Relapse - Advances in Parasitology - page 119

prevalent in the United States and Southern Europe, were considered
the 'typical' P. vivax infections. A primary illness followed approximately
2 weeks after mosquito inoculation, and, although relapse could follow
some 3 weeks later, there was often a 7-10-month interval before a sub-
sequent relapse. Sometimes, the latency could be as long as 1 year, and
there were well-documented, but apparently unusual, cases reported of
latencies greater than 2 years. Further north in the Netherlands, Northern
Germany, Scandinavia, Finland and Central Russia, long-incubation phe-
notypes were prevalent ( P. vivax hibernans ) in which the primary infection
occurred 8-10 months after inoculation ( Swellengrebel and De Buck,
1938 ; Winckel, 1955 ; Gill, 1938 ; Hackett, 1937 ; Bignami, 1913 ; Yorke and
MacFie, 1924 ; Yorke, 1925 ; James, 1931a ; James et al., 1936 ; James and
Shute, 1926 ; Schuffner et al., 1929 ; Tiburskaja et al., 1968 ; Nikolaiev, 1949 ;
Shute et al., 1978 ; Boyd, 1940a ; Coatney et al., 1950a ; Tiburskaya, 1961 ;
Moshkovsky, 1973 ; Huldén et al., 2005 ). It seemed that the proportion of
infections, which had a short incubation period ( circa 2 weeks), declined
steadily with increasing latitude (and shorter summer mosquito breeding
seasons).
There was one very important feature of the long-latency P. vivax infec-
tions, which was noted particularly in soldiers who had acquired vivax
malaria in the Korean war; once the relapse had occurred (after a latency of
7-10 months), subsequent relapses would then usually occur with intervals
of approximately 3-4 weeks following quinine or 6-8 weeks if chloro-
quine was given for treatment ( Fig. 2.3 ), i.e. similar intervals in the tropical
frequent relapse 'Chesson'-phenotype vivax malaria ( Hankey et al., 1953 ;
Coatney et al., 1950b ; Hill and Amatuzio, 1949 ). It was also noted that in
artificial infection studies, the duration of latency was independent of the
season when the infection was induced ( James, 1931a ; James et al., 1936 ).
4. RELAPSE DETERMINANTS
The proportion of patients whose vivax malaria relapses depends on
many factors including 'strain', sporozoite inoculum, immunity and drug
treatment.
4.1. Effects of the Sporozoite Inoculum on Relapse Intervals
For long-latency vivax malaria, the sporozoite dose determined the clinical
phenotype. In long-term observations of infections with the St Elizabeth
strain and a North Korean strain used for malaria therapy in a Moscow