238 
MALARIA 
put forth the theory that quinine destroys 
numerous parasites if given during a 
period of heavy infection thus liberating 
large quantities of antigen that in turn 
stimulates the immune mechanism to 
greater activity resulting in a greater de¬ 
gree of immunity. Sinton (1938) has ad¬ 
mirably reviewed the question and both 
his experimental work and references to 
observations and experiments of others bear 
out the results obtained in other types of 
immune response, namely, that within cer¬ 
tain limits the degree of the immune 
response is proportional to the amount of 
antigen absorbed. A large quantity of 
antigen made available in a short period 
of time will be less effective than the same 
amount over a longer period, however. On 
this basis a high infection of malaria ter¬ 
minated by drugs after a few paroxysms 
will produce only a slight degree of im¬ 
munity, while if allowed to continue to 
spontaneous recovery followed by relapses 
and recrudescences the immunity will be 
of such a degree that no new infection with 
the homologous strain will be possible. 
Drug treatment interferes with the im¬ 
munity only to the extent that it interferes 
with the normal development of the para¬ 
sitic infection. Since the clinical symptoms 
are affected only indirectly, that is, by the 
effect of the drug on the parasite, any 
control of febrile attacks will in a cor¬ 
responding measure limit the number of 
parasites available for stimulation of the 
immune mechanism. 
From these facts it would appear that 
in isolated cases of malaria where the possi¬ 
bility of reinfection following cure was 
very slight interference with the develop¬ 
ment of immunity would be of little im¬ 
portance and intensive drug treatment 
could be used effectively. However, in 
hyperendemic areas where reinfection is 
certain the development of immunity is 
important. A cure under these conditions 
would be followed by reinfection and would 
probably result in the lowering of the re¬ 
sistance of the individual. Kligler (1930) 
found that two weeks after treatment and 
cure of malaria in children under 10 years 
of age the infections were more severe than 
before. Such individuals cannot be pro¬ 
tected from reinfection under these condi¬ 
tions and it is doubtful that alternate cure 
and reinfection would be of material benefit 
in the development of immunity. 
The results obtained by Sinton and 
others with monkey malaria coincide with 
the observations on most human experi¬ 
ments. When infections Of P. knowlesi 
in 8. rhesus are held to a low parasite count 
the infection will relapse as soon as the 
treatment is withheld and the monkey will 
die unless the same treatment is again used. 
If the infection is allowed to develop, with 
treatment sufficient to save the life of the 
animal, the resultant immunity will pre¬ 
vent further infection with the same strain. 
In view of this fact therapeutic measures 
employed to reduce the incidence of malaria 
will greatly reduce the effectiveness of the 
immunity resulting from natural infections. 
