Infectious diseases are caused by organisms inside or outside the human body. These diseases are transmitted through bites from insects and animals, through contaminated food and water (Anderson & May, 1991). Many infectious diseases like measles can be prevented through vaccination.
Studies on genetics have indicated that indeed genetic variations have a direct link to vulnerability to infectious diseases. Interest for research into infectious diseases was motivated by the need to develop reliable disease control strategies. The research into the impact of genetic variation in disease resistance aims to present a window for establishing disease resistance traits. Much focus has been put on susceptibility to HIV and malaria but recently interest is being generated by parasitic diseases. The genetic architecture presents the role that evolution has played in resistance and vulnerability to infectious disease. Clustering Studies on families have suggested a strong genetic component to mycobacterial diseases such as leprosy.
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There have been numerous gene-based and genome-based studies on the genetic impact of Tuberculosis. WHO established that a meager 10 percent of those infected with TB developed the heterogeneous disease. This is to demonstrate that the host has a significant part in susceptibility. Pulmonary tuberculosis clinically characterized by fever, weight loss, persistent cough and abnormal chest X-ray. On the other hand, non-pulmonary TB’s symptoms are different dependent on the affected organs (Community Environmental Center & Electric Power Research Institute, 1996). A study of affected families from West and South Africa established evidence of susceptibility loci. In one family, it was on the 11 chromosome while on the other family, it was found on the Y chromosome. In a study of over 333,000 genes from 11,000 people, scientists found that there was an individual gene that was associable with an increased susceptibility to TB. The research sought to establish a genetic link to TB rather than an inherited condition (Kaslow & McNicholl, 2008). For TB, it was established that the genes that might cause a person to be susceptible to TB do not exist inside the current human population. A person with such a gene is likely to die way before they reach the average human reproductive age. A gene named rs4331426 is associated with a marginal increase in the risk of vulnerability to TB. This gene is expected to provide an avenue to further exploration of other genetic variances in susceptible individuals and eventually lead to an understanding of how bodies of sensitive people vary from those of resistant individuals (Rowan, 2010).
Tuberculosis is an airborne disease. While pulmonary Tb affects the lungs, extrapulmonary TB can affect any organ of the body. When a person with infected lungs talks or expel air from their lungs, the TB causing microorganisms are let into the air. A person that breathes this air becomes prone to contracting TB. Other means of contracting TB exposure to autopsy material, venereal transmission and also through the percutaneous transmission. There are cases where TB can be transmitted from animals to human beings. Such cases are through exposure to infected cattle, Monkeys, humans, parrots, sheep, goats, dogs, cats, fomites aerosols and bites. Primary TB does not have symptoms and is only recognize through a skin test. After the inhalation of the TB bacteria, however, repeated contact is necessary for one to get infected. In 90-95% of infection cases, the person with the highest immunity levels can limit the multiplication and growth of the bacteria. The limiting leads to an inactive infection that poses no clinical symptoms. An infected person is mot same as a sick person, in that, the infected person has the TB causing bacteria in their body while the sick person is affected and can spread the disease to others. In an infected person, the body’s defense mechanisms can resist and prevent them from becoming ill. Commonly TB is spread among family members, workmates or people who are exposed to each other for prolonged periods of time. Further, there is a higher probability of TB infection in areas that are closed or minimally ventilated over an extended period. Nonetheless, there have been recorded cases of TB transmission in airplanes (World Health Organization, Tuberculosis and air travel : guidelines for prevention and control., 2008).
Worldwide, TB presents a significant health problem. In 2008, the World Health Organization stated an estimated over 9 million incident cases and close to 13 million prevalent cases of TB worldwide. The deaths caused by TB were documented as over 1.5 million cases. The deaths were predominantly reported in Asia followed closely by Africa. Increased TB mortality rate in Asia followed by Africa (World Health Organization, 2009).
Tuberculosis prevalence is higher in; people surrounded by infected persons. In that, they remain continually exposed to the TB bacteria. Diabetic people are also prone to contracting the disease; this is because diabetes weakens the body’s resistance system reducing its ability to fend off the TB bacteria. HIV positive individuals are also more prone to active TB because HIV compromises the entire defense system of the body causing it to be unable to fight off the TB bacteria. Infants and aged are also very susceptible to TB. In infants, it is because they are yet to develop a fully functional immune system. In the aged, it is because they have a worn out immune system. Organ transplant and kidney failure patients have a high risk of contracting TB. The medicine used in organ transplantation suppresses the body’s defense system so as not to reject the foreign part. Kidney disease weakens the entire body including the security system. As a result, this makes it vulnerable to tuberculosis and other diseases (World Health Organization, Diagnostics for Tuberculosis – Global Demand and Market Potential : Nonserial Publication., 2006). Other individuals who are at a bigger risk are drug users, alcoholics, and a low-income persons who cannot get or afford proper medical attention; this has an adverse effect on the population’s health index. The WHO indicates that 33 percent of the global infections are reported in Africa (Jamison & World, 2006). This situation has been mainly contributed by insistence on cultural practices such as refusal to use drugs, use of traditional medicine and even their feeding patterns. In Asia, the high prevalence rates are attributable the vast populations in Asian nations.
Host-pathogen co-evolution can be defined as the adaptations and genetic alterations that occur in the interaction between a pathogen and the host. It is difficult to note such change in the human being or the host, thus looking into it from the pathogen view is more objective. Research has shown that different traits of the tuberculosis bacteria MTBC are adapted to various populaces. The MTBC has exhibited variant strains concerning global biogeographical population structures. The association between certain strains of the MTBC seems to be maintained in cosmopolitan environments where the host and the associated pathogen are bound to experience a degree of interaction (Gagneux, 2012).
