Q.Which of the following is NOT caused by unsterilized needles?

AIDS and hepatitis B are blood-borne, and so is malaria in a less obvious way: infected red cells in transfused blood or on a shared needle can carry the parasite's blood stages straight into a new person. The filarial worm has no such shortcut - its microfilariae are not infective until they have developed into L3 larvae inside the mosquito.

Step 1. AIDS - HIV is present in blood, and sharing an unsterilised needle or syringe is one of its recognised routes (section 10.3, K).

Step 2. Hepatitis B - a blood-borne virus; contaminated needles are a well-known way it spreads.

Step 3. Malaria - normally spread by the female Anopheles mosquito, but the parasite's blood stages (merozoites inside red cells) can also be carried directly from person to person by transfused blood or a shared needle, producing an infection without any mosquito. So malaria CAN be caused by an unsterilised needle.

Step 4. Elephantiasis - the microfilariae circulating in an infected person's blood are the diagnostic stage, not the infective stage. They must be taken up by a Culex mosquito and develop through L1 to L3 larvae in its thoracic muscles (Fig. 10.8) before they can infect anyone. A needle carrying microfilariae therefore cannot cause the disease.

Check each disease against whether unsterilized needles/contaminated blood is one of its recognised transmission routes.

• Picking Malaria because it is 'mosquito-borne' - the blood stages of Plasmodium are infective in transfused or needle-carried blood too, which is exactly why blood banks screen for malaria.
• Forgetting that filarial microfilariae are only the diagnostic stage; the infective L3 larva forms inside the mosquito, so filariasis has no direct blood-to-blood route.