Tuberculosis: The things you need to know about the disease caused by a bacterium called Mycobacterium tuberculosis, very fatal as it usually attack the lungs.

 By

Eloke Onyebuchi

Public Health Specialist/Principal Consultant.

Description of Tuberculosis

Tuberculosis, often referred to as TB, is a curable infectious disease caused by the tubercle bacillus - also known as Mycobacterium tuberculosis or M. tuberculosis. 'Mycobacterium' means spore-like bacteria. TB bacilli have a thick waxy coat, are slow growing and can survive in the body for many years in a dormant or inactive state whereby people are infected but show no signs of TB disease. When the bacilli are awake and dividing people are said to have 'active TB'. TB can affect any part of the body but is most common in the lungs and lymph glands. People with active TB affecting the respiratory tract can infect others but not all people with respiratory TB are infectious. Other forms of TB e.g. lymph or bone are not infectious. The microscopic bacillus hitches a lift on an aerosol of tiny droplets of mucus and saliva produced when an infectious person talks, coughs or sneezes - others then inhale these droplets. In poorly ventilated areas the bacillus can remain suspended for several hours. Most people who get TB have had a prolonged exposure to an infectious person - usually someone in the same household. It is extremely rare for children with TB disease to be infectious - children get TB from adults with active respiratory TB (HPA).

The majority of TB contacts experience nothing. Studies have demonstrated that only about 30% of healthy people closely exposed to TB will get infected and of those only 5%-10% will go on to develop TB disease. Young children exposed to TB are more likely to develop disease than healthy adults. What happens to the TB bacilli once in the lung is largely determined by individual immune response - 70% of healthy TB contacts will completely eradicate the bacilli and show no signs of infection, the remainder will become infected and have a positive reaction to a skin test. For the 5%-10% who go on to develop TB disease the risk is greatest within the first 5 years following infection. A small number of people who become infected develop what is called primary disease, usually within 8 weeks of exposure. This can pass unnoticed and usually resolves without treatment leaving a small scar on the lung and surrounding lymph nodes that can be seen by chest X-ray. Children are more likely to develop primary disease than adults. If the immune system cannot kill or contain the bacilli they multiply resulting in damage to the surrounding tissues. TB bacilli can live in almost any part of the body so the effects are extremely varied depending on the site of disease (WHO; HPA).

Tuberculosis is diagnosed by contact tracing, this is done by looking for source of contact; screening suspects with Monteux or heaf test or by passive method – clinical presentation. Most undeveloped countries with inadequate funds use sputum smear microscopy for diagnosis. This is because it is fast, cheap, realistic and receptive to patients with complex pulmonary TB, even though it is not receptive to those with early or extra pulmonary TB (Dines, etal., 2007). TB can be prevented by Bacillus Calmette Guerin (BCG) immunisation. This vaccine increases the body immunity and protects against the most severe forms of the disease known as TB meningitis. At extreme cases, TB can be treated with a chemoprophylaxis like Rifampin, Isoniazid, or Rifampin plus pyrazinamide depending on the immunity of the patients.

Global Epidemiology

Throughout the nineteenth and early twentieth century TB was rife in the cities of Europe and North America - London and New York were two of the worst affected cities. TB in the England, and other industrialised nations, declined rapidly last century but never went away. Today, an estimated one third of the world's population - nearly two billion people - is infected. Nine million people a year develop the active disease and nearly two million die - one TB death every twenty seconds.

TB was declared a global health emergency by the World Health Organization in 1993. Nearly all countries in the world are now affected by the global resurgence of TB caused primarily by increasing poverty and poor access to health services, migration and HIV, overcrowding (WHO; HPA; Walls, T., and Shingadia, D., 2003).

Evidence based studies show that about 15 million people infected with HIV also suffer from tuberculosis and out of the 3 million HIV deaths in 2003, 600,000 were traced to tuberculosis (WHO, 2005; Hernandez, etal., 2008).

           

                     Table 1.   TB case notification rates, 1990–2007

Region	1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Africa America Eastern Mediterranean Europe South East Asia Western Pacific	82    78      80   75     96     86      97       97      108   115   117   126   143   150   160     157     161  158  32    34      34  22     31      33     32        32       32     29     28     27     27     26     27       26      25     24 61     80      27  49     28      28     33        30       50     36     29     34     38     40      45        54     59     68 29     27      29  28     28      33      37       41        40     43     43     42     43     41     40         41     41     39 131  131     97  93     92      97    100       88         84     95     90     89     92     94    101       105  112  115 59    50      49  46     46       51      54        53        50     49      47     47     47     57     67        73    75     77
Global	71   69       57  55    56        59      63       60         61      63     61      62     65    69     75        79    82     84

Rates are per 100 000 population. From 1995 on, number shown is notification rate of new and relapse cases.                                 Source: WHO, 2009.

Data from WHO indicates an increase in TB cases from 9.3 million in 2007 to 9.4 million in 2008 as a result of poverty and increase in population. Out of the 9.4 million in 2008, 1.2 – 1.6 million were HIV/AIDS positive. 78% of the HIV – positive TB cases was in Africa and 13% were in South East Asia. In the same 2008, 11.1 million prevalent cases of TB were reported, comparable to 164 cases per 100,000 populations. The data indicated that majority of TB cases occurred in India (55%), Africa (30%), with significant but little size of the cases occurring in the Eastern Mediterranean Region (7%), European Region (5%), and Americans (3%). 22 Countries with high burden of TB cases ranked by WHO according to their high incidence of TB accounted 80% of all cases worldwide. The first five of these countries according to incident cases are India (1.6 – 2.4 million),China (1.0 – 1.6 million), South Africa (0.38 – 0.57 million) and Indonesia (0.34 – 0.52 million). The first two among the five countries accounted for 35% of cases globally (WHO, 2009).

