## **Core Concept**
The infective form of the malarial parasite that can be transmitted through blood transfusion is a critical aspect of malaria epidemiology. Malarial parasites have several life stages, but not all are infectious through blood transfusion. The key stage that can be transmitted via blood transfusion is the one that invades red blood cells.

## **Why the Correct Answer is Right**
The correct answer, ., refers to the **erythrocytic schizont or trophozoite stages** of the malarial parasite. These stages are the ones that infect red blood cells. When blood from an infected individual is transfused into a recipient, the infected red blood cells can introduce the parasite into the recipient's circulation. The parasites can then continue their life cycle within the recipient's red blood cells, leading to infection. This mode of transmission bypasses the liver stage, which is typically the initial site of infection in mosquito-borne malaria transmission.

## **Why Each Wrong Option is Incorrect**
- **Option A:** . This option is incorrect because sporozoites are the infective form of the parasite transmitted by mosquitoes. They primarily infect liver cells, not red blood cells directly, and are not the stage transmitted through blood transfusions.
- **Option B:** . This option is incorrect because merozoites are the form of the parasite that invades red blood cells after the liver stage. While they are involved in the erythrocytic cycle, the specific context of blood transfusion transmission points more directly to the stages already within red blood cells.
- **Option D:** . This option is incorrect because hypnozoites are the dormant liver stages of certain Plasmodium species (like P. vivax and P. ovale) that can cause relapse. They are not transmitted through blood transfusions.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that malaria can be transmitted through blood transfusions, organ transplants, and from mother to child during childbirth. The risk of transmission through blood transfusion is a critical consideration in endemic areas, highlighting the importance of screening blood donations for malaria parasites.

## **Correct Answer:** . trophozoites