The American Journal of Tropical Medicine and Hygiene - Volume 12, Issue 4, July 1963

The synthesis of CI-501 is described.

The drug was examined in mice and monkeys for potential value as a repository antimalarial substance. The dihydrotriazine moiety of CI-501 as the hydrochloride was tested in mice for background purposes. Activity was assessed on the basis of the period of protection against patent infections afforded by a parenteral dose prior to challenge with blood stages of Plasmodium berghei or P. cynomolgi.

The duration of protection was directly related to the amount of CI-501 injected. Protection of mice ranged from 1 to 9 weeks with a subcutaneous dose of 50 to 660 mg/kg. In monkeys, protection ranged from 5 weeks to more than 94 weeks with an intramuscular or subcutaneous dose of 38 to 400 mg/kg. A gradual but strong therapeutic response in monkeys with patent infections was induced by 50 mg/kg intramuscularly. The doses used in mice and monkeys were well-tolerated, locally and systemically.

Corroborative evidence of a slow and sustained release of the active moiety from the injection site is cited from chemical tests, microbiological assays, and dialysis studies in rats.

The results of this first report on CI-501 encourage further study of it as a repository antimalarial drug.

This report deals with the activities of a pamoate salt of the triazine metabolite of chlorguanide (CGT·P) against experimental infections with Plasmodium cynomolgi, with special emphasis on sporozoite-induced disease. The major objectives of the study were: (1) to determine the duration of protection afforded by a single dose of CGT·P against repeated challenge with massive doses of sporozoites; (2) to ascertain whether resistance of the plasmodia to chlorguanide triazine (CGT) develops during the protective period, especially in its terminal phases; (3) to determine whether CGT·P acts in effect as a “prophylactic” or merely as a long-term suppressive; and (4) to compare the rapidity of clearance of established parasitemias in recipients of CGT·P with the rates of parasite clearance achieved by the water-soluble hydrochloride salts of CGT and chlorguanide (CG).

The results of these explorations have led to the following conclusions: (1) A single 50 mg per kg dose of CGT·P confers protection against repeated sporozoite challenges for at least 6 months and in isolated cases for 11 to 15. (2) When breakthroughs do occur, the parasites which appear exhibit no evidence of resistance to CGT. (3) CGT·P administered in an appropriate doseacts as an effective “prophylactic” against challenge with a massive dose of sporozoites. (4) Parasite clearance in established infections is as rapid in recipients of a single 50 mg per kg dose of CGT·P as it is when conventional daily doses of the hydrochlorides of CGT and CG are administered.

The significance of the above findings for control of human malarias is discussed as are some of the problems which must be dealt with before the full potential of CGT·P can be realized.

A repository preparation of the dihydrotriazine metabolite of chlorguanide, CI-501, was tested in 28 volunteers for its efficacy as an antimalarial drug. A single intramuscular injection at a dose of 5 mg (base)/kg body weight was given to each volunteer.

The medicated volunteers were exposed to infection with the Chesson strain of Plasmodium vivax either by bites of heavily infected mosquitoes or by the intravenous inoculation of parasitized homologous blood. The number of challenges (exposures to infection) ranged from one to ten. The intervals of time between exposures were variable. Twenty-three volunteers were used as controls to prove mosquito infectivity.

To date (24 January 1963), CI-501 continues to protect 20 out of 24 volunteers exposed to vivax malaria by the bites of infected mosquitoes. The duration of protection ranges from 267 to 367 days (9 to 12 months). The four volunteers who developed patent parasitemias were protected for 169, 264, 341 and 426 days.

Four volunteers challenged with parasitized homologous blood at 49 to 146 days after medication were completely protected.

Four infected control volunteers were treated therapeutically with this repository preparation. The response was equal to that following administration of a single 600 mg (base) dose of chloroquine. There has been no evidence of relapse through 181 to 246 days.

These results indicate that the repository preparation known as CI-501 has the capacity to exert long-term protection and is therapeutically effective against human vivax malaria. The importance of such a preparation in a program of world-wide malaria eradication is obvious.

