Gametocyte Density Research Articles

Induction of sexual differentiation in malaria

Buckling, A., Crooks, L., and Read A. 1999. Plasmodium chabaudi: Effect of antimalarial drugs on gametocytogenesis. Experimental Parasitology93, 45–54. The proportion of asexual blood-stage malaria parasites that develop into transmission stages (gametocytes) can increase in response to stress. We investigated whether stress imposed by a variety of antimalarial drugs administered before or during infection increased gametocyte production (gametocytogenesis) in vivo in the rodent malaria parasite, Plasmodium chabaudi. All methods of drug treatment greatly reduced the numbers of asexual parasites produced during an infection but resulted in either no reduction in numbers of gametocytes or a smaller reduction than that experienced by asexuals. We used a simple model to estimate temporal variation in gametocyte production. Temporal patterns of gametocytogenesis did not greatly differ between untreated and prophylaxis infections, with rates of gametocytogenesis always increasing as the infection progressed. In contrast, administration of drugs 5 days after infection stimulated increased rates of gametocytogenesis early in the infection, resulting in earlier peak gametocyte densities relative to untreated infections. Given the correlation between gametocyte densities and infectivity to mosquito vectors, and the high frequency of subcurative drug therapy and prophylaxis in human populations, these data suggest that antimalarial drugs may frequently have only a small effect on reducing malaria transmission and may help to explain the rapid spread of drug-resistant geno-types.

Forest malaria in Bangladesh. I. Parasitology.

Malaria in the eastern forests of Bangladesh has never been controlled and has been the major source of the country-wide resurgence that has occurred since 1971. The malaria status of an isolated, forest-dwelling community was studied for 21 consecutive months. Blood examination, indirect hemagglutination testing, and detailed histories were used. Nearly 88% were found patent for Plasmodium falciparum and 70% for Plasmodium vivax at least once during the study. The population displayed characteristics of intense, annual transmission: asymptomatic patent infections, low trophozoite and gametocyte densities, and increasing antibody and decreasing parasite prevalence with advancing age. Prevalence and mean titer of antibody increased in each age group during the 7-month transmission season. Chloroquine-resistant P. falciparum was demonstrated epidemiologically.

The effect of temperature, age and density of gametocytes, and changes in gas composition on exflagellation of Leucocytozoon simondi.

The rate of initiation of exflagellation of microgametocytes of Leucocytozoon simondi was studied in relation to temperature, age and density of gametocytes, and changes in gas composition. Observations were made in vitro through examination of fresh blood, and thin blood films were prepared at appropriate intervals. An inverse relationship between temperature and the time required for initiation of ex-flagellation was demonstrated. There was a decrease in the time required for initiation of exflagellation as the temperature increased from 15 to 26C. Between 26 and 40C exflagellation usually occurred in 1–1½ min. Exflagellation at 40C, which approximates the body temperature of the host, indicates that a drop in temperature per se is not necessary for the initiation of exflagellation. Gametocytes appear to be capable of exflagellation for about 5 days postmaturity. Differences in density of parasitemia do not affect the time for initiation of exflagellation. The presence of O2 and a decrease in CO2 are important stimuli for exflagellation. The effect of the above factors on the initiation of exflagellation is discussed in relation to the uptake of infected blood by the simuliid vector of the parasite, and compared with the situation in related Haemosporina

Turkey Leucocytozoon Infection.: 2. Cryobiologic Preservation of Leucocytozoon Smithi Sporozoites

Five different cryoprotective agents at various concentrations were evaluated for their effectiveness in preserving the infectivity of Leucocytozoon smithi sporozoites at low temperatures for an indefinite period of time as determined by the degree of parasitemia in inoculated turkey poults.Glycerol at concentrations of 10 and 5 percent, DMSO at 10 percent ethylene and trimethylene glycols at 2.5 percent, and propylene glycol at five percent when dissolved in medium 199 plus 10 percent fetal bovine serum yielded excellent sporozoite survival at a temperature of −196° C. When dissolved in medium 199 supplemented with 10 percent turkey serum, cryoprotection by those chemicals was less effective. In the absence of animal sera, sporozoite survival to freezing was very poor. Regardless of suspending media, all sporozoites frozen by direct immersion in liquid nitrogen lost their infectivity. No differences were observed in the parasite’s prepatent period, time of maximum gametocyte density, nor RBC count pattern between turkey poults infected with frozen, stored sporozoites and those infected with fresh unfrozen sporozoites from the same original stock.

