Disease Vectors and Pathogens

Chagas disease is caused by Trypanosoma cruzi. Sleeping sickness is caused by Trypanosoma gambiense. Malaria is caused by Plasmodium falciparum. Plague is caused by Yersinia pestis.

Racial immunity is when different races within a species show differences in susceptibility to infections. In some parts of Africa, resistance to Plasmodium falciparum malaria is an example of racial immunity.

Dengue fever is transmitted specifically by Aedes mosquitoes, particularly Aedes aegypti. Anopheles mosquitoes transmit malaria, Culex mosquitoes transmit West Nile virus and filariasis, making Aedes the correct answer.

Rice water stool - watery, pale, flecked with mucus resembling rice water - is the classic diagnostic symptom of cholera. It's caused by the cholera toxin producing massive fluid secretion into the intestine.

Yellow fever virus is transmitted through Aedes mosquitoes (Aedes aegypti).

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This is the correct option. Wuchereria bancrofti causes elephantiasis, in which enlargement of limbs, scrotum and mammae of humans takes place due to infection.

Kala-azar (visceral leishmaniasis) is spread by the bite of infected female sand flies belonging to the genus Phlebotomus (Old World) and Lutzomyia (New World). Sand flies transmit the protozoan parasite Leishmania donovani.

Yellow fever is primarily transmitted by the Aedes aegypti mosquito. Aedes mosquitoes are also responsible for transmitting other diseases including dengue, Zika, and chikungunya viruses. Anopheles transmits malaria, Culex transmits West Nile virus, and houseflies are mechanical vectors for bacterial diseases.

Malarial parasites (Plasmodium) rupture from red blood cells synchronously, causing the characteristic fever spikes. The parasites are most abundant in peripheral blood immediately after the temperature rise, which corresponds to the release of merozoites from infected RBCs. This timing offers the best chance for detection in blood smears.

The trophozoite stage of Plasmodium develops within human erythrocytes (red blood cells) after merozoite invasion. Here, the parasite multiplies asexually, consumes hemoglobin, and develops into schizonts. The liver cells contain the exo-erythrocytic stages (sporozoites and merozoites), while the salivary glands of mosquitoes contain sporozoites, not trophozoites.

A digenetic parasite requires two hosts to complete its life cycle. Plasmodium vivax needs both a human host (asexual reproduction) and a mosquito host (sexual reproduction). Monogenetic parasites need only one host, and trigenetic is not a standard parasitological term.

Leishmania donovani causes visceral leishmaniasis, commonly known as kala-azar or black fever. Sleeping sickness is caused by Trypanosoma, amoebiasis by Entamoeba histolytica, and dengue fever by a flavivirus.

Malaria parasites infect and destroy red blood cells (erythrocytes) during their reproductive cycle. The spleen acts as a filter for damaged and abnormal blood cells, removing the massive numbers of dead erythrocytes resulting from malaria infection. This increased workload causes the spleen to enlarge (splenomegaly) as it accumulates the destroyed cells.

Female mosquitoes require blood proteins for egg development and have evolved specialized piercing mouthparts (proboscis) to penetrate skin. Male mosquitoes feed only on plant nectar and have mouthparts adapted for sucking liquids from surfaces, lacking the sharp, piercing structures necessary to break skin. This anatomical difference prevents them from feeding on blood.