Pathogenesis of parasites

Question 1

What is Schistosomiasis?

Answer 1

• Can experience disease from exposure
• Allergic-type reaction
• Requires pre-sensitization
• Rash-like lesions
• Parasites live in the venous system and release loads of eggs and often a backflow to the liver causes granulomas - repeated insults and tissue repair leads to fibrosis and organ damage
• Pathology cause by immune response to the eggs
• Urinary schistosomiasis - blood in urine = haematuria

Question 2

What is onchocerciasis?

Answer 2

• Historically cause of blindness in Africa
• Caused by filarial parasite
• Transmitted by blackflies which takes blood meal, and transmits lava in skin, which will then migrate into adults and invests the skin and gets into the eyes
• Caused by repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in the skin and eyes
• Chronic - loss of elasticity of skin
• Damage to eyes - punctate keratitis
• Immune system is switched on initially but with time and chronic infections, it gets shut down and you get alternativity activated macrophages which supress the immune response

Question 3

What are ticks? and describe their disease…

Answer 3

Mechanical injury at bite

Tick’s toxin produces a block in the motor nerve fibres

Carriers of Lyme disease

Question 4

What are lice?

Answer 4

Head lice - suck blood from scalp and lay eggs on hair

Body lice - suck blood from body and lay eggs on clothing

Uncommon and spread by bodily contact

Related to poor sanitation, crowded conditions, long periods without bathing

Crab lice - around pubic area, large claws and cause nasty reactions, spread by sexual contact

Question 5

What is botfly disease?

Answer 5

Catches a mosquito mid-flight and it lays eggs on the mosquito, so then the eggs will stick to the coat of the skin when it invades and live in burrows under the skin

Removed surgically or with a drug to kill it

Has thick spines to keep it within the skin and hard to remove

Question 6

How are parasitic infections controlled?

Answer 6

Giving drugs to treat

Behaviours - education, hand-washing and hygiene behaviours

Environmental - spraying of insecticides for household vectors, mosquito nets, improved housing, sewage disposal and potable water, drainage of swamps

Poverty reduction

For many infections in an endemic setting, treatment must be given periodically over long periods of time between re-infections are rapid or because the treatment kills larval rather than adult stages