A STUDY OF THE RATE OF REPRODUCTION IN THE AVIAN
MALARIA PARASITE, PLASMODIUM CATHEMEBIUM1
BY
GEOEGE H. BOTD
(Eeceived for publication November 16th, 1938)
i From the Department of Zoology, University of Georgia, Athens, Ga.
fied in concluding that the interval between peaks of schizogony represents
the length of the asexual cycle of this
organism. Concerning the number of
merozoites produced by each sehizont,
this author showed that the average
number derived from an individual, as
determined from a sample of 250 schizonts taken during the acute period of
an infection, was 15.5. Using a sample
of thirty schizonts taken during a relapse she found this number to be 15.4
merozoites.
Hartman (1927) showed that as the
initial attack of an infection advances
toward its peak the adult (maximum)
size of the organisms diminishes, but returns to a higher value as the infection
subsides at its crisis. Boyd and Allen
(1934) confirmed this observation of
Hartman and further noted that the
number of merozoites produced by a
sehizont varies with the changes in this
adult size.
PROBLEM
The primary purpose of this study has
been that of obtaining data bearing
upon the problem of the size of merozoite groups formed by schizonts of the H
strain of Plasmodium cathemerium in
their process of reproduction. Some attention has also been given to the relation which this feature of reproduction
may possibly bear to the course of the
infection. No effort has been made by
us to study the frequency of reproduction.
119
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
As a point of departure in certain
studies of the influence of various experimental factors on the rate of reproduction of malaria parasites, it has been
necessary for us to obtain information
regarding the reproduction rate of these
organisms under the usual conditions of
the laboratory. Some of the facts which
we have encountered seem to have importance that would justify their recording. The present paper is an attempt to call attention to a few of these
facts.
In its asexual reproduction the malaria parasite undergoes multiple division.
There are, therefore, two features of its
reproduction which influence its rate of
multiplication. These are (a) frequency of reproduction and (6) the
number of merozoites formed by each
sehizont. Concerning the frequency of
reproduction a number of the malaria
parasites which infect man or lower vertebrates are characterized by a definite
periodicity of schizogony, and it is commonly assumed, whether correctly or
not, that the intervals between successive peaks of reproduction represent the
length of the combined developmental
and reproductive cycles of the organism
involved.
Taliaferro, L. G. (1925), showed that
the peaks of reproduction in P. cathemerium occur at 24-hour intervals and, on
account of the high degree of uniformity
of size which she found in the trophozoites of any single sample, she felt justi-
120
Sec. C
GEORGE H . BOYD
METHODS
OBSERVATIONS
Figures 1 and 2, representing our observations upon the infections of birds
874 and 876, respectively, are illustrative of what we have encountered in this
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
Our observations on the size of merozoite groups have been based upon
counts made daily upon slides taken late
in each period of schizogony (i.e., at
8 P.M.) and stained with MacNeal's
tetrachrome stain. These observations
were continued only through the acute
stage of infections of canaries with P.
cathemerium.
On account of the small size of merozoites and the manner in which they
are ordinarily massed together within
the erythrocyte at the completion of
schizogony the problem of merozoite
counting is one which necessitates carefully prepared slides and careful observation. In order to determine accurately the number of progeny of each
schizont the process of schizogony must
be complete and the merozoites must be
sufficiently separated to show clearly.
We have found the counting of these
merozoites to be greatly facilitated by
bringing about hemolysis of the erythrocytes after the blood smear has been
spread upon the slide. This was accomplished by us quite effectively by exposing the smear to ether before it had time
to dry. Such exposure may be given
either by inverting the slide for an instant over boiling ether or by simply
dipping the slide for an instant into
ether. Chloroform may also be used
with good effect. Exposure of the fresh
smear to these substances brings about
an instantaneous rupture of erythrocytes and causes the groups of merozoites to be so spread out as to make the
counts easy to accomplish. It might
appear that by the sudden rupture of
erythrocytes this procedure would result in the probable loss of merozoites
from the groups, thus causing the counts
to be inaccurate. Our comparison of
counts made upon smears which re-
ceived such treatment with those made
upon smears which did not receive it,
however, indicates that such is not the
case. On the other hand, merozoite
groups are so spread out by this treatment that they can often be counted
with accuracy and ease where otherwise
they could not be counted at all.
