The American Journal of Tropical Medicine and Hygiene - Volume 25, Issue 3, May 1976

I have been highly honored by the Society with the privilege of serving as your president and of presenting an address to the annual meeting. In similar circumstances, one of our former presidents, Dr. Clay Huff, with his characteristic modesty, once described the genesis of such an honor as “some quirk in the democratic process followed by this Society,” but quirk, accident, or otherwise, I am most grateful.

Perhaps the most significant challenge to the president of this Society is that of selecting an appropriate topic for the presidential address. I suppose the usual course of events is to review, as far back as possible, the addresses given by presidents in the past. This can be a devastating experience, for one soon discovers that almost everything worth saying has already been said. A number of presidents have pointed with justifiable pride to the accomplishments of the past; others have pointed with equally justifiable alarm at the problems of the future.

Anopheles freeborni mosquitoes with oocyst infections had salivary gland infections at a higher rate with strains of Plasmodium vivax from the New World than with strains from Asia, particularly those from South Vietnam. Anopheles maculatus mosquitoes supported development from oocysts to heavily infected salivary glands for all the strains of P. vivax tested. The results suggest that P. vivax introduced from Vietnam would be less likely to be transmitted by native A. freeborni mosquitoes than would malaria from some other areas.

An asymptomatic infection with Babesia sp. was diagnosed in an epidemiologic investigation of transfusion-acquired malaria. This is the seventh human piroplasmosis infection that has been reported in the literature.

Treatment with combined pyrimethamine and sulfadiazine prolonged the prepatent period and shortened the patent period of cyst-induced toxoplasmosis in cats. Oocyst excretion was inhibited in 3 of 4 cats treated intramuscularly with 2 mg/kg body weight pyrimethamine and 100 mg/kg body weight sulfadiazine but not in 4 cats treated with one-half that dosage. Treatment with 2.2 mg/kg body weight pyrimethamine and 132 mg/kg body weight sulfadiazine mixed in cat food did not inhibit oocyst production but prevented antibody formation. No parasites were found upon histological examination of intramuscularly treated cats on days 3, 5, and 7 after infection. Infection with Toxoplasma gondii induced immunity to an oocyst-producing reinfection in both control and treated cats.

Thirty-four of 54 campers on a 2-week trip in mountains of Utah had diarrhea during and after their trip. Twenty-two (79%) of 28 symptomatic campers' stools examined contained Giardia lamblia cysts, whereas 4 (29%) of 14 asymptomatic campers' stools had cysts. The temporal distribution of cases and the absence of clustering among food preparation subgroups suggested a common source exposure. Although the epidemiologic data and fecal coliform counts implicated the remote mountain stream used as water source by the group as the vehicle of transmission, Giardia lamblia cysts were not recovered from stream water nor were they found in intestines or feces of sampled mammals living in the drainage area. Twenty-five other campers had stools examined before and after a subsequent hiking trip in another area of Utah; none had Giardia cysts before, but 6 (24%) had them after return. Questionnaires returned by 133 other campers showed that 5% had an illness compatible with giardiasis within 2 weeks after their trip. These surveys show that campers exposed to mountain stream water are at risk of acquiring giardiasis.

Simple coagulation studies were carried out in 18 patients with advanced Trypanosoma gambiense infection. No evidence of disseminated intravascular coagulation was found. Many patients had a moderate degree of thrombocytopenia which may have been due to enhanced splenic trapping of platelets. Most patients had raised levels of fibrin degradation products in their cerebrospinal fluid, perhaps reflecting the presence of underlying cerebral and meningeal vascular damage. Addition of viable trypanosomes or of trypanosome extracts to human and rat blood did not produce significant thrombocytopenia in vitro.

A test system has been developed to evaluate the trypanosomicidal activity of large numbers of candidate drugs. Based on mortality of mice with blood induced Trypanosoma rhodesiense infections, it serves as a primary screen or as a secondary and confirmatory test for active compounds. Over 5,500 selected compounds have been tested; more than 6% were active.

