The American Journal of Tropical Medicine and Hygiene - Volume 4, Issue 5, September 1955

The trend in the teaching of Parasitology and Tropical Medicine in the medical schools of the continental United States is described from the results of surveys made in 1941, 1945 and 1954. The 1954 survey was made at the request of the Parasitology and Tropical Medicine Study Section of the National Institutes of Health. Since World War II there has been only a slight decline in the average number of hours devoted to Parasitology, but Tropical Medicine as a distinct subject has nearly disappeared from the medical curriculum. The 1954 survey was followed by a questionnaire sent to all persons listed as teachers of Parasitology in the medical schools, in order to determine their qualifications and experience, and their interest in obtaining a fellowship to gain practical experience in the American Tropics. Sixty-four per cent of the 120 persons who replied expressed an interest in such a fellowship.

The China Medical Board of New York has made a grant to Louisiana State University to conduct a program of fellowships for a two year period. The first group of six fellows was assigned to Costa Rica for the months of July and August 1955. It is planned to offer four similar fellowship periods each year. Teachers of Tropical Medicine who are not included among the teachers of parasitology will be included in the program.

Having to discuss before you the contribution of medical geography to the etiology of disease, it behooves me to start with a definition of geography, followed by one of pathology. If I succeed in doing so in adequate fashion the contribution of one to the other will be made obvious, and obviousness is the often unattainable goal of any demonstration.

“Geography is not just the study of landforms, it is also the study of the factors that have fostered these landforms, the climates and soils connected with them, the plants that live on the soil, the animals that live on the plants, and the societies of men who have established themselves on these landmasses, in these climates, and who live in commensality with these plants and animals.”

If this is a fair definition of geography, it then encompasses a good half of the factors that affect the occurrence of disease, and also implies a study of their interrelationships.

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.

Malaria suppression by pyrimethamine, chloroquine and the two combined, administered at monthly intervals, was attempted in West African school children. Primaquine given at weekly intervals was also tested. Effective suppression was achieved in children receiving pyrimethamine alone and in combination with chloroquine; chloroquine alone was not found to be as efficient. Primaquine in weekly doses showed little or no effect on asexual parasitemia. There was an apparent inhibition of gametocyte production in children given the drugs. There was no evidence that the spleen rate or average enlarged spleen were affected by the treatment. The development of pyrimethamine-resistant strains was not observed throughout the six to eight month periods of the experiment.

The efforts to control malaria in the vicinity of the Panama Canal during a half century were progressively more successful as new methods developed. Sanitary engineering works of a permanent type have controlled mosquito breeding in the vicinity of communities in the Canal Zone. A battery of chemicals are in use for destroying mosquitoes in all phases of their life cycle and new drugs for effectively attacking the malaria parasite in the human carrier and patient are now at our disposal.

Malaria has been reduced to an uncommon disease in the Canal Zone and urban communities of the Republic of Panama enjoy a considerable degree of freedom from infection, but rural communities and hamlets continue to lose much of their economic production potential due to malaria. Aggressive antimalaria programs temporarily reduce the disease but eradication has not been achieved in Panama. Temporary inactivity of malaria in a community may delude the inhabitants but the disease is unlikely to remain quiescent for long. Continuing and unremittent application of control measures by the individual and the community aimed at reducing the vector and treating the carriers is the solution to this problem in the Panama area. Once initiated, the control should be integrated into the community functions and become a permanent part of the community routine.

Twenty-nine of 371 patients found to have E. histolytica demonstrated in ironhemotoxylin stained preparations, had clinical-laboratory evidence of hepatic involvement. More objective criteria than hitherto used have been found helpful in the detection of hepatitis believed to be due to E. histolytica. Of the twelve tests and signs employed, six were significantly altered in one-third or more of the patients. These abnormalities were corrected on application of erythromycin stearate therapy, as described, in the majority of patients treated.

Twenty-one patients out of 29 treated with erythromycin stearate (one received a combination of erythromycin and fumagillin) showed a favorable response in clearance of their liver disease. In the nine cases resistant to erythromycin therapy, subsequent therapy with chloroquine resulted in a good response in six and equivocal results in two. One patient did not respond to therapy.

These studies have led to the cultivation of Entamoeba histolytica in a simple medium limited in nutrient to rice flour. The inclusion of other nutrients in media used heretofore has hindered adequate observation of the growth-supporting capabilities of this substance.

The medium, magnesium phosphate agar-phosphate buffered saline, is composed of an agar slant containing two per cent dibasic magnesium phosphate overlaid with phosphate buffered saline (pH 7.4). If sterile rice flour is added as food, E. histolytica accompanied by a mixed bacterial flora can be cultivated indefinitely by serial transfer at four to six day intervals.

