The effect of oral contraceptives in malaria infections in rhesus monkeys*

Bulletin ofthe WorldHealth Organization, 62 (4): 627 - 637 (1984) © World Health Organization 1984 The effect of oral contraceptives in malaria infections in rhesus monkeys* WILLIAM E. COLLINS,' CARLOS C. CAMPBELL,2 ANN BARBER,3 JIMMIE C. SKINNER,3 & ALAN Y. HUONG4 Rhesus monkeys, Macaca mulatta, were treated with the oral contraceptives Brevicon (norethisterone with ethinylestradiol) and Ovral (norgestrel with ethinylestradiol), and subsequently inoculated with the simian malaria parasites Plasmodium cynomolgi basti- anellii or P. coatneyi. Parasitological, serological, and serum biochemical studies indicated that although there were some significant differences, in general the patterns ofresponse to infection in both treated and control animals were similar. During the primary infection, however, Brevicon resulted in increased levels ofparasitaemia, whereas Ovral resulted in decreased parasitaemias, as compared with the untreated control animals. There were no differences in the responses following secondary parasite infection. On the basis of results of clinical and parasito- logical studies from areas of holoendemic malaria in Africa, it is generally agreed that pregnant women are more vulnerable to severe malaria infection than those who are not pregnant (1, 2). Logie et al. (3) and Kortman (4), for example, found that maternal immunoglobulins were depressed during pregnancy, and McGregor et al. (5) and Campbell et al. (6) have reported that the serological response to malaria, as measured by the indirect fluorescent antibody test (IFA), was diminished during pregnancy. Although hormonal changes during pregnancy might account for alterations in the immune response, there is no exact information on this matter. It is not clear to what extent this diminished immune response may also be observed in women using oral contraceptive hormones. Bray (7) described a limited field study from the Gambia which provided suggestive evidence of an enhancement of parasitaemia and an impair- ment of the immune response to malaria in women taking an oral contraceptive. The extensive use of hormonal oral contraceptives in areas endemic for malaria has raised the possibility that such usage may alter the response of women to malaria infection. To investigate this possibility, female rhesus mon- keys receiving two different oral contraceptive prep- * From the Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, US Department of Health and Human Services, Atlanta, GA 30333, USA. Research Biologist, Malaria Branch. Requests for reprints should be addressed to this author. 2 Chief, Malaria Branch. 3 Biologist, Malaria Branch. 4 Statistician. arations were inoculated with one of two different species of primate malaria parasites, and their response to infection was measured by the levels of parasitaemia, the antibody response, and selected serum enzyme levels. The results of these studies are reported here. MATERIALS AND METHODS Monkeys Feral female rhesus monkeys (Macaca mulatta) of breeding age were obtained from the National Insti- tutes of Health, Bethesda, MD, USA. The animals had been under quarantine and were reported to be free of tuberculosis after ocular intradermal tuber- culin tests. Prior parasitological and serological examinations indicated that the animals were free of natural malaria infection. The animals were main- tained under controlled fluorescent lighting with 12- hour cycles of light and darkness; three dominant male monkeys were kept in view of the test animals throughout the entire period. All the animals were tranquillized with ketamine dihydrochloride (0.3 to 0.6 ml) prior to treatment or bleeding. Oral contraceptives Two different oral contraceptives were ad- ministered. The pills were ground in a mortar, sus- pended in water, and the dosage administered by oral intubation on days 1 through 21 of six menstrual cycles, each cycle lasting 28 days. The two drugs used were: 4440 -627- 628 W. E. COLLINS ET AL. Ovral: each human-dose tablet contained 0.5 mg norgestrel and 0.05 mg of ethinylestradiol.' Brevicon: each human-dose tablet contained 0.5 mg norethisterone and 0.035 mg ethinylestradiol.' Ovulation inhibition A radioimmunoassay for serum progesterone was carried out to monitor the ovulation cycle and to determine whether ovulation had been suppressed. The assay was patterned after the WHO guidelinesb using a progesterone standard supplied by WHO. Parasitological studies In the initial trial, the animals were inoculated intravenously with 50 000 blood-stage parasites of Plasmodium