7 Module 08: Major Water Borne Diseases Part II

Dr. Sunil Mittal

8.1 Water borne protozoan diseases

It has been discussed in the previous chapter that water borne diseases are those that occur due to contamination of water with human, animal and chemical wastes. In this chapter, we will discuss briefly about the water borne diseases that are caused by protozoa and other parasites.

8.1.1    Amoebiasis

This disease occurs due to infection by Entamoeba. Two species of Entamoeba are known to infect humans. One is E. dispar (non-pathogenic) and other is E. histolytica (pathogenic).

Epidemiology

Amoebiasis is a worldwide disease. But most of its cases are reported in those countries that have bad sanitary and hygiene practices, e.g., tropical and developing countries. Estimated annual mortality due to this parasite is 40,000–70,000. This disease spreads mostly through fecal-oral route, by ingestion of cysts and also through contaminated food.

Taxonomy

Kingdom: Protozoa

Sub-kingdom: neozoa

Phylum: amoebozoa

Class: archamoebae

Family: Entamoebidae

Genus: Entamoeba

Species: histolytica

Patogenesis and Pathology

Initially, the cyst divides into four amoebae. After an incubation period of 1-4 weeks, the number of amoebae increases to eight. Usually, the infection is asymptomatic. E. histolytica destroys almost all the tissues of human body, liver and intestinal mucosa.

Life cycle

Entamoeba histolytica is responsible for amebiasis i.e., amebic dysentery. Entamoeba is a very common parasite in those areas where sanitation and hygiene are lacking. Life cycle of Entamoeba histolytica in humans begins with the ingestion of mature cysts via contaminated water (figure 1). Mature cyst undergoes excystation in the lower region of small intestine.

Excystation results in the production of metacyst. Metacyst divides rapidly to produce eight trophozoites. Trophozoites either migrate to large intestine and invade the intestinal mucosa or undergo encystation and pass out of the host through faeces.

Symptoms

1. Fulminating dysentery.
2. Diarrhea accompanied by blood and mucus.
3. Appendicitis.
4. Abscesses in the liver, lungs and brain.

Diagnosis

1. Stool examination showing trophozoites.
2. X-ray of the chest helps to detect whether the infection has spread to the lungs or not.

Preventive measures

1. Drugs for amoebiasis include metronidazole and iodoquinol.
2. Destruction of viable cysts by hyperchlorination or iodination.
3. Avoid consumption of contaminated water and food.

8.1.2     Cryptosporidiosis

Description

Cryptosporidium is a small protozoan that infects the respiratory and digestive tract of vertebrates. It is a parasite of mammals, reptiles, fishes and birds. It requires a host for its multiplication.

Taxonomy

Phylum: apicomplexa

Class: Conoidasida

Order: Eucoccidiorida

Family: Cryptosporidiidae

Genus: Cryptosporidium

Species: parvum

Life cycle

The causative agent of this disease is a parasite i.e., Cryptosporidium parvum. This parasite is present in the intestine of many birds and mammals. The oocysts enter the human body by the ingestion of contaminated food and water. The oocyst undergoes excystation in the small intestine and produces sporozoites. Sporozoites enter the epithelial cells and develops into merozoites. Merozoites undergo sexual reproduction and produce zygotes. The zygotes differentiate into thick walled oocysts. Oocysts are released into the environment and again the life cycle begins (as shown in figure 2).

Certain characteristics of Cryptosporidium facilitate its transmission through water.

These characteristics are:

1. Tremendous resistance to chemical disinfection: Cryptosporidium is highly resistant to chlorine disinfection. Cryptosporidium becomes inactive only after exposure to multiple disinfectants.
2. Persistence in the environment: survival rate of oocysts extend up to several months in surface water.
3. Small size: due to small size (4-6 μm) of Cryptosporidium, their removal is highly difficult.
4. High infectivity: ingestion of single oocyst can cause high level of infection.
5. Oocysts sheds in high numbers.
6. Oocysts of Cryptosporidium do not require maturation period after shedding with faeces. They may immediately infect new host.

