Module 3: Environmentally-Related Infectious Diseases
The burden of disease in the developing world seems easily remedied by making desired treatments and vaccinations more readily available. While these certainly play an important role in eradicating many illnesses, especially in developing countries, it is important to also focus on improving the environmental conditions in urban and rural settings in developing countries. A significant number of diseases and injuries are impacted by environmental risks. This 'environmentally-mediated' disease burden is much higher in the developing world than in developed countries. The populations of developing regions who lack many basic resources and healthcare access are most vulnerable to environmentally-mediated diseases. Many World Health Organization studies have examined the collective disease burden attributed to environmental risks globally and regionally, quantifying the amount of death and disease caused by factors such as unsafe drinking water, sanitation problems, and indoor and outdoor air pollution. These reports confirm that approximately 25% of the global disease burden, and more than one-third of the burden among children, is due to modifiable environmental factors.(1)
Neglected tropical diseases are a symptom of poverty and disadvantage. Those most affected are the poorest populations who often live in remote, rural areas, urban slums or in conflict zones. With little political voice, neglected tropical diseases have a low status in public health priorities.(2)
However, there is good news. Many measures can be taken almost immediately to reduce this environmental disease burden. Just a few examples include the promotion of safe household water storage and better hygiene measures, and control of the use of toxic substances in the home and workplace. This modules provides a comprehensive review of major neglected tropical diseases. They cause severe pain and life-long disabilities and are often less visible and have a low priority. The good news is that many of these diseases can be treated with simple, inexpensive medications. There is a need for this type of treatment and prevention to be scaled up by governments and organizations.
Trachoma is the world’s leading cause of preventable blindness. Trachoma is an infectious disease of the eye caused by the bacterium Chlamydia trachomatis, which is spread easily by contact with an infected person’s hands or clothing, or by flies that have come in contact with the eyes or nose of an infected person. Infected individuals do not instantly go blind; instead, the disease manifests gradually. Scarring from repeated infections causes the eyelashes to turn inward and scratch the cornea, leading slowly and painfully to complete blindness. Since trachoma is transmitted through close personal contact, it tends to occur in clusters, often infecting entire families and communities. Over 8.2 million people living today have advanced trachoma (trichiasis) and face visual impairment or blindness unless treated by a simple surgical procedure.(3)
Blindness from trachoma strikes adults in their prime years, hindering their ability to care for themselves and their families. Women, traditionally the caretakers of the home, are three times more likely than men to be affected by the disease. When a woman can no longer perform vital activities for her household, an older daughter is often removed from school to assume her mother’s duties, thus losing her opportunity for a formal education. In some communities, the disease is so common that blindness from trachoma is simply accepted as a fact of life.(4)
Trachoma is treatable and preventable with an approach known as the SAFE strategy. Recommended by the World Health Organization, the SAFE strategy is a comprehensive public health approach that combines treatment (Surgery and Antibiotics) with prevention (Facial cleanliness and Environmental improvement). The strategy works as follows:
S= Surgery to correct advances of the disease
A= Antibiotics, Pfizer-donated Zithromax, to treat infected individuals
F= Face washing to reduce transmission
E= Environmental improvement through increased access to clean water and improved sanitation
Onchocerciasis, also known as river blindness, infects 37 million people of sub-Saharan Africa. It is the fourth leading cause of preventable blindness. 500,000 of those infected with onchocerciasis are severely visually impaired, and another 270,000 have been left permanently blind from the disease. People living near the fast-moving streams of Africa are at high risk since these areas are breeding grounds for the Simulium black fly. Infected flies carry larvae of the filarial parasitic worm Onchocerca volvulus from person to person. Larvae, which enter the skin at the black fly bite site, move throughout the body and then die, resulting in a variety of health problems including skin rashes and de-pigmentation, itching, and skin nodules. It can also result in visual impairment and blindness if larvae enter the eye. (7)
99% of cases are found in Africa. The severe socioeconomic impact of this disease prompted creation of an Onchocerciasis Control Program. This program included making treatment more widely available, and spraying of black fly breeding sites with environmentally safe insecticides. Community-driven distribution of the drug ivermectin has significantly reduced disease burden.(8)
Guinea Worm disease
Guinea worm disease, formally known as Dracunculiasis, is caused by the parasitic worm (nematode) Dracunculus medinensis. It is transmitted through ingestion of stagnant water that is contaminated with guinea worm larvae. Global spread of guinea worm disease has actually been significantly reduced in recent times. It may even be the first Neglected Tropical Disease (NTD) to be eradicated.(9)
In the human body, the larvae are released and migrate into body tissues, and develop into adult worms. Female worms move through the person’s tissue, causing intense pain, and eventually emerge through the skin, producing oedema, a blister and eventually an ulcer, accompanied by fever. There are no drugs available for treatment of the disease. However, protecting water sources and filtering contaminated water can help prevent spread.(10)
Disease Overview & Treatment
Schistosomiaisis is acquired by contact with freshwater sources where infected snails live who carry the disease. It is prevalent in 74 countries, with half of all recorded cases in Africa. The most susceptible populations include children under age 14, as well as individuals with chores around freshwater areas. Inside the body, the larvae develop into worms. Female worms release thousands of eggs which are passed out of the body and released into bodies of freshwater by urination or defecation. They migrate to snails and begin the cycle again. Some eggs trapped in the body migrate to specific organs and inflict major damage such as scarring and tearing of the bladder and kidneys. However, a single dose of praziquantel has been shown to reduce the severity of symptoms in those re-infected with the disease.(11)
Soil Transmitted Helminthes
Ascariasis, also known as roundworm, is an intestinal infection caused by the soil transmitted parasitic worm Ascaris lumbricoidesart. It is most prevalent in warm tropical and sub-tropical climates in Sub-Saharan Africa and Southeast Asia. The disease flourishes in areas with poor sanitation and poorly irrigated crops treated with wastewater. It is the most common human worm infection. More than 807 million people worldwide are infected with ascariasis, and more than 60,000 die from the disease annually. It is transmitted by accidental ingestion of ascaris eggs in contaminated food, water or soil. The larvae migrate into the bloodstream and cause severe coughing and wheezing. The eggs are then passed into the feces, where from the cycle continues. (12)
In 2001, the WHO adopted a resolution aimed at the “deworming” of 75% of all at-risk school children by 2010, the largest public health program ever attempted to date. The program is currently underway and has been able to achieve some success in reducing the severity of worm infections in some areas, particularly in Africa. Education efforts aimed at prevention through proper sanitation, hand washing and food preparation techniques are also critical to reducing incidence of the disease in regions of Africa.(13), (14)
Lymphatic Filariasis is common in tropical and sub-tropical climates, in both rural and urban areas where infected mosquitoes tend to breed. Initially, no symptoms may be present, but as the disease progresses, the following may occur: swelling or hardening of the skin, severe swelling/lymphedema of extremities or genitals, and “filarial fevers” which are episodes of severe swelling in chronic patients. It is transmitted by infected mosquitoes which bite humans and pass microfilariae into the skin. Larvae migrate through the body and settle in the lymphatic system, where they lay eggs that pass into the blood. The worms can live for up to six years here. When they die, they can cause severe disfiguring ailments.
