Environmental Epidemiology; Its Classification, Prevention and Control

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Environmental epidemiology is the branch of epidemiology that focuses on how various environmental factors contribute towards diseases. These diseases are waterborne, foodborne, or airborne. According to World Health Organization(WHO) 50.4 million deaths occurred worldwide in 2012 out of which 12.6 million deaths were due to unfavorable environmental factors.

Classification of Environmental Determinants:

There are several environmental determinants and every environmental determinant cause several diseases in human beings and animals.


Figure no.1: Classification of environmental determinants for disease production

Classification of environmental epidemics:

Generally, environmental related diseases can be classified as following:

• Waterborne diseases
• Airborne diseases
• Foodborne diseases
• Vectorborne diseases

Water-related diseases:

The word “borne” means “carried or transported by the thing specified.” Hence, waterborne diseases are the diseases which are transported by water. The most common examples include diarrhea and cholera. The most common cause of diarrhea and cholera include drinking water and food ingestion that contains Campylobacter link, Escherichia coli link (E. coli), Salmonella link, Shigella link and Vibrio cholerae respectively. According to research, more than 5 million people die each year because of water related diseases alone.

Classification of water-related diseases:

Water-related diseases are further classified into four categories and this classification was first done by Bradley in 1972.
Following is the Bradley’s classification of water-related diseases:

Bradley’s Classification of water-borne diseases

1-Waterborne Example
Classical Typhoid
Non-classical Infectious Hepatitis
2-Water-washed diseases
Superficial Trachoma, scabies
Intestinal Shigella dysentery
3-Water-based
Water-multiplied percutaneous Bilharziasis
Ingested Guinea worm
4-Water-related insect vectors
Water biting Gambian sleeping sickness
Water breeding Onchocerciasis

Waterborne diseases:

Waterborne diseases are caused by microorganisms present in drinking water. The most common examples include diarrhea and vomiting. Waterborne diseases are caused by many kinds of bacteria, viruses, protozoa and parasites the most common types of bacteria which cause diseases are Campylobacter link, Escherichia coli link (E. coli), Salmonella link and Shigella link.
Water-related diseases are just not simply waterborne diseases and significance of waterborne diseases cannot be denied. [e.g., Payment et al. (1997) shows that 14% to 40% of gastrointestinal diseases were attributed to the diseases which were caused by consuming tap water meeting North America’s microbiological quality requirements. Hence, other water related diseases are of environmental and epidemiological significance particularly in developing countries.

Figure no.2

 Salmonella bacteria

Figure no.3

E. coli bacteria

 

Prevention and Control:

Waterborne diseases can be prevented and can be controlled by improved water quality and sanitation. Everyone has a right to clean water and public water supplies should be free from microorganisms causing diseases. Moreover, public awareness should be created about waterborne diseases and in case of contamination in drinking water in underprivileged regions treatment plants should be installed.

Water-washed diseases:

Bradley’s classification of water-related diseases introduced a very important category called water-washed diseases. Water-washed diseases are the diseases which are caused by using insufficient quantities of water regardless of its quality for personal and domestic hygiene. According to his study most of the waterborne diseases are transmitted by watershed route and the later is more epidemiologically harmful when it comes to water scarce areas typically in developing countries. Moreover, areas where water is available but not used in enough quantities can also become victim of water-washed diseases.

Prevention and Control:

Improved water quantity, availability, reliabilitty and hygiene education are the preventions and controls of water-washed diseases.

Water-based diseases:

Water based diseases can be classified into bacterial, helminthic and fungal diseases. These diseases include:
Bacterial: Leptospirosis Tularemia Legionellosis
Helminthic: Schistosomiasis Clonorchis’s Fasciolopsiasis Guinea worm infection
Fungal: Pulmonary hemorrhage due to Stachybotrystara infection.

Prevention and Control:

Decrease contact with contaminated water; improve domestic plumbing; public education sanitation; treatment of excreta or wastewater prior to reuse; public education.

Water-related insect vectors:

These diseases are caused by insects which breed and grow on water examples include Malaria, dengue and yellow fever etc.

