The American Journal of Tropical Medicine and Hygiene - Volume 21, Issue 4, July 1972

This is one of those precious moments in our Society's life when we honor both a member who has preceded us and also a member who, because of his prominent position in health science today, addresses us as the 36th Charles Franklin Craig Lecturer.

I willingly accepted the invitation from our President, Dr. Reeves, to join the Craig Lectureship Committee and serve with Dr. Neva and Dr. Lennette who was to be the Chairman. I was even more delighted when I was selected by the Chairman to introduce the Craig Lecturer, knowing by then who the lecturer was to be.

Our honored predecessor, Colonel Craig, was in his time, not the man of a decade, but of many decades of tropical medicine. Because the centennial of his birth will be celebrated before our Society meets again, I wish to devote a moment to his career because he was identified with research and teaching in tropical medicine for so many years.

Thirty-five individuals have delivered an address to this Society in honor of Charles Franklin Craig, a pioneer among pioneers in tropical medicine, a prolific contributor to the scientific literature, a distinguished officer in the medical corps of the United States Army, a tireless and devoted member of this Society who edited many volumes of our journal. Doctors Simmons and Bass wrote eloquent tributes in the special memorial issue of the journal in 1952, tributes which should be read by all who belong to the Society of Tropical Medicine and Hygiene. Instead of trying to embellish or repeat what has been written about Doctor Craig, I shall begin with a few comments about the annual Craig addresses themselves. Regrettably from my point of view, I have not been present when the previous Craig lectures were delivered. Consequently, in preparation for this talk today, I analyzed the published versions of the addresses—an exercise which has been very illuminating to me personally.

The rocker dilution technique was adapted for in vitro testing of antimalarial drugs on five strains of Plasmodium falciparum. Seven antimalarial drugs, chloroquine (concentrations: 0.0075, 0.015, 0.03, 0.06, 0.12, 0.3, 0.6, 1.2 µg/ml culture), amodiaquine (0.12 and 0.3 µg/ml), pyrimethamine (3.6 and 5.5 µg/ml), quinine (2.5 and 5.0 µg/ml), cycloguanil (0.144 µg/ml), trimethoprim (50.0 µg/ml) and dapsone (2.5 µg/ml) were tested. The various strains of P. falciparum were classified as susceptible or resistant to a drug depending upon the concentration of agent required to: a) inhibit maturation of rings to trophozoites (i.e., prevent cytoplasmic growth); b) block formation of schizonts and segmenters (i.e., prevent nuclear multiplication); or c) produce aberrant distribution of chromatin within the parasite. A strain of P. falciparum obtained from Arnold and Martin is resistant to pyrimethamine and quinine, but susceptible to chloroquine. The Malayan-Camp. strain is susceptible to chloroquine. The Vietnam-Oak Knoll strain is resistant to chloroquine. Two strains (the Uganda-Palo Alto and the Vietnam-Monterey) were studied in greater detail. Of the five strains studied, the Uganda-Palo Alto strain proved to be the most susceptible and the Vietnam-Monterey strain the most resistant to chloroquine. Both of these strains are susceptible to amodiaquine, cycloguanil and dapsone. The Uganda-Palo Alto strain is resistant to trimethoprim and pyrimethamine, while the Vietnam-Monterey strain is susceptible to these two drugs.

Results of a drug treatment program for control of amebic disease in an Amerindian reservation in northern Canada are reported. The population of approximately 350 was treated with metronidazole for a 12-month period. The drug was given in a single dose monthly for the first 3 months and bimonthly thereafter. Good results were achieved, with a 7-fold reduction from the 27 and 28 cases, respectively, seen during the two previous consecutive 12-month periods to only 4 cases during the 12 months of periodic treatments. A neighboring reservation, which served as a control, did not show a similar reduction in amebic disease over the same period of time. The drug was generally well tolerated except by infants and young toddlers, who showed a high incidence of vomiting. This improved when the dosage was reduced.

