Phthisis ('Consumption' - Tissue wasting), Pearl disease (Grape-like lesions in the peritoneum and pleura), Scrofula (King's evil), Pott's disease (paralysis of the hind limbs due to TB nodules of the spine), 'Rajajakshman' (the King of diseases as per Hindu texts), ‘Elumpurikki noiy’ (Tamil)
Type of zoonosis
Direct anthropozoonosis, Zooanthroponosis
Definition
It is a chronic disease of man and animals caused by pathogenic Mycobacterium spp. causing development of tubercle in vital organs. The pulmonary tuberculosis is the most common form, characterized by protective cough, fever, fatigue, weight loss, chest pain and night sweat in human beings.
Brief history
Tuberculosis (TB) is an ancient disease known as early as 4000 B.C. Tuberculosis was well described by Hippocrates and Aristotle in the fifteen century BC. As ‘Phthisis’ (described in Greek literatures) which was translated in to English as ‘Consumption’.
Robert Koch in 1882, cultivated the agent and demonstrated tuberculin testing first in guinea pigs in 1890.
French scientists, Calmette and Guerin (veterinarian) in 1906, developed vaccine against TB, is known as "BCG vaccine". It was developed by attenuating a virulent strain of Mycobacterium bovis. They made 230 subcultures over a period of 13 years and evolved a strain known as "Bacille Calmette Guerin", which was avirulent for man while retaining its immunogenicity. In 1927, the first human was vaccinated and in 1948, the vaccine was accepted by TB workers.
Tuberculin test was first discovered by Von Pirquet in 1907.
Etiology
Tuberculosis is caused by bacillus of the bacteria belong to the genus Mycobacterium.Mycobacterium organisms are facultative intracellular pathogens, Gram positive, acid fast (because Mycobacterium has mycolic acid in its cell wall) and aerobic. The most common zoonotic species of Mycobacteria are:
M.bovis - Cattle, dogs and swine
M.avium complex (MAC) - Birds, swine and sheep
M.tuberculosis - Man, nonhuman primates, cattle, dogs, swine and psittacines
M.marinum, M.fortuitum, M.platypolcitis - Fish
Atypical Mycobacterium such as M.scrofulaceum, M.kansasii and M.intracellulare have been reported in NHP's and are also present in soil and water. They can cause pulmonary disease refractory to treatment in man, and are most often seen in immunocompromised people.
MAC is composed of 28 serotypes. MAC includes M.avium - intracelluare (MAI) and M.avium - intracellulare - scrofulaceum (MAIS). The disease produced by MAC complex is called as Mycobacteriosis in man.
The disease is discovered more than 100 years ago. There are about 60 million cases of tuberculosis in the world. Around 5000 people die from tuberculosis daily. According to the estimates of WHO about one third of the total population of the world is infected with tubercle bacteria. This has made the disease an international health problem.
Morbidity and mortality rates continue to be higher among urbanites, minorities, the poor, the homeless, substance abusers and persons infected with HIV.
South-east Asia region countries carry 38% of the global burden of tuberculosis, with 3 million new cases and nearly 0.6 million deaths occurring every year.
Rising trend in HIV infection and emergence of multidrug resistant strains of TB (MDR-TB) pose additional threat.
The incidence of TB is influenced by may factors, are:
Poor or inadequate health care
Poor standard of living and socioeconomic conditions
Malnutrition
Higher population density
Occupational contraction
Poor personal hygiene
Lack of education and awareness
Other diseases like, HIV/AIDS, Diabetes mellitus.
Close confinement of the human population.
The DOTS (Directly Observed Treatment, Short-course) strategy has been globally recognized as the best cost-effective approach to control TB and to reduce the disease burden and to reduce the spread of infection. DOTS, by which cure can be ensured.
Categorization of countries by DOTS strategy
"0" - Not reporting to WHO.
"1" - Not implementing the DOTS and case rate over 10 cases per 100000 populations.
"2" (Pilot phase) - Implementing the DOTS and case rate of 10% of the total population.