The experimental transmission of Plasmodium malariae to Anopheles labranchiae atroparvus.

The Vs strain of P. malariae proved very infective for laboratory-bred A. l. atroparvus; of 31 batches fed on 11 gametocyte carriers, 24 (77·4%) became infective. Oöcysts were first seen 5 days after the blood meal; development was slow, 5–14 days, after which they measured 6–64μ. The greatest number of oöcysts per gut was 60 (average 24) in one batch; the average for all batches was 3·5. Sporozoites first appeared in the salivary glands on day 15; they measured 12–14μ in length in fresh preparations, and 10·5μ in stained preparations. Sporogony developed in 15–20 days, in mosquitoes kept at 19°–30°C. From 1 to 98·6% of A. l. atroparvus in the various batches became infected, but not in accordance with the density of male gametocytes. The ability of male gametocytes to originate sporogony in A. l. atroparvus extends from 8 to 404 days of patency. The highest degree of infectivity was 98·6% of one batch of mosquitoes, fed during the second week of patency. Success in infecting mosquitoes depends upon the quality of the gametocytes, the susceptibility of the mosquitoes, and the number of mosquitoes in each batch used.

Prepatent Period and Parasitemia in Leucocytozoon simondi Infections Resulting from Short Exposures to Sporozoites

Of 38 Pekin ducklings infected with L. simondi by 24-hr exposures or intraperitoneal injection of ground-up black flies, 94.3% showed prepatencies of 7 days (? 24 hr). Most of the naturally infected ducks showed two peaks of gametocyte density, the first on the 10th day postexposure composed entirely of round forms, and the second on the 14th to 16th days postexposure composed of approximately 90% elongate forms. Elongate gametocytes appeared on the 11th day postexposure in 30 ducks, the 12th day in four ducks, and four did not show elongate forms. Eight ducks infected by injection of black flies died within 48 hr of the first appearance of elongate gametocytes, and ten ducks infected the same way showed a sharp increase in gametocyte density following the appearance of the elongate forms. The length of the prepatent period of Leucocytozoon simondi given by O'Roke (1934) and Fallis et al. (1951) is between 6 and 14 days. Several investigators have described the length of the initial infection to be about 30 days (O'Roke, 1934; Chernin, 1952b; Fallis et al., 1951). O'Roke (1934), Huff (1942), and Fallis et al. (1951, 1956) reported that the gametocyte population rose to a maximum density early, decreasing gradually into latency, and Chernin (1952a) pointed out that if there was any mortality the ducks died between 10 and 19 days postexposure. The pleomorphic gametocytes of L. simondi have been described by Fallis et al. (1951) and Chernin (1952b), who noted that round forms are most prominent early in patency while elongate or spindle forms predominate as the infection progresses. Chernin's (1952b) differential counts on the two forms show that the round form reaches a maximum density earlier than the elongate form. Chernin and Sadun (1949) thought that there might be a cyclic variation in the gametocyte density in primary infections, but Chernin (1952b) later refuted this. It is our intention to describe the occurrence and timing of the prepatent period, the appearance of elongate gametocytes, gametocyte density fluctuation, and mortality. Received for publication 14 March 1966. * Contribution Number 116 from the W. K. Kellogg Biological Station, Michigan State University. 962 MATERIALS AND METHODS Ducks were infected by exposure to black flies for 24 hr or sporozoites were inoculated intraperitoneally, thus allowing all sporozoite development to begin at approximately the same time. Thirty-eight white Pekin ducks ranging from 2 to 3 weeks of age were used as hosts for L. simondi. Group 1 consisted of 20 ducks exposed to black flies at Indian River, Michigan for 24 hr on 16 July 1964. Group 2 consisted of 18 ducks, of which ten were infected on 6 June 1965 by intraperitoneal injection of ground-up black flies collected at the Fox River in Seney, Michigan, on 3 June 1965, and eight were infected the salme way with black flies collected at the same location on 13 July 1965. All ducks were maintained in outdoor pens at the W. K. Kellogg Biological Station near Kalamazoo, Michigan, an area where L. simondi is not transmitted (Kocan and Clark, 1965). The naturally infected ducks of Group 1 were examined for parasites by thin blood films taken daily beginning with the day following exposure to black flies. Gametocyte densities were recorded every other day beginning with the 8th day postexposure. Ducks in Group 2 were sampled for gametocyte density daily. Blood for a slide and an erythrocyte count was obtained from a web vein puncture. Erythrocyte counts were done on a hemocytometer with blood diluted in a standard RBC diluting pipette, using Hayem's fluid as a diluent. All blood films were stained with Giemsa. Parasite counts were recorded as gametocytes per mm3 of venous blood. This was done by counting the mean number of gametocytes per 1 000 RBC's and the number of RBC's per mmm of blood. These values were used in the equation gametocytes _ RBC per mm3 gametocytes per mm 1,000 per 1,000 RBC's thus giving gametocytes per mm3 of blood. DifThis content downloaded from 157.55.39.120 on Sun, 04 Dec 2016 04:52:30 UTC All use subject to http://about.jstor.org/terms KOCAN AND CLARK-PREPATENT PERIOD AND PARASITEMIA IN LEUCOCYTOZOON TABLE I. Number of birds becoming patent and showing first elongate gametocytes on nth day postexposure. * Days postexposure 6 7 8 9 10 11 12