Treatment and Prevention
Unfortunately, there is no cure or vaccine for the disease, but symptoms can be managed with a treatment plan. The treatment to reduce the symptoms of Lympathic Filariasis includes a combination of albendazole and diethylcarbamazine (DEC) medicines. Careful cleansing of the skin to remove bacteria can reduce or reverse skin or tissue damage. The WHO’s Global Program to Eliminate Lymphatic Filariasis aims to stop the spread of transmission and to lessen the severity of the disease in those already infected. In areas of high infection, DEC and albendazole are distributed once a year for up to six years to help stop the spread of infection. Hygiene education efforts are aimed at reducing acute episodes of filarial fevers and have been effective at lessening the social stigmas associated with the manifestations of the disease.(15)
Infection and Transmission
Tuberculosis (TB) is a contagious disease that spreads through the air. People who have TB in their lungs are infectious. Coughing, sneezing, or talking can propel TB bacilli into the air. Only a small number of bacilli need to be inhaled to infect an individual. If left untreated, an infected individual will on average infect 10-15 people. Sometimes TB can lie dormant for years, and when the immune system is weakened, the chances of becoming sick are greater. TB is highly prevalent in Southeast Asia, accounting for 34% of the global cases.(16)
People living with HIV are at a much greater risk for TB because their immune systems are highly compromised. 1.77 million people died from TB in 2007, equal to about 4800 deaths a day. TB is a disease of poverty, affecting mostly young adults in their most productive years. Per capita the global TB incidence rate is falling, but the rate of decline is very slow at less than 1%.(17)
TB is a worldwide pandemic. Among the 15 countries with the highest estimated TB incidence rates, 13 are in Africa. Half of all new cases are in six Asian countries (Bangladesh, China, India, Indonesia, Pakistan and the Philippines). Multidrug-resistant TB (MDR-TB) is a form of TB that does not respond to the standard treatments using first-line drugs. MDR-TB is present in virtually all countries surveyed by the WHO. Extensively drug-resistant TB (XDR-TB) occurs when resistance to second-line drugs develops. It is extremely difficult to treat these cases. WHO’s Stop TB Strategy aims to reach all patients and achieve the the Millennium Development Goals (MDG) target, which aims to to reduce by 2015 the prevalence of and deaths due to TB by 50% relative to 1990 and to reverse the trend in incidence. The MDG goal emphasizes the need for proper health systems and the importance of effective primary health care to address the TB epidemic. The Global Plan to Stop TB aims to achieve the MDG target with an investment of US $67 billion. (18)
Go To Module 4: Innovations in the Control, Treatment, and Prevention of Environmentally Related Infectious Diseases >>
(1) Prüss-Üstün, A., & Corvalán, C. (2006). WHO: Preventing disease through healthy environments: Towards an estimate of the environmental burden of disease. Retrieved 12 July 2010. <http://www.who.int/quantifying_ehimpacts/publications/preventingdisease.pdf>.
(3) “What is trachoma?” (2009). Retrieved 2 July 2010.
(6) “The seven most common NTDs: Trachoma.” (2010). Retrieved 2 July 2010. < http://www.globalnetwork.org/about-ntds/factsheets>.
(7) “The seven most common NTDs: River blindness.” (2010). Retrieved 2 July 2010. <http://www.globalnetwork.org/about-ntds/factsheets>.
(11) “The seven most common NTDs: Schistosomiasis.” (2010). Retrieved 2 July 2010. <http://www.globalnetwork.org/about-ntds/factsheets>.
(12) “Neglected Tropical Diseases.” Retrieved 1 July 2010.
(14) “Neglected Worm Infections Affect Millions.” (2008). Retrieved 2 July 2010. <http://globalnetwork.org/press/article/2008/9/30/neglected-worm-infections-affect-millions>.
(15) “The seven most common NTDs.”(2010). Retrieved 2 July 2010. <http://www.globalnetwork.org/about-ntds/factsheets>.
(16) “WHO: Tuberculosis.” (2010). Retrieved 7 July 2010. <http://www.who.int/mediacentre/factsheets/fs104/en/>.