"3" (Expansion phase) - Implementing the DOTS in 10 to 90% of the total population.
"4" (Routine implementation) - Implementing the DOTS in over 90% of the total population.
"5" (Low incidence) - Not implementing the DOTS and case notification rate of 10 cases per 100000 populations.
As on 2002, 180 countries have implemented the DOTS, covering 69% of the world's population.
In India
India globally ranks first in tuberculosis.
It is estimated that one-third of the current global population is infected asymptomatically with tuberculosis, of whom 5 to 10% will develop clinical disease during their lifetime.
India falls under MDR-TB zone.
TB is one of the biggest public health problems in India. As per the statistics, every year approximately 1.8 million people develop TB, of which 4.17 lakhs people die, that means, it was observed that every second an adult in India is infected with TB and every minute one Indian dies of this disease.
It is estimated that loss of an average about 83 work-days annually due to TB.
More burden in childhood and deaths from tuberculosis by meningitis and disseminated disease.
Since 1993, India has successfully implemented Revised National Tuberculosis Control Programme (RNTCP) using DOTS strategy.
Reservoir and source of infection
Human source: Sputum.
Bovine source: Milk and faeces.
Environmental source: Water, soil and dust contaminated with human and animal sources. Mycobacterium multiply in the water and soil.
Infected patients are infective as long as they remain untreated.
Effective treatment for TB reduces infectivity by 90% with in 48 hrs.
Mycobacterium bacilli are transmitted from infected animals or infected tissue primarily via the aerosol route.
Inhalation of droplets or droplet nuclei of sputum-positive patients, coughed up materials and fomites contaminated with droplets of sputum.
Contracted via ingestion or cutaneous inoculation of the bacilli.
Exposure to dusty bedding of infected animals, coughing of infected animals and aerosolization of the organism during sanitation procedures may also be sources of the disease in the laboratory environment.
Consumption of infected milk.
In animals
Directly through contact with tuberculosis animals or their discharges or their sputum.
Contact with tuberculosis peoples.
Calves by ingestion of contaminated milk.
Congenital infection.
Through artificial insemination with infected semen.
Clinical signs
Disease in man
Incubation period ranges from 3 to 6 weeks, but uncertain. There after the development of disease depends upon the host-parasite relationship. It may take weeks or months or years.
The patient may be asymptomatic for years. General signs may include anorexia, weight loss, lassitude, fatigue, fever, chills and cachexia.
Primary tuberculosis is often asymptomatic. Basic sequence of events may be as (i). conversion of tuberculin sensitivity in 3 to 8 weeks, (ii). miliary and meningeal TB in 3 months, (iii). pleural effusion an pneumonia in 3 to 6 months and (iv). first appearance of post primary lesions in renal, bone and joints in one year.
In humans, the clinical signs depend on the organ system involved.
Chronic pulmonary TB: The most familiar signs related to pulmonary TB are cough, sputum production and hemoptysis. It is common in middle aged people who have preexisting pulmonary lesions.
Lymphadenitis: It is common in children from 18 months to 5 years of age. Lymph nodes are primarily those of the neck close to the jaw bone (cervical lymph nodes) affected.
Skin or cutaneous TB: Skin lesions are characterized by ulcers or by papular lesions progressing to dark suppurative lesions.
Miliary TB is most often seen in the very young and old people.
M.marinum of fish strain causes granulomas on the extremities as a group of papules that ulcerate and scab over, is described as "swimming pool granuloma or fish tank granuloma". Lesions may persist for months, and healing is usually spontaneous. Swimming pool granuloma may also be due to M.xenopi.
Disease in animals
High fever and emaciation
Loss of body weight slowly
Difficult in breathing
Painful dry cough
Abdominal pain
Chronic bloat
Figure: Tuberculous nodules in lungs (cattle)
Diagnosis
The diagnosis of TB is often difficult.
Clinical support with laboratory tests commonly used for presumptive diagnosis are: intradermal TB test with mammalian tuberculin, radiography, acid fast stained sputum smear (Ziehl-Neesen staining) and ELISA. Confirmation by culture, histopathology or animal inoculation.