We have confirmed that, after passage through mosquitoes, a strain of Plasmodium falciparum from Colombia, South America, is resistant to standard doses of chloroquine, hydroxychloroquine, and amodiaquine, and that radical cure of infections with this strain can be achieved by the administration of either pyrimethamine or quinine. The Colombia strain is resistant to BW 377C54, a hydroxynaphthalene derivative known to be effective against chloroquine-resistant Plasmodium berghei in mice. Preliminary investigations suggest that the concurrent weekly administration of primaquine and chloroquine, although ineffective for treatment of patent infections, may be effective in preventing patency of moderately-seeded, mosquito-induced infections of this strain.

Burroughs-Wellcome 377C54 was tested for therapeutic efficacy against 3 strains of Plasmodium falciparum (S. Rhodesian, Colombian, Thai) and the Chesson strain of P. vivax. The dosage regimen was 300 mg every 12 hours for 4 doses; i.e., a total of 1200 mg in 36 hours.

Of 14 volunteers with falciparum malaria given an initial treatment with this drug, only 4 were cleared of parasites in the circulating blood. All 4 experienced a reappearance of parasites in 6 to 21 days after treatment.

All 15 volunteers with vivax infections, whether induced by sporozoites (mosquito bite) or the intravenous inoculation of parasitized blood, had parasites removed from the circulating blood in from 2 to 4 days, with a median of 3 days. Parasites reappeared in all but 2 of the 15 in from 10 to 39 days. Of interest is the fact that 2 of the recurrences were in blood-induced infections, which indicates inadequate therapy.

It would appear from these results that this compound, even in the high-dosage regimen used here, is not as efficacious as chloroquine or other commonly employed antimalarials.

Under the conditions of the experiments, it appears that sporozoites are not demonstrable in the blood stream of the non-susceptible species up to 1 hour after their deposit by the mosquito in the skin, and only rarely so in that of the susceptible species; that sporozoites survive fully when added to, and incubated in, the whole blood and plasma of the non-susceptible species, but not quite so well in the blood of the susceptible species; and that sporozoites are somehow inactivated practically immediately in the skin of the non-susceptible species when deposited there by the mosquito, though they can be recovered quite well from the site for at least an hour in the susceptible species.

The results of a survey of 223 Peruvian and Colombian monkeys and marmosets for trypanosomes are presented. Eight Trypanosoma cruzi or Trypanosoma cruzi-like infections and 42 infections with trypanosomes identified as Trypanosoma minasense were detected in 47 (21%) of the animals. There were three double infections. Trypanosomes were found in 11 of 14 species, representing eight of nine surveyed primate genera.

Strains of T. cruzi were identified in Peruvian squirrel monkeys (Saimiri boliviensis) and marmosets (Tamarinus nigricollis). Infections in other Peruvian and Colombian squirrel monkeys (S. sciurea) were presumed to be due to T. cruzi. The Tamarinus strain of T. cruzi grew well in culture, developed normally in posterior station in reduviid bugs (Triatoma protracta) and was highly virulent for suckling and immature mice. Previous records for T. cruzi and/or T. cruzi-like trypanosomes in Neotropical lower primates are discussed. T. sanmartini is more likely an aberrant strain of T. cruzi than a distinct species. A presumed arboreal T. cruzi cycle involving primates and unknown arboreal intermediate hosts is discussed.

T. minasense, a T. rangeli-like trypanosome, is apparently common in Neotropical arboreal primates. Saimiri strains of T. minasense grew well in culture, but Saimiri and Cebus strains failed to infect adults and nymphs of Triatoma infestans and T. protracta. A Saimiri strain was non-pathogenic for suckling mice and did not produce tissue forms. The synonymy of the T. rangeli-like trypanosomes is considered, and mechanisms of transmission of trypanosomes between arboreal primates are discussed, with particular reference to T. minasense. Both transmission by ingestion of infected insects and transmission by biting (or biting-plus-defecation) probably take place.

Primates infected with T. cruzi are known to be imported into the United States from the New World tropics. It is unlikely that these trypanosome strains will find their way into native invertebrates and vertebrates, including man, in this country. On the other hand the laboratory investigator should be aware, both from the point of view of his own health and that of his animals, that T. cruzi may occur in these animals.