Symptoms

1. Diarrhea
2. Abdominal pain, nausea, fever and fatigue.

Preventive measures

1. Avoid contact with contaminated water and feces.
2. Maintain hygiene to combat this parasite.

8.1.3    Giardiasis/beaver fever:

Giardiasis is a very common gastrointestinal disease characterized by chronic or acute diarrhea. Its causative agent is Giardia lamblia or duodenalis. In addition to diarrhea, G. duodenalis also results in mal-sorption. Children are more sensitive to this protozoan as compared to adults. Its transmission occurs by the ingestion of cyst contaminated water or contaminated food.

Taxonomy

Phylum: metamonada

Order: diplomonadida

Family: Hexamitidae

Genus: Giardia

Species: duodenalis

Incubation period: incubation period in humans is 1-45 days (figure 3).

Symptoms

1. Acute giardiasis: characterized by severe diarrhea, gastric pain, cramps, voluminous flatulence and anorexia.
2. Chronic giardiasis: intermittent diarrhea with periodic appearance of symptoms.

Treatment: there are number of drugs that are used for the treatment of giardiasis, such as benzimidazole compounds, nitroimidazole derivatives and acridine dyes.

                    Figure 3: Schematic representation of Giardia lamblia infection in human being

Prevention: number of Giardia can be reduced in drinking water using conventional water treatment processes such as filtration followed by physical or chemical disinfection. Chlorine is the most commonly employed method for disinfection. However, ozone, chlorine dioxide and UV irradiation is also used in some plants.

1. Untreated water from rivers, lakes and wells should not be used for drinking purpose.
2. Water should be boiled before consumption.
3. Good hygiene reduces the risk of transmission to others.
4. Contact should be avoided between contaminated items and food/water. Vegetables and fruits should be washed.

Diagnosis

Giardia spp. can be found in faeces by direct microscopic examination using Lugol’s solution. This method is having an advantage that it can be used for the detection of other parasites that cause diarrhea. Direct immunofluorescence can be used to detect the organism.

Other diagnostic methods include ELISA (enzyme linked immunosorbent assay) and immunochromatography assays.

8.1.4     Malaria

Malaria is a major health problem and its causative agent is Plasmodium. Different species of Plasmodium like P. falciparum, P. malariae, P. vivax and P. ovale are responsible for different types of malaria. Life cycle of Plasmodium begins with its entry into blood through the bite of an infected female Anopheles mosquito (figure 4). The infectious form of Plasmodium is sporozoite. Sporozoites enter the hepatic cells of the liver, undergo multiplication and result in the production of merozoites. Merozoites attack the red blood cells (RBCs) and rupture them. Rupturing of RBCs results in the production of a toxic substance termed as haemozoin. This toxic substance is responsible for chilling and high fever.

Symptoms

1. Chilling, fever followed by sweating.
2. Joint pain, vomiting, hemolytic anemia, jaundice, hemoglobin in the blood and convulsions.
3. Diarrhea
4. Burning micturition
5. Skin rashes
6. Ear discharge
7. Running nose and cough

Diagnosis

1. Microscopy: the standard method for the diagnosis of malaria is microscopic examination of thin and thick blood smears. This method is having high sensitivity. Moreover, various species of malaria parasite and their different stages can be easily distinguished.
2. Rapid Diagnostic Test (RDT): this test is based on the detection of those parasites that are present in blood circulation. Presently, National Vector Borne Disease Control Programme (NVBDCP) is supplying RDT kits for detection of P. falciparum within 24 hours of sample collection, at those locations where microscopy results are not available. The results should be read within specific time. The kit should be used within its expiry date and transported and stored under recommended conditions.

Treatment

Administration of chloroquine, amodiaquine or mefloquine. Artemisin Combination Therapy (ACT) has to be given in resistant areas while chloroquine is used in sensitive areas. ACT is a combination of artemisin derivative and lumefantrine or mefloquine.

Preventive measures

1. Insect repellants should be used.
2. Insecticide treated mosquito nets and spraying is highly effective.
3. Health education strategies promoting awareness of malaria.

8.1.5     Cyclosporiasis

Cyclosporiasis disease is caused by infection with Cyclospora cayatanensis. Cyclospora is a pathogenic protozoan transmitted by feces contaminated food and water. Cyclospora mainly infects the small intestine and causes an illness characterized by watery diarrhea. The symptoms appear between 1-7 days.

Taxonomy

Phylum: Apicomplexa

Class: Conoidasida

Order: Eucoccidiorida

Family: Eimeriidae

Genus: Cyclospora

Species: cayetanensis

Size of Cyclospora ranges from 7.7-9.9 μm.