Molecular diagnosis by polymerase chain reaction.
In humans
Tuberculin test, which is recognized by WHO for screening.
Tuberculin test: Mantoux intradermal test, Heaf multiple puncture test and Tine multiple puncture test.
Heaf multiple puncture test for screening large population, quick and easy test, and reliable and cheap test.
Tine multiple puncture test is an unreliable test, and not recommended.
Mantoux intradermal test: Inject 1 ml of 1 TU of PPD-RT-23 with Tween 80 intadermally on the flexor surface of the forearm and then read the result after 72 hrs. Tuberculin reaction is erythema and induration at the site of injection. Reaction exceeding 10 mm is positive, <6 mm is negative (but having risk of developing TB), between 6 mm and 9 mm is doubtful and 20 mm is strong positive. The positive reaction does not prove that the person is suffering from the disease. It may produce cross-reaction in people who had BCG vaccination.
Case finding in humans includes, Sputum positivity by acid-fast staining is the first choice of test (Zieh-Neelsen staining); X-rays (even sputum negative cases could be identified; Symptoms of pulmonary TB and sputum positivity, persistent cough for 3 to 4 weeks, continuous fever, chest pain and hemoptyis); Sputum culture in specific media like, Dorset egg media or Lowenstein Jensen media or Harrold egg yolk media (it takes at least 6 weeks, expensive, but second choice of test) and Tuberculin test (diagnostic value is invalidated, but has very little value in case finding).
In animals
Single intradermal skin test, double intradermal skin test and comparative intradermal skin test.
Acid fast staining of faecal materials
Treatment
Objective of chemotherapy is to cure and eliminate the both slow and fast growing bacilli.
The patient must take the correct drug at the correct dosage for the correct length of time.
Incomplete treatment leads to relapse and development of MDR-TB and XDR-TB (Extreme Drug Resistant TB).
Anti-tuberculosis drugs are:
Bactericidal drugs: Rifampicin (10 - 12 mg/kg body weight), Isoniazid (4 - 5 mg/kg body weight), Streptomycin (0.5 - 1 gm/kg body weight) and Pyrazinamide (30 mg/kg body weight), which kill the bacilli in-vivo.
Bacteriostatic drugs: Ethambutol (15 mg/kg body weight) and Thioacetazone (2 mg/kg body weight), which inhibit the multiplication and lead to their destruction by the cell mediated immune response.
Triple therapy means treatment with isoniazid, rifampicin and ethambutol.
DOTS strategy: It is effective world wide. It follows two phases viz. Intensive phase and Continuous phase.
Intensive phase: Patients swallow drugs in the presence of health workers (daily for 1 to 3 months).
Continuous phase: Drugs given for a week and patients swallow medicines in the presence of health worker (for 6 to 9 months).
In DOTS strategy, the cases are divided in to three categories
Note: H - Isoniazid (600 mg); R - Rifampicin (450 mg); Z - Pyrazinamide (1500 mg); E - Ethambutol (1200 mg); S - Streptomycin (750 mg)
World Tuberculosis Day, falling on 24th March each year, is designed to build public awareness that tuberculosis today remains an epidemic, causing the deaths of about 1.6 million people each year. 24th March commemorates the day in 1882 when Dr.Robert Koch astounded the scientific community by announcing that he had discovered the cause of tuberculosis, the TB bacillus. At the time of Koch's announcement in Berlin, TB was raging through Europe and the Americas, causing the death of one out of every seven people. Koch's discovery opened the way towards diagnosing and curing tuberculosis.
In 1982, on the one-hundredth anniversary of Dr. Koch's presentation, the International Union Against Tuberculosis and Lung Disease (IUATLD) proposed that 24th MARCH be proclaimed an official WORLD TUBERCULOSIS DAY. In 1996, the World Health Organization (WHO) joined with the IUATLD and a wide range of other concerned organizations to increase the impact of World TB Day.
Last modified: Saturday, 17 September 2011, 6:03 AM
Participants