PARASITOLOGY

NUTRITION AND BIOCHEMISTRY OF PARASITES

n BOX 6.6

Drug Effective against

Chloroquine phosphate Plamodiumspp (Malaria therapy & prophylaxis)

Diethylacarbamazine Filarial nematodes

Ivermectin Filarial nematodes

Mebendazole Most cestodes

Albendazole Mainly cestodes

Praziquantel Mainly Schistosomaspp

n SUMMARY

Parasites live surrounded by their food and hence they have reduced the musculature and

sense required in searching for food. The gut-dwelling parasites are immersed in digested

and semi-digested food. The nutrients are generally absorbed as amino-acid, carbohydrate

or fat molecules either by passive or active absorption. The kinetics of absorption are

similar to those of the cells that line the gut of the host.

A great deal of the energy requirement of the parasite relates to maintaining its large

fecundity — the ability to produce large numbers of eggs or larvae. The metabolic path-

ways that are part of protein synthesis and energy synthesis are similar to those of most

vertebrates. In many cases parasites have become facultative anaerobes. The chemical

signals and stimuli that are required for establishing growth and development are obtained

from the host.

Knowledge of differences between the parasite’s and the host’s biochemical pathways

can be explored for the possible development of drugs.

End of chapter questions

Question 6.1 What is the main difference with regard to feeding between a free-living
animal and a parasitic animal?
Question 6.2 What are the main feeding methods found in the protozoa, cestodes,
trematodes and nematodes?
Question 6.3 What is the difference between passive uptake and active uptake?
Question 6.4 Describe mediated or facilitated uptake, contact digestion and
pinocytosis.
Question 6.5 What factors affect the uptake of nutrients by cestodes?
Question 6.6 Describe the uptake of glucose by cestodes.
Question 6.7 How are amino-acids absorbed by tapeworms?
Question 6.8 How do trematodes absorb their nutrients?
Question 6.9 What feeding mechanisms are used by nematodes?
Question 6.10 Outline the methods of respiration that occur in the protozoa, cestodes,
trematodes and nematodes.
Question 6.11 Describe what functions of a parasitic helminth use most of the metabolic
energy produced.
Question 6.12 Describe some of the more important features of parasites in relation to the
metabolism and physiology.