Trypanosoma cruzi has been isolated from wild animals and triatomid bugs in five states within the southeastern United States, but human infection has not yet been reported from this area. This study was undertaken to determine the prevalence of antibody to T. cruzi among individuals living in southern Georgia, including patients with primary myocardial disease in the same geographic region. A total of 3,883 sera was examined by means of the complement-fixation test: 3,761 unselected sera, 54 specimens from patients with primary myocardial disease, and 68 sera from matched control patients having well-documented rheumatic, congenital, hypertensive or arteriosclerotic heart disease. No positive reactions were found among unselected sera or sera from patients with primary myocardial disease. Two weakly positive reactions were found among the 68 sera from patients with other types of heart disease. These findings indicate that the prevalence of antibody to Trypanosoma cruzi is extremely low in southern Georgia, even among patients with primary myocardial disease.

Young cats were infected in the hind feet with Brugia malayi in order to localize the parasite in an area where the regional lymphatics could be readily observed. Following injection of contrast material into afferent vessels in infected cats, lymphograms showed a number of vessels not seen in controls. Although changes seen in lymphograms in general correlated well with gross observations following injection of lymphatic-staining dye, occlusion of vessels seen on lymphography were not visible grossly. When these areas of occlusion were examined on dissection, thrombi, which often contained dead worms, were seen. Living worms usually were recovered in a dilated area just distal to a partial or complete occlusion of the vessel.

Serum and cerebrospinal fluid (CSF) from patients with eosinophilic meningoencephalitis were analyzed for changes in the protein profile and for antibodies to an Angiostrongylus cantonensis extract to seek evidence for a local immune response in the central nervous system. The results showed increased serum IgG and increased CSF total protein, albumin, IgG, IgA, and IgM. Although the CSF immunoglobulin levels were much lower than the corresponding serum levels, antibody activity of both fluids to A. cantonensis extract were similar. These findings are compatible with the idea that CSF antibodies may be synthesized locally within the central nervous system in response to antigenic stimulation.

During studies on schistosomiasis in the Yemen Arab Republic, 1,302 urine and 397 stool samples from inhabitants of various areas (mostly rural) were examined, and 137 water bodies were searched for snails. Results indicate the occurrence in most localities of both urinary and intestinal schistosomiasis, with a patchy distribution and various infection rates. The highest prevalence of Schistosoma haematobium infection, reaching 100%, was found in villages in the south. Snail intermediate hosts of both schistosomes were found in many habitats in 5 of the 6 provinces visited, and experimental studies showed Bulinus truncatus and Biomphalaria pfeifferi to be susceptible to infection with Schistosoma haematobium and S. mansoni, respectively. It is estimated that more than one million people in Yemen may be infected with one or both of these schistosomes.

Susceptibility to infection with Schistosoma mansoni was studied in juvenile Biomphalaria glabrata by isolated selfing and by crosses. True-breeding snail stocks were derived testing 100% or 0% juvenile susceptible. Crosses suggested that juvenile susceptibility was regulated by a complex of four or more genetic factors. Genes for insusceptibility could be transmitted by susceptible snails and genes for susceptibility by refractory snails.

A juvenile strobilate tapeworm was found in the spinal cord of a young man from Thailand who had suffered from paraplegia for several months. The recovered worm was 76 mm long and its scolex had four muscular suckers and a rostellum with hooks. Reproductive organs were not present in any of the more than 300 segments but a genital primordium was present in many. The immature state of the worm and the loss of many of the hooks from the scolex make its specific identification impossible, but it probably belongs to the family Taeniidae. Apparently this is only the second case in which a strobilate form of a tapeworm has been found in the extraintestinal tissues of man.

