Leprosy Why Certain Populations Vulnerable Biology Essay

History and Current Epidemiology of Disease. Leprosy is literally an ancient disease, one that has been around several millenary, get downing with the Ancient Greek and Egyptian civilisations. To derive better thought of what the current position of the Hansen’s disease is in this twenty-four hours and age, it is necessary to look into where it came from, and how it evolved into the disease it is today. Gordon Grice ( 2000 ) , writer of “ Where Leprosy Lurks ” , an article in the November 2000 issue of Discover Magazine, cites that the Hansen’s disease has gone back every bit far as 200 BC in Egypt, where four skulls were discovered to been infected the Hansen’s disease. Dr. Grimm ( 2005 ) , writer of “ The Global Spread of Leprosy Tied to Human Migration ” , besides believes that Hansen’s disease foremost originated in Egypt based on the comparative survey he conducted on the beginning of different strains of Hansen’s disease.

The spread of the disease to other parts of the universe was to a great extent aided by the major conquerings of imperiums such as that of Alexander the Great, who conquered East Africa and the Middle East and brought the disease back to Greece along with assorted spices and silks ( Grice, 2000 ) . From Greece, the disease spread around the Mediterranean basin as Romans introduced it into Western Europe ( Grice, 2000 ) . Over clip, this procedure was farther carried out as war, trade, and colonialism established a complex path of transmittal for Hansen’s disease that involved the migration and inflow of many people in many different parts of the universe. Throughout Africa, Europe, and parts of Asia, much stigma developed around people affected with disease. Many were frequently persecuted and isolated from the remainder of the community based on their status, giving rise to the term “ lazars ” ( White, 2009 ) . During the colonial epoch, many European missionaries believed that a grade of shame should be put on the disease because it was considered unhallowed ( Vaughan, 1991 ) . Furthermore, the popular belief among societies at this clip was that Hansen’s disease was a familial status that could merely be contracted by relations of lazars, and non anyone else ( Grice, 2000 ) . This premise was contradicted in 1870 when Father Damien, a Christian missionary on the Hawaii Island of Molokai, contracted the disease while he was working with Lepers ( Grice, 2000 ) . His instance was peculiarly challenging because it was apparent that he had contracted the disease from infected person, since he did non hold household history of the disease. This lead to a terrible panic among European societies as many people believed one could contract the disease merely by standing following to some one else. Although, this premise was put to rest in 1873, when Hanson discovered that the disease was caused by an infection of bacteriums called Mycobacterium leprae ( Grice, 2000 ) . In 1940, Dr. Guy Faget, a doctor at Carville Treatment Center, a specialised establishment designed for leprosy patients in the U.S. , discovered a remedy of leprosy by proving the putting to death rate of sulfone on the B ( White, 2009 ) . This intervention was really successful until M. leprae began to turn immune to dapsone, a sulfone derived function. This prompted the use of multidrug therapy, which began in 1981 when it was administered by the WHO utilizing a combination of dapsone, clofazimine, and rifampcin ( White, 2009 ) .

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Since 1981, the combination of these drugs has about decreased 90 % of Hansen’s disease ‘s prevalence, and the figure of registered instances of leprosy worldwide has dropped from 5.4 million to 211,903 instances in 2010 ( World Health Organization, 2010 ) . Furthermore, since 2000, 4 million leprosy patients have been cured, and over 14 million patients have been cured in the last 20 old ages with the aid of WHO, who now provide the multidrug therapy for free around the universe ( World Health Organization, 2010 ) . While the effectivity of these interventions has helped to significantly diminish leprosy rates around the universe, there are still countries of high leprosy prevalence in a choice few developing states. Dr. Felisa Lewis ( 2010 ) , a doctor at the Madigan Army Medical Centers, reports that 86 % of today ‘s worldwide instances occur in Brazil, India, Indonesia, Ethiopia, Philippines, Nepal, Tanzania, Thailand, Bangladesh, and Congo. The two states with the highest leprosy rates are Brazil and India severally, and between the two, they contain about 150,000 instances, over 71 % of the current 211, 903 instances ( World Health Organization, 2010 ) . Based on these statistics, it would interesting to look into this disparity through a evolutionary theoretical account by finding if these choice populations exhibit any type of familial susceptibleness to the Hansen’s disease.

