Tuberculosis is a zoonotic disease with a major public health concern affecting human and animal life Worldwide.

By Hafiz M. Hamza Rasool, Prof. Dr. Farzana Rizvi

Zoonosis or zoonotic diseases are those diseases or infections which are transferred from animals to humans or humans to animals. According to a report from United Nations Environment Programme (UNEP) and the International Livestock Research Institute (ILRI) in 2020 about 60 percent of known infectious diseases in humans and 75 percent of all emerging infectious diseases are zoonotic. World Zoonosis Day celebrated on 6th of July every year highlights the importance of zoonotic diseases and to prevent, detect, and pre-empt the spread of zoonotic pathogens, such as bacteria or viruses.

Tuberculosis is caused by a lethal airborne infectious bacterium from a group of closely related species of Mycobacterium tuberculosis complex (MTBC). These species differ in their epidemiological profiles, host ranges, pathogenicity, geographic distributions and drug resistances. Mycobacterium tuberculosis complex (MTBC), primary cause of Tuberculosis in human and animals, consists of Mycobacterium tuberculosis, M. bovis, M. africanum, M. microti and M. caprae. Mycobacterium is a facultative intracellular microbe that is non-capsular, non- spore forming, non-motile and obligate aerobic thin-rod bacteria. These are usually straight or slightly curved bacteria with a length of 1–10 μm and a width of 0.2–0.6 μm. Its cell wall is high in lipids, specifically mycolic acid, a thick waxy layer that contributes to bacterium resistance to numerous disinfectants, common laboratory stains, antibiotics, and physical damage by providing acid fastness and hydrophobicity. Zoonotic tuberculosis (TB) is a form of tuberculosis in people caused by Mycobacterium bovis via direct or indirect contact (inhalation) and consumption of contaminated animal products or water (ingestion).

Epidemiology of Mycobacterium bovis in human:-

Tuberculosis (TB) is a major global health problem and the leading cause of mortality worldwide with 10 million deaths. It is the second leading infectious killer disease in 2020 after Covid’19, surpassing HIV/AIDS (WHO). In 2020, an estimated 140,000 new cases of zoonotic tuberculosis were recorded worldwide, with 12,500 fatalities owing to the disease with Asia and Africa having the greatest frequency. M. bovis (zoonotic transmission) is thought to be responsible for 10-15% of new cases of human tuberculosis in developing countries. Bovine tuberculosis (zTB)


is common in Africa and Asia (Pakistan, India, Afghanistan) and its real incidence in human population of these countries is poorly known.

Transmission of Mycobacterium bovis in human: –

Humans acquire M. bovis infection from cattle directly by erogenous route or through direct contact with materials contaminated with the secretions of an infected animal. People in specific occupations such as veterinarians, farmers, zookeepers, milkers, animal dealers and abattoir workers are at high risk. People in these occupation may develop pulmonary tuberculosis from

  1. bovis and in turn put other human and susceptible animals at risk. Indirectly, man acquires the diseases from animals by consuming unpasteurized infected milk and ingestion of meat and meat products of slaughtered infected cattle.


Clinical Manifestation of Tuberculosis: –

Mycobacterium bovis infection in humans has similar clinical forms as those caused by M. tuberculosis. The majority of cases have a gradual, non-alerting start that varies depending on the virulence of the causing infection, the patient’s age, the organ affected, and the hosts immunological condition. It has been suggested that the common clinical manifestation of M. bovis infection in human is majorly associated with extra pulmonary form of the disease like Pleural TB, Lymph nodes TB, Genitourinary TB and Bone TB.


Systemic symptoms include fever, lack of appetite, weight loss, asthenia, copious nocturnal sweating, and overall malaise. Organ specific symptoms vary by organ and illness location: Tuberculosis of the lungs (dry or productive cough, hemoptysis, pleuritic pain, dyspnea and pneumonia), Pleural TB (Pleuritic chest discomfort, low-grade fever, dry cough, worsening of health, weight loss, and increasing dyspnea), Lymph nodes TB (painless swelling develops in the cervical and supraclavicular area), Genitourinary TB ( pollakiuria, dysuria, hematuria and flank pain) and Bone TB (inflammation of the peripheral joints, tuberculous meningitis with anorexia, malaise, headache, consciousness, neck stiffness, and nausea).

Diagnosis: –

Bovine tuberculosis in live animals is usually diagnosed on the basis of delayed hypersensitivity reactions. Diagnosis of active TB in people is based on interferon gamma release assay (IGRA), immunoglobulin G-test, sputum smear examination and some rapid gene assays like Xpert MTB/RIF. But these commonly used tests are not able to differentiate Mycobacterium tuberculosis complex into the distinct species of M. tuberculosis and M. bovis. Therefore, most cases of zoonotic Tb are misclassified. The identification of M. bovis in human can be done by PCR and gene sequencing of culture isolates, but for these tests the proper collection of sample is very essential.

Treatment: –

The treatment and recovery of patients with zoonotic tuberculosis is difficult. Patients with zoonotic TB may get suboptimal therapy because most healthcare professionals begin treatment without doing medication susceptibility testing. As a result, zoonotic tuberculosis is underdiagnosed. BCG vaccination is the only TB vaccine approved for use in humans against pulmonary tuberculosis in children and adults with a cure rate of 0–80%. Because M. bovis is completely resistant to pyrazinamide, a major first-line TB treatment therefore precise illness diagnosis and distinction are critical. Isoniazid, streptomycin, para-amino salicylic acid combos are routinely used to treat human TB. The need for long-term medication for the condition can lead to the emergence of multidrug-resistant (MDR), exceptionally drug-resistant (XDR), and even fully drug-resistant (TDR) bacterial strains. The majority of MDR-TB medication regimens now contain an aminoglycoside (e.g., streptomycin, kanamycin, amikacin) as well as a fluoroquinolone. DOTS (directly observed treatment short course) is a very efficient and cost- effective TB control approach that is widely approved by WHO.


Control: –

Zoonotic TB has a significant economic impact on international commerce, animal productivity (e.g., lower meat output, low reproductive rate, and low milk yield), human health costs, and compensation from control programmes. The disease load in people cannot be minimized until food safety standards are improved and bovine tuberculosis is controlled in animals. To eradicate bovine TB, identify critical demographics and TB transmission risk routes, slaughterhouse monitoring, mandatory milk pasteurization, “test and slaughter” laws, effective education and suitable hygiene practices should be appropriately implemented. National TB control program of Pakistan (NTP) aims to achieve a TB-free Pakistan by 2025, lowering the prevalence of tuberculosis in the general population by 50% compared to 2012, by providing universal access to high-quality TB care and eliminating TB deaths. Therefore, it is the need of the hour to add zoonotic tuberculosis in National Tuberculosis control program to control and eradicate bovine tuberculosis and make Pakistan a Tuberculosis free country.