Life cycle:

1. Infected individuals excrete unsporulated oocysts in their faeces (figure 5).
2. Oocysts undergo sporulation within 7-15 days under ideal environmental conditions (23-27° C).
3. Ingestion of contaminated water and food leads to the excystation of oocysts.
4. Sporozoites get released and infect the epithelial cells of small intestine.
5. Sporozoites undergo asexual multiplication producing meronts.
6. Meronts undergo differentiation into gametocytes (sexual stage).
7. Macrogametocyte and microgametocyte undergo fertilization and produce zygote.
8. This leads to the formation of oocysts.
9. Unsporulated oocysts are excreted into the environment.

Symptoms

1. Severe watery diarrhea, bloating, fever, stomach cramps and muscle aches

Diagnosis

Stool samples containing Cyclospora can be examined via microscopy, sporulation studies and molecular techniques. Samples are stored in 10% formamide for microscopic examination and 2.5% potassium dichromate for detection via sporulation study or microscopic techniques.

Treatment

1. Administration of trimethaprine-sulfamethaxozol (TMP-SMX).

Preventive measure

1. Avoid contact with contaminated water and food.

8.2 Water borne parasitic diseases

8.2.1     Schistosomiasis

Schistosomiasis disease is caused by a parasitic worm, Schistosoma (blood fluke). Snail is an intermediate host while human is a primary host. Infection by Schistosoma is a series of events that are illustrated through its life cycle (figure 6).

Taxonomy:

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Order: Strigeidida

Family: Schistosomatidae

Genus: Schistosoma

Species: mansoni

Life cycle

1. Eggs are excreted out either via urination or defecation.
2. Eggs undergo the process of hatching and produce miracidia.
3. Miracidia penetrate the intermediate host i.e., snail.
4. Inside snail body, miracidia include two generations of sporocysts and produce cercaria.
5. Infective cercariae penetrate human body.
6. During the penetration process, cercariae lose tails and become schistosomulae.
7. Schistosomulae migrate to liver via blood circulation and undergo maturation into adults.
8. Adult worms migrate to mesenteric venules of rectum.
9. Adult female worm lays eggs that circulate to the liver or excreted out in stools.

Symptoms

1. Abdominal pain, diarrhea and blood in stools.
2. Liver and spleen enlargement.
3. Accumulation of fluid in peritoneal cavity.
4. Hypertension of abdominal blood vessels.

Disease impact

• 20 million people suffering from schistosomiasis develop severe complications and sometimes bladder cancer.
• Chronic cases of this disease in children leads to anemia and malnutrition.

Preventive measures

1. Avoid contact with contaminated water.
2. Periodic treatment of affected populations with praziquantel.

Educational campaigns about the risk of infection while taking bath in ponds and fresh water lakes

                                                                   Figure 6: Life cycle of Schistosoma

8.2.2    Dracunculiasis/Guinea worm disease

Dracunculiasis is an infection caused by Dracunculus medinensis (guinea worm). Guinea worm is a nematode.

Taxonomy:

Kingdom: Animalia

Phylum: Nematoda

Class: Secrenentea

Family: Dracunculoidae

Genus: Dracunculus

Species: medinensis

Stages involved in the infection are:

• Infection occurs due to the ingestion of contaminated water. Contaminated water contains copepods which are infected with larvae of D. medinensis (figure 7).
• After ingestion, copepods die and release the larvae. Larvae penetrate the host stomach and intestine and enter the abdominal cavity.
• Male worms die after maturation while female worms migrate towards the subcutaneous tissues.
• After one year of the infection, female worm produces a blister on the skin. The blister ruptures and the female worm releases larvae.
• The larvae are ingested by a copepod.
• Ingestion of copepod contaminated water closes the cycle.

Life Cycle:

Symptoms

1. Difficulty in walking.
2. Allergic reaction, nausea, vomiting, diarrhea and asthmatic attack.

Diagnosis

Immersion of affected body parts leads to the development of characteristic white cloud, thus representing the release of larvae.

Treatment

No medications are available for the treatment of this disease.