cynomolgi bastianellii. This parasite has biological similarities to the human malaria parasite, P. vivax. The parasite has a 48-hour asexual cycle, produces moderate parasitaemias which seldom threaten the life of the animal, and is morphologically and developmentally very much like P. vivax (8). Inoculation was on the 5th day of treatment during the third menstrual cycle. After two further menstrual cycles with parasitaemia, the animals were cured of their infections by the administration of chloroquine (150 mg daily for 2 days). To determine whether or not the continued administration of the oral contra- ceptive might affect the immunity of the animals, all the monkeys were again challenged with the hom- ologous parasite on the 5th day of the sixth menstrual cycle. In a subsequent trial, a second set of animals was inoculated with 50 000 parasites of P. coatneyi. This parasite is generally much more virulent than P. cyno- molgi and has biological similarities to P.falciparum. There is a marked sequestration of the mature para- sites, and death of M. mulatta monkeys frequently occurs, particularly those animals inoculated with large numbers of parasites. The animals were inocu- lated on the 5th day of the third menstrual cycle, treated with chloroquine at the end of the fourth cycle, and rechallenged on the 5th day of the sixth cycle with drug administration. During the course of the parasitaemia, thick and thin blood films were made daily according to the method of Earle & Perez (9) and stained with Giemsa stain. Parasites were quantified per mm3 of blood. a Use of trade names and commercial sources does not constitute endorsement by the Public Health Service or the US Department of Health and Human Services, or by the World Health Organ- ization. " WHO SPECIAL PROGRAMME OF RESEARCH, DEVELOPMENT AND RESEARCH TRAINING IN HUMAN REPRODUCTION. Pro- gramme for the provision of matched assay reagents for the radio- immunoassay of hormones in reproductive physiology. Method manual. 3rd edition, February 1979 (unpublished document). This manual is revised every year; the latest is the 7th edition, 1983. Serological studies Serum samples, taken prior to the administration of the oral contraceptive drugs and thrice weekly during the remainder of the study, were stored frozen at - 68 °C and were subsequently examined by the indirect fluorescent antibody technique (IFA) to determine the antibody levels using the homologous parasites as antigen (10). The same lot of homologous antigen was used for testing all sera, and all serum specimens from an individual animal were examined on a single day. To determine the effect of oral contraceptives and malaria infection on liver function, serum specimens drawn prior to initiation of oral contraceptive dosing, during the second menstrual cycle of oral contra- ceptive administration, during the course of the primary and rechallenge malaria parasitaemia, and during the post-therapy recovery period were assayed for selected liver enzymes. Alkaline phosphatase, glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT) were assayed using the Automatic Chemical Analyzer II (E. I. Dupont, Newtown, CT, USA). All results are expressed in units/litre. RESULTS The results of the progesterone assays (Tables I and 2) indicated that one-sixth of the human dosage was insufficient to inhibit ovulation in all animals given either of the oral contraceptives. It was apparent that inhibition was obtained in most of the animals given Ovral (only three animals had elevated progesterone levels after the third cycle). By using one-third of the human dose (Table 2), however, only one animal given Brevicon had an elevated progesterone level after the second treatment cycle. Ovral-treated animals Eleven monkeys were treated with one-sixth of the human dose of Ovral and then inoculated during the third treatment cycle with P. cynomolgi bastianellii. Eleven animals served as controls. Analysis of the results of the parasitological examinations (Fig. 1) indicated that the mean parasitaemias were significantly lower (f-test) in the treated than in the control animals (third cycle, P < 0.01; fourth cycle, P < 0.05). Following rechallenge (sixth cycle, Fig. 2), there was no significant difference between the course of the malaria parasitaemia in the treated and the control animals. In the second phase of the study, ten monkeys were treated with one-third of the human dose and then inoculated with P. coatneyi. Eleven animals served as EFFECT OF ORAL CONTRACEPTIVES ON MALARIA IN MONKEYS Table 1. Menstrual bleeding and serum progesterone patterns in monkeys given