Common Diseases In Human Beings

Step 1: Understanding the life cycle of Plasmodium.

When a female Anopheles mosquito bites a human, it injects the sporozoites into the bloodstream. Sporozoites are the infective stage of the Plasmodium parasite.

Step 2: Role of sporozoites.

The sporozoites travel to the liver cells, where they multiply asexually and form merozoites. This marks the beginning of the parasite's life cycle within the human host.

Step 3: Key Point.

The sporozoite phase is the entry stage of the parasite into the human body, making it the correct answer.

Step 1: Causative organism of typhoid fever

Typhoid fever is caused by the bacterium Salmonella typhi. This bacterium is transmitted through contaminated food and water.

Step 2: Symptoms of typhoid fever

Symptoms include:

• High fever
• Weakness
• Abdominal pain
• Headaches
• Constipation or diarrhea

Step 3: Elimination of incorrect options

(B) Incorrect: Mosquitoes transmit diseases like malaria and dengue, not typhoid.

(C) Incorrect: Plasmodium is a parasite responsible for malaria.

(D) Incorrect: Nicotine is a chemical compound and not a causative agent of infectious diseases.

The female Anopheles mosquito transmits the Plasmodium parasite, which causes malaria.

Dengue, Zika, and Chikungunya are transmitted by Aedes mosquitoes.

Therefore, the correct answer is: Malaria.

Step 1: Understanding malaria.
Malaria is a disease caused by protozoan parasites of the genus \textit{Plasmodium}. Among the species, Plasmodium falciparum is the most severe and deadly.

Step 2: Role of Anopheles mosquito.
The female Anopheles mosquito acts as the vector for the transmission of \textit{Plasmodium} species but is not the causative agent itself.

Step 3: Explanation of other options.
Option (B): Incorrect. The Anopheles mosquito is a vector, not the causative agent.

Option (C): Incorrect. Trypanosoma brucei causes sleeping sickness.

Option (D): Incorrect. Entamoeba histolytica} causes amoebiasis.

The correct answer is: Plasmodium falciparum