Global Burden of Diseases Caused By Unsafe Water
Zainab AKINTAYO
Civil Engineer ?? Data Scientist ?? Water and Environmental Engineer
Water quality is as important as the availability of water because unsafe water is a non-negligible cause of many diseases. But, did you know that water-borne diseases are not the only classes of disease caused by unsafe water?
I found out recently too, and that reemphasized the need to seek more knowledge, cos how much more do I not know?
Classification of Diseases Caused by Unsafe Water
1. Water-borne Diseases: Caused by directly drinking, ingesting water that has some pathogens in it. Diarrheal diseases caused by different pathogens like Rotavirus, Cholera, Shigella, Cryptosporidiosis, Hepatitis A and E, Polio. The best intervention would be to improve water quality.
2. Water-washed Diseases: Caused by poor hygiene due to lack of water as opposed to direct ingestion. Most water-borne diseases are also water-washed because they can be transmitted through hands and contact with other surfaces, e.g. Trachoma (transmitted by flies) which is the leading cause of preventable blindness, Acute Respiratory Infections which are transmitted through contact with pathogens on hands or other surfaces. These can be prevented by increasing the quantity of water to improve hygiene.
3. Water-based Diseases: Caused by parasites which live part of their life-cycle in water e.g. schistosomiasis (bilharzia) which affects 160million people globally mostly in the Sub-Saharan Africa, and Dracunculiasis (Guinea worm) which used to affect a lot of people but has reduced now. These can be prevented by targeting the aquatic organism host and protecting surface water bodies.
4. Water-related Diseases: Caused by insects which breed in water especially mosquitoes. An example is malaria which affects about 250 million people each year causing about 589,000 deaths, majority of which is once again in the Sub-Saharan Africa and affect children under the age of five. Dengue fever which is growing in numbers and causes explosive outbreaks especially in urban areas is another example. A good control mechanism would be to remove the habitats of the insects.
As at 2012, the global mortality recorded for these common diseases were;
I can’t be the only one that thought Malaria would have a higher global mortality figure than diarrheal disease, right?
The most important of the Water, Sanitation and Hygiene (WASH) diseases and a major contributor of the global burden of diseases is Diarrheal Diseases raking in about 1.5 million deaths per year, causing about 1 in 10 deaths for children less than 5 years i.e. about 1,000 child deaths per day. 56% of these deaths is attributed to inadequate WASH. It is therefore apparent that poor access to basic WASH services have a major impact in global deaths.
However, asides deaths as a burden of diseases, it is important to consider sickness which can greatly reduce the quality of life and this can be done using a metric called Disability Adjusted Life Years (DALYs).
Disability Adjusted Life Years
DALY = YLL + YLD
YLL: Years of Life Lost = Number of Deaths * Standard Life Expectancy at age of death in years
YLD: Years Lost to Disability/ Years Lived with Disability = Number of years you lived with the disability * Disability Weight.
Note: Each disability has a weight dependent on its severity defined by WHO.
Example 1: A person with a life expectancy of 70 years, lives a healthy life through to 70.
Therefore, there is no life lost due to premature death or due to disability.
YLL = 0
YLD = 0
Hence, DALYs = YLL + YLD = 0 years
Example 2: Life Expectancy = 80 years
Accident leading to death at age 70
YLL = 80 -70 = 10
Since, there’s no life lost due to disability, YLD = 0
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Therefore, DALYs = YLL + YLD = 10 + 0 = 10 years
Example 3:
Life Expectancy = 80 years
Contracted AIDs at age 36.
Started medication after 4 years, i.e., at age 40
Lives up to age 70 before death.
Disability Weight for full blown AIDs without medication = 0.5
Disability Weight for AIDs with medication = 0.167
YLL = 80–70 =10
Years spent with AIDs without medication = 4
Years spent with AIDs with medication = 70–40 = 30
YLD = Years Lost Due to AIDs without Medication + Years Lost Due to AIDs with medication
= (4 0.5) + (30 0.167) = 2 + 5 = 7
DALYs = YLL + YLD = 10 + 7 = 17
Now, imagine how high the DALYs of diarrhea that affects kids will be due to years of life lost.
As at 2008 according to WHO, Diarrhea causes 52.5 million DALYs per year, which is 3.1% of the global total and 9% of child disease burden, with my dearest country??, Nigeria standing tall at the number 3 on the list with 3.9 million DALYs.
Remember how I mentioned earlier that diarrheal diseases are water-borne diseases caused by pathogens? There are different classes of pathogens such as Protozoa, Bacteria, Viruses, and Helminths with the first three being the most important.