Anemia in ducks infected with Leucocytozoon simondi.

SYNOPSIS. Thirty‐four white Pekin ducklings were used to study the anemia associated with infection by Leucocytozoon simondi.The first appearance of gametocytes in the peripheral blood, as detected by thin smears, marked the onset of anemia. This anemia lasted for the duration of the initial parasitemia, usually reaching a low point early in the infection (1 to 5 days post patency) and returning slowly to normal as the parasitemia decreased. Greatest gametocyte density occurred 5 to 8 days post patency. In a number of cases recovery from anemia began simultaneously or even prior to the highest level in the gametocyte density.In low level parasitemias a fluctuation occurred in erythrocyte numbers which corresponded with the peaks of gametocyte density.In none of the infections was a sufficient number of parasite observed to account for the existing anemia.Haemopoietic activity was observed for a brief period at the time of maximum erythrocyte loss in only a few birds. The overcompensation for erythrocyte loss at the end of the primary parasitermia favors the view that increased erythrocyte production may account for the short duration of haemopoiesis.

Experimental malaria infections in “saltwater” and “freshwater” Anopheles gambiae from East Africa

1. 1) Two insectary strains of Anopheles gambiae, a typical “freshwater” strain and a “saltwater” variant, from East Africa, were found to be susceptible to infection with local strains of Plasmodium falciparum. 2. 2) The data indicated that the “freshwater,” or “Kisumu,” strain was slightly more susceptible to infection than the “saltwater” strain when fed on subjects with moderate to high gametocyte densities.

Infectivity to Mosquitoes of Plasmodium Vivax and Plasmodium Falciparum under Various Conditions

Some of the most interesting studies in human malaria in which I have participated have concerned factors of importance in the epidemiology of the disease, especially the conditions under which the infection is transmissible to mosquitoes, and the possible alteration of this transmissibility through the judicious selection and use of antimalarial drugs. One who is engaged in this field of research soon discovers that these conditions can be quite complex and puzzling. For example, the correlation between gametocyte densities in the human host and the infectivity to mosquitoes may be extremely variable, depending on the stage of the infection, the species—or even the strain—of parasite, and many other factors. It is felt that an understanding of these conditions is of considerable importance as an aid to the efforts now underway toward eradication of the disease.