Metronidazole has a potent inhibitory effect upon the multiplication of Trichomonas vaginalis in vitro. It completely inhibits growth of this organism at a concentration of 0.8 micrograms per milliliter.

Infection of the vagina of rats with T. vaginalis was induced experimentally after castration and implantation of estradiol.

A dose of 20 mg of metronidazole per kg given by mouth for 5 days resulted in complete disappearance of the organism from the vagina of a small series of rats experimentally infected. Ten mg per kg, which is similar to the dosage used in some human cases in which treatment failures have occurred, similarly resulted in a lower rate of cure in rats.

The use of rats with induced vaginal trichomoniasis seems to be valuable for screening of systemic trichomonacidal agents.

Agar gel diffusion tests using extracts from adults and larvae of Trichinella spiralis have revealed qualitatively different antigenic substances. When adult antigen was tested against sera from rabbits infected with this parasite, two bands of precipitate were observed while three formed against larval antigen. The variations in position and density, and the noncoalescence of the larval and adult bands suggest different antigen-antibody systems. Results of immunoelectrophoretic studies using the same antigens and antisera have given further evidence for the presence of qualitatively different adult and larval antibodies.

Materials and Methods. Rabbits weighing from 5 to 6 kg were fed infective Trichinella spiralis larvae, each animal receiving 5 doses of 10,000 larvae at intervals of 5 days for a 30-day period. Ten days after the last dose and every 7 days thereafter blood samples were obtained from the ear vein and the sera separated.

In Georgetown, British Guiana, 100 Cimex hemipterus (older nymphs and adults) were collected from a bed used by two persons who were positive and two persons who were negative for microfilariae of Wuchereria bancrofti. Eighty-three of the bedbugs contained at least one living or dead parasite. Early first-stage larvae were found in the abdomen, thorax, legs, and antennae. Eight bugs had a total of 9 sausage forms, of which 2 were dead and 3 apparently moribund. Also found were 2 sluggish second-stage larvae, and 3 infective larvae of which 2 were non-motile. Rupture of the stomach from overengorgement and consequent release of the parasites into the hemocoele was observed in 12 bugs.

The development of W. bancrofti was studied in five lots of bedbugs fed on a human carrier having 165 to 200 microfilariae per 20 cmm of blood at the time of feeding. Little development occurred in 100 first- and second-instar nymphs, which sucked up relatively few parasites. Four lots of 50 older bedbugs were given, respectively, 0, 1, 2, and 3 non-infective blood meals at 4-day intervals after the infective meal. It was found that as the number of additional feedings increased, the parasites survived longer and developed further. No infective larvae had developed by the 20th day. Because the mortality of larvae was high in both natural and experimental infections, and only a few developed to more advanced stages, it is concluded that C. hemipterus is not a suitable host for W. bancrofti.

The indirect hemagglutination test and the bentonite flocculation test utilizing a saline extract of Dirofilaria immitis have been evaluated. The test was reactive with sera from individuals with infections of Acanthocheilonema perstans and showed higher titers for symptomatic patients with microfilariae in the blood. In a group of 42 symptomatic patients, 92% of 13 microfilariae-positive patients and 62% of 29 microfilariae-negative patients showed positive serologic tests. In a group of 15 asymptomatic individuals with microfilariae in the blood, 67% were positive. From a group of 295 asymptomatic-microfilariae-negative individuals, 21 sera (7%) were positive.

Testing 632 sera from 295 normal missionaries, 84 normal Americans, and 253 individuals with various other parasitic and bacterial infections, an over-all non-specific response of 10% was obtained, utilizing the following criteria for a positive serologic test: (1) a hemagglutination titer of 1:200 or higher with a positive flocculation of 1:5 or higher, or (2) a hemagglutination titer of 1:400 with a negative flocculation reaction. Sera from 141 patients with helminth diseases showed a non-specific rate of 21%. This high rate was due to cross-reactions with trichinosis sera (35%) schistosomiasis (20%) and ascariasis (27%). Since the schistosomiasis and ascariasis sera were from individuals born in an area endemic for filariasis, the reactions may represent a serologic response to past experience with filariasis. Only 5% of 112 sera from individuals with non-helminthic diseases and 5% of 84 sera from normal individuals were positive.