In some cases an effort has been made
to determine the daily destruction rate
of parasites. For this purpose the ratio
of parasites to red cells was determined
from smears made at 6 P.M. each day.
Merozoite counts were made from the 8
P.M. smears, and the number of parasites per 10,000 red cells, multiplied by
the average number of merozoites produced by individual schizonts for the
day in question was taken as indicating
the population which faced the hazards
of the next 24-hour period. The 6
o 'clock count on the following afternoon
indicated the population which had survived these hazards. This method of
calculating parasite destruction is, of
course, open to the objection that we are
measuring against a variable standard;
i.e., the red cell count. We know of no
other method, however, which may be
used with an equivalent degree of accuracy where the experimental animal is so
small as the canary. Where there is a
rapid decline in the erythrocyte count
our percentage of parasite destruction
is lower than it should be. It does not
seem probable, however, that there
should be, in any 24-hour period, such
a rapid decline in the erythrocyte count
as to affect greatly our computations
on parasite destruction.
REPRODUCTION OF PLASMODIUM CATHEMERIUM
See. C
group of infections. The infection of
bird 874 is one in which the initial attack runs a rather brief course and the
infection then declines to the level characteristic of latent malaria. On the first
day of our observations upon this infection the average number of merozoites
formed by each schizont was 16.3 ± .3.
20
50
-
(0
70
(,60
16
i
iu
8
a
I,
trend of events in those infections in
which the parasite numbers rise sharply
and the attack soon subsides.
The infection of bird 876 is of a more
extended type. Following the appearance of parasites in the blood of this
bird the infection rapidly rose to a peak
and this was immediately followed by
Io
BUS
17*
5 <
6 «
8
s.
10
K
*
2
1
const or ntRonoii
2
»
}
«
5
»
7
(
9
1
O
U
1
2
putioo or OBaamnar orm a HATS
KTROZOITIS m. SCHIZOBTI—-©---nura E A U I — - • - —
FIGURE 1. Infection of bird 874 showing (a) course of the infection, (6)
average number of merozoites formed by each schizont, and (c) rate of parasite destruction as computed from the number of organisms surviving to each reproduction
period and the number of merozoites formed by each individual. These computations
are based upon the assumption that the entire population undergoes schizogony every
24 hours.
As the infection rose from a count of 68
per 10,000 red cells to a count of 880
parasites per 10,000 red cells 3 days
later, the size of merozoite groups fell
to 8.6 ± .2. As the infection then subsided the size of merozoite groups gradually increased but did not reach the initial level. This is rather generally the
a number crisis. The infection did not
fall to a level of latency, however, but
continued in a more or less active condition for some time. During the initial
rise of the infection the size of merozoite
groups fell from 16.0 ± .5 to 8.7 ± .3.
At the end of 4 days from this low
point in merozoite production the num-
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
100
121
122
100.
Sec. C
GEORGE H . BOYD
20fc
10,
«0
g 3
>DQ> (7€
6
7
•
9 10 11 12
raion or OBsnrimai »rtn a ma
13
1»
15
16
const or uncTicm
FIGURE 2. Infection of bird 876 showing (a) course of infection, (b) average number
of merozoites formed by each schizont, and (c) rate of parasite destruction as computed from
the number of organisms surviving to each reproduction period and the number of merozoites
formed by each individual. These computations are based upon the assumption that the entire
population undergoes schizogony every 24 hours.
ber had risen to 12.3 ± .2 per schizont
and continued to fluctuate about this
level for several days. Upon the seventeenth day from our first count the merozoite groups had again decreased in size
to 8.5 ± .4 and this was followed by a
decline in total parasite numbers which
soon rendered it impossible to obtain
counts.
Table 1 is a summary record of the
size of merozoite groups from day to
day in each of the thirty infections used
in this series. In seven of these infections this table covers a period of 13
days. The remaining infections subsided so rapidly that observations were
necessarily confined to a more limited
period. In birds 873, 876, and 885 we
were able to continue our observations
for a longer period than is indicated in
the table. In these cases observations
were continued for 23, 18, and 20 days,
respectively. Reference to individual
infections in this table shows that infections are quite commonly characterized
by high merozoite counts at the time of
the appearance of parasites. Our experience indicates that this is practically
always true when the rise in parasite
numbers is sufficiently rapid to permit
counts to be begun at once. The size
of merozoite groups then shows a daily
decline for from 3 to 5 days followed
by an incline which continues for a somewhat similar period. This incline may
or may not continue to the initial level
of merozoite production and usually does
not do so.