A study of the same conducted in San Francisco found that strains of MTBC are majorly transmitted among their sympatric hosts. Sympatric transmissions on the other hand were closely linked to already established risk factors like HIV infection. It has been proven that there is a significant consistency with host specific adaptations in MTBC strains. In order identify host-pathogen co-evolution, it is important to note molecular changes in parts of the bacteria that are in contact with the human immune system. An essential feature of co-evolution in many diseases is a continuous defense race between the host immune system and the pathogen. Many pathogenic bacteria, viruses and protozoa escape the host immunity by changing their antigenic genes. When the test was taken on 21 human beings representative of varying biogeographical areas, scientists found that the essential genes of the pathogen remained largely unchanged as compared to their non-essential genes. The known human T-cell epitopes were found as the most conserved genes of the pathogen genome. This observation led the scientists to conclude that the immune responses by the T-cell might be of more benefit to the pathogen than to the host. It implies that instead of escaping from the resistance system, the pathogen needs the body to recognize its presence. When the host’s immune system responds, there is a massive tissue destruction and cavity formation which enhances transmission. The reason for the evolutionary conservation of the T-cell epitopes is so that they can contribute to the spread of the MTBC. Further support is by the fact that HIV-positive hosts with a low CD-4 T cell count are less likely to have cavitary TB as compared to those with a higher CD-4 T-cell count.
Cultural beliefs and customary practices may cause different health-related preferences and concepts; as such it may act as an impediment to seeking proper medical attention in case of illness. In Africa, for instance, there is still the use of traditional medicine men and herbs for treatment, this removes the probability of early detection of diseases as they concentrate more on curation than prevention. The drug used is not scientifically tested and proven to cure the disease. A classic case is in South Africa. Here the people have a belief that TB is as a result of breaking traditional rules that demand abstinence from sex following the demise of a family member or after an abortion. The people believe that this disease can only be cured by a traditional healer. Thus, it demands an approach to high cultural competence to introduce new testing and treatment approaches to the people of Africa.
After the foundation of the WHO, it expanded the immunization cover for Bacille Calmette-Gu?rin (BCG) the drug used for TB. The organization now aims to reach 80 percent of the affected countries in the recent future. Currently, the BCG vaccine is among the most used vaccines. It is estimated to reach about 80 percent of all newborn children in countries that have taken up the national childhood immunization program. In 2011, WHO estimated the presence of BCG in every country Due to the differences in the strains of the TB bacteria, high efficacy values for BCG have been recorded. BCG has been observed not to prevent the reactivation of dormant TB. In spite of this and the emergence of multi-drug resistant strain, BCG continues to be an important tool in the fight for a TB-free world. At the same time, countries with an aim to vaccinate every child had attained 54 percent for Ethiopia, 53 0ercent for Equatorial Guinea and an impressive 99.5 percent for China and India.
Tuberculosis vaccination is however not done in all countries; countries with high prevalence rates of TB vaccinate all children while countries with low TB risk like USA and England only give children considered to be at risk. In fact USA has never protected all children; England had a BCG vaccination campaign in 2005.
A release by the United Nations warned of the minimal budgets allocated to health in Africa. It noted that twelve years since the African countries made a formal commitment to allocate at least 15 percent of their state budgets to health; only six countries had done it. Globally Africa remains the sole continent, not on track towards halving TB deaths by the year 2015. Inadequate funding has resulted in inadequate medical facilities.
The link between genetics and infectious diseases remains marginal. However, this does not imply the nonexistence of the risk. Further research into this subject will indeed help in giving a deeper insight. TB has become the second highest infectious disease just behind HIV, thus serious efforts should be put in the fight against this disease. Immunization efforts should be geared up especially in areas highlighted as high risk areas. This would make a great shift towards the prevention of contracting TB. Further, the establishment of a bridge between culture and medicine is now very essential this will eliminate the misinformed beliefs that are held in societies about certain diseases. The mergence multi-drug resistant TB is poised to bring a new challenge to global health, this is largely attributable to host-pathogen coevolution dynamics. Essentially he TB bacteria seems to be finding new survival techniques, that is the reason behind the emergence of new strains of TB as well as the variations in the current strains.
The only way to contain Tb and other infectious diseases remains to be thorough immunization. When this is backed up by research efforts, the battle beteen humans and infectious diseases will definitely be contained.
- Anderson, R. M., & May, R. M. (1991). Infectious diseases of humans : dynamics and control. Oxford: Oxford University Press.
- Community Environmental Center, & Electric Power Research Institute. (1996). Tuberculosis resource guide. Upland, Pa: DIANE Publishers.
- Gagneux, S. (2012). Philosophical Transactions of the Royal Society B. Host Pathogen Coevlotion in human tuberculosis, 5.
- Jamison, D. T., & World, B. (2006). Disease and mortality in Sub-Saharan Africa. Washington, D.C: World Bank.
- Kaslow, R. A., & McNicholl, J. (2008). Genetic susceptibility to infectious diseases. New York: Oxford University Press.
- Rowan, K. (2010, August 10). Gene Linked to Tuberculosis Susceptibility Identified. Retrieved April 9, 2015, from Live Science
- World Health Organization. (2006). Diagnostics for Tuberculosis – Global Demand and Market Potential : Nonserial Publication. Geneva: World Health Organization.
- World Health Organization. (2008). Tuberculosis and air travel : guidelines for prevention and control. Geneva: World Health Organization.
- World Health Organization. (2009). Global tuberculosis control: WHO report 2010. Geneva: World Health Organization.
