INFECTION OF THE INTERMEDIATE HOST 
177 
TABLE XI 
Relative Frequency of Renewed Activity at 
Different Intervals Following Termina¬ 
tion of Primary Attack (Fig. 5) 
Per cent with secondary attacks 
Interval 
subsequent 
P. vivax b 
P. falciparum 
to primary 
attack 
McCoy 
(46) 
Mada¬ 
gascar 
(107) 
Vari¬ 
ous 
(63) 
Vari¬ 
ous 
(87) 
Under 8 
weeks . 
66.0 
18.6a 
97.1 
72.4a 
8-24 
weeks . 
13.7 
17.8a 
2.9 
24.2a 
Over 24 
weeks . 
20.6 
63.6« 
OjO 
3.3a 
a James, Nicol and Shute (1936). 
b Primary attacks interrupted. 
inevitable when the attack is interrupted, 
but not followed by intensive treatment. 
It is interesting to note that the exotic 
strains in the hands of James have shown 
a much higher proportion of secondary at¬ 
tacks even when intensively treated. 
The extent to which this characteristic 
may be related to the strain of parasite, is 
shown by the occurrence of secondary at¬ 
tacks in 68 (45.6 per cent) of 149 patients 
inoculated with the McCoy strain of P. 
vivax, while of 21 other patients inoculated 
with six other strains, only one (4.7 per 
cent) had a secondary attack (Boyd and 
Kitchen 1937d). 
Some observations on the frequency of 
secondary attacks at varying intervals sub¬ 
sequent to the termination of the primary 
attack are shown in Table XI. 
While the falciparum observations cited 
from James, Nicol and Shute (1936) are 
not strictly comparable with our own, prob¬ 
ably due to the use of different criteria 
for distinguishing the termination of the 
primary attack, the data as a whole, never¬ 
theless, present an agreement in certain 
essential characteristics. It will be noted 
that renewal of activity after the lapse of 
24 weeks is more definitely a characteristic 
of vivax strains than of falciparum strains, 
while the New World strains have exhibited 
a decidedly less frequent tendency to be¬ 
come reactivated after long intervals of 
quiescence than have the Old World strains. 
While it is likely that our criterion of 
the end of the primary attack is based on 
too short a period of quiescence, which 
might better be marked by a three-week 
interval, it appears unquestionable that the 
secondary attacks occurring within 8, and 
perhaps even 12, weeks of the termination 
of the primary attack are really a direct 
continuation of the latter. 
TABLE XII 
P. vivax : Interval Elapsing from the End of the Primary Attack to Various Periods of Renewed 
Activity, in Relation to the Length of the Primary Attack 
Duration 
primary 
attack 
in days 
Natural inoculation 
Artificial inoculation 
Total 
cases 
Secondary 
attack 
in weeks 
Further 
secondary 
attacks 
in weeks 
Total 
cases 
Secondary 
attack 
in weeks 
Further 
secondary 
attacks 
in weeks 
0-7 
8-24 24 + 
0-7 
8-24 
24 + 
0-7 8-24 
24 + 
0-7 8-24 24 + 
0-6 .• 
13 
2 
1 
7 
2 
7-13 . 
44 
13 
3 
3 
3 
4 
7 
1 
... 
14-20 . 
27 
15 
1 
1 
9 
2 
8 
5 
2 . 
21-27 ....'. 
25 
16 
1 
5 
2 
3 
7 
5 
1 . 
28-34 . 
16 
4 
1 
1 
1 
1 
2 
35-41 . 
12 
4 
2 
1 
1 
2 
4 
... 
. 
42-48 . 
5 
3 
1 
3 
49-69 . 
7 
3 
... 
. 
Total . 
149 
57 
4 
7 
20 
10 
8 
41 
13 
0 
0 
3 0 0 