one-sixth of the human dosage of Brevicon or Ovral Oral contraceptive administration during menstrual cycles: I 11III lVlIV V Vl Drug Animal no. Pro' Men' Pro Men Pro Men Pro Men Pro Men Pro Men x~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x a Pro = elevated progesterone; Men = evidence of menstrual bleeding; X = positive reaction. x x X x x x x x x x x x x x x x Brevicon Ovral Controls (no drug) x x x xa x x x x x x x x x x x x x x x 240 206 275 205 657 211 783 789 55 186 197 184 789 266 112 232 788 170 265 780 785 235 792 655 260 245 786 105 272 800 759 273 264 263 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x 629 630 W. E. COLLINS ET AL. Table 2. Menstrual bleeding and serum progesterone patterns in monkeys given one-third of the human dosage of Brevicon or Ovral Oral contraceptive administration during menstrual cycles: I 11 III IV V VI Drug Animal no. Pro' Men' Pro Men Pro Men Pro Men Pro Men Pro Men X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X x X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X x x x x x x x x x x x x x x x x x x x x x a Pro = elevated progesterone; Men = evidence of menstrual bleeding; X = positive reaction. Brevicon Ovral Controls (no drug) X X X X X X X X X X X X 33 189 191 244 291 846 848 855 857 875 864 103 215 258 801 830 823 847 856 858 833 193 194 195 254 641 656 803 821 826 827 861 Xa X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X x x x x EFFECT OF ORAL CONTRACEPTIVES ON MALARIA IN MONKEYS CYCLE III CYCLE IV P. cynomolgi i05, CHLOROQUINE - OVRAL - BREVICON mmmmm CONTROL DAYS Fig. 1. Mean parasitaemias in Macaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium cynomolgi bastianellii. UYULt- VI P. cynomolgi CHLOROQUINE 1051! + , n ci) cn LL 103. 2 10 10- OVRAL BREVICON CONTROL 10 20 DAYS Fig. 2. Mean parasitaemias in Macaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and reinoculated with Plasmodium cynomolgi bastia- nellii. controls. The results of the parasitological examin- ations (Fig. 3) indicated that there was a significant difference between the treated and the control groups during the third cycle (P < 0.01), but not during the fourth cycle (P> 0.05). The treated animals again had lower parasitaemias during the third cycle. Following rechallenge (sixth cycle, Fig. 4), no signifi- cant difference in the course of parasitaemia was noted between the groups. Brevicon-treated animals Twelve monkeys were treated with one-sixth of the human dose of Brevicon and inoculated with P. cyno- molgi. Eleven animals served as controls. The results of the parasitological examinations (Fig. 1) indicated a significant difference between the mean para- sitaemias of the treated and the control animals (third cycle, P < 0.05; fourth cycle, P < 0.01). During the third cycle, the animals treated with Brevicon had higher mean parasitaemias, whereas during the fourth cycle the control animals exhibited higher parasitaemias. Following rechallenge (sixth cycle, Fig. 2), there was no significant difference between the treated and control animals. Eleven monkeys were treated with one-third of the human dose of Brevicon and inoculated with P. coat- neyi. Eleven animals served as controls. The results of the parasitological examinations (Fig. 3) indicated a co 2 L) w l-_ co 0r 0- z z w o I 631 I I ,>s,nI I ,,.r_ W. E. COLLINS ET AL. CHLOROQUINE - OVRAL - BREVICON ----- CONTROL 30 DAYS Fig. 3. Mean parasitaemias in Mucaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium coatneyi. P. coatneyi 105 * 103. 2<102 10, CYCLE VI I CHLOROQUINE - OVRAL - BREVICON CONTROL 10 DAYS Fig. 4. Mean parasitaemias in Mucaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and reinoculated with Plasmodium coatneyi. significant difference between the treated and the control animals (third cycle, P < 0.01; fourth cycle, P < 0.01). The treated animals had higher para- sitaemias than did the control animals. Following rechallenge (sixth cycle, Fig. 4), there was no signifi- cant difference between the treated and the control animals. Serological studies The results of the fluorescent antibody tests with the P. cynomolgi antigen (Fig. 5) indicated that each group of animals had a similar pattern of response. There was an initial peak in the IFA titre approxi- mately 2 weeks after inoculation, which was followed by a gradual decline during the primary parasitaemia and following the end of the fourth cycle. Following rechallenge, the mean IFA titres rose, but not as high as the levels obtained after the primary inoculation. The mean titres of the Ovral-treated animals were consistently higher than those of the control and the Brevicon-treated animals. The results of the IFA tests with the P. coatneyi antigen (Fig. 6) indicated that the serological response to infection with this parasite was somewhat different from that of the animals infected with P. cynomolgi. As a result of the primary infection, the mean IFA titres rose to moderate levels and then formed a plateau, declining slightly as the infection progressed CYCLE III P. coatneyi 105 1 f CYCLE IV 1 o4. 