A study on the infectivity of patients to mosquitoes in the early stages of primary plasmodium vivax malaria (madagascar strain)

1. (1) Daily feedings of laboratory-bred Anopheles atroparvus were carried out on 54 patients during the early stages of primary P. vivax malaria (Madagascar strain). 2. (2) One hundred mosquitoes were fed daily on each patient from the onset of symptoms or parasitaemia, and continued until the patient was given suppressive or curative therapy. 3. (3) On the 7th day after feeding, 40 mosquitoes from each batch were dissected to determine the percentage of mosquitoes infected and the number of oocysts per gut. 4. (4) The earliest infection in the mosquito occurred 2 days after fever or parasitaemia, and the latest 7 days after. 5. (5) The percentage of mosquitoes which became positive on the 1st day of infection varied between five and 100. 6. (6) From 32 patients, mosquitoes became infected before gametocytes were detected in blood films; and from 22 patients, mosquitoes became infected on the 1st day that male gametocytes were found. 7. (7) It is well known that in primary untreated P. vivax infections, maximum gametocyte density is reached on or about the 10th day. The work described in this paper shows that ripe gametocytes may be present in sufficient numbers to infect mosquitoes as early as the 3rd, and even in one case, on the 2nd day. 8. (8) In P. vivax endemic areas, even where there are good medical services, not many patients would be admitted to hospital or treated, as early as the 3rd day of a primary attack, by which time they might have infected mosquitoes. 9. (9) We believe that in malaria eradication and control schemes, success is more likely to be achieved if gametocytocidal drugs are given to coincide with mosquito control.

Infectivity to mosquitoes of Plasmodium falciparum as related to gametocyte density and duration of infection.

Summary and Conclusions Mosquitoes were fed at all stages of infection on 88 cases of Plasmodium falciparum. Observations were made on the relations of gametocyte densities and length of patency to infectivity. Mosquitoes frequently became infected when fed on gametocyte densities of less than 10 per cmm. of blood, and were infected as late as day 321 of parasite patency in the South Carolina strain, and 410 in the Panama strain. It is concluded that the long enduring parasitemias of these South Carolina and Panama strains of P. falciparum are of considerable epidemiological importance and may be responsible for a large part of the transmission of this species in certain endemic areas.

Problems concerned with gametogenesis in Haemosporidiidea, with particular reference to the genus Plasmodium.

Although many interesting observations have been made upon gametogenesis in Haemosporidiidea many fundamental problems await solution. Our knowledge of the nuclear changes occurring during the development of the gametes and the fertilization of the female gamete is still incomplete. Little is known of the factors which control gametocyte production, though there is evidence that in some species, i.e. Leucocytozoon simondi and Haemoproteus columbae in the duck, it is influenced by the physiological stage of the host. The type of host and the method of transmission have also been shown to affect the numbers of gametocytes formed in some species. No correlation has been found in Plasmodium, the genus in which this subject has been studied extensively, between acquired immunity and gametocyte formation. Although a broad relationship has been demonstrated in Plasmodium between the density of gametocytes in the blood and the oocyst rate and density assessed in susceptible mosquitoes, hosts heavily infected with apparently ripe gametocytes may prove non-infective to susceptible mosquitoes. In birds heavily infected with P. gallinaceum, serum taken at the peak of parasitaemia has been shown to affect adversely the infectivity of gametocytes to mosquitoes. Pamaquin and primaquine, in small doses, inhibit the development of gametocytes completely, whereas proguanil may not prevent the formation of oocysts though it inhibits their subsequent development. High densities of gametocytes have been observed in patients treated with proguanil or sulphamethazine. An actual in crease in the number of gametocytes produced, as compared with the untreated control strain, was observed in strains of P. gallinaceum in process of developing resistance to sulphadiazine, proguanil or 2:4-diamino-6:7-diisopropylpteridine as a result of treatment with those drugs.