It was postulated that the anemia commonly seen in mammalian trypanosomiasis, and specifically in Trypanosoma congolense-infected calves, was of immunological origin. Specifically, we postulated that trypanosome antigen-antibody-complement complexes, deposited on the surface of erythrocytes of infected calves, resulted in their immune elimination leading to clinical anemia. This hypothesis was tested experimentally. Immunoglobulins bound to the erythrocytes of 13 infected calves were detected by a direct antiglobulin test from 7 to 10 days post infection. The reaction was strongest between 3 and 9 weeks and remained inconsistently positive until the calves were killed by euthanasia 15 to 18 weeks after infection. Erythrocytes reacting positively in this test were then lysed and immunoglobulins were eluted from the washed stromata by means of a low pH buffer. Sixteen out of 74 eluates prepared in this way and concentrated, contained IgM and IgG. Antibody activity of these eluates against T. congolense was demonstrated by means of the complement fixation test, the indirect hemagglutination test, and the indirect antiglobulin test. It is considered that the original hypothesis has been essentially proven.

From August 1973 through May 1974 a total of 148 marmosets (Saguinus geoffroyi) were examined for blood parasites. Parasites were detected in 93.2% of the monkeys. Direct examination of blood revealed 82.4% infected with trypanosomes; Trypanosoma cruzi was seen in 1.3% of the animals examined, T. minasense in 52.7% and T. rangeli in 25%. However, the use of several diagnostic tests (direct microscopic examination, hemoculture, xenodiagnosis, and animal inoculation) in 15 marmosets revealed T. cruzi in 40%, T. rangeli in 93%, and T. minasense in 87%. The high rate of infection among marmosets suggests that they are important natural hosts of T. cruzi and T. rangeli in the Panama Canal Zone.

Physiological tests of work performance and measurements of field productivity were made in 194 Sudanese cane cutters in order to study the effect of Schistosoma mansoni infection. The cane cutters were selected from two age ranges (16–24 and 25–45 years) and subdivided into three clinical groups: not infected, infected with, and infected without clinical signs of hepatosplenomegaly. Men infected with Schistosoma haematobium, malaria (blood film), or with hemoglobin levels less than 10 g/100 ml were excluded. There was a statistically significant (P < 0.002) higher mean hemoglobin concentration in those not infected, but the mean difference was less than 1 g/100 ml. Submaximal responses to exercise on a stationary bicycle ergometer, oxygen intake, ventilation, tidal volume, cardiac frequency and estimated maximal aerobic power output calculated both in absolute terms and relative to lean body mass and leg volume were similar in the six groups of cane cutters. No significant differences were found in physique, body composition or in thermoregulatory function tests. The cane cutters were found to have little natural acclimatization to heat in terms of sweating capacity when compared with a group of fully acclimatized Sudanese soldiers. The mean productivity (mean daily weight of cane cut per man) was significantly correlated with the individual's estimated maximum aerobic capacity determined in the laboratory, but not with the degree of S. mansoni infection. The noninfected group was less “efficient” (mean productivity:oxygen intake) during cutting than the infected groups but a larger proportion of the noninfected were in their first season of cutting. There was a positive correlation between the number of seasons' cutting experience and the individual's age, degree of infection and mean productivity. Cane cutters studied in this investigation were a relatively fit, active population from whom the more seriously ill were excluded. These results do not, therefore, necessarily reflect the effects of S. mansoni on physiological work capacity and productivity of more static populations in areas of high endemicity.

