(1973) n°3 - Royal Academy for Overseas Sciences

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significance of the so-called « relapse bodies » or « secondary
e::oerythrocytic schizonts ». Col. Sh o r t t and I reported such
parasites in 1948 in the liver of monkeys about a hundred
days after the inoculation of P. cynomolgi sporozoites and just
before a relapse. This work was confirmed by B r a y (1957)
and Eyles (i960) also with P. cynomolgi. R o d h a in (1956)
by accident encountered a few exoerythrocytic schizonts of P.
vivax in the liver of a chimpanzee which he had inoculated
with sporozoites 9 months previously. Similarly, we found tissue
forms of P. vivax hibernans in a chimpanzee 8 1/2 months
after infection.
W e at first assumed that here was material evidence of the
origin of relapses, probably arising from the production of
successive generations of exoerythrocytic schizonts. But there
are many reasons for doubting this hypothesis, and now (G a r n ­
h a m 1967) it is more generally thought that the so-called
« secondary » forms are really delayed « primaries » or in other
words that they represent latency of the sporozoite. After all,
the sporozoite is known to be capable of remaining alive for
many months in the cells of the salivary glands of mosquitoes
— so why not also in the liver ?
How is latency maintained? Why is the true relapse phenomenon
confined to P. vivax and P. ovale in man and possible
P. cynomolgi in monkeys? W hat is responsible for the relapse
of P. malariae after 20-50 years?
A rather sim ilar p u zzle to relapses is th e nature o f th e d elayed
prep aten t p eriod in P. vivax, w h ich apparen tly is d ep en d en t
u p o n the d osag e o f sp orozoites. I cannot discuss th e q u estion
here, n or th e in terestin g « relapse » b od ies fou n d by La n d a u and
C h a b a u d (1 9 6 8 ) in roden t m alaria.
Co n c l u s io n
In conclusion, I wish to emphasize most strongly the profound
taxonomic importance of the tissue stages. If good techniques
of staining are used, morphological details are properly
revealed; if attention is paid to the exact time of appearance
of the parasite in the blood after sporozoite inoculation, the
true pre-patent period can be determined. Some workers will not