Disease Vectors and Pathogens

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.

• 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. 

• Dracunculus medinensis or Guinea worm is a nematode that causes dracunculiasis( guinea worm disease).
  
• Usually, the disease has no initial symptoms. About one year later, there is a painful burning feeling as a blister forms, usually on the legs. The blister bursts as the worm then come out of the skin over a few weeks.
• this Disease has been eradicated and India was declared as guinea worm disease free country by WHO in 2000.
• Hence The parasite which has been recently eradicated from India is Dracunculus medinensis.
• So, the correct answer is 'Dracunculus medinensis '.

Brain fever is caused by virus and transmitted through Culex tritaeniorhynchus, female mosquitoes. Mosquitoes acquire virus, while taking blood meal and pass it to next healthy person. 
When Anopheles female mosquito bites a malaria patient then malarial parasite also enters in mosquito, while blood suction. Malarial parasite can grow in mosquito body and pass to another person, when mosquito bites. Dengue virus is transmitted due to mosquitoes, Aedes aegypti.  
Typhoid is caused by bacteria called as Salmonella typhi. It is water borne disease. Typhoid patient's feces show presence of Salmonella typhi. When such feces comes in contact with drinking water bodies then water gets polluted. Such, water if used for consumption then person gets infected with typhoid. Hence, typhoid is not transmitted by mosquito. 

Housefly transmits various diseases like typhoid diarrhoea, dysentery, cholera, tuberculosis etc.