Preventive measure

1. Early diagnosis.
2. Keep away the person from putting the wound in drinking water to decrease the spread of the parasite.
3. Always use filtered water only for consumption.
4. Affected body parts should be kept clean, bandaged and disinfected.
5. If pulled with force, emerging worms can be easily torn.

8.2.3     Taeniasis

This is a parasitic disease that occurs due to infection with tapeworm. Tapeworm belongs to the genus Taenia. Two pathogenic species of this genus are Taenia saginata (pork tapeworm) and Taenia solium (beef tapeworm). Humans are the definitive host of T. saginata and T. solium. Mode of transmission is the ingestion of contaminated water with eggs (figure 8).

Taxonomy

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Cestoda

Order: Cyclophyllidea

Family: Taeniidae

Genus: Taenia

Species: solium

Stages involved in Taeniasis are:

• Eggs of Taenia saginata and Taenia solium are passed with faeces.
• Cattle and pigs become infected by the ingestion of vegetation contaminated with the eggs of Taenia.
• Oncosphere hatches, invades the intestinal wall and migrates to striated muscles and develop into cysticerci.
• Cysticerci develop into an adult tapeworm.
• Adult tapeworm attaches to the small intestine by its scolex. Adult produces proglottids.
• Proglottids mature and migrate to the anus.
• Eggs contained in the proglottids are passed with faeces.

Symptoms

1. Intestinal disturbances, loss of weight, neurocysticercosis and epilepsy.

Incubation period

1. After the ingestion of larvae, eggs appear in human stools within 2-3 months.

Preventive measure

1. The fundamental prevention strategy is hygiene and sanitation.
2. Secondary measures include strict meat-inspection standards, livestock confinement, health education, safe meat preparation, mass drug therapy, and identifying and treating human and pig carriers.
3. Proper meat cooking.

8.2.4     Fascioliasis:

Fascioliasis is a parasitic worm infection caused by Fasciola hepatica (liver fluke). Diagnosis of this disease is very difficult as eggs are often missing in fecal examination. Transmission

Symptoms

1. Intestinal disturbances, loss of weight, neurocysticercosis and epilepsy.

Incubation period

1. After the ingestion of larvae, eggs appear in human stools within 2-3 months.

Preventive measure

1. The fundamental prevention strategy is hygiene and sanitation.
2. Secondary measures include strict meat-inspection standards, livestock confinement, health education, safe meat preparation, mass drug therapy, and identifying and treating human and pig carriers.
3. Proper meat cooking.

8.2.4     Fascioliasis:

Fascioliasis is a parasitic worm infection caused by Fasciola hepatica (liver fluke). Diagnosis of this disease is very difficult as eggs are often missing in fecal examination. Transmission occurs due to consumption of contaminated drinking water with encysted metacercaria (figure 9).

Taxonomy

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Order: Echinostomida

Family: Fasciolidae

Genus: Fasciola

Species: hepatica

Stages involved:

• Adult worm lives in liver and bile duct of sheep, humans and other ruminants.
• Eggs of the worm are passed out via defecation.
• Eggs hatch into miracidium inside water.
• Miracidium is either ingested or penetrates land snail.
• Miracidium then transforms into sporocyst, redia and cercaria.
• Cercaria leaves the snail and encysts as metacercariae on vegetation.
• Infected vegetation is eaten by sheep and adult moves to the liver.

Factors affecting the life cycle of liver fluke

1. Moisture content

2. Temperature

Symptoms

GIT disturbance, diarrhea, liver enlargement, cholecystitis, obstructive jaundice and anemia

Diagnosis and Treatment

Diagnosis of fascioliasis is based upon an increase in liver enzymes in blood samples.

Presence of fluke eggs in faecal samples indicates chronic fascioliasis.

Preventive measures

1. Triclabendazole is given in the treatment of fascioliasis.
2. Consumption of filtered water only.

There are many diseases that occur due to consumption of contaminated water. Major diseases have been discussed in detail.

Summary

In this chapter, water borne diseases were discussed in brief. Clearly, the important source of water borne infections was consumption of contaminated water and food. In the first part, major water borne protozoan diseases were discussed and all the stages involved in the infection process were elaborated via cyclic diagrams. Moreover, symptoms associated with each disease were discussed along with their preventive measure. In the second part, water borne parasitic diseases majorly caused by helminthes were discussed. Preventive measures included awareness programmes and maintenance of proper hygiene and sanitation.