The present study was conducted to determine whether extracts from adult Schistosoma mansoni could be coated onto cholesterol-lecithin crystals. Of particular interest was the use of stunted schistosomes (SS) recovered from rabbits. The reactions obtained with this antigen in the slide flocculation (SF) test were compared with those employing antigens from cercariae and mature adult worms. The stunted schistosome SF test (SFSS) showed high sensitivity and specificity while cercarial antigen showed extensive cross reactions with Trichinella spiralis, Ascaris lumbricoides, and Echinococcus granulosus antisera. Both SS and cercarial antigens reacted with syphilitic sera, but the former only with high titer sera. The antigen from mature adult worms could not be coated onto cholesterol crystals, a finding which is in agreement with previous investigations. The relative simplicity of the SFSS test and its apparent high sensitivity and specificity indicates that the test may be an ideal epidemiological tool for schistosomiasis surveys. The results obtained should encourage additional study of the procedure involved and investigation into the role of lipids in flocculation tests. In addition, the findings should stimulate immunological studies of the stunted schistosomes.

The prevalence of schistosomiasis has been measured by parasitological examination and by fluorescent antibody titering in a number of communities in different parts of Rhodesia. The samples were taken from areas of high, medium, and low transmission of the disease. A correlation was detected between the mean titer and prevalence of infection, particularly in the younger people (4–13 yars old). It is suggested that fluorescent antibody titrating may be a useful epidemiological tool.

Chimpanzees infected with Schistosoma japonicum develop circulating schistosome antigens in their circulation between 6 and 9 weeks post-exposure. The minimum number of circulating antigens ranges from one to three. These antigens also cross-react with an antiserum against S. mansoni adult worms. Clearance of these antigens from the circulation several weeks later typically occurs. Persistence of these antigens could result in the observed renal damage.

Patients with previously untreated borderline-lepromatous or fully lepromatous leprosy were treated with one of five clofazimine (B663) regimens: 1) 200 mg daily 6 days per week; 2) 100 mg three times weekly; 3) 300 mg weekly; 4) 600 mg every other week; and 5) 600 mg on 2 consecutive days every 4 weeks. After 24 weeks of treatment, the patients were randomly allocated to treatment either with 200 mg B663 daily 6 days per week (regimen 6) or with dapsone, beginning with a small dosage and increasing over a period of 8 weeks to 100 mg daily 6 days per week (regimen 7). Death of Mycobacterium leprae was monitored by mouse inoculation with organisms recovered from skin biopsy specimens obtained at intervals during the first 24 weeks. Killing of M. leprae proceeded most rapidly in regimen 1 and 2 patients, least rapidly in the patients of regimens 4 and 5, and at an intermediate rate in regimen 3 patients. Erythema nodosum leprosum (ENL) was no more frequent nor more severe during treatment with any one of the first-24-weeks regimens. ENL was more frequent in regimen 7 than in regimen 6 patients. Pigmentation of the skin, assessed only during the first 24 weeks, occurred in patients of all regimens, but was most marked in regimen 1 patients. No evidence of B663 toxicity was noted. Although all of the first-24-weeks regimens were effective in terms of the rate of killing of M. leprae, greater effectiveness was associated with more frequent administration of the drug. The B663 that accumulated in the tissues did not appear to be available to exert an antimicrobial effect.

Complete and partial facial nerve paralysis can result from leprosy. The latter is more prevalent and results in lagophthalmos and corneal hypoesthesia. The former is characterized by loss of facial expression, deviation of the face to the nonparalyzed side, difficulty in chewing, and drooling, in addition to lagophthalmos and corneal hypoesthesia. Affected patients are at risk to develop blindness, as well as suffering social and economic deprivation because of the effects of facial nerve paralysis. Prevention of blindness and amelioration of the latter were successfully achieved by muscle transfer procedures, temporalis transfer to the eyelid, and masseter transfer to the mouth and nasolabial fold in small, minimally equipped hospitals in Africa.