Prevention and Control:

Avoid walking across breeding sites and allow less contact. Destroy those sites having breeding of insects such as mosquitoes. Better storm-water management systems and public awareness is the key to prevent such diseases.

Airborne diseases:

Airborne diseases are the diseases which can be caught through air. Several bacteria and viruses are being transferred through air from one human to another. Particulate matter and aerosols become the source on which viruses and bacteria can grow and hence can be transferred. Airborne diseases can be caused by poor ventilation or poor air exchange. Airborne diseases cause flu or cold and they include the following symptoms:

• Cough
• Chill
• Muscle pain
• Body aches
• Sneezing\Sore throat
• Stuffy nose
• Sinus pressure
• Sore throat

There is a new addition in airborne diseases of our generation and that is diseases by air pollution. Massive industrialization and poor transportation infrastructure causes a lot of chemicals in the air to react and form hazardous compounds resulting in Los angels and London type smog. Pollution from such sources cause aggravated asthma many cardiovascular and respiratory illnesses. It is a research that shut down of iron, coke and steel factory resulted in reduced wheezing among children of less than 2 years old. In another study it has been observed that 24-hour exposure to PM10 resulted in life-time asthma.Moreover,SO2 exposure in the first year of life resulted in life-time asthma as well. Community air pollution exposure depends upon
many factors the most important one is the industrial proximity of the residential communities. Community air pollution has been reported to cause asthma, bronchitis, cardiovascular diseases, skin infections and eye irritation.

Figure no.4

 Figure no.5

Foodborne diseases:

These diseases are transmitted by drinking contaminated food and water. Such diseases are caused by bacterial and viral infections transmitted by microorganisms present in food or water. Climate change and water pollution is going to make condition even worse. Food systems are complex and there is not a straight relationship between climate change and foodborne diseases. It has been studied that the flooding can cause diseases to spread as water from one crop can take the microorganisms to another crop system.
As an environmental engineer we should know that how environmental systems can become hazardous to health. Heavy metals accumulation in vegetables and fruits is another problem for health of people. Lead, cadmium, mercury and arsenic are the most reported heavy metals consumed by contaminated food.
Food contamination can happen at any stage from process to production by contaminated water, air and contaminated soil. It can cause severe gastrointestinal, neurological and immunological symptoms. Contamination in foodstuff is often carcinogenic. Hence, represents a major burden on disability as well as mortality.

Prevention and Control:

Foodborne diseases can only be avoided by preparing the food in hygienic conditions ,using clean water and should use clean air.

Figure no.6

Figure no.7

Vectorborne diseases:

Vectorborne diseases are the diseases which are transmitted by vectors. Vectors can transmit diseases from animals to humans and from humans to humans. Most of them are blood-feeding insects. They suck the blood from an infected host and later inject the blood in another human being hence causing to spread the diseases.
Vectors have several breeding grounds. They can grow on stagnant water and contaminated water. According to W.H.O 17% of the infectious diseases are Vectorborne diseases. Most common types of diseases include malaria and dengue fever. Another risk of vectorborne diseases is climate change. As temperature of the northern region is going to increase vectors will move towards those regions and hence the inhabitants will die as they do not have developed immunity against such infections.

Prevention and Control:

Proper solid waste management, removal of all water stagnant sites, using nets to protect exposure to mosquitoes can reduce the risk of these diseases.

Figure no.6

 Figure no.7

(Improper solid waste management)

 

Author: Rabia Nusrat

Rabia is an environmental engineer from University of Engineering and Technology Lahore and currently working in EveryWater as a graduate engineer trainee.

 

References:

Buteau, S., Geng, X., Labelle, R. and Smargiassi, A. (2020). Review of the effect of air pollution exposure from industrial point sources on asthma-related effects in childhood.
Ascelibrary.org. (2020). Water- and Excreta-Related Diseases: Unitary Environmental Classification | Journal of Environmental Engineering | Vol 125, No 4. [online] Available at: https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%290733-9372%281999%29125%3A4%28334%29 [Accessed 23 Feb. 2020].
World Health Organization. (2020). Public Health, Environmental and Social Determinants of Health. [online] Available at: https://www.who.int/phe/en/ [Accessed 23 Feb. 2020].

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