Pathogenesis of parasitic infections

Question 1

What are the 3 main species of Schistosomiasis?

Answer 1

→ Schistosoma mansoni
→ Schistosoma haematobium
→ Schistosoma japonicum

Question 2

What is Schistosomiasis; cercarial dermatitis?

Answer 2

→ Exposure to cercariae from animal or bird schistosomes
→ Requires pre-sensitization
→ Allergic-type reaction
→ Key feature of immune response:
1. Granuloma formation
2. Eggs become organised in granulomas
3. Repeated insults and tissue repair leads to fibrosis and organ damage

Question 3

What is pathology caused by in Hepato-intestinal schistosomiasis?

Answer 3

→ Infections with Schistosoma mansoni and Schistosoma haematobium

→ Pathology caused by immune response to eggs

Question 4

What do we know about Helminths: onchocerciasis?

Answer 4

→ Major blinding disease
→ Caused by filarial parasite (Onchocercavolvulus)
→ Transmitted by blackflies

Question 5

What do we know about the pathology of Onchocerciasis?

Answer 5

Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes

Question 6

What drugs are used in the Control of parasite infections for protozoa, helminths and ectoparasites?

Answer 6

Protozoa:
1. Tinidazole
2. Metronidazole
3. Nitazoxanide
4. Benznidazole
5. Heavy metals (meglumine antimoniate)

Helminths:
1. Albendazole/mebendazole
2. Praziquantel
3. Ivermectin
4. Diethylcarbamazine
5. Pyrantel

Ectoparasites:
1. Ivermectin
2. Benzyl/malathion lotions

Question 7

How can we take Control of parasite infections?

Answer 7

Behaviours:
→ Education
→ Hand washing and hygiene behaviours

Environmental interventions:
→ Spraying of residual insecticides for household vectors
→ Mosquito nets for malaria
→ Improved housing
→ Sewage disposal and potable water
→ Drainage of swamps

Poverty reduction:
→ Micro-financing, etc

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

Question 8

Summarise the above lecture:

Answer 8

→ Parasites are important infections of humans
→ They have a worldwide distribution but are found predominantly in tropical regions among populations living in poverty
→ Although there are effective treatments for most parasitic infections, limited investment still means limited treatment options and problems of drug toxicity for many infections.
→ Poverty reduction and education interventions combined with drug treatments will control/eliminate many parasite infections.