103, CY)cs 1- c) LL cc z LL 10 20 40 50 C) U) wI- 0~ 0- z z W ll 632 EFFECT OF ORAL CONTRACEPTIVES ON MALARIA IN MONKEYS CYCLE III I CYCLE IV I P. cynomolgi CYCLE V I CYCLE VI I r I I I I CHLOROOUINE fn- CHLOROQUINE f-I - OVRAL - BREVICON mm- CONTROL 20 40 DAYS Fig. 5. Indirect immunofluorescent antibody (IFA) responses of animals treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium cynomolgi bastianellii. I CYCLE IV CYCLE V I CYCLE VI I I I I I CHLOROuUINE f-I P. coatneyi CHLOROQUINE f-I OVRAL BREVICON CONTROL I . I I 1 20 40 60 80 100 120 DAYS Fig. 6. Indirect immunofluorescent antibody (IFA) responses of animals treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium coatneyi. P. cynomolgi f 1 0 320LU 1-- F 160 lL -j 80 08 O 40 0 20 LU 10- 5- 80 r CYCLF 1II P. coatneyi _ 1:1280- 1:640- Cr 1:320 - 1-- H- 1:160- LL 1 1:80- 0 o 1:40- 0- O 1:20- 1:10- 1:5' w . . . . .. I * 633 I I W. E. COLLINS ET AL. and following treatment. Upon rechallenge, however, the antibody titre to the homologous parasite rose to very high levels similar to that seen with P. cynomolgi during the primary infection. There was a significant difference between the mean titres of the animals treated with Ovral and Brevicon, but no difference between the control animals and either of the treat- ment groups. Biochemical studies The results of the liver function studies for those rhesus monkeys given one-sixth of the human dose are summarized in Table 3; the results for those ani- mals given one-third of the human dose are sum- marized in Table 4. In general, there was a wide vari- ation in GOT and GPT values, and there was little consistent difference between the mean GOT and GPT values for the treated versus the control animals. There were a number of individual monkeys in the oral contraceptive groups, however, where the values varied markedly from those in the control animals. For those animals given one-sixth of the human dose, the alkaline phasphatase values were lower than those of the controls for samples 4, 5, and 6. With the ani- mals given one-third of the human dose, these values were lower for samples 2, 3, 4, and 5; for sample 6, the mean alkaline phosphatase values showed a marked reduction in the control animals rather than an increase in the treated animals. The samples taken after the longest period of continuous parasitaemia (sample 4) were particularly noted as indicators of the effect of oral contraceptives and malaria on liver function. At one-sixth of the human dose, there was no difference between the treated and control animals with regard to GOT and GPT, but there was a significant decrease in the alkaline phosphatase values in animals receiving oral contraceptives. With one-third of the human dose, there was no difference with regard to GOT, but there was a significant increase in the GPT values with both drugs accompanied by a decrease in alkaline phosphatase values. DISCUSSION Both oral contraceptive drugs were initially investi- gated on the assumption that one-sixth of the human dose would be sufficient to suppress ovulation. The results, as shown in Table 1, indicated that this was definitely not the case with Brevicon, and that some of the animals treated with Ovral continued to ovulate. Nevertheless, this dosage was evaluated since it approached more closely the dose given to women, even though the effect on ovulation in monkeys was less than expected. The administration of one-third of the human dose definitely suppressed ovulation, but this dosage may have been greater than that ad- ministered to women. The course of the parasitaemia in the control animals was typical of that following the inoculation of relatively small numbers of parasites. The maxi- mum parasitaemia in the P. cynomolgi- and the P. coatneyi-infected animals was similar to that usually seen. The use of this primate malaria model system provides probably the closest possible dupli- cation of human malaria infections. Ovral was investigated to determine the effect of both dosages on malaria infection. There was a marked variation in the maximum parasitaemias seen in animals inoculated with either P. cynomolgi or P. coatneyi. Thus, geometric mean