Unfortunately, it was not feasible to
use the same size of inoculating dose of
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
B
18.3 ±.6
13.9±.5
12.0±.3
14.3 ±.4
13.8 ±.4
17.8±.6
19.7±.4
23.1 ±.4
14.2 ±.5
19.8±.6
13.8±.5
12.0 ±.4
10.2±.2
13.3±.3
10.4 ±.3
18.9 ±.4
11.7±.4
16.2±.4
12.5±.4
16.5±.4
14.1 ±.4
15.3 ±.5
14.3±.3
16.8 ±.6
14.1 db.5
13.0±.4
17.9±.5
11.8±.3
16.7±.7
9.5 ±.3
14.8±.l
24.4±.4
15.4±.7
13.1 ±.5
16.0±.4
12.8 ±.4
16.0±.5
18.6±.5
19.1 ±.4
16.3 db.5
20.6±.6
16.3 ±.3
13.4±.6
12.1 ±.7
18.5±.4
12.2±.4
18.8±.6
10.4±.3
18.6±.5
13.6±.4
21.3±.6
13.1 ±.4
16.0±.6
19.0±.7
15.9±.2
10.7±.3
16.4±.5
20.8 ±.8
16.2±.3
15.7±.5
11.2±.2
16.0±.l
814..
820..
870..
871..
873..
876..
885..
883..
887..
857..
874..
877..
821..
823..
827..
858.
825..
854..
856..
881..
882..
822.,
828..
815.,
816.,
819.,
824.,
853..
855.,
872.,
Ave:
Birds:
12.3±.l
17.8±.4
9.5±.2
8.8±.2
12.4±.3
10.6±.2
11.3±.4
15.6±.4
13.7±.6
13.4d=.3
13.8 ±.4
12.6 ±.4
12.5±.4
9.3±.3
12.3 ±.3
10.9 ±.3
14.4±.4
13.0db.5
15.5ifc.4
10.0 ±.3
10.8±.4
10.4=fc.2
11.3±.3
11.7±.3
16.1±.4
12.0±.3
10.8±.3
12.9 ±.3
12.6±.3
14.8 ±.5
7.7±.2
3
12.1 ±.1 12.7±.l
17.9±.3 15.5±.4
8.9 ±.2 9.0±.2
9.5±.3 13.4±.5
11.4±.4 12.5 ±.6
9.3±.2 11.4±.4
8.7±.3 11.2 dz.3
15.6±.5 13.1 ±.5
15.9±.4 15.3 ±.5
13.7±.4 13.4±.2
12.1±.3 10.8±.4
8.6±.2 9.7±.5
9.8±.4 15.6ifc.5
13.1 ±.4 13.0±.3
9.7±.2 13.4±.5
13.1±.5 12.5±.3
10.9±.4 12.5±.3
11.3±.3 15.0±.4
12.4±.4 14.2±.5
8.5±.3 9.4±.5
14.1±.4 11.7±.3
12.4±.3 10.8±.3
9.4 ±.2 9.4d=.2
13.1 ±.5 17.5±.4
16.0±.4 13.7±.4
12.0±.4 13.5±.4
10.8 ±.3 10.5±.2
12.1 ±.4 11.6±.3
10.1 ±.4 12.9±.4
13.8 ±.5 17.5±.4
5
19.2± .4
10.3 ± .2
14.6 ± .5
14.3d= .5
12.2± .3
12.2 ± .5
13.8d= .4
17.0 ± .2
14.9± .4
11.4± .3
15.5± .4
12.5 ± .5
14.1 ± .3
15.8± .7
15.3± .4
12.0 ± .4
14.9 ± .4
22.8 ± .6
15.1 ± .4
16.7±1.0
13.5± .4
15.4±.5
13.2±.3
14.1 d=.4
12.9 db.3
12.5±.3
12.3±.2
18.8d=.5
15.5 ±.3
16.2 ±.5
11.0±.3
13.8±.4
10.5 ±.5
12.2d=.3
17.1 ±.6
14.2d=.5
16.4±.5
8
13.2 dz.l 14.9± .1 14.0±.l
11.5 ±.4
11.9±.5
12.3 ±.3
18.6±.6
12.6±.5
11.7±.6
13.5±.3
8.3=fc.3
16.6 ±.5
16.2±.5
9.0d=.2
14.8±.3
13.8±.4
13.3 ±.3
11.3 ±.4
14.7±.8
15.1db.4
14.2 ±.4
11.8±.4
13.1 ±.4
14.6±.4
12.9 ±.3
6
Period of observations given (days)
13.8±.l
16.1 ±.4
13.0 ±.3
16.8±.6
12.3±.4
12.5±.4
11.9±.3
17.0 ±.5
15.2±.3
14.8±.4
10.6±.5
12.2±.4
12.3 d=.3
13
17.7±.5
13.5 ±.3
14.4±.4
13.7±.3
12.2 ±.3
12.7 ±.4
16.8 ±.3
12
17.5±.5
12.7±.3
13.6±.3
13.7±.3
12.6±.4
11.6±.3
16.7 ±.4
11
15.7±.5
13.6±.3
15.6±.5
12.4±.3
11.2±.3
13.3±.4
13.5±.4
14.9±.2 13.6±.2 13.9±.2 14.3±.2
16.5±.4
13.1 ±.2
18.6±.5
13.6±.4
11.1±.4
12.5d=.3
19.9 ±.3
16.0 ±.4
14.9±.5
10
S3
§
3
i
3
Table showing the average size ofmerozoite groups formed by schizontsfrom day to day during the initial stage in thirty infections with P. cathemerium. The general
average given at the bottom of the table is weighted upon a basis of the number of counts involved in each case
