Disease Vectors and Pathogens

Global eradication of yaws in underway. Yaws is a rarely fatal but highly disfiguring disease that is caused by spiral-shaped bacterium (Spirochete) Treponema pallidum pertenue. No cases have been seen in India since 2004 and hopefully, global elimination will be achieved by 2020.

Echinococcus granulosus causes cystic hydatid disease in humans.

Quinine is a natural alkaloid extracted from cinchona tree bark. It has been used for centuries to treat malaria by killing the Plasmodium parasites in red blood cells. Quinine does not cause malaria, kill mosquitoes directly, or prevent mosquito bites.

This is the sequence of larva formation in liver fluke.

Malaria primarily affects the spleen, causing splenomegaly (enlargement of the spleen). The malaria parasite (Plasmodium) infects red blood cells, which are then filtered by the spleen. The spleen becomes enlarged due to increased work in removing infected and damaged red blood cells. While the liver is also involved (malarial parasites initially infect liver cells), splenomegaly is the most characteristic clinical feature of malaria.

West Africa is the region of the continent historically and currently most prone to outbreaks of Yellow Fever, primarily due to environmental and vector conditions favorable to mosquitoes like Aedes aegypti.

Yes, the people working there get infected by a bacterium called anthrax, which causes a fatal blood disease called the sorter’s disease.

This is caused by the protozoan Leishmania.

Sleeping sickness is a disease caused by a protozoan parasite Trypanosoma brucei. The tsetse fly spreads it.

Predator-prey transmission of encysted larvae within prey animals (vertebrate or invertebrate) being eaten by predators where adult worms develop and produce eggs (e.g. Dracunculus larvae in copepods ingested by humans leading to guinea worm infection, Taenia cysticerci in beef and pork being eaten by humans, Echinococcus hydatid cysts in offal being eaten by dogs).

Rhabditid ‘threadworms’ have tiny bodies which become embedded in the host mucosa. Their life-cycle includes parasitic parthenogenetic females producing eggs which may hatch internally (leading to auto-infection) or externally (leading to transmission of infection or formation of free-living male and female adults). Super-infections by Strongyloides may cause severe haemorrhagic enteritis in humans.

Schistosoma japonicum is the only human blood fluke that occurs in China. It is the cause of schistosomiasis japonica, a disease that still remains a significant health problem especially in the lake and marshland regions.

Filariasis is a parasitic disease that is caused by thread-like roundworms belonging to the Filarioidea type. These are spread by blood-feeding black flies and mosquitoes.

Adult worms have a life-span of 1–2 years which means that individuals may be infected all their lives as worms die and new worms are acquired.