(1973) n°3 - Royal Academy for Overseas Sciences
(1973) n°3 - Royal Academy for Overseas Sciences
(1973) n°3 - Royal Academy for Overseas Sciences
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— 517 —<br />
significance of the so-called « relapse bodies » or « secondary<br />
e::oerythrocytic schizonts ». Col. Sh o r t t and I reported such<br />
parasites in 1948 in the liver of monkeys about a hundred<br />
days after the inoculation of P. cynomolgi sporozoites and just<br />
be<strong>for</strong>e a relapse. This work was confirmed by B r a y (1957)<br />
and Eyles (i960) also with P. cynomolgi. R o d h a in (1956)<br />
by accident encountered a few exoerythrocytic schizonts of P.<br />
vivax in the liver of a chimpanzee which he had inoculated<br />
with sporozoites 9 months previously. Similarly, we found tissue<br />
<strong>for</strong>ms of P. vivax hibernans in a chimpanzee 8 1/2 months<br />
after infection.<br />
W e at first assumed that here was material evidence of the<br />
origin of relapses, probably arising from the production of<br />
successive generations of exoerythrocytic schizonts. But there<br />
are many reasons <strong>for</strong> doubting this hypothesis, and now (G a r n <br />
h a m 1967) it is more generally thought that the so-called<br />
« secondary » <strong>for</strong>ms are really delayed « primaries » or in other<br />
words that they represent latency of the sporozoite. After all,<br />
the sporozoite is known to be capable of remaining alive <strong>for</strong><br />
many months in the cells of the salivary glands of mosquitoes<br />
— so why not also in the liver ?<br />
How is latency maintained? Why is the true relapse phenomenon<br />
confined to P. vivax and P. ovale in man and possible<br />
P. cynomolgi in monkeys? W hat is responsible <strong>for</strong> the relapse<br />
of P. malariae after 20-50 years?<br />
A rather sim ilar p u zzle to relapses is th e nature o f th e d elayed<br />
prep aten t p eriod in P. vivax, w h ich apparen tly is d ep en d en t<br />
u p o n the d osag e o f sp orozoites. I cannot discuss th e q u estion<br />
here, n or th e in terestin g « relapse » b od ies fou n d by La n d a u and<br />
C h a b a u d (1 9 6 8 ) in roden t m alaria.<br />
Co n c l u s io n<br />
In conclusion, I wish to emphasize most strongly the profound<br />
taxonomic importance of the tissue stages. If good techniques<br />
of staining are used, morphological details are properly<br />
revealed; if attention is paid to the exact time of appearance<br />
of the parasite in the blood after sporozoite inoculation, the<br />
true pre-patent period can be determined. Some workers will not