a
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
124
GEORGE H . BOYD
M E R <D Z O 1 T E S
14
12
16 18
4 5 6 7 8 9 10
Sec. C
PER
20 22
S C H I Z O N T
24
26 28
30
32
34
34
MCKOZOITI
CROUPS
TO
.1,1I.I
10
20
10
20
10
20
10
10
J.I 1 1.
I | |I |
... i | |I |
, . . . 1 .1.1I.I. . •
. - •
K>
.
i
20
10
.. •
20
10
20
10
.1.1II.
.1
.1.
1
|
I
I
I
|.
20
10
•
>
m
t l *
20
DC
Ul
</>
fD
O
10
m | .
II
1
|
20
|
10
12
20
10
ID
13
.
•. 1
20
10
14
1
20
10
|
15
20
10
1I6
|
20
10
.17
1 1
|
|l
|
|1
||
|
20
10
20
19
10
20
C
20
• .1
i •
I.I
.
.
812
|
863
|
906
|
863
• . -
|
CO
_ .
•
.
|
. •
1
•
|
.1
.
_.
|
. •
•
-
.
328
.
.
24 5
I.I
•
_
834
|
|
!
.
•
H
•
•
•
624
•
•
554
456
|
21
|
.1...
.
.
219
|
. 1 -•
-
-
222
|
. 1
.
124
|
85
|
|
|
1
_ _
1
•
•
_ -
65
11 . .
•
11 .
_
66
.
10
65
.
57
FIGURE 3. A chart indicating the trend in the numbers of merozoites produced by individual schizonts during a period of 20 days' observations on thirty infections. The height of each
column represents the percentage of the total merozoite groups counted on that particular day
which were of the size indicated by the number corresponding in position at the head of the
chart. A dot above a base line denotes the occurrence of merozoite groups of the indicated
size to the extent of less than 1 per cent.
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
20
1 1. . . .
|
Sec. 0
REPRODUCTION OF PLASMODIUM CATHEMERIUM
curs and the most frequently occurring
family is one composed of ten merozoites. The next 2 days are much the
same as regards the size of merozoite
groups. Following these first 5 days
there is at least a temporary tendency
for large groups to be formed and the
median shifts upward somewhat. After
this there is a return to a lower level
of merozoite production.
One thing which may be called to the
reader's attention is the very rare occurrence of an odd number of merozoites from a reproducing schizont. We
are unable to account for the distribution of merozoite groups which we encounter in any sample. If schizogony
consists of the mere fragmentation of
the nucleus and subsequently of the cytoplasm, it would seem that odd and
even numbers might be expected in equal
frequency. On the other hand, if schizogony is initiated by a series of binary
divisions of the nucleus, it would seem
likely that more even numbers than odd
numbers of merozoites would be produced and that there would be a concentration of merozoite numbers around 4,
8, 16, 32, etc. This latter course of
events does not appear to occur. One
possible explanation of the infrequent
occurrence of odd numbers may be that
the process of schizogony is initiated by
fragmentation of the nucleus and that
this is followed by a well synchronized
series of binary divisions of the nucleus
with subsequent divisions of the cytoplasm of the schizont to correspond with
nuclear masses.
