MALARIA AND THE COMMUNITY 
151 
there is relatively little cross immunity 
among them. An individual would soon 
become completely immune to any one or¬ 
ganism with which he might be constantly 
reinfected, but each new strain, like a new 
species, finds the host defenceless and initi¬ 
ates a train of events culminating in an 
acute attack, and a period of gametocyte 
production. 
5. The effect of age and exposure. Since 
immunity is developed by exposure except 
in very young infants, it has nothing really 
to do with age, but only with number and 
frequency of infections. A high inocula¬ 
tion rate tends to concentrate the persistent 
and dangerous carriers in the earlier age- 
groups. D. B. Wilson (1939), in a series 
of important papers on malaria in East 
Africa, describes such a situation among 
the Bantu in Tanganyika, who live in an 
area of high endemicity. All the babies 
are infected before they are 5 months old 
and the period of acute infestation lasts 
about 18 months. There is little danger to 
life after 6 months. Gametocytes reach 
their height at the end of the second year, 
and are seldom seen in adults. There are 
all gradations between such a situation and 
areas of sporadic malaria with no measur¬ 
able immunity at all. In rural -districts of 
Kenya 29 per cent of the natives under 10 
years of age were gametocyte carriers, but 
less than 2 per cent of the rest, while Clark 
and Komp in Panama, with a less estab¬ 
lished immunity, found 41 per cent of the 
children carriers, and 29 per cent of the 
adults. 
In very young babies there appears to be 
a resistance to infection derived possibly 
from the mother. Clark (1937) found in 
Panama that infants enjoyed almost com¬ 
plete protection in the first two months of 
life although even more exposed to mos¬ 
quito bites than adults. Strickland, Sen 
Gupta and Mazumdar observed in India 
that the average age of infants at the first 
attack was from 3 to 4 months depending 
on the season, while Barber, Mandekos and 
Rice found in Macedonia that older infants 
were more susceptible to infection than 
younger ones. 
6. The effect of treatment. None of the 
drugs now at our disposal is able to prevent 
malaria from relapsing, or the appearance 
of gametocytes. We can possibly cut down 
the number of relapses somewhat, but never 
sufficiently to protect a community from 
continual reinfection. Even small groups 
under discipline cannot be sterilized. Ciuca 
found that neither quinine nor atabrine 
prevented the appearance of gametocytes 
in as many as 149 out of 269 cases of in¬ 
duced P. falciparum infections in hospital. 
Simmons (1939a) reports that in Panama 
more than 20 per cent of soldiers receiving 
the standard treatment of quinine followed 
by 15 grains daily for 3 months, became 
carriers while still taking the drug. Bis- 
pham claims that with suitable atabrine 
treatment, over 90 per cent of P. vivax car¬ 
riers can be cleared of parasites. His ex¬ 
perience was confined to encampments of 
young men, while communities with chil¬ 
dren and babies are quite another problem. 
Even so, the clearing of only 90 per cent of 
parasites would hardly be adequate protec¬ 
tion for a community. Barber, Rice and 
Mandekos present proof that both in the 
Balkans and in Liberia even one heavy 
carrier in a village could raise the sporozo¬ 
ite index of the anopheles and cause a not¬ 
able increase in transmission. 
Neither in Spain nor Holland, where the 
malaria is principally a mild tertian, nor 
in Sardinia or the Balkans where the ma¬ 
laria is severe, nor in Panama where the 
climate is tropical and infection goes on the 
year round, have the most intensive and 
persistent treatment campaigns been able 
to destroy the seedbed of the disease. 
7. The effect of race. The subject of 
carriers is complicated in many regions, 
such as Panama, Africa and the Southern 
United States, by the presence of a mixture 
of races. Negroes have a notable tolerance 
for P. vivax infections and while they are 
susceptible to P. falciparum and P. ma- 
lariae, the clinical course of the disease is 
milder than in the white race. In the 
southern states, the white children have 
more P. vivax parasites and the negro chil¬ 
dren more P. falciparum. Thus in the 