The United Nations Conference on the Application of Science and Technology for the Benefit of the Less Developed Areas is concerned with the practical means by which “science and technology can best serve the needs of the less developed countries.” The problem of fatal, infantile diarrheal diseases is being considered in this connection, because they are a major or principal cause of death in infancy and early childhood among the economically underprivileged populations of the world.

According to Hardy and Schliessmann, consultants of the World Health Organization, the acute diarrheal diseases are estimated to account for about 5 million deaths of infants and children each year throughout the world. Among the economically more privileged populations, these diseases disappeared as an important cause of death only after the achievement of high living standards, which include improved nutrition, better housing supplied with safe, abundant water, sanitary disposal of excreta and facilities for proper refrigeration and storage of food, sanitary control of processing, storage and distribution of milk and other food products, control of feces-transmitting insects, increased availability of good medical care, and last but not least a markedly increased level of education.

The acute diarrheas and dysenteries of infancy and early childhood predominate among intestinal disorders of Guatemalan highland villages. The correlation with weaning practices and the attendant malnutrition is sufficient to characterize weanling diarrhea as an epidemiologic entity, as distinct among the diarrheas and the dysenteries as epidemic diarrhea of the newborn.

Transmission is primarily by direct contact, highly favored by the habits and customs of the people, and also indirectly by food contaminated by the environment or through the agency of other family members. The index case in family outbreaks is predominantly the infant or young child, and yet with strong indication that this does not mark the original introduction of infection into the family. Conceivably, manifest disease depends upon two factors. First, an immunity having its origin in a more or less universal disease occurring at an early age protects older children and adults. Secondly, the prevailing malnutrition conditions the immature host to invasion by infectious agents ordinarily of low pathogenicity and perhaps not numbered among the normal adult intestinal flora, as well as to infection by recognized enteropathogens.

A serological survey for leptospirosis in domestic animals was conducted in a coastal tropical area and an adjacent plateau and mountainous area located in the southwest sector of Guatemala. Sera from a total of 122 cattle, 120 swine, 86 horses, 77 dogs, 90 sheep and 20 goats were tested for the presence of agglutinins employing screening antigens of 18 different serotypes. The percentages of significant positive reactions in the various species were as follows: cattle, 41.8; swine, 27.5; horses, 4.6; dogs, 1.3; goats, 10.0. All of the sheep tested were negative. With few exceptions the reactions in cattle were elicited with screening antigens in the hebdomadis group, whereas most of the reactions in the other livestock species were obtained with pomona and/or autumnalis serotypes. The single positive dog had a titer against canicola serotype. Generally there was a higher prevalence of positive animals in the mountainous region than in the coastal region. Significant serological titers against serotype bataviae were also disclosed in two of 59 normal human beings in the study area who were engaged in agricultural work or in the handling of meat, and in one of 23 hospitalized patients with undiagnosed febrile diseases.

These findings not only provided unequivocal evidence of the presence of leptospirosis in Guatemala but of its widespread occurrence in cattle and swine. The difference in antibody types found in cattle and swine may reflect animal husbandry practices.

The number of viruses included in the arbo group has increased rapidly in recent years. Many of the new additions bear exotic names of villages or crossroads in faraway places. This plethora of names confuses the uninitiated and is apt to give pause to even the avant-garde among the arbovirologists. The expanding arbovirus group also includes many of the old familiar viruses such as those of yellow fever, the dengues, the encephalitis groups, and others. While the medical importance of a host of the newly recognized members of the group remains to be evaluated, there is no question regarding the capacity of a number of long-recognized viruses, now grouped as arboviruses, to induce disease in man. Among these diseases, only one has an entirely satisfactory means of immunoprophylactic control, namely, yellow fever.

The program for this Symposium has been designed to accomplish several purposes.