Significance of variations in the rate of
multiplication of the parasite
The foregoing figures seem to indicate
a definite decrease in the rate of multiplication of this parasite as the infection
advances in its initial stages, this de-
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
parasites for all members of this series
and the same route of inoculation was
not followed in all cases. Birds 876,
877, 881, 882, 883, 885, and 887 were inoculated intravenously. All the others
in the series were inoculated intramuscularly. These factors probably resulted in some irregularity in the length
of the incubation period and in the
speed with which infections developed.
This probably means that, in its relation
to the course of the infection, the first
day of our observations upon one infection is not identical with the first day
of our observations upon all other infections. Despite any irregularity in this
respect, however, reference to the
weighted averages of table 1 shows that
there is a significant daily decrease in
the size of merozoite groups for the entire series from the first day of our observations forward to the initiation of
the crisis of the infection. The crisis
is accompanied by an upward trend in
merozoite production which fails, however, to return to the level which characterizes the initial period of the infection. The average size of merozoite
groups falls from 16.0 ± .1 on the first
day of our observations to 12.1 ± .1 on
the fourth day. From that level it again
increases to 14.9 ± .1 on the seventh
day and fluctuates in the neighborhood
of that level for the remainder of the
period of our observations.
Figure 3 demonstrates some interesting facts concerning the sizes of merozoite groups which occur from day to
day. On the first day of observations the
most frequently occurring family size is
sixteen and a wide range of size of
groups characterized this day (6 to 34
inclusive). On the second day almost
an equivalent range in group size occurs
but the most frequently occurring number is twelve merozoites. On the third
day a narrower range of family size oc-
125
126
TABLE 2
Probable errors of the differences between
successive means
Means
16.0-14.8
14.8-12.3
12.3-12.1
12.7-12.1
13.2-12.7
14.9-13.2
14.9-14.0
14.0-13.8
14.9-13.8
14.9-13.6
Mu-Mn.... 13.9-13.6
Mu-Mij
14.3-13.9
Mi - M i . . . . 16.0-12.1
M T - M 4 . . . . 14.9-12.1
-Mj....
M, - M , . . . .
Ms-Mi....
Mt - M i . . .
Me — M s . . . .
MT - M ,
MT - M 8
Ms - M , . . . .
Mio-M,....
M10—Mu —
Differences
of
means
P. E.
of
differences
of
means
Ratio of
differences to
P. E. of
differences
1.2
2.5
0.2
0.6
0.5
1.7
0.9
0.2
1.1
1.3
0.3
0.4
3.9
2.8
.158
.136
.121
.126
.143
.168
.169
.175
.213
.232
.226
.229
.145
.154
7.6
18.4
1.7
4.8
3.5
10.1
5.4
1.1
5.2
6
1.3
1.7
26.9
18.2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
We have pointed out the statistical
validity of certain variations, but our
interest centers ultimately in the significance which these may have in relation to the course of these infections.
In this connection attention is again
called to figures 1 and 2 which indicate
not only merozoite production but also
the daily rate of parasite destruction.
From these figures it will be seen that,
at the first appearance of parasites, the
daily rate of parasite destruction was
relatively low; being in the neighborhood of 50 per cent of the number of
parasites produced at the previous reproduction period. Within 3 or 4 days
from the initial count, however, the daily
destruction rate increased to 90 per cent
or above. It then continued at approximately this high level as long as our
observations were continued.
Table 3 includes ten infections in
which parasite destruction was followed
during the initial attack. The figures
given in this table show (1) the rate of
parasite destruction from day to day in
per cent, and (2) the course of each infection in parasites per 10,000 red cells.
Each of these infections appears to follow the same general tendency in parasite destruction as is displayed in the
graphs shown in figures 1 and 2. The
average rate of destruction for these ten
infections for the first 24-hour period of
our observations is about 50 per cent,
but by the third day this average has
increased to above 90 per cent of all
parasites produced. From that time on
it remains above 90 per cent. This increase in the rate of destruction during
the initial stages of the infection, though
somewhat greater in degree than that
recorded by them, is in accord with the
observations of Taliaferro and Mulligan
(1937) upon phagocytic activity in the
spleen, liver and other organs.
