Human Health and Disease MCQs

Malaria is transmitted by the bite of infected Anopheles mosquitoes, which inject the protozoan parasite into the bloodstream.

The parasite that multiplies in human red blood cells and causes the characteristic fever cycles is a Plasmodium species.

Wuchereria causes filariasis, Salmonella causes typhoid, and Entamoeba causes amoebiasis, so they are not the malaria agent.

Hence the causative agent of malaria in humans is Plasmodium.

Amoebiasis is caused by Entamoeba histolytica, whose cysts are passed in feces.

Cysts can adhere to the legs, wings or mouthparts of insects that land on fecal matter.

When the insect later contacts food, it mechanically transfers the cysts to the food.

The insect that commonly does this is the housefly, so the correct answer is Housefly.

Ringworm is a superficial fungal infection of the skin caused by dermatophytes.

The fungi invade keratinized layers, producing circular, dry, scaly patches that itch intensely.

Systemic signs like fever, diarrhoea or limb swelling are not typical of this localized skin disease.

Hence the correct answer is Dry, scaly lesions with intense itching on skin.

Interferons are secreted proteins released by cells after viral infection.

They act on neighboring cells to induce antiviral states, preventing virus replication.

Such secreted signaling molecules constitute a chemical (cytokine) defense rather than a physical or cellular barrier.

Hence interferons represent a cytokine barrier.

Antibodies given from an external source are not produced by the recipient’s own immune system.

Since the protection comes from transferred immunoglobulins, the individual does not develop memory cells.

This type of protection is termed passive immunity.

Answer: Passive immunity

Amoebic dysentery is characterized by bloody diarrhea and intestinal ulceration.

The disease is specifically linked to the pathogenic protozoan that invades the colon lining.

Entamoeba histolytica is the only species among the options known to cause such intestinal infection.

Thus the correct answer is Entamoeba histolytica.

Ringworm is a superficial skin infection characterized by circular, scaly lesions.

The causative agents are dermatophyte fungi that invade keratinized tissues.

Common dermatophytes include species of Microsporum and Trichophyton, which produce the typical ring‑shaped rash.

Thus the correct answer is Fungi such as Microsporum and Trichophyton.

Neutrophils and macrophages are cells that ingest and destroy microbes by phagocytosis.

Since they are living cells forming a defensive line, they constitute a cellular component of immunity.

Thus they belong to the cellular barrier of the body’s defense system. Cellular barrier

Active immunity involves the host’s own immune response producing specific antibodies and memory cells. It requires time for antigen exposure, lymphocyte activation and clonal expansion, so it is not immediate. Once established, memory cells persist, giving long‑lasting protection. Hence active immunity is slow to develop but long‑lasting.

Bone marrow is the primary site of haematopoiesis, the process that generates all formed elements of blood.

Stem cells in marrow differentiate into erythrocytes, granulocytes, monocytes and lymphoid precursors.

Lymphoid precursors further mature into B‑lymphocytes, while T‑cell precursors migrate to the thymus.

Thus all blood cells, including lymphocytes, are produced in bone marrow.

Severe, life‑threatening malaria (high parasitemia, cerebral involvement, severe anemia) is linked to the species that multiplies most rapidly in red cells.

Plasmodium falciparum invades erythrocytes of all ages, causing high parasite loads and complications.

Other species (vivax, malariae, ovale) cause milder or relapsing malaria and rarely produce malignant forms.

Hence malignant malaria in humans is caused by Plasmodium falciparum.

Typhoid fever is a systemic infection characterized by prolonged fever, abdominal pain and rose‑spots.

The disease is transmitted via contaminated food or water and is caused by a gram‑negative, non‑sporing bacillus that invades the intestinal mucosa and spreads through the bloodstream.

Among the listed organisms, only Salmonella typhi fits this description as the specific pathogen responsible for typhoid fever.

Fungi need a humid environment to maintain their spores and hyphae viability.

Skin areas that are warm retain moisture, providing the ideal temperature and water activity for fungal growth.

Thus infections like ringworm are common in warm, moist sites such as skin folds and between the toes. Warm and moist (e.g. skin folds, between toes)

Pathogen‑specific immunity involves recognition of antigens by lymphocytes, which is a feature of the adaptive (acquired) system.

During the primary response, antigen‑specific cells are generated and some become long‑lived memory cells.

On re‑exposure, these memory cells mount a faster, stronger response, distinguishing it from innate or passive immunity.

Thus the immunity that is pathogen‑specific and has memory is acquired immunity.

Colostrum is rich in immunoglobulin A (IgA) which is not produced by the infant’s own immune system.

IgA antibodies bind to pathogens in the gut, preventing their attachment and invasion.

Thus the infant receives protection without having to mount its own response, i.e., passive immunity.

Malaria parasites develop only inside the female mosquito’s gut after a blood meal.

Only Anopheles species can support the sporogonic cycle of Plasmodium.

Male mosquitoes do not take blood, and Culex and Aedes transmit other diseases.

Thus the vector is the female Anopheles mosquito.

Salmonella typhi penetrates the intestinal epithelium and enters the lamina propria.

From there it gains access to the capillaries and enters the systemic circulation.

The organism is then transported via the bloodstream to reticulo‑endothelial organs (liver, spleen, bone marrow).

Thus the correct route of spread is Blood.

Filariasis is transmitted by mosquito vectors that carry filarial nematodes, which are multicellular parasitic worms.

Helminths are classified as flatworms or roundworms, and the causative agents of filariasis (e.g., Wuchereria bancrofti) are roundworms.

The other options are caused by viruses (common cold), bacteria (typhoid), or protozoa (amoebiasis).

Hence the disease caused by a helminth is Filariasis.

Acquired immunity involves lymphocytes that recognize particular antigens → gives specificity.

After first exposure, memory B and T cells are generated, allowing a faster, stronger response on re‑exposure → gives memory.

Thus the two special properties are specificity and memory. Specificity and memory.

Antibodies are supplied directly from an external source, not produced by the recipient’s own immune system.

Since the protection is conferred without the host generating its own immune response, it is not active.

This transfer of ready‑made antibodies is called passive immunisation.

Hence the correct answer is Passive immunisation.