Patients with previously untreated lepromatous leprosy were treated by injections of acedapsone (DADDS), a repository sulfone given at 77-day intervals. The response to therapy was evaluated primarily by the results of inoculation of mice with Mycobacterium leprae from serially obtained skin punch biopsy specimens. In 3 of 10 patients, infectivity for mice was lost in less than 100 days; in the others the infectivity was lost more slowly, and in the slowest more than 300 days were required. The results were compared with those in 14 patients treated with dapsone (DDS) in dosages of 50 mg daily; in 12 of these, infectivity of the bacilli was not demonstrable after 100 days. Tests of the M. leprae isolates for DDS-sensitivity in mice showed that drug-resistance, in the usual sense, was not involved in the slower loss of infectivity. The implications of this slower response for the long-term therapeutic response to acedapsone are not yet clear.

Rifampin was rapidly bactericidal for Mycobacterium leprae. Leprosy responds very slowly to current therapy, so there is a special need for more rapidly effective drugs. In mice rifampin exerted a bactericidal-type effect with single administration by gavage; the effect increased with dosage in the range 10 to 40 mg/kg of body weight. Five patients with lepromatous disease were treated with 600 mg rifampin daily, and the viability of the bacilli in their skin lesions was tested by inoculation of mice. Infectivity for mice had completely disappeared in the 1st specimen collected after the start of therapy—at 7 days in 4 patients and 14 days in 1. In 4 control patients treated with dapsone, infectivity for mice was lost much more slowly and in 1 was still present, though decreased, 112 days after the start of treatment. The slower loss of infectivity with dapsone is in accord with our previous experience in which the same methods were used.

A genetic polymorphism for acetylation of dapsone was demonstrated in 50 Philippine subjects native to the island of Cebu; a direct correlation was found between percentage acetylation of dapsone in plasma and of sulfamethazine in urine. Repeat studies with sulfamethazine in 32 of these subjects showed that the results from plasma and urinary assays were directly related, and that plasma assays gave a better differentiation of individuals into rapid and slow phenotypes. The high percentage (72%) of rapid acetylators is consistent with the Mongoloid origin of these Philippine subjects. Percentage acetylation of sulfamethazine was inversely related to plasma levels of this drug, and directly related to levels of N4-acetylsulfamethazine. Percentage acetylation of dapsone was directly related to plasma monoacetyldapsone levels, but was not related in any way to dapsone levels. No evidence for the presence of dapsone conjugates in plasma was found. Half-time of disappearance of either dapsone or monoacetyldapsone were not different in the two phenotypes and ranged from 14 to 53 hours in the entire group. Repeat studies in the six subjects showing the most divergent values confirmed the initial observations. The mean half-times were substantially higher than had been observed previously in American subjects.

Yersinia pseudotuberculosis infection has been reporte in the United States in six species of domestic mammal (cat, cow, goat, rabbit, sheep, and swine), five species of wild mammal including black-tailed jack rabbit (Lepus californicus), white-tailed antelope squirrel (Citellus lecurus), eastern cottontail (Sylvilagus floridanus), black-faced kangaroo (Macropus melanops), and albino fallow deer (Dama dama), and three birds (canary, dove, and pigeon). Also, epizootics in chinchilla caused by Yersinia enterocolitica have been recorded in the United States. The importance of intestinal carriers in fecal-oral spread of infection is emphasized in the epizootiology of yersiniosis (infection with Y. pseudotuberculosis or Y. enterocolitica). Wild birds and rodents appear to be significant reservoirs of Y. pseudotuberculosis, but birds have not been found infected with Y. enterocolitica.

Vibrio parahemolyticus was isolated from 8.5% of adult Vietnamese civilians with gastroenteritis and 2.5% of United States servicemen with gastroenteritis. No isolates were obtained from persons without gastroenteritis. The organism also was isolated from various seafood specimens and from sea water.

