 3

Differential Diagnosis

Sarcocystosis: Distinguished by different cyst morphology and specific serological cross-reactivity tests.

Toxoplasmosis: Identified through Toxoplasma-specific serological tests and distinct histopathological features.

Other Parasitic Infections: Managed by ruling out based on clinical context and specific diagnostic markers unique to each parasite. 3

Management

First-Line Treatment

Supportive Care: Focus on alleviating clinical symptoms, including anti-inflammatory medications to manage fever and inflammation.

Hygiene and Isolation: Quarantine infected animals to prevent disease spread within herds.

Nutritional Support: Ensure adequate nutrition to support overall health and immune function.

Second-Line Treatment

Antiparasitic Agents: Currently, no specific antiparasitic drugs are widely approved for besnoitiosis. Research is ongoing, but options may include experimental treatments targeting protozoan infections.

Monitoring: Regular clinical assessments and serological monitoring to track disease progression and treatment efficacy.

Refractory Cases / Specialist Escalation

Consultation with Parasitologists: For persistent or severe cases, seek expert advice for advanced diagnostic and therapeutic strategies.

Experimental Therapies: Consider enrollment in clinical trials for novel treatments targeting Besnoitia besnoiti.

Contraindications

Drug Interactions: Monitor for potential interactions with concurrent medications.

Animal Welfare: Ensure that any intervention does not compromise the animal's welfare.

Complications

Chronic Lesions: Persistent subcutaneous cysts leading to hyperkeratosis, alopecia, and hyper-sclerodermia.

Reproductive Failure: Significant testicular damage in bulls resulting in infertility.

Referral Triggers: Severe clinical deterioration, refractory disease, or complications requiring specialized intervention. 1

Prognosis & Follow-Up

The prognosis for bovine besnoitiosis varies based on the stage of infection and the effectiveness of management. Early detection and intervention can mitigate chronic complications, but once cysts are extensively formed, the prognosis is guarded due to irreversible tissue damage. Follow-up should include:

Regular Serological Testing: Every 3-6 months to monitor disease progression.

Clinical Examinations: Quarterly assessments to detect new lesions or worsening symptoms.

Reproductive Monitoring: Special attention in bulls to assess fertility post-treatment. 3

Special Populations

Bulls: Higher risk of severe reproductive complications, necessitating close monitoring and early intervention.

Older Cattle: Higher seroprevalence suggests increased susceptibility and chronic manifestations, requiring vigilant management strategies. 4

Key Recommendations

Implement Regular Serological Screening: Especially in endemic regions and older cattle populations to detect subclinical infections early. (Evidence: Moderate)

Utilize Skin Biopsy Smears for Confirmation: Employ skin or conjunctival scrapings for definitive diagnosis, especially in chronic cases. (Evidence: Strong)

Supportive Care is Essential: Focus on symptom management and hygiene practices to control disease spread. (Evidence: Expert opinion)

Monitor for Reproductive Impact in Bulls: Regular testicular examinations to prevent irreversible damage. (Evidence: Moderate)

Consider Experimental Treatments for Refractory Cases: Engage with parasitology experts for advanced therapeutic options. (Evidence: Weak)

Quarantine Infected Animals: To prevent herd-wide transmission of besnoitiosis. (Evidence: Strong)

Integrate Clinical and Serological Data: Correlate clinical signs with serological test results for accurate diagnosis. (Evidence: Moderate)

Educate Herd Managers: On recognizing early signs and implementing biosecurity measures. (Evidence: Expert opinion)

Follow-Up Monitoring: Conduct regular clinical and serological follow-ups to assess disease progression and treatment efficacy. (Evidence: Moderate)

Evaluate Cross-Reactivity in Serological Tests: To rule out other parasitic infections accurately. (Evidence: Strong)

References

1 Cortes HC, Reis Y, Waap H, Vidal R, Soares H, Marques I et al.. Isolation of Besnoitia besnoiti from infected cattle in Portugal. Veterinary parasitology 2006. link 2 Sannusi A. A simple field diagnostic smear test for bovine besnoitiosis. Veterinary parasitology 1991. link90073-5) 3 Janitschke K, De Vos AJ, Bigalke RD. Serodiagnosis of bovine besnoitiosis by ELISA and immunofluorescence tests. The Onderstepoort journal of veterinary research 1984. link 4 Goldman M, Pipano E. Serological studies on bovine besnoitiosis in Israel. Tropical animal health and production 1983. link

Infection by Besnoitia