Disease Vectors and Pathogens

Trypanosoma parasites cause sleeping sickness or African trypanosomiasis or Chagas disease which is found in sub-Saharan Africa.

• The parasite which causes malaria, Plasmodium requires two different hosts a vertebrate intermediate host, such as a human, and an insect definitive host, also known as the vector i.e female Anopheles mosquito. 
• When the mosquito bites humans it ingests blood cells containing gametocytes. The mosquito digests the blood cells, releasing the male and female gametes, which fuse together and burrow into the mosquito’s gut wall, where they mature inside oocysts.
• After 8-15 days (depending on the species) the oocysts burst and sporozoites are released into the body cavity of the mosquito. From there, they travel to the salivary glands. when the mosquito bites these infective sporozoite enters the blood of the humans.
• Hence sporozoites are the infective stages of the malaria parasite is found in salivary glands of the mosquito.
• So, the correct answer is 'Salivary glands of mosquito'.

The plasmodium parasite is spread by female Anopheles mosquitoes, which are known as "night-biting" mosquitoes because they most commonly bite between dusk and dawn. If a mosquito bites a person already infected with malaria, it can also become infected and spread the parasite on to other people.

In the life cycle of Taenia solium, humans are the definitive host because they harbor the adult stage of the tapeworm in their intestine. Pigs act as the intermediate host where the larval stages develop.

The definitive host for both lifecycles is humans, but the intermediate hosts are different for each species. A cow is the primary intermediate host for Taenia saginata and a pig is the primary intermediate host for Taenia solium.

Sheep become infected with the liver fluke (Fasciola hepatica) by ingesting aquatic vegetation contaminated with encysted cercariae, which are known as metacercariae. The other stages listed are part of the life cycle but are not the infective stage for the final host.

Taenia solium also known as tapeworm is a pathogen that causes taeniasis. It enters the human body due to consumption of uncooked pork hence also known as pork worm. Thus, the correct answer is option A.

The pigs are the intermediate host for Taenia solium they are affected by the ingestion of the eggs. The eggs enter the intestine and penetrate the epithelial and reach the muscles. In muscles, they develop an infection known as Cysticercosis. The humans are affected by eating infected pigs. 

• Schistosomiasis, also known as snail fever and bilharzia is a disease caused by parasitic flatworms called schistosomes. The disease is spread by contact with fresh water contaminated with the parasites. The disease is especially common among children in developing countries, as they are more likely to play in contaminated water.
  
• Hepatitis is an inflammation of the liver tissue. Hepatitis is majorly caused by the virus known as infective hepatitis. Infective hepatitis is mainly spread by contaminated food and water.
  
• Diarrhoea is the condition of having at least three loose or liquid bowel movements each day. Diarrhoea lasts for a few days and can result in dehydration due to fluid loss. These infections are often acquired from food or water that has been contaminated by faeces, or directly from another person who is infected.
  
• Hence, these diseases may occur when children play bare-footed in pools of dirty water and flood water.

Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Ascariasis does not spread directly from person to person. Infection occurs by eating food or drink contaminated with Ascaris eggs from feces. The eggs hatch in the intestines, burrow through the gut wall, and migrate to the lungs via the blood. There they break into the alveoli and pass up the trachea, where they are coughed up and swallowed. The larvae then pass through the stomach for a second time into the intestine where they become adult worms.

• Wuchereria bancrofti is commonly called the Filarial worm as it causes Filariasis or Elephantiasis in humans. It lives in the lymph vessels of man and female Culex mosquito is its secondary host and acts as a vector. Yellow fever (YF) is an African mosquito-borne infection of primates. It is caused by a virus of the Flavivirus genus of the Flaviviridae family. In its natural habitat, it is transmitted between monkeys by forest-dwelling primatophilic Aedes mosquitoes.
• Aedes mosquitoes cause yellow fever and filarial worm cause Filariasis. 
•  Malaria, caused by Female Anopheles mosquitoes pick up the parasites by feeding on infected humans. The parasites develop in a mosquito’s body for 10 to 18 days, then is passed on when the mosquito injects saliva while feeding.
• The Oriental Rat flea (Xenopsylla cheopis), also known as the tropical rat flea, is a parasite of rodents, primarily of the genus Rattus, and is a primary vector for bubonic plague and murine typhus. This occurs when the flea has fed on an infected rodent, and then bites a human. Diarrhoea is when your bowel movements become loose or watery. The definition of diarrhoea is passing loose or watery bowel movements 3 or more times in a day (or more frequently than usual). Diarrhoea occurs when the lining of the intestine is unable to absorb fluid, or it actively secretes fluid. 
• .

Insects like mosquitoes act as a vector to transfer infection from one host to another. This happens when one mosquito sucks blood from the infected person and the same mosquito bites a healthy person.  Therefore, (a) is the correct answer.

The mosquitoes act as a vector and help in the transmission of several diseases. Dengue fever is transmitted by the biting of the Aedes mosquito and the malaria is transmitted by the biting of the female Anopheles mosquito.