NUTRITION AND BIOCHEMISTRY OF PARASITESn BOX 6.3
Cornford (1991) studied the glucose transporter kinetics in H. diminutaand observed the
following results after culturing the worms in vitro.
The Michaelis constant (Km) for 8-day-old worms was Km=0.34 mM, and the maximum
uptake rate(Vmax) was Vmax=14 nmol per min per g
For 10-day old worms the Km=0.46 mM, and the Vmax=18 nmol per min per g
For 17-day old worms the Km=0.51 mM, and the Vmax=21 nmol per min per gThe age of the worms appears to be a factor affecting uptake and it could also apply
to drug uptake. An older parasite may be more susceptible than younger parasites and
the dose rate could be altered accordingly, especially where the drug has side effects upon
the host.
n BOX 6.4
Ito et al. (1988) studied antibody responses in H. nana. In susceptible mice they found anti-
bodies to eggs, cysticercoids and adults. In a BALB/c non-susceptible strain of mice (that
is, they expel the adult worms after 30 days) antibodies were produced to egg antigens
only. However worms were rejected when there were few or no detectable antibodies in
the serum. This suggests that antibodies alone do not have an effective role in the expul-
sion of parasites and that other aspects of the immune system may be involved. The dif-
ferent antibody responses suggest that there is a difference in antigen specificity between
eggs, cysts and adults. This latter observation may have to be taken into account in attempts
to develop vaccines and prophylactic drugs.
The in vivo and in vitro culture used in studying the kinetics of nutrient uptake can also
be applied to drug studies particularly the uptake and the biochemical effects of the drug.
McCracken and Taylor (1983) examined what effect in vivo, then in vitro, the drugs
(benzimidazole anthelmintics) thiabendazole (TBZ) and cambendazole (CBZ) had upon H.
diminuta. Their results demonstrated that a single oral dose of TBZ, at a dose rate of 250
mg/kg, on day 15 eliminated 100% of the worms.
Some the observed effects upon the worms were:nChanges in weight and chemical composition.
nThey were significantly smaller and with a smaller percentage body weight glycogen.
nThe protein concentrations had increased to offset the decline in glycogen.
nThe glycogen/protein ratio in TBZ treated worms was lower than in control worms.
nCBZ was found to be five times more potent than TBZ against H. diminutaand produced the
same basic changes within 18 h of treatment.
nIn vitro studies of treated worms showed that they metabolised smaller quantities of exoge-
nous glucose than controls.
nThe ability to accumulate glucose against a concentration difference was significantly
depressed.