parasitaemias were determined for each day and then compared with the geometric mean parasitaemias for the control animals. During the acute phases of the infection with both P. cynomolgi and P. coatneyi (third cycle), there was a higher mean parasitaemia in the control animals than in the treated animals. During the fourth cycle, those animals given one-sixth of the human dose also had lower parasitaemias than the controls. There were no differences during the sixth cycle. Of impor- tance was the pattern of the parasitological response (Fig. 1-4) which indicated the close similarity between the groups and the control monkeys. Brevicon was also investigated at one-sixth and one-third of the human dose and was less effective in suppressing ovulation. At the lower concentration of the oral contraceptive, animals treated with Brevicon had higher parasitaemias than did the controls during the acute phase of the infection with P. cynomolgi (third cycle); the reverse was true during the fourth cycle. After treatment with one-third of the human dose, the parasitaemias were significantly higher in the treated animals than in the controls during both the third and fourth cycles. There was no difference during the sixth cycle following reinoculation. Thus, it appears that, whereas Ovral appeared to have a suppressive effect on the parasitaemia, Brevicon was associated with increased parasite levels. The serological responses, as measured by the IFA technique, indicated an interesting difference in the patterns of the control and the treated animals to infection with the two malaria parasites. The fact that the patterns of the treated animals were similar to the control animals for each parasite indicates that the patterns of IFA response were typical for the species of Plasmodium rather than due to any effect of the oral contraceptive. An examination of the serological responses following rechallenge showed that the response to reinfection was similar in both the control and the drug-treated groups. 634 EFFECT OF ORAL CONTRACEPTIVES ON MALARIA IN MONKEYS 635 Table 3. Alkaline phosphatase, glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) values for Macaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium cynomolgi bastianellii Mean serum enzyme levels (units/litre) * Glutamic-oxaloacetic Glutamic-pyruvic Alkaline phosphatase transaminase transaminase Sample Cycle Day Control Brevicon Ovral Control Brevicon Ovral Control Brevicon Ovral 1 Pre- - 17.7a 12.8b 14.2ab 45.6 46.00 39.7 24.70 31.1a 24.70 (7.8) (7.4) (10.8) (5.3) (18.2) (6.4) (4.9) (51.7) (14.9) 2 3 2 12.1 7.4b 18 8ab 42.9a 51.30 64.1a 24.6a 47.5 39.5 (4.3) (2.6) (6.8) (5.6) (15.6) (52.5) (10.9) (35.1) (28.4) 3 3 23 12.5a 9.3 12.5a 49.4 65.50 50.4a 27.00 42.2b 24.00c (8.3) (4.3) (6.0) (10.7) (33.4) (9.0) (1 1.0) (28.9) (4.9) 4 4 23 14.1 a 5.4b 6.7b 39.6a 46.7a 60.5a 21.4a 39.9 50.1 (3.2) (1.2) (2.6) (6.4) (13.1) (37.7) (9.8) (41.4) (36.0) 5 6 7 1 5.2a 6.6b 7.9b 41.7e 41.30 64.8 35.9 52.7a 90.5b (4.6) (1.4) (2.9) (8.5) (7.6) (28.7) (7.8) (33.2) (52.8) 6 6 21 14.1 a 5.0b 6.5b 37.4 40.2a 58.60 32.60 40.50 640.0 (5.5) (1.5) (2.2) (5.7) (7.6) (41.4) (9.0) (19.5) (42.3) Mean values for 11 control animals and 12 Brevicon- and 11 Ovral-treated monkeys. Figures in parentheses show the standard deviation. In a comparison of the groups of means (sets of three, reading horizontally), those with the same superscript letter = no significant difference; those with dissimilar letters = significant difference (P < 0.05). Analysis of variance by Duncan's multiple range test for variable value. Table 4. Alkaline phosphatase, glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) values for Macaca mulatta monkeys treated with the oral contraceptives Ovral and Brevicon and inoculated with Plasmodium coatneyi Mean serum enzyme levels (units/litre) Glutamic-oxaloacetic Glutamic-pyruvic Alkaline phosphatase transaminase transaminase Sample Cycle Day Control Brevicon Ovral Control Brevicon Ovral Control Brevicon Ovral 1 Pre- 13.1a 12.3a 14.0a 46.5a 58.9b 42.1 a 34.1a 43.3b 25.80a (3.3) (4.4) (4.4) (5.6) (19.7) (5.4) (15.1) (14.9) (9.5) 2 3 2 10.9a 7.7b 70b 54.10 57.7 55.8a 24.80 49.5 46.8a (3.2) (2.0) (1.8) (14.8) (12.8) (26.4) (11.6) (30.1) (38.7) 3 3 23 18.0a 10.1 b 59b 76.4a 76.4a 52.1a 23.4a 38.60 35.0 (8.2) (3.7) (1.6) (23.8) (26.3) (19.9) (3.4) (27.7) (9.8) 4 4 23 13.1 a 6.3b 5.1 b 48.50 57.5 52.1a 23.4 49.8b 55.9 (4.9) (1.9) (1.3) (9.9) (21.2) (34.8) (9.9) (34.0) (27.2) 5 6 7 11.3a 7.3b 7.1 b 47.0 74.3 56.5a 29.2a 68.80 71.70 (3.5) (3.5) (3.8) (9.6) (50.4) (32.4) (14.8) (55.0) (59.2) 6 6 21 4.6a 6.1 a 6.1 a 44.4 47.9 34.5 20.20 49.80 26.4a (2.1) (2.6) (2.5) (14.5) (7.9) (5.8) (6.8) (34.4) (11.1) * Mean values for 11 control animals and 11 Brevicon- and 10 Ovral-treated monkeys. Figures in parentheses show the standard deviation. In a comparison of the groups of means (sets of three, reading horizontally), those with the same superscript letter = no significant difference; those with dissimilar letters = significant difference (P < 0.05). Analysis of variance by Duncan's multiple range test for variable value. 