Enteric bacteria pathogenic to man were sought in a total of 974 forest mammals collected from a variety of sites in rural and jungle areas of Panamá. The highest incidence of infection among the mammals was observed during the Panamanian dry season, which normally extends from January through April. A minimum of 10 Salmonella serotypes including, three of the Arizona group and Edwardsiella tarda, was isolated. Opossums of the genera Philander, 11 of 54 (20.1%), and Didelphis, 12 of 102 (11.8%) demonstrated high infection rates. One sloth of the genus Choloepus and specimens of two genera of rodents also were infected to varying degrees: 1 (11.1%) of 9 Choloepus, 8 (1.1%) of 704 Proechimys and 1 (16.7%) of 6 Diplomys.

Twenty volunteers were inoculated with various doses of human serum containing Phlebotomus fever virus (Sicilian type) to determine their clinical and serologic responses as well as the human infectious dose50 of the virus. All infected subjects developed fever which varied in duration from 6 to 74 hours. The most common symptoms during sandfly fever were headache, anorexia, myalgia, photophobia, low back and retro-orbital pain. Infected individuals developed a marked leukopenia characterized by an initial lymphopenia followed by protracted neutropenia. Little complement fixing antibody was detected in convalescent sera but most subjects developed significant rises in hemagglutination inhibiting antibodies. All infected subjects developed specific neutralizing antibodies with titers ranging from 1:40 to 1:2,560. Of the three serologic tests performed, the plaque reduction neutralization method appears to be the most sensitive test for detecting antibodies to Phlebotomus fever viruses.

A virus surveillance project was established and maintained during 1972 along 10 major river drainages in six states. Mosquitoes, biting flies, and blood specimens from sentinel equines were collected during 83 field trip visits to 141 arthropod collecting sites and 22 sentinel locations from April into December 1972. There were 173,074 mosquitoes tested and 303 arboviruses isolated from 11 of 41 species. From 13,388 biting flies tested, 8 arbovirus isolations were obtained in 1 of 5 species. There was no isolation of Venezuelan equine encephalitis (VEE) virus. Western equine encephalitis (WEE) virus isolates were the most numerous and were followed by Turlock, St. Louis encephalitis, Hart Park, California encephalitis, and Bunyamwera (BUN) group viruses. The first isolation of WEE from the mosquito Culex (Mel.) erraticus is reported, as is the extension of the ranges for Buttonwillow virus from California to New Mexico and Texas. Also a single isolation of the BUN group from Culicoides variipennis extends the range of this virus-vector relationship from California to Texas. New distribution records for mosquito species previously unreported for Arizona, Louisiana, New Mexico, and Oklahoma are reported. The sentinel burros detected WEE serologic conversions at two sites in New Mexico and at one in Texas. The surveillance project provided state and federal officials with current information on the status of arbovirus activity, including the absence of VEE activity during 1972, and it demonstrated the existence of the potential for WEE epizootics and epidemics throughout a wide geographic area of the Western United States.

Sentinel pigs were bled and mosquitoes were collected for isolation of Japanese encephalitis virus (JEV) between 1969 and 1973 in a rural area of northern Taiwan which reported a high annual incidence of human cases. The study site included a farmyard, schools, a bat cave, rice paddies and a heronry. Although Culex annulus was collected in every month of the year, isolations were made only in midsummer and only from Culex annulus and (once) from Culex tritaeniorhynchus. These isolates were usually collected from pig-related sources. Human cases in the vicinity of the study site were reported 3 to 6 weeks following the initial isolations from sentinel pigs. Isolations were made only for 4 to 8 weeks each summer. The isolation of JEV was not related to the availability of susceptible pigs or the spring or summer peaks in prevalence of Culex annulus. Despite periodic draining of rice paddies and the application of insecticides, sufficient numbers of Culex annulus were available to support transmission of JEV in each year of the study.

Twenty-two different arbovirus antigens derived from five antigenic groups were examined for their ability to agglutinate normal and trypsinized human group O eryth-rocytes. Trypsinization rendered the cells susceptible to agglutination by 18 viruses, chiefly in the pH 5.85 to 6.2 range, yielding hemagglutinin titers comparable with those obtained with gander cells at their optimal pH.