Research has shown that three factors was responsible for re – emergence of tuberculosis and they are drug – resistant TB, co – infection with HIV and lack of appropriate access to medical care due to social and economic deprivation (Gandy, M., and Zumla, A., 2002). In 2007, 27 countries were reported to have accounted 85% of multidrug resistant tuberculosis (MDR – TB). 15 of the 27 countries were from the European countries and an estimate of 500,000 MDR – TB was reported globally with India (131,000), reporting the highest MDR – TB cases worldwide  and 57 countries reporting a case of XDR – TB (WHO, 2009).

Evidence from WHO indicate that out of the 1.3 million deaths occurred in 2008, 0.5 million deaths occurred in women with HIV negative incidence cases of TB. The same goes for HIV positive TB deaths which was estimated to be 0.5 million. The report shows that the addition of the number of deaths of both HIV – negative and positive people is liken to 28 deaths per 100,000 populations (WHO, 2009).

Statement of the problem in England

Tuberculosis resurgence in England over the last ten years swelled by 25% and is still growing as 1700 cases occur each year more than in the late eighties when the disease is at its lowest. Tuberculosis in England is more common among inner city inhabitants as evidence based studies show that every two out of five cases occur in London (DH, 2004). This is because most cases in England are as a result of high immigrants, overcrowding and homelessness. Evidence based studies show that most TB patients in England were born abroad (Crofts, etal., 1991; Breathnach, etal., 1998; HPA, 2003; DH, 2004; Ohkado, etal., 2004).This is because people are at risk of TB if they have lived in parts of the world where the disease is common. TB follows a pattern of migration and it is therefore more common in certain ethnic groups especially if they were born abroad. Research has shown that the burden of TB in England is concentrated on Multi – drug resistant tuberculosis, hard to reach population and innovations for new vaccines. Co – infection with HIV is found to be fairly small in England compared to other developing countries of the world like India. Evidence show that 3% of people with TB are HIV positive in England (DH, 2004). 

                                        Table 2: Tuberculosis case report in England, 2000 – 2008

Year	Number of cases	Rates (per 100,000)
2000	6075	12.3
2001	6296	12.7
2002	6296	12.7
2003	6691	13.4
2004	7011	14.0
2005	7763	15.4
2006	7828	15.4
2007	7736	15.1
2008	7970	15.5

                                                        Adapted from (HPA).

                   Figure 1. Tuberculosis case rates by place of birth and ethnic group, England, 2002-2008

                                                     Source: (HPA)

Hard to reach populations include the homeless (those without permanent accommodation, sofa surfers, hostel accommodation), mobile travellers, alcohol and drug users, migrants and those with minimal income or educational levels (NHS, 2010).These people are easily affected by the disease because of their inconsistency in adhering to TB screening, treatment and  loss to follow up. Evidence show that these factors increases risk of TB infection, discontinuation of regimen, chances of MDR – TB and co – infection with HIV. These factors underline the reasons why management of Tb in hard to reach populations are very difficult due to lack of basic information and history about them. A report from NHS quoted a survey in London which stated that hard to reach population estimates 17% of TB cases in London, half of MDR – TB and uncompleted regimen (NHS, 2010).

However, global research for a new vaccine is a good development to end the threat that tuberculosis poses to the world. Bacille Calmette – Guerin (BCG) has been effective in protecting people against tuberculosis as it is a live attenuation of mycobacterium bovis – a strain that causes Tuberculosis. Irrespective of the success that this vaccine has registered in the last century, it is also a threat to tuberculosis management. Studies have shown that long time usage of BCG vaccine against TB has proven successful (NHS 2010; Antas and Castello – Branco, 2008) and has been a platform for development of new vaccine after the discovery of the demographic factors that have affected BCG in the last century (Antas and Castello – Branco, 2008). Present innovation for new vaccine involves changing the widely used BCG vaccine with an improved recombinant version of cellular CD8+ T cell response or with the real strain of the causative organism itself and increasing the immunity with a virally vectored vaccine. An NHS evidence report stated that “Several such candidate vaccines are now being evaluated in clinical trials, including Modified Vaccinia virus Ankara (MVA) expressing Ag85A (MVA85A); Adenovirus expressing antigen 85A, B and TB10.4; and a fusion protein of two antigens, M72 with adjuvant. One of the factors most hampering TB vaccine developments is the lack of a validated immunological correlate of protection. A strong cell mediated immune response is required for protection, and certain cytokines such as interferon gamma and tumor necrosis factor alpha are essential. However simple measurement of the levels of these cytokines has not been found to correlate with protection. At present the only way the efficacy of the new generation of TB vaccines can be evaluated is in large, expensive and time consuming Phase Iib/ Phase III efficacy trials in high incidence populations within TB endemic countries. The first of these new generation vaccines has now entered into efficacy testing, and although there are many challenges in the development of a new TB vaccine, there is optimism within the field that considerable progress has been made over the last 10 - 15 years" (NHS, 2010).