The medium was applied to study of nutrients in a series of tests to observe the growth response of E. histolytica to a number of rice products. It was observed that rice bran will not support growth. Rice polish obtains survival for only a few transfers possibly because of intensified bacterial growth. Rice flour, ground from either unpolished or polished rice, will support growth and multiplication with serial transfer indefinitely. Pure rice starch will not support growth and survival is limited to a few transfers. The deficiency of this product may be due to the elimination of the intergranular protein matrix associated with the starch granules in the rice kernel.

Magnesium phosphate agar-phosphate buffered saline medium appears to meet the need for a simple easily prepared medium for use in E. histolytica growth studies. It should afford added opportunity for study of the role of the bacterial flora and other factors requiring elucidation in order to establish E. histolytica in pure culture.

Compound S does not depress the resistance of d b a mice to Trypanosoma cruzi, but cortisone and hydrocortisone induce acute fatal trypanosomiasis. Whereas cortisone gives rise to marked peripheral parasitemia, and only 11.1% of mice survive more than two weeks, hydrocortisone induces a mild but transient peripheral parasitemia with 45 % of mice surviving longer than two weeks. Compound S does not protect mice infected with T. cruzi against cortisone if the latter is administered within five days, but there is a partial and increasing protection against cortisone as the interval between administration of Compound S and cortisone is increased (9 to 26 days).

Serological surveys of Trinidad residents by the Trinidad Regional Virus Laboratory demonstrated yellow fever immunes in eight individuals 15–19 years of age, and in a high proportion of older individuals. Yellow fever virus was isolated from a human case in April 1954. Subsequently virus isolations have been made from 13 other human cases, 7 red howler (Alouatta) monkeys which were brought in dead, 21 pools of Haemagogus mosquitoes, and 1 pool of mixed mosquitoes—a total of 43 virus isolations. Yellow fever virus was repeatedly recovered from Haemagogus mosquitoes captured at ground level.

• 1.  Studies on Sindbis virus, a newly recognized member of the arthropod-transmitted viruses, are described; these include data on its immunological characteristics, distribution in the Nile Valley, vertebrate host range, and transmissibility by arthropods.
• 2.  The virus has been isolated from mosquitoes during three successive summers, and once from a juvenile hooded crow (Corvus corone sardonius).
• 3.  It has been placed by Casals and Brown (1954) in Group A of the arthropod-transmitted viruses, but is distinguishable from other members of this group by the neutralization test.
• 4.  Its particle size, estimated by gradacol membrane filtration, is between 40 and 48 mu.
• 5.  On initial passages by brain-to-brain transfer it is fatal to infant mice but not to adult mice.
• 6.  It is highly fatal to embryonated hens' eggs and is markedly cytopathogenic to outgrowths of fibroblastic cells in chick embryo tissue cultures.
• 7.  Experimentally it is easily transmitted by Culex mosquitoes (Culex pipiens L. and Culex univittatus Theobald), and Ornithodoros savignyi (Audouin) ticks are infectible by parenteral puncture and will subsequently transmit the infection by feeding upon infant mice.
• 8.  Antibody surveys imply a) a wide vertebrate host range including man, domestic quadrupeds, birds, and domestic fowl, and b) frequent human infection (27 per cent), particularly in the age group of 15 years and over (34 per cent), in the Nile Delta, and less frequent human infection (12 per cent) in the Southern Sudan.
• 9.  No information is available on the symptomatology of natural infections.

• 1.  The Ar-339 strain of Sindbis virus rapidly multiplies in plasma clot cultures of chick embryonic tissue and produces a marked cytopathogenic effect on fibroblast-like outgrowths. Similar changes are induced by the virus in cultures of human adult uterine tissue, and monkey testicle tissue. No cytopathogenic effect was observed in cultures of HeLa cells or in fibroblast-like outgrowths from human embryonic skin-muscle tissue.
• 2.  On occasion fragments of chick embryo heart were observed to continue to rhythmically contract although the surrounding outgrowth of fibroblastic cells showed the typical degeneration.
• 3.  A satisfactory neutralization test for the demonstration of neutralizing antibodies in human sera was developed, using cultures of embryonic chick cells. The results of comparative tests indicate that with Sindbis virus, chick embryonic tissue cultures are more practical for use in serological surveys than are infant mice.

Observations leading to the investigation of common indigenous wild birds of the Nile Delta as potential circulating reservoirs of West Nile virus are outlined. Methods are described for accomplishing a serological survey of the six commonest avian species, namely: house sparrow, Passer domesticus; hooded crow, Corvus corone sardonicus; buff-backed heron, Bubulcus ibis; palm dove, Streptopelia senegalensis; kestrel, Falco tinnunculus; and rock pigeon, Columba livia. Neutralization testing of more than 500 specimens of avian sera showed a significant incidence of neutralizing antibodies in all six species collected in the West Nile virus-endemic area.