636 W. E. COLLINS ET AL. Liver enzymes were analysed at strategic stages of this experiment in order to determine whether hepato- cellular and cholestatic changes were induced by oral contraceptive agents and/or malaria. While there was a significant elevation of hepatocellular enzymes (GOT and GPT) during the peak of parasitaemia with both species of Plasmodium, the increase was no greater than an approximate doubling of the enzyme value over the values in the controls. The significant increase was associated with the malaria parasitaemia rather than with the oral contraceptives. The depression in alkaline phosphatase noted during both primary parasitaemia and rechallenge was apparent prior to the presence of detectable para- sitaemia so that it was probably more associated with the drug treatment than with the malaria infection, although the combination may have accentuated the effect. Depression of alkaline phosphatase was of no physiological consequence, although the exact basis for this change remains unexplained. ACKNOWLEDGEMENT This work was sponsored and supported by the Task Force on Oral Contraceptives of the WHO Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, Geneva, Switzerland. RESUMt EFFET DES CONTRACEPTIFS ORAUX SUR LES INFECTIONS PALUDEENNES CHEZ DES SINGES RHESUS Des singes rhesus, Macaca mulatta, avant d'etre inocules avec les parasites du paludisme simien Plasmodium cyno- molgi bastianelli ou P. coatneyi, ont e traites par des contraceptifs oraux: Brevicon (norethisterone avec ethinyl- estradiol) et Ovral (norgestrel avec ethinylestradiol). Chez les animaux temoins, la parasitemie etait typiquement celle qui suit l'inoculation d'un relativement petit nombre de parasites. Les parasitemies maximales chez les animaux infectes par P. cynomolgi et par P. coatneyi etaient sem- blables A celles qu'on observe habituellement. L'utilisation de ce modele du paludisme des primates permet d'obtenir la reproduction la plus proche possible des infections palu- deennes humaines. Avec l'Ovral, on constatait une variation notable des parasitemies maximales chez les animaux inocules avec soit P. cynomolgi, soit P. coatneyi. Les moyennes geom6triques des parasitemies etaient determin&es chaque jour, puis compar&es avec les moyennes geometriques des parasitemies chez les animaux temoins. Pendant les phases aigues de l'infection tant par P. cynomolgi que par P. coatneyi, la parasitemie moyenne etait plus elevee chez les temoins que chez les animaux traites. Les types de reponses parasito- logiques etaient similaires. Avec le Brevicon, chez les animaux traites par un sixiSme de la dose humaine on observait des parasitemies plus elevees que chez les temoins, au cours de la phase aigue de l'infection par P. cynomolgi. Apres traitement par un tiers de la dose humaine, les parasitemies etaient nettement plus 6lev6es chez les animaux traites que chez les temoins lorsque le parasite infectant etait P. coatneyi. II est apparu que l'Ovral avait un effet suppressif sur la parasitemie alors que le Brevicon etait associe a une augmentation du nombre des parasites. Les mesures de la reponse serologique au moyen de l'immunofluorescence indirecte ont revele des tableaux similaires dans les groupes temoins et traites par les medica- ments. I1 y avait une elevation significative des enzymes hepatocellulaires (GOT et GPT) au cours de la parasitemie maximale due a l'une comme a l'autre espece de Plasmodium, mais les taux ne depassaient pas environ le double de ceux qui etaient enregistres chez les temoins. Cet accroissement significatif etait associe a la parasitemie paludeenne plut6t qu'aux contraceptifs oraux. L'abaisse- ment de la phosphatase alcaline, note au cours de la parasitemie primaire de meme qu'apres reinfection, se manifestait avant toute parasitemie decelable et etait probablement plus en rapport avec le traitement medica- menteux qu'avec l'infection paludeenne. REFERENCES 1. WHO Technical Report Series, No. 537, 1974 (Malaria control in countries where time-limited eradication is impracticable at present). 2. MORLEY, D. 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