DISCUSSION
The course of events in the early
stages of a malaria infection is such a
rapid one and the defense mechanism
of the host rapidly reaches such a high
degree of effectiveness that it is no easy
task to analyze accurately the factors
which determine the course an infection
takes. Our observations upon this series
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
crease being occasioned by a reduction
in the number of merozoites formed by
each reproducing schizont. As may be
seen by reference to table 2, with the exception of the difference between the
means of the third and fourth days, all
variations from the first to the eighth
day of observations are sufficiently large
to be statistically significant. It may be
noted also that the difference between the
first mean and the fourth mean is 26.9
times the magnitude of its probable error, and that the difference in the opposite direction between M4 and M7 is 18.2
times its probable error.
Ml
See. C
GEORGE H. BOTD
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
(1)
(2)
871
873
874
876
877
881
883
885
887
Average daily destruction:
(1)
(2)
870
Contro birds:
49.4
47.6
80.4
47.9
45.0
18.7
60.9
50.4
69.2
29.0
80.5
50.7
89.9
74.5
78.2
94.3
550
96.3
230
88.8
85.8
320
400
89.8
90.2
6
450
580
49.5
56.9
830
660
91.3
93.3
8
933
660
95.9
93.8
9
570
680
91.7
89.3
10
76.2
2
13
640
90.2
780
89.5
92.1
90.0
780
880
90.8
96.3
616
266
96.2
94.5
258
140
94.8
87.0
147
230
93.5
93.3
115
240
92.7
97.1
107
95
97.1
93.8
87.3
96.2
95.1
78.9
2,000 960
440
380
650
250
800
880
760
230
7
83.5
475
94.3
360
88.5
480
91.8
94.3
94.3
92.5
93.3
91.0
91.1
92.1
90.2
91.6
90.0
91.5
80.4
98.0
94.9
95.9
91.0
93.5
93.6
96.1
97.0
89.3
89.9
520
1,520
360
400
120
980
60
67
300
540
155
97.5
92.8
96.5
91.7
91.0
94.0
92.9
3,580 1,233
1,750
1,400
1,943
2,480 2,800 1,533
82.0
99.4
14
is
920
500
960
92.5
94.8
94.1
740
370
90.6
1,220
90.5
92.6
1,430
1,090
1,100
87.1
91.6
1,350 2,720 3,120
n
89.2
95.4
89.9
94.6
94.8
93.6
89.9
93.9
93.6
1,420 2,040 1,740
1,340
2,570 2,100
2,880 2,160
1,920
1,660
153
360
87.1
92.2
7
89.2
95.0
83.6
93.9
92.9
93.9
88.6
94.5
91.5
89.3
91.8
740
560
471
760
580
1,560 833
280
710
380
950
780
210
5
96.4
97.3
93.8
98.6
96.0
720
3,000 830
300
50
23
820
100
550
446
250
91.8
270
95.2
640
94.3
940
44.9
166
42
36
330
84
16
68
113
22
130
4
3
2
l
Period of observations given (days)
Observed number of parasites per 10,000 red cells and computed parasite destruction rate from day to day during the initial stage in ten infections
.LAHLdS O
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
S
1
o
i
§
128
Sec. C
GEORGE H . BOYD
duced, at the time of the crisis and beyond it exceeds the death rate recorded
by Taliaferro and Cannon (1936) for
P. brasilianum of monkeys. So long as
the destruction rate remains in the
neighborhood of 67 per cent such variations in parasite reproduction as we
have noted might be disregarded, but
they can hardly be left out of account
when the destruction rate reaches a level
of 90 per cent or above. To us it seems
that the temporary decrease in parasite
reproduction which occurs as the total
parasite population increases must undoubtedly play an important part in
bringing about the crisis of the malaria
attack. It also seems probable that the
resumption of a level of merozoite production slightly below the initial level
plays a part in the delicate adjustment
between parasite and host during developed and latent conditions of the infection following the initial attack.
SUMMARY
This paper is based upon observations
on thirty infections of canaries with
Plasmodium cathemerium and includes
information bearing upon the number of
merozoites produced by the schizonts of
this parasite in their process of schizogony and upon the rate of destruction
of the parasites in these infections. The
indications from this study are as follows:
1. On the whole, the largest groups
of merozoites are formed by schizonts in
the initial stages of the attack.