Factors determining the true reservoir of infection of Plasmodium falciparum and Wuchereria bancrofti in a West African village

1. (1) An investigation was carried out in a hyperendemic malarious village in the Gold Coast to study the factors determining the true reservoir of falciparum malaria infection in the human population. 2. (2) A falciparum gametocyte (crescent) survey was carried out on the, population, and the actual infectivity of as many crescent carriers as possible was tested by means of feeds with laboratory-bred A. gambiae. 3. (3) My previous findings in Jamaica and Young's in South Carolina were confirmed in showing that some carriers are still infective to Anopheles at a time when crescents are so scanty that they can hardly be detected in the thick blood film.In this survey these cryptic carriers formed about 25 per cent. of all infective carriers. Nearly half of all infective carriers were infective at crescent densities lower than 20 per c.mm. 4. (4) About 10 per cent. of crescent carriers were non-infective at a time when crescents were abundant in the blood. The highest proportion of these non-infective carriers was in the infant group. 5. (5) The incidence of good infectors was highest in the pre-school children (toddlers) and school children (juveniles), the latter group, aged,5–9 years, being probably more important as a source of infection. 6. (6) Despite the low gametocyte rates and gametocyte density in adults, random test feeds revealed two out of 30, i.e. 7 per cent., infective. For this and other reasons the adult group may be a more important source of infection than usually considered under hyperendemic conditions. 7. (7) The rôle of these infectors is discussed in the light of recent knowledge about the uneven distribution of anopheline bites and feeds among different age-groups. 8. (8) Preliminary study on the reservoir of bancroftian filariasis showed, in random tests, about one-third of the adult population infective. The youngest infector was aged about 5, and the oldest about 75. Most infectors had a very low grade of infectivity. 9. (9) Below 100 microfilariae per 20 c.mm. there is no obvious relation between microfilarial density and the proportion of the mosquito batch which becomes infected and infective. Above 100 microfilariae per 20 c.mm., increased microfilarial density tends to produce a high infection rate, but there is no corresponding increase in the intensity of each infection. 10. (10) Preliminary studies on the nocturnal infectivity of human infectors to A. gambiae suggests that a fairly steady degree of infectivity is maintained from about 9 p.m. till about 4 a.m. 11. (11) In dissections of the mosquitoes caught in the village, the oocyst rate of A. gambiae was a little over four times that of A. funestus, but the sporozoite rate was 30 times greater. Similarly, despite an almost equally high rate of infection with immature filaria larvae, A. funestus had a very much lower rate of infection with mature filaria larvae than A. gambiae. 12. (12) A method is described of interpreting the mosquito infection rates in such a way as to throw some light on the fluctuations in infectivity of the human population as a whole.

Observations on the infectiousness of gametocytes in hyperendemic malaria

1. (1) There is a correlation between the probability of a mosquito's becoming infected and the gametocyte density of the carrier, when densities are broadly grouped. 2. (2) A small series of experiments in the hyperendemic zone of S. W. Nigeria are reported in which A. gambiae gambiae were allowed to feed on children carrying different densities of P. falciparum gametocytes. 3. (3) In the community from which these subjects came the average density of gametocytes was low, approximately 5 6 of all gametocyte carriers showing less than 100 per c.mm., and 1 6 more than 100 per c.mm. 4. (4) Of mosquitoes feeding once on the first group (less than 100 gametocytes per c.mm.) 5 per cent. could become infected if they survived long enough for completion of the extrinsic cycle, while of mosquitoes feeding on the second group (more than 100 per c.mm.) 50 per cent. could become infected. Other workers have found a higher proportion infected in the first group. 5. (5) These figures are used in a hypothetical example to calculate the proportion of all A. gambiae feeding on the population at one moment which could become infected.

