A camel may appear clinically normal despite having substantial pulmonary lesions. Conversely, advanced respiratory pathology does not always produce obvious respiratory distress. For veterinarians examining camels, this makes tuberculosis particularly challenging: clinical appearance alone may not reflect the extent of disease. 

When should tuberculosis enter the differential?^[1] 

Camel tuberculosis is a chronic, debilitating disease. Clinical suspicion should increase when a camel shows a combination of progressive weight loss, weakness, anorexia, and respiratory abnormalities, particularly when superficial lymph nodes are enlarged. 

Reported clinical signs include: 

• Chronic weight loss or emaciation 
• Wasting and weakness 
• Anorexia 
• Cough 
• Dyspnea or respiratory distress 
• Enlargement of superficial lymph nodes 
• Decumbency 

However, these signs are not consistently present. Some infected camels remain asymptomatic until the disease is advanced, while animals with severe pulmonary lesions may show surprisingly little respiratory distress. Occasionally, animals may even be found dead without previous clinical observations. 

This makes a normal-looking camel an unreliable indicator of absence of disease. 

Lung and thoracic lymph nodes deserve close attention^[1] 

At pathological examination, the lungs and associated thoracic lymph nodes are the sites most frequently affected in both Old and New World camelids. Typical lesions can be extensive and caseous-necrotic. 

Gross examination may reveal multiple yellowish, firm or confluent nodules, sometimes reaching up to 10 cm in diameter. Their centres may be friable, partially mineralized and arranged in an onion-skin-like pattern on the cut section. Lesions may occur in the lungs as well as bronchial and mediastinal lymph nodes. 

Other organs should not be overlooked. Tuberculous lesions have also been reported in the liver, spleen, kidney, trachea, and pericardium, while intestinal and cutaneous involvement has been observed in llamas. 

What does the lesion look like microscopically?^[1] 

The characteristic microscopic picture is a granuloma. Caseous nodules contain closely packed epithelioid macrophages accompanied by variable numbers of lymphocytes, plasma cells, and neutrophils. Larger granulomas may develop central necrosis, mineralization, and fibrous capsules. 

Ziehl-Neelsen and Fite-Faraco staining may demonstrate abundant acid-fast bacilli within epithelioid macrophages. 

Thus, the combination of gross caseous nodules, granulomatous inflammation, and demonstrable acid-fast organisms can provide important diagnostic direction, although confirmation requires appropriate laboratory investigation. 

A practical pathological point^[1],[2] 

The severity of lesions can vary considerably depending on how the animal is identified. Camels detected because of clinical disease may have extensive pathology, whereas animals identified through ante-mortem immunological testing before clinical disease develops may have considerably less severe gross lesions. 

For veterinarians, the key message is straightforward: Absence of dramatic clinical signs does not exclude significant tuberculosis-associated pathology. When tuberculosis is suspected, careful examination of the lungs and regional lymph nodes during post-mortem inspection, followed by appropriate confirmatory testing, is important for reaching a reliable diagnosis. 

Clinical Bottom Line: In camels, chronic wasting and respiratory or lymph-node abnormalities should raise suspicion for tuberculosis, but clinical findings alone may underestimate disease. Careful recognition of pulmonary, lymph-node and extrapulmonary lesions can provide an important diagnostic lead.

Reference(s):

1. Yessuf JA, Jibril Y, Tekle Y, Mammo G. Review on camel tuberculosis: diagnosis, pathology and public health significance. World J Pharm Life Sci. 2016. https://www.researchgate.net/publication/361485849

2. Wernery U, Kinne J, Jahans KL, Vordermeier HM, Esfandiari J, Greenwald R, Johnson B, Ul-Haq A, Lyashchenko KP. Tuberculosis outbreak in a dromedary racing herd and rapid serological detection of infected camels. Veterinary microbiology. 2007 May 16;122(1-2):108-15. https://www.sciencedirect.com/science/article/abs/pii/S0378113507000375