Pathogenesis of parasitic infection

Question 1

Describe and explain how selected Helmiths cause disease

Answer 1

Helmiths: Schistosomiasis:

Caused by flukes of the genus Schistosoma, infected when come into contact with fresh water contaminated with the parasite’s larvae

1) Tissue damage:

• After entering the human host, Schistosoma worms settle in the blood vessels around the intestines or bladder, depending on the species
• The female worms lay eggs, some of which are passed out of the body in feces or urine to continue the life cycle. However, other eggs get stuck in body tissues, causing an immune reaction and progressive damage to organs

2) Granulomas:

• The host’s immune system responds to the eggs by encasing them in a type of immune cell cluster known as a granuloma
• can limit the damage caused by the eggs, it also contributes to disease pathology when these granulomas form in response to eggs lodged in tissues

3) Chronic inflammation:

• The granulomas and chronic inflammation can lead to complications such as liver fibrosis in intestinal schistosomiasis or bladder cancer in urinary schistosomiasis

Helminths: onchocerciasis:

Known as river blindness, caused by the parasitic worm Onochocera volvulus, transmitted through repeated bites by the blackflies of the genus Simulium

1) Microfilariae and Nodules:

• Adult worms in the human body produce thousands of microscopic larvae, called microfilariae, which live in the skin and the eyes.
• Adult worms tend to form nodules in the body where they stay protected

2) Immune Response:

• When microfilariae die, they can cause intense itching and skin changes, known as “leopard skin”

3) Ocular Damage:

• If the microfilariae reach the eyes, they can cause lesions and inflammation leading to blindness, giving the disease its common name of “river blindness.”

4) Secondary Infections:

• The skin changes and itching can lead to secondary bacterial infections due to scratching

Question 2

Describe and explain how selected Ectoparasites cause disease

Answer 2

Ticks:

• Ticks are arachnids that are vectors for a number of serious diseases, including Lyme disease, Rocky Mountain spotted fever, and tick-borne encephalitis
• Ticks attach to their host to feed on their blood
• While feeding, they can transmit pathogens that they carry in their salivary glands into the host’s bloodstream
• Lyme disease is caused by the bacterium Borrelia burgdorferi, which is transmitted by certain species of ticks

Lice:

• There are three types of lice that infest humans: head lice, body lice, and pubic lice
• All three feed on human blood and lay their eggs on hair or clothing
• While lice infestations (pediculosis) are often merely annoying due to the intense itching they cause, body lice can also be vectors for serious diseases such as typhus, trench fever, and louse-borne relapsing fever
• excessive scratching can lead to secondary bacterial infections

Botflies:

• a family of flies whose larvae are internal parasites of mammals, including humans
• Human botfly infestation (myiasis) typically occurs when the fly deposits its eggs on a mosquito, tick, or another fly. When the vector lands on a human, the eggs hatch due to the body’s warmth, and the larvae penetrate the skin
• Once under the skin, the larvae feed on tissue exudates, causing a painful, swollen lesion

Question 3

Describe and explain how parasitic infections are controlled

Answer 3

1) Behaviours:

• Education
• Hand washing and hygiene behaviours

2) Environmental interventions:

• Spraying of residual insecticides for household vectors
• Mosquito nets for malaria
• Improved housing
• Sewage disposal and potable water
• Drainage of swamps

3) Poverty reduction

• Micro-fiancing