A study of gametocytes in a west african strain of plasmodium falciparum

A West African strain of P. falciparum was maintained in our laboratory over a period of 17 months and during this time 85 patients were infected. The percentage of our patients who developed gametocytes was very much higher than the percentage in any age group of the cases examined by malariologists where the strain originated. The density of gametocytes per c.mm. in our patients has greatly exceeded the number found by workers who have examined cases where the strain originated. Anopheles stephensi (type) imported from Delhi, has proved to be an efficient carrier of this strain of parasite. On the other hand, the strain of English Anopheles atroparvus maintained in our insectarium is a very poor carrier. Gametocyte output was always greater in cases in which the primary attack was aborted by the administration of antimalarial drugs. It is believed that inadequate treatment of the primary attack, irrespective of the drug used, conduces to gametocyte production. If this is so, it indicates at least two important factors—(1) that patients leaving hospital should be given a course of a gametocytocidal drug, e.g., proguanil, between the 14th and 21st day after the last day of fever; (2) that a clinical and radical cure of a primary attack, in addition to being in the best interests of the patient, is also of major importance epidemiologically in preventing mosquitoes from becoming infected. This applies especially to unseasoned personnel in the services. In this series of cases, macrogametocytes always appeared before microgametocytes and persisted for days or weeks after microgametocytes disappeared. Gametocytes were never found in cases where antimalarial drugs cured the disease in the primary attack. The study of gametocytes in this series of cases indicates that the maximum longevity of individual gametocytes is about 60 days. Many of our patients showed gametocytes for the first time about 3 weeks after the beginning of the primary attack and 2 to 4 days after the first day of the recrudescence. We suggest that gametocytes evolve from asexual parasites circulating in the blood during the remissions between attacks. The percentage of gametocyte carriers, calculated from the findings in thick films, may not be an accurate index to the percentage of a population infective to Anopheles. Differentiation of the sexes is more difficult in thick films than in thin films. Thick films take several minutes to dry. The gametocytes, providing they are ripe, may become round organisms and be mistaken for other parasites, especially P. malariae.

The Infectivity of Native Malarias in South Carolina to Anopheles Quadrimaculatus 1

Summary and Conclusions In a field study in South Carolina, Anopheles quadrimaculatus mosquitoes were applied to native cases of malaria in Negroes to determine the infectivity of such malaria cases. Of 142 feedings upon Plasmodium falciparum patients, 21 showed infections. Of 12,606 mosquitoes dissected, 2.5 per cent were infected. These infections developed normally in the mosquito and in one out of two trials transmission was successful. The majority of the mosquito infections occurred during the months of October through January. Mosquitoes kept at outside temperatures during October and November became infected. One patient remained infective to mosquitoes over an 8-month period. Of the 25 patients showing gametocytes, 64 per cent infected mosquitoes. The gametocyte densities resulting in infections were relatively low, none being over 90 per cmm. Thirteen of the infections resulted when the gametocytes were fewer than 10 per cmm. Patients with asymptomatic parasitemias infected mosquitoes at about the same rate as did those who were symptomatic. As the asymptomatic group is considerably larger than the other, it is concluded that the former is mainly responsible for the transmission of malaria. There were 14 feedings upon P. malariae. Four cases showed gametocytes of a low density at feeding and three lots of mosquitoes were infected. Of 586 mosquitoes dissected, 1.7 per cent were infected. Of nine feedings upon P. vivax, none became infected nor were gametocytes present. It is concluded that the patient with an asymptomatic parasitemia, usually with a relatively low gametocyte density, is the important factor in the transmission and maintenance of P. falciparum and P. malariae malaria in the area studied.

