Biology Reference
In-Depth Information
Figure 2.3
Schematic diagram by Hankey et al. (
Sinha et al., 1953
) of relapse patterns
following Korean vivax malaria (upper panel) and tropical frequent-relapse
P. vivax
(lower panel). It is important to note the frequent-relapse pattern after a long interval
with Korean vivax malaria.
hospital, there was a clear bimodal pattern in which a long pre-patent
period (∼300 days) only occurred following smaller sporozoite inocula
(more reflective of natural infection) (
Coatney et al., 1950a
;
Tiburskaya,
1961
;
Moshkovsky, 1973
). For the Moscow strain, it required ≥1000 sporo-
zoites to produce illness after a 'short' incubation period of 2 weeks. When
increasing sporozoite doses of the tropical 'Chesson' strain were inoculated,
the incubation period shortened slightly, but even with a single mosquito
bite, there was no evidence for a long pre-patent period. These observations,
and a series of experimental investigations in chimpanzees (
Ungureanu et al.,
1976
), led Garnham to propose that the ratio of hypnozoites to immediately
developing forms in the Korean
P. vivax
strain was 999:1 compared with the
Chesson strain, where he estimated the ratio as 50:50 (
Garnham, 1988
;
Bray
and Garnham, 1982
).
In contrast, the initial inter-relapse intervals of Chesson strain
P. vivax
in volunteers, and also
P. cynomolgi
in Rhesus monkeys, were remarkably
regular although they gradually lengthened with each successive relapse
(
Krotoski et al., 1986
;
Schmidt, 1986
) (
Fig. 2.4
). Two factors were prob-
ably responsible for gradually increasing inter-relapse intervals. The first is