The concept of antigenic groups within the arthropod-borne animal viruses (arboviruses * ) has now been established for several years. Once the concept is accepted, a question that logically presents itself is what effect previous exposure of an individual host or the herd to one or several viruses of an antigenic group would have on subsequent challenge with other viruses of the same group.

There are a number of reports in the literature showing that experimental animals can be protected to some degree against fatal infection with an arbovirus by previous immunization with another, immunologically related agent. Thus, cross-protection has been reported between Russian spring-summer encephalitis (RSSE) and louping ill viruses by the author; between Japanese B (JBE) and Murray Valley encephalitis (MVE) by Pond, Russ, Rogers and Smadel; between JBE, MVE and St. Louis encephalitis by Hammon and Sather; and between Sindbis and Western equine encephalitis (WEE) by Parks and Price.

An attenuated strain of Venezuelan equine encephalomyelitis (VEE) virus has been employed for the immunization of persons at the risk of infection with virulent strains of this virus.

Systemic reactions following inoculation of either 50th or 80th passage virus occurred in approximately 40% of persons who had previously received several doses of killed vaccine. In persons who had not received the vaccine such reactions occurred in approximately 85%.

The attenuated virus elicited immunity in man against challenge with virulent unmodified virus.

A substrain was derived by plaque selection which differed from the original attenuated virus in its reduced capacity to induce untoward reactions in selected laboratory hosts and in man.

Animals inoculated with the substrain of attenuated virus resisted challenge with 109 lethal doses of four other strains of virulent VEE virus.

Western encephalitis virus strains obtained from naturally infected birds by inoculation into chick embryos, young chicks and hamster kidney tissue culture were subcultured by various methods in an effort to develop variants of low pathogenicity. Prolonged passage of the virus in chick embryos and chicks did not reduce the neuro-pathogenicity of the virus for mice and hamsters. A variant of low pathogenicity was obtained by cloning on chick embryo cells. Clones were at first selected on the basis of pathogenicity of the progeny of the cloned virus for young adult mice inoculated intracerebrally. Later clonal selections were done on the basis of the relative average survival time (in days) (AST) in infant mice inoculated intracerebrally and intraperitoneally, looking for variants having a long AST or the same AST for both routes of inoculation. The clone 15 variant was selected for study as a live virus vaccine because the neurotropic character of the virus was either markedly reduced or eliminated and animals vaccinated with the virus were immune to subsequent intracerebral challenge with the natural virus as obtained from wild birds.

The procedure for the production of Rift Valley fever vaccine (RVF) has been described. Infectious vacuolating virus, SV 40, was present in 3 of 6 lots of inactivated RVF vaccine prepared from rhesus kidney cell cultures but was not detected in any of 5 sequential lots prepared in Cercopithecus cell cultures. Moreover, formalin-killed RVF virus vaccines derived from the African green monkey kidney cells are as immunogenic as those produced in rhesus cell cultures. The addition of 2% human serum albumin increases the heat stability of lyophilized RVF vaccine. The lyophilized vaccine is as antigenic as the fluid vaccine for the immunization of man when used either for the primary series or as a booster dose. The formalin-killed RVF vaccine prepared in monkey kidney cell cultures with the pantropic virus has protected exposed laboratory workers, thereby indicating the efficacy of the vaccine.

Last year we presented at these meetings a very brief report on the derivation and characteristics of an attenuated strain of Japanese B encephalitis (JBE) virus. This will be briefly summarized before presenting new work, including human trials.

From Okayama Culex tritaeniorhynchus pool 541 (abbreviated OCT-541), known to contain JBE virus, we reisolated the virus directly in hamster kidney tissue culture (HKC), passed it serially in heavy inoculum by decreasing temperature steps, finally at 24°C. Then three serial plaque selections were made for particles of lowest mouse neurovirulence. Several pools grown at 24°C from this line proved to have exceedingly low neurovirulence for all laboratory animals by essentially all routes of inoculation, including more limited trials in monkeys and Mexican burros. Failure to develop antibody or immunity by almost all animals, except those inoculated intracerebrally with tremendous amounts of virus, suggested that this was too “cold” a strain and was essentially incapable of multiplying at the normal temperature of these animals.