Observations on the Mechanism of the Parasite Cycle in Falciparum Malaria 1

Summary and ConclusionsA study of the mechanism of the parasite cycle has been made through an analysis of its component trophozoite and gametocyte waves in fifty-five Negro patients, thirty-four of whom were naturally inoculated and twenty-one artificially infected with a single strain of P. falciparum.The day of modal density proves to be a reasonably good centering point for the trophozoite and gametocyte waves to which curves are fitted. Computed densities on the modal day are utilized.Key points in the parasite cycle, the days of first appearance (microscopic detection) of trophozoites and gametocytes following inoculation and the days of maximum or of modal density, are surprisingly constant. Failure of quinine to affect these points and of artificial inoculation to alter greatly the lengths of the segments between them supplies further evidence of the stable nature of the cycle.The timing of certain key points may be altered in individual patients by natural resistance, acquired immunity, or treatment but all points are not similarly affected. The correlations between adjacent segments are predominantly negative indicating that when one is lengthened the other becomes shorter and vice versa so that the cycle is brought back into line.This stability leads to the belief that the events in the parasite cycle are determined prior to the appearance of trophozoites in the peripheral blood and possibly at the time of inoculation.Significant positive correlation exists between the computed densities of trophozoites and gametocytes on the modal day. This relationship supports the thesis that sexual forms arise from the segmenting asexual parasites.The negative relationships between adjacent segments of trophozoite and gametocyte waves indicate, we believe, that production of gametocytes begins prior to the end of the prepatent period and possibly soon after inoculation of the patient. Consequently, the interval of approximately ten days between the first appearance of trophozoites and gametocytes and between their peak densities indicates that a period for development is required by gametocytes over and above that needed for them to accumulate sufficiently to reach microscopic visibility.

On the Infectiousness of Patients Infected with Plasmodium Vivax and Plasmodium Falciparum 1

In a previous paper (1) we expressed our opinion as to the minimal leucocyte-gametocyte ratios requisite for the certain propagative recovery of malaria parasites, in order to secure the maximum degree of qualitative and quantitative infection of the anophelines employed. For the intensive infection of A. quadrimaculatus we consider that, with an equal distribution of the sexes, the desirable ratios are approximately 2 gametocytes to 100 leucocytes in the case of P. vivax and 22 gametocytes to 100 leucocytes in the case of P. falciparum. These roughly may be considered the equivalent of 100 and 1100 gametocytes per cubic millimeter. While these data are technically important to a naturally induced malaria therapy service, they have little epidemiological significance. The latter viewpoint requires data illustrating the minimal gametocyte density capable of producing the least possible infection of anophelines.

On the Schizogonous Cycle of Plasmodium Vivax, Grassi and Feletti 1

SummaryBy nuclear and cytoplasmic criteria we believe we have demonstrated the occurrence, in patients infected with a pure strain of P. vivax, five series of cells, which for convenience we have designated A, B, C, D and E. Of these series C and series D are the well known micro- and macro-gametocytes. The cells of series A reproduce by schizogony, and are generally recognized as trophozoites. Our observations lead us to entertain the opinion that at the schizogony of certain cells in series A, a merozoite differentiated from the others is produced (figs. 48 and 110), which gives rise to a schizont of either series B or D. The cells of these series we regard as pregametocytes. On the schizogony of the cells of the pregametocytes of series B or D, the merozoites become the gametocytes of either series C or E respectively. The cells of series A thus may be regarded as stem cells for the other series, and are numerically the backbone of the infection. Our present observations do not suggest the existence of more than one series of stem cells, from which it is likely both sexes of gametocytes are produced by the schizogony of the intermediary pregametocytes. Our inability to detect more than one series of stem cells suggests that the sporozoites which initiated the attack were not sexually differentiated.In a paper (1) to appear shortly by Boyd, Stratman-Thomas and Muench, it is shown that frequent oscillations of gametocyte density occur, with upward trends recurring at five day intervals. If, as appears probable, the cells of series C or E require 48 hours for maturation, and the cells of series B or D are assumed to require the same period until they produce gametocytes on schizogony, a total of 96 hours are required for the production of gametocytes from the stem cells. With afternoon paroxysms the development would require a period of five days, an interval in line with observations reported in the study cited.