Protozoan Diseases
Protozoans are single-celled, microscopic organisms. Unlike bacteria, protozoans have a more complex cellular structure with a well-defined nucleus (making them eukaryotes). Many protozoans live freely in fresh or marine water, but several are parasitic and cause serious diseases in humans.
Below is a detailed study of the major protozoan diseases, their transmission, treatment, and associated public health initiatives.
Pathogen | Disease | Transmission |
Plasmodium spp. | Malaria | Bite of infected female Anopheles mosquito |
Entamoeba histolytica | Amoebiasis (Amoebic Dysentery) | Contaminated food and water |
Giardia lamblia | Giardiasis | Contaminated water |
Toxoplasma gondii | Toxoplasmosis | Ingestion of undercooked meat, contact with infected cat faeces |
1. Malaria
2. Poliomyelitis (Polio)
Malaria is one of the most widespread and deadly vector-borne diseases in human history.
- Pathogen: It is caused by a tiny protozoan parasite called Plasmodium. There are four main species that infect humans:
- Plasmodium vivax (Most common in India)
- Plasmodium falciparum (Causes malignant malaria, which is the most severe and fatal form)
- Plasmodium malariae
- Plasmodium ovale
- Mode of Transmission: Vector-borne. The disease is transmitted to humans through the bite of an infected female Anopheles mosquito.
- Affected Organs: The parasite primarily attacks the liver and then enters and destroys the Red Blood Cells (RBCs).
- Symptoms:
- The classic symptom is a sudden onset of high fever accompanied by severe chills (shivering) that occurs in cycles (every 48 to 72 hours).
- Other symptoms include headache, muscle pain, nausea, and severe fatigue.
- Treatment and Management:
- Malaria is curable if diagnosed early through a blood smear test. The standard treatment involves antimalarial drugs such as Chloroquine.
- For falciparum infections, Artemisinin-based Combination Therapy (ACT) is recommended by the WHO.
- Clinical Note:
- The Plasmodium parasite requires two hosts to complete its life cycle: humans and the female Anopheles
- When the parasite ruptures the human Red Blood Cells, a toxic substance called hemozoin is released into the bloodstream. It is this hemozoin that causes the characteristic cyclical chills and high fever.
- Government Initiatives:
- National Framework for Malaria Elimination (NFME): India aims to achieve zero indigenous cases of malaria throughout the entire country by 2030.
- This operates under the broader National Vector Borne Disease Control Programme (NVBDCP), which heavily promotes the use of Long-Lasting Insecticidal Nets (LLINs) and Indoor Residual Spraying (IRS) in high-risk rural areas.
2. Amoebiasis (Amoebic Dysentery)
Amoebiasis is a highly common infection of the human gastrointestinal tract, especially in areas with poor sanitation.
- Pathogen: A protozoan parasite named Entamoeba histolytica.
- Mode of Transmission: It spreads primarily through the fecal-oral route by consuming food and drinking water contaminated with the cysts of the parasite. Houseflies act as mechanical carriers, transferring the parasite from infected feces to uncovered food items.
- Affected Organs: It infects the large intestine.
- Symptoms: Constipation, abdominal pain, cramps, and the frequent passage of stools containing excess mucous and blood clots.
- Treatment and Management: It is diagnosed through a stool test. Treatment involves a course of anti-amoebic antibiotics (such as Metronidazole). Prevention is highly dependent on basic sanitation, proper disposal of human waste, and drinking boiled or purified water.
- Key Point: While both bacterial dysentery (caused by Shigella) and amoebic dysentery cause bloody stools, amoebiasis is typically characterized by a more gradual onset and prominent mucous in the stool without a high fever.
3. Kala-azar (Visceral Leishmaniasis)
Kala-azar is a slow-progressing, potentially fatal disease caused by a blood parasite. In Hindi, “Kala-azar” translates to “Black Fever.”
- Pathogen: The protozoan parasite Leishmania donovani.
- Mode of Transmission: Vector-borne. It is transmitted to humans by the bite of an infected female Sandfly (Phlebotomus argentipes). The sandfly usually breeds in damp, dark, and muddy areas of rural homes.
- Affected Organs: The parasite attacks the reticuloendothelial system of the body, heavily infecting and enlarging the spleen, liver, and bone marrow.
- Symptoms:
- Recurrent high fever that lasts for weeks or months, significant weight loss, anaemia , weakness, and a notable darkening of the skin (especially on the face, hands, and abdomen).
- A classic physical sign is a massively enlarged spleen (splenomegaly).
- Treatment and Management: Kala-azar is completely curable if treated on time. The current preferred treatment in India involves a single-dose intravenous infusion of Liposomal Amphotericin B.
- Government Initiatives:
- National Kala-azar Elimination Programme: India has been running a highly focused campaign to eliminate Kala-azar. The strategy involves early diagnosis, free treatment, and aggressive vector control through indoor spraying in endemic states. The disease is primarily endemic to specific blocks in four states: Bihar, Jharkhand, Uttar Pradesh, and West Bengal.