Etiology/ Symptoms of Leprosy

Before building an evolutionary model to why worlds are vulnerable to leprosy, it is necessary to to the full understand the causes of the disease. The most familiar symptoms of Hansen’s disease are the visual aspect of one or more lesions on the tegument. Marcia Gaudet ( 2009 ) , the writer of the groundbreaking book Carville: Remembering Leprosy in America, concludes that one of the major misconceptions of Hansen’s disease is that there is a immediate loss of limbs, but this is non true as untreated leprosy ab initio starts out by interrupting nervousnesss in the organic structure, which finally cause a loss of temperature esthesis, loss of musculus control, and above all else, skin lesions. Most of these skin spots are non painful, and because the disease grows really easy compared to other bacteriums ( doubles every 14 yearss ) , it can go hibernating for months and even old ages, demoing no marks of symptoms. Leprosy transmittal is chiefly based in the respiratory, and is passed from individual to individual through the ejection of rhinal droplets when one sneezes or coughs ( Lewis, 2010 ) . Once it enters the organic structure, the B replicate within the Schwann cells and assail the peripheral nervous system, accordingly damaging nervus terminations, which leads to cut down sensitiveness and numbness in the organic structure ‘s appendages ( White, 2009 ) . As a consequence, a individual afflicted with Hansen’s disease could foster perplex his or her status by walking about barefoot and exposing themselves infections through unfastened lesions. Unfortunately, one time leprosy is left untreated, it can ensue in more terrible complications that include malformations in the limbs such as the “ claw manus ” , where the fingers become paralyzed in a claw-like place, “ penciling ” , which give the custodies and pess a shrunken and conceited visual aspect ( White, 2009 ) . Leprosy finally causes the impairment of limbs and external organic structure parts, for illustration, in many parts of Africa, Hansen’s disease is referred to as “ leonine ” or “ lion face ” because the B can place in the brow and give the outward visual aspect of king of beasts ‘s face ( White, 2009 ) . Leprosy can besides do devastation in the rhinal castanetss, gristle, every bit good as the country environing the eyes. Dr. Brand and Dr. Yancey ( 1993 ) , writers of Pain: The Gift Cipher Wants, concluded that until a decennary ago, Hansen’s disease was one of the prima causes of sightlessness in developing states as the disease ‘s B accumulate in the cornea and cause major harm in the eyes.

Proximate Explanation: Immunological Response of Leprosy

The proximate mechanisms that underlie leprosy chiefly revolve around the immune system of the septic person. Once M. leprae enters the organic structure, the immune system engages a response against the B that consequence in figure of reactions, such as hurting, febrility, and inflammatory tegument lesions. These responses are known as type 1 reactions because they result in an self-generated addition in cell-mediated unsusceptibility, which becomes activated when the occupying B ‘s antigens stimulate the organic structure ‘s defence cells. These cells, called lymph cells, attack the M. leprae antigens and bring forthing an inflammatory response to the organic structure that cause the assorted tegument spots associated with leprosy ( White, 2009 ) . The lymph cells chief map is to release certain chemicals that attract larger macrophages to the antigen build-up site, and help the macrophages in digesting the B since they can non really perform phagocytosis themselves. The B have a peculiar affinity to cooler countries of the organic structure such as the peripheral nervousnesss, which is why malformations in the appendages are the most distinguishable symptom of Hansen’s disease. Type 2 reactions of Hansen’s disease are inflammatory responses that are more comprehensive in their interactions within the organic structure. It mediates a humoral unsusceptibility, which is besides known as antibody mediated unsusceptibility, because it involves bring forthing certain antibodies that aim to destruct foreign antigens that invade the immune system. While humoral unsusceptibility is peculiarly effectual in contending assorted signifiers of pathogens, it uncharacteristically has small consequence against M. leprae, and normally increases with the badness of the disease ( Lewis, 2010 ) .

Both the type 1 and type 2 reactions form the footing of the two chief signifiers of Hansen’s disease: tuberculoid Hansen’s disease and lepromatous Hansen’s disease ( White, 2009 ) . Tuberculoid Hansen’s disease is a paucibaccillary status because it contains a little figure of skin lesions ( less than 5 ) , while lepromatous Hansen’s diseases, a multibaccillary status, can incorporate more than six skin lesions ( World Health Organization, 2010 ) . Lepromatous Hansen’s disease is the most contagious signifier of the disease because persons who have it contain a strong humoral response, but a weak immune response. As a consequence, their organic structures are unable to halt the proliferation of B, and they can non assist but let go of the bacterium into the environment ( Scollard, 2004 ) . Tuberculoid Hansen’s disease, on the other manus, is characterized by a stronger cell-mediated response because it allows persons to contend the B so that they do n’t prevail in the organic structure. This signifier is much less milder, less contagious, and unluckily, less common because of its passiveness ( Scollard, 2004 ) .