2. From an average of 16 ± .1 merozoites per schizont on the first day of observations the size of groups diminishes
to 12.1 ± .1 on the fourth day. The
number then increases to 14.9 ± .1 on
the seventh day and goes no higher than
that for the remainder of the period of
our observation.
3. In the most active infections there
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
of infections, however, are not fully in
accord with the position to which Taliaferro has been led in his monumental
study of the mechanism of vertebrate
host defense against malaria. Unless we
have misinterpreted statements made by
him in several of his papers (see Taliaferro 1926, 1931, 1932a, 1932b, Cannon
and Taliaferro 1931, Taliaferro and Taliaferro 1934, Taliaferro and Cannon 1936
and Taliaferro and Mulligan 1937) his
view is that the rate of reproduction of
a given species of malaria parasite is essentially constant. The only exception
to this fact which he notes is that during
the crisis there is a temporary delay in
the occurrence of schizogony and decrease in the number of merozoites produced by a schizont. In a recent paper
(Taliaferro and Mulligan, 1937) he
states: "From this it can be concluded
that the entire patent infection is an
expression of parasiticidal mechanisms
uncomplicated by any changes in the
rate of reproduction.''
The data presented in this paper do
not seem to us to indicate that the reproduction rate of this particular species
of Plasmodium could be designated as
constant. On the contrary, not only
does the rate of reproduction vary, but
the variations are of such magnitude
that when coupled with the prevailing
rate of parasite destruction they must
undoubtedly play a part in determining
the course of the infection.
There is nothing in this work which
would lead to a lessening of emphasis
upon parasite destruction. Except for
the first day or two after parasites become plentiful enough for counts, these
data indicate that it greatly exceeds the
destruction rate (about 67 per cent) indicated by Taliaferro, L. G. (1925), for
this species of Plasmodium. In fact,
when reckoned in terms of the ratio of
parasites destroyed to parasites pro-
Sec. C
REPRODUCTION OF PLASMODIUM CATHEMERIUM
rapid crisis in numbers which commonly
characterizes the initial attack is apparently due to the combined effects of lowered multiplication rate and increased
destruction of parasites,
Hemolysis by means of ether before
the blood smears have dried is given as
a method of facilitating the counting of
merozoites.
REFERENCES
Boyd, G. H., and Allen, L. H.
1934 Adult size in relation to reproduction of the avian malaria parasite, Plasmodium
cathemeriitm. Amer. Jour. Hyg., SO: 73-83.
Cannon, P . B., and Taliaferro, W. H.
1931 Acquired immunity in avian malaria—III. Cellular reactions in infection and
superinfection. Jour. Prev. Med., 5 : 37-64.
Hartman, E,
1927 Certain interrelations between Plasmodium and its host. Amer. Jour. Hyg., 7;
407-432.
Taliaferro, L. G.
1925 Infection and resistance in bird malaria with special reference to periodicity and
rate of reproduction of the parasite. Amer. Jour. Hyg. 5: 742-789.
Taliaferro, W. H.
1926 Host resistance and types of infections in trypanosomiasis and malaria. The
Quart. Eev. Biol. 1: 246-269.
1931 The mechanism of acquired immunity in avian malaria. South. Med. Jour., Si:
409-415.
1932a Infection and resistance in the blood inhabiting protozoa. Science, 75: 619-629.
1932b Experimental studies on the malaria of monkeys. Amer. Jour. Hyg., 16: 429449.
Taliaferro, W. H., and Cannon, Paul E.
1936 The cellular reactions during primary infections and superinfections of Plusmodium brasilianum in monkeys. Jour. Inf. Dis., 59: 72—125.
Taliaferro, W. H., and Mulligan, H. W.
1937 The histopathology of malaria with speeial reference to the function and origin
of the macrophages in defense. The Indian Med. Res. Mem., Z9: 1-138.
Taliaferro, W. H., and Taliaferro, L. G.
1934 Morphology, periodicity and course of infection of Plasmodium brasilianum in
Panamanian monkeys. Amer. Jour. Hyg., gO: 1-49.
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016
is often a greater degree of variation in
merozoite production than is shown by
the general average.
4. Parasite destruction is relatively
low in the beginning of infection but
rapidly rises until, on the third day of
our observations, it was 90 per cent. It
continued to approximate this level for
the remainder of our observations. The
129
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on September 19, 2016