Primate Tuberculosis Study Guide

Overview and Clinical Importance

Tuberculosis (TB) in nonhuman primates is a critical zoonotic disease caused by Mycobacterium tuberculosis complex (MTBC). This chronic, progressive disease represents one of the most significant infectious threats in captive primate populations with approximately 75 percent of cases caused by M. tuberculosis from human transmission.

Etiology and Transmission

Causative Organisms

• M. tuberculosis - causes 75 percent of primate TB, primarily from human transmission
• M. bovis - less common, possible from infected milk or animal sources
• M. avium complex - can cause disease in immunocompromised primates

Transmission

Primary route: Aerosol inhalation of infected droplets from respiratory secretions

Secondary routes: Ingestion (milk, contaminated food/water), direct contact, urinary shedding (rare)

Species Susceptibility

Clinical Signs and Pathology

Critical point: Clinical signs are UNRELIABLE indicators of disease severity. Seemingly healthy animals may have extensive miliary disease.

Active Pulmonary TB

• Intermittent coughing - most characteristic sign
• Chronic weight loss, decreased appetite, lethargy
• Dull hair coat, weakness, dyspnea in advanced cases

Extrapulmonary TB

Cutaneous: Non-healing wounds, draining ulcers, fistulous tracts, lymphadenopathy

Vertebral (Pott's disease): Paraplegia, kyphosis, spinal deformity

Cerebral: Seizures, ataxia, behavioral changes, paralysis

Intestinal: Chronic diarrhea, abdominal masses, peritoneal effusion

Pathology

Classical tuberculoid granuloma consists of: central caseous necrosis, epithelioid macrophages and Langhans giant cells (middle zone), lymphocytic cuff with fibrosis (outer zone). Primates show ABUNDANT acid-fast bacilli in lesions, unlike some species where organisms are sparse.

Diagnostic Approach

Multi-test approach required - no single test is absolutely predictive. Combine TST, IGRA, imaging, PCR, and culture.

Tuberculin Skin Testing (TST)

Technique: 0.1 mL mammalian old tuberculin (MOT) injected intradermally into UPPER EYELID (NOT abdomen - abdominal testing is unreliable). Read at 24, 48, 72 hours. Positive = palpebral swelling with lid droop.

TST conversion: Typically 4-8 weeks post-infection in rhesus macaques

False negatives: Early infection (less than 4-8 weeks), advanced disease (anergy), immunosuppression, poor tuberculin potency

False positives: Cross-reactivity with nontuberculous mycobacteria, general immunologic reactivity

Interferon-Gamma Release Assay (IGRA)

The gamma interferon tuberculosis (GIFT) test achieved 100 percent sensitivity and 97 percent specificity in experimentally infected animals. Combining TST with IGRA significantly enhances detection.

Imaging

Thoracic radiography has high predictive value and detects disease BEFORE clinical signs. Look for: pulmonary consolidation, nodular/miliary pattern, hilar lymphadenopathy, cavitary lesions.

Molecular Diagnostics

• Tracheal wash/BAL: Predictive in 90 percent of infected animals for PCR and culture
• IS6110 PCR: Highly specific for M. tuberculosis complex, results in hours
• Acid-fast staining: 85-95 percent positive predictive value when AFB detected
• Culture: Gold standard but takes 4-15 weeks, allows sensitivity testing

Management and Public Health

Treatment Considerations

Treatment is RARELY attempted in veterinary practice. Euthanasia is the standard recommendation due to:

• Zoonotic risk to handlers even during treatment
• Risk of selecting multidrug-resistant strains transmissible to humans
• Interference with elimination programs
• High cost (6-9 months multidrug therapy)
• High relapse rates

When treatment is attempted (endangered species only): Use human TB regimens - isoniazid, rifampin, pyrazinamide, ethambutol for minimum 6 months (9 months for M. bovis which is pyrazinamide-resistant).

Quarantine Requirements

• All imported NHP must complete minimum 3 negative TSTs at least 2 weeks apart
• Last test within 14 days of quarantine release
• Semiannual testing mandatory for established colonies
• Outbreak situations: test every 2 weeks until negative

Zoonotic Transmission

Bidirectional transmission documented between humans and primates. Humans typically source of primate infections, but infected primates can transmit to handlers. Nosocomial transmission in veterinary clinics documented - infected animals transmitted to surgical patients and staff.

Personal protection: Baseline and annual TB testing for primate workers, N95 respirators or PAPRs for suspect cases, BSL-3 precautions for necropsy.