Ultimate Explanation: Why We Are Vulnerable to Leprosy

Based on what has been discussed about the history, epidemiology, etiology, and immunology of Hansen’s disease, the inquiry still remains why people in states such as Brazil and India are exceptionally susceptible to leprosy in comparing to other Third World states, . Evidence has shown that the rates of leprosy infections are significantly higher than rates of really developing the clinical signifier of the disease ( Lewis, 2010 ) . This disparity has shown that while initial exposure is a major factor that can find whether an person will develop leprosy, it is non the lone cause. For rather some clip, it has been suspected that there is familial sensitivity to leprosy as shown by the history of the disease, which was normally referred to as a familial status before Dr. Hansen ‘s find of its mycobacterial beginning. Finally, in 2001, the leprosy genome was decoded and a nexus was identified which showed that a specific stretch of DNA in 5 % of the universe ‘s population contained a important susceptibleness to the Hansen’s disease based on a deficiency of innate unsusceptibility to the disease, something that most persons have ( Gaudet, 2004 ) . Dr. Han ( 2008 ) et Al, leprosy research workers at the National Allergy and Infectious Disease Institute in Washington, D.C. , believe that Hansen’s disease ‘s pathogenicity is inherently connected to an person ‘s cell-mediated unsusceptibility, which as noted earlier, is a critical defence needed to protect persons against M. leprae antigens. Fortunately, about 90 % of the human race has cell-mediated unsusceptibility to leprosy, which has led research workers and evolutionary life scientists to believe that people who develop Hansen’s diseases have a certain familial sensitivity to the Hansen’s disease because they do non hold the proper immunological defences that provide them the ability to contend off the disease and prevent it from declining ( Comeu, 2003 ) . So while the disease may non be familial, there may be an familial susceptibleness to the disease that may weaken a individual ‘s immune response to leprosy.

This familial sensitivity has been synonymous with research workers around the universe, peculiarly McGill University ‘s prima familial scientists Erwin Scharr and Tom Hudson. With the aid of a squad of research workers, Scharr and Hudson ( 2003 ) were successfully able to insulate a subdivision in human chromosome 6 that has shown to do people more vulnerable to leprosy. Schurr ( 2003 ) lead the squad to India, Brazil, Thailand, and Ethiopia to analyze and roll up DNA samples from members of affected households. The research squad used cistron mapping techniques to look for common similarities in familial make-up between households affected with leprosy. They noticed that many brothers and sisters were both afflicted with leprosy because they inherited the same pieces of chromosome 6, and since siblings portion 50 % of the same cistrons, there appeared to be analogues between heredity and leprosy susceptibleness ( Comeu, 2003 ) . While the existent cistron has non been identified yet, Schurr and Hudson found that a specific country on chromosome 6 contains familial information that provides M. leprae a friendly environment to coexist in, basically supplying a choice for it over other bacteriums ( Comeu, 2003 ) .

Furthermore, the Major Histocompatibility Complex ( MHC ) , which is located on the short arm of chromosome 6, has shown to hold a of import interaction with CMI as it contains specific HLA type cistrons, which are human leucocyte antigens that contain cistrons related to the immune response in worlds ( Silva et al. , 2009 ) . These cistrons have late shown to modulate the clinical patterned advance of Hansen’s disease, and most significantly, increase the susceptibleness of infection ( Silva et al. , 2009 ) . Silva et Al. ( 2009 ) studied the polymorphous MHC familial system by carry oning a cross-cultural genome analysis on which HLA polymorphism has the greatest susceptibleness to leprotamous Hansen’s disease. The populations studied were Brazil, India, and Bangladesh. The consequences showed that a peculiar HLA cistron, specifically the HLA-DR2 venue, was present in about 90 % of the sample, reasoning that the cistron showed a discernible exposure to leprosy ( Silva et al. , 2009 ) . Interestingly, Fitness et Al. ( 2002 ) besides found out that the next HLA-DR3 venue was mapped among a bulk of patients in South American populations such as Surinam and Venezuela. The familial susceptiblenesss in these surveies were due to a malfunction in the HLA system, as the mutant HLA cistrons failed to relay peptides from the B to human T cells, thereby giving the organic structure the inability to protect itself from the infected M. leprae cells ( Silva et al. , 2009 ) . Consequently, an person with this susceptibleness would be less likely to defy the invasion of the M. leprae antigens because of defective cistrons in the HLA system. As shown by these surveies, it is evident that there is a familial exposure to leprosy among persons populating in figure of developing states, specifically Brazil and India. Is it a happenstance that both of these states have the highest rates of Hansen’s disease in the universe? Why is it that both of these states have proven familial sensitivities to leprosy when there are many other developing states like Brazil and India that do non expose any grounds of susceptibleness? While the reply is still unsure, there are a few implicit in factors that may supply penetration as to why these phenomenon is happening. The first measure might be to analyse the hazard factors associated with leprosy, such as poorness, low societal position, and hapless life conditions such as a deficiency of sanitation ( White, 2009 ) . While these factors are associated with both developed and developing states, they are more debatable in developing states, which may explicate why Hansen’s disease is more prevailing in the underdeveloped universe. Consequently, finding what hazard factors are selective for Hansen’s disease in Brazil and India is irrelevant, because these elements are consistent throughout other developing states every bit good, peculiarly 1s that do n’t exhibit any susceptiblenesss.