In a serologic survey undertaken between 1968 and 1971 among domestic animals and man in Egypt, prevalences of leptospiral microscopic agglutination titers of 1:128 and greater were 42.1% in 195 goats, 26.1% in 218 buffalo, 43.8% in 130 pigs, 34.5% in 206 cows, 4.2% in 330 sheep, 34.0% in 50 camels, 29.0% in 31 donkeys and 5.6% in 513 humans. While seropositivity rates did differ among geographic areas for buffalo and cows, these rates were not consistently high or low for any one area; hence, differences among geographic areas in potential leptospiral infection hazards could not be demonstrated. Agglutination reactions were elicited with 15 of the 16 Leptospira serotypes used. Differences in distribution of positive Leptospira serotypes were related more to the species tested than to the geographic origin of the samples. Based upon these results, it is concluded that subclinical leptospirosis is not a rare disease in Egypt and may well constitute a significant public health hazard.

A series of Australia antigen-positive sera from healthy Nigerians was examined using the electron microscope. One serum was outstanding inasmuch as it contained a vast preponderance of the large 420 A Dane particles. Other sera exhibited the appearance accepted as the usual one in Australia antigen-positive sera. The significance of this variation in proportion of antigen forms is discussed and it is suggested that variations of this type could be of importance in prognosis.

Viremia and antibody responses of chipmunks and squirrels inoculated with La Crosse (LAC) and Trivittatus (TVT) viruses were determined and compared. High level viremias were detected in 5 of 6 chipmunks (Tamias striatus griseus), and 4 of 5 gray squirrels (Sciurus carolinensis) infected with LAC virus. Only 2 of 6 chipmunks infected with TVT virus developed detectable viremias. No associated clinical disease was noted. Neutralizing antibody persisted for at least 200 days in all chipmunks with LAC virus while in two of those inoculated with TVT virus it was detectable for only 140 days. Squirrels inoculated with LAC virus produced an antibody pattern similar to that in chipmunks but the titers were lower. None of the 4 gray squirrels inoculated with TVT virus had a detectable serologic response. Antibody appearing after a single inoculation of either LAC or TVT virus showed partial heterologous neutralizations of LAC, TVT, snowshoe hare (SSH), and Jamestown Canyon (JC) viruses. Transmission of LAC virus from infected chipmunks and squirrels to suckling mice was accomplished with Aedes triseriatus mosquitoes.

A number of parameters related to vector efficiency were investigated in the laboratory for Culex fuscocephala, a suspected Japanese encephalitis (JE) vector, and for Culex tritaeniorhynchus, a proven vector of JE virus. It was demonstrated that 97% of C. fuscocephala and 92% of C. tritaeniorhynchus became infected after ingesting very small amounts of JE virus (average infecting dose = 8 plaque-forming units (PFU/mosquito). JE virus multiplied in both mosquito species to comparable high titers (above 105 PFU/mosquito) within 10 days after the infectious blood meal. Once infected, both species maintained high virus titers through at least 4 weeks. The average transmission rates were found to be very similar in both mosquito species. Evidence suggests that virus transmission occurred after mosquito probing as well as after feeding to repletion. This demonstrates a high vector efficiency of C. fuscocephala in the laboratory as compared with that of C. tritaeniorhynchus, a confirmed JE virus vector. Together with field observations, these data provide strong evidence to incriminate Culex fuscocephala as a potentially important vector of JE virus in Thailand.

A night heron, a green heron, a white ibis, and a cattle egret were individually exposed overnight in 8-ft cages to densities of Culex nigripalpus ranging from 25 to 1,200 per cage. Surviving mosquitoes were examined the following morning and engorgement rates were determined as a measure of effect of antimosquito activity. In addition, the behavior of each bird was recorded for 2-hr periods at three different mosquito densities. Results indicated an inverse relationship between the density of mosquitoes and the proportion that successfully obtained blood. This relationship was ascribed to the increase in defensive activity displayed by the birds (differing in degree according to species) when exposed to increases in mosquito density. The frequency of interrupted feeding (= partial blood meals) was also related to host behavior and mosquito density.