Classes of Pathogens
The first thing to note is that pathogens are very small, much more smaller than the human hair which is about 0.1 millimeter (mm) or 100 microns (μm) in diameter.
1. Protozoa: The largest class of pathogens with a size of 10–50 μm and are one-celled eukaryotes i.e. the cells have nucleus. Some protozoa form an egg-like cyst to survive harsh conditions such as extreme temperature, chemicals or prolonged periods without food and water. Many protozoa are parasites and cause diseases like malaria and gardia.
Entomoeba histolytica and cryptosporidium parvum are causes of severe diarrhea with the former causing amoebic dysentery/ bloody diarrhea which affects more adults than children and the latter commonly called crypto ?? is the leading cause of diarrhea in children. Crypto is the most commonly isolated pathogen after rotavirus, forming cysts of about 5 μm in diameter which are highly resistant to treatment with even chlorine having no effect on it. It is also a major cause of deaths among HIV/AIDs patients. The infectious dose (the amount needed to cause disease) for Crypto and other protozoa is low, even a single cyst can cause disease.
2. Bacteria: Unlike protozoa, bacteria have prokaryotic cells i.e. the cells do not contain nucleus. Bacteria are few μm in size, have varying shape such as spheres, rods, or spirals and can be found everywhere, in the soil, deep ocean and even acidic hot springs with a gram of soil or milliliter of water containing several millions of bacterial cells. The vast majority of which are harmless or even beneficial to humans. However, few like E.coli, Vibrio Cholera cause diseases such as cholera, trachoma or salmonella. Like most bacteria, E.coli is about 1–2 μm in size and is universally found in human and animal faeces but isn’t normally pathogenic, in fact it is the preferred indicator bacteria used to demonstrate faecal contamination.
However, some strains of E.coli called pathogenic e.coli cause diseases, of which one group is the enterotoxogenic E.coli (ETEC) which is found to be among top 5 pathogens isolated from children with diarrhea. Another one is shigella, a distant relative of e.coli. Together, both cause 1/3 of global mortality due to diarrheal diseases. Vibrio Cholera like its name is responsible for cholera which spreads very rapidly in the right conditions like places with overcrowding and poor sanitation and hygiene, and can cause severe diarrhea and death within hours if not treated. Cholera has an estimated 3–5 million cases and 100,000–200,000 deaths every year.
3. Viruses: The smallest pathogens, typically 0.1 μm (100 nanometers) or even smaller in diameter have no independent metabolism i.e. only grows on or reproduce within a living host cell and can’t multiply within the environment. Many viruses are host specific, causing diseases in humans or specific animals only. The most widespread water-borne viruses affecting humans are rotavirus and hepatitis A and E with the former being the main pathogen causing diarrheal diseases and the single most commonly isolated pathogen among children with diarrhea. It is particularly prevalent among the youngest children and infected people shed large numbers of rotavirus in their faeces.
The virus is also highly infective with only 10–100 virus particles needed to cause infection (meaning it also has low infection dose). Rotavirus is estimated to cause over 500,000 deaths each year in 2004, with more than 85% of these deaths occurring in Africa and Asia. Hepatitis A and E is spread through food, water or direct contact with infected people. Both are widely spread in the developing world in countries with poor sanitation and hygiene, with nearly all the children being infected before age 10.
Although Polio is nearly eradicated, it still remains an important water-borne virus with only 3 countries — Afghanistan, Nigeria and Pakistan remaining polio endemic.
4. Helminths/Parasitic worms: These invade human intestines or tissues with transmission mainly due to poor sanitation and hygiene. However, dracunculus medinesis (Guinea worm) is mainly transmitted through drinking water. Its larvae lives in freshwater, gets eaten by small aquatic insects called copepods, which are typically 1mm, big enough to be seen by the naked eye.
Once a person drinks water containing copepods, the hydrochloric acid in the stomach kills the insect and releases the larvae, matures into adult worms which can reach a length of nearly a meter and width of a spaghetti noodle. The worms migrate through the body and emerge through the skin often near the feet. The worm has to be removed slowly, winding it up and pulling it out of the body bit by bit over weeks, which is extremely painful and creates sores and blisters. Thankfully, because the copepods are large, guineaworm can be beaten without vaccines or drugs but through community-scale interventions which involve the protection and treatment of drinking water like using simple cloth or sand filters to readily remove them. This refers to the intervention for water-based diseases by targeting the aquatic organism host.