Although, on an evolutionary degree, one may be able to explicate Brazil and India ‘s familial exposure to leprosy based on the disease ‘s history of migration. Gene flow, which is the displacement of allelomorphs from one population to another, may be the most fit in explicating why states such as Brazil and India have high rates of leprosy. As one of the four chief procedures of development, cistron flow explains why migration and blending between one or more population can take to abnormalcies in cistron pools. Brazil is a state characterized by an exceeding diverseness that stems from the blending Black slaves that migrated from Africa to work for European colonists, most notably the Portuguese, during the 1500s ( Geographia, 2006 ) . Based on these migration forms, it may be possible that the cistron pools of both these populations mixed, making a familial exposure to leprosy over clip as both populations may hold been exposed to the disease prior to coming in contact with each other. This may be really plausible based on the beginning of leprosy, as it originated in East Africa and was brought over to Europe by migration through trade paths and imperium conquerings like the Greek imperium of Alexander the Great. The instance can even be made for India as Alexander ‘s imperium stretched over to Punjab, a northwest portion of India, go forthing behind many of his generals to set up Grecian regulation ( Marshall, 2010 ) . This could hold lead to a transportation and intermixing of allele frequences within the two populations, which may hold besides occurred when the British Empire came in and ruled India from 1858 to 1947.

While the reply is still unknown, Dr. Randolph Nesse and Dr. George Williams ( 1994 ) , writers of Why We Get Sick, supplying an alternate ultimate account as to why mutant cistrons, such as the 1s identified in the populations of Brazil and India, did non decease out. They argue that because natural choice selects for generative success, and non wellness, a mutant cistron may stay common if it does non diminish the mean figure of offspring, even if it may do enfeebling effects ( Nesse & A ; Williams, 1994 ) . Such is the instance of Hansen’s disease, which can frequently to be difficult to analyse because it exists in multiple signifiers which determine if the disease is serious plenty to prevail. Tuberculoid Hansen’s disease may take more than four old ages for the symptoms to develop, while the fatal lepromatous signifier develops much slower, taking every bit long as 10 old ages for the initial tegument lesions to go seeable ( Lewis, 2010 ) . Since there are no current statistics on the mean age of Hansen’s disease, and whether grownup leprosy patients have kids before they are diagnosed, it is hard to find if this mutate cistron hypothesis applies to leprosy. In any instance, there is no grounds that shows that leprosy affects birthrate, so an person could really good hold kids before they even know they have disease. Therefore, every bit long as the mutant cistron can passed itself off to the following coevals of offspring, the forces of equilibrating choice will go on to let it to distribute. While it is still unsure why this disease continues to prevail in a choice figure of developing states, the forces of cistron flow and migration, every bit good as the host cistron tract proposed by Nesse and Williams, provides a more knowing evolutionary penetration as to why leprosy continues to permeate throughout certain parts the development universe.


While there might be a assortment grounds why the HLA-DR cistrons are merely exhibited in minority of developing states such as Brazil and India, it is apparent that there is so a familial susceptibleness to leprosy. By analyzing the proximate mechanisms of the organic structure ‘s immune response to leprosy, it was concluded that persons who contained a mutant signifier of the HL-DR cistron on chromosome 6 lacked a proper cell-mediated unsusceptibility. Based on this abnormalcy, they are more vulnerable to contract the more fatal, lepromatous signifier, seting themselves at a selective disadvantage in comparing to other persons who do non hold this familial sensitivity. By analysing the history and beginning of Hansen’s disease, a account on why this exposure persists in merely a choice few populations. Whether this hypothesis is plausible or non, the of import thing to take away is that in order to to the full analyse a infective disease, one needs to measure all facets of the disease, including its ‘ history, epidemiology, etiology, and most significantly, its proximate causes ultimate causes. Just like a mystifier, a disease can non be looked in its entireness until all of its parts are connected and put together. Furthermore, while the informations in these surveies merely provided accounts about the population as a whole, it would be interesting to find which persons within the vulnerable population are at more hazard based on factors such as household family tree.


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