The hooded crow showed a remarkably high incidence of immunity—more than 80 per cent in several localities. In the Sindbis area, the positive incidence in this species diminished in the late spring collection, probably as a reflection of the new nonimmune fledgelings introduced during the nesting season, just prior to the most active mosquito transmission period.

To test the implications of this serological survey, experimental infection by feeding of West Nile virus-infected Culex pipiens and Culex univittatus mosquitoes on specimens of the common avian species was carried out. Susceptibility of all the species was demonstrated by measurement of the titer and duration of the postinoculation virus circulation. Similarity of susceptibility and virus circulating capacity of individuals in the same species was consistently demonstrated. The number of infective mosquito feedings had no relation to titer or duration of virus circulation, one bite being as effective as many. Mosquitoes were infected by feeding on the infected birds, and subsequently transmitted the virus.

Evidence for specificity of the neutralizing antibody against West Nile virus is given. Variable circulating virus titer and virulence relative to strain and passage level were verified.

The hooded crow proved to be the best virus circulator in titer as well as duration. The bird-mosquito-bird cycle of transmission was easily demonstrated with the hooded crow, house sparrow, and buff-backed heron, as an example of what may occur under natural conditions in the endemic environment of the Nile Delta of Egypt.

Structures which superficially resembled microfilariae were found on blood films and in other types of clinical material. These organisms, however, apparently are airborne spores of helicosporous fungi and represent contaminants on the blood films. It is believed that these objects have been mistakenly identified by other workers as microfilariae or as other species of worms.

Examination of fecal specimens from 79 natives living in a tropical region of the Sudan revealed that 67 per cent of the people were infected with Endamoeba histolytica (“small” and “large” races), one per cent with Dientamoeba fragilis, 5 per cent with Entermonas hominis, and there was one infection with Isospora. Eggs of Ancylostoma and Trichostronglyus were recorded in 3 per cent and 2 per cent, respectively, of stools examined. Ascaris was absent although conditions for its propagation seemed favorable. There was a single case of infection with Trichuris and one with Hymenolepis. Eggs of Schistosoma mansoni were detected in 10 per cent of the stools.

The incidence of parasitism in Scotts Bluff County, Nebraska approximates the estimated national average. Intestinal protozoa appear to be generally transmitted by some method other than in feces. Importation of the heavily infected Mexican laborers into the county could supply the infective material for an epidemic or a build-up of amebiasis, although at present no important transfer to permanent residents seems to have occurred.

Fifteen individuals infected with Schistosoma mansoni received daily intramuscular injections of 5 cc. of Fuadin until toxic reactions to the drug made it necessary to give this amount on alternate days. The treatment was continued until a total of 100 cc. had been given. The sera from these patients were tested for circumoval precipitins before and at regular intervals after therapy. For comparison seven untreated cases were given similar tests. The circumoval test became negative in 13 of the sera tested between the 120th and 183rd days of observation. It is believed that the two cases that remained positive represented treatment failures. The sera of the seven untreated patients remained positive throughout the period of study.

The skin reactions to antigens prepared from schistosome eggs were negative before treatment but became positive in 11 of 14 patients tested 183 days after therapy. Positivity was first manifested on the 150th day after treatment. The observations indicate that the circumoval precipitin content of sera and the skin response to egg antigen are inversely altered as a consequence of treatment. The results of the former are believed to indicate that all but two patients were cured with Fuadin. The change from negative to positive skin reaction observed in 11 out of 14 patients is suggestive of some action by the drug which sets up skin sensitization but not necessarily that treatment was successful.

The most important toxic reactions caused by treatment were loss of weight, anorexia and vomiting. These reactions, however, did not warrant discontinuation of the drug.

In a series of 50 cases of hepatic fibrosis associated with bilharzial mansoni infection, hematemesis occurred in 14 per cent, esophageal varicosities in 30 per cent, and collateral veins in the anterior abdominal wall in 54 per cent. Their incidence was greater in cases with ascites than in those without ascites. The ether-portal circulation was prolonged in the majority of cases. The spleencarotid time was frequently normal or reduced. Splenic venography yielded evidences of portal hypertension, degree of hepatic fibrosis and of patency or thrombosis of the splenic or portal veins.

Our thanks to Messrs. “Sandoz” for a liberal supply of Lobeline.

• 1.  Subcutaneous nodules were palpated on 469 or 19.4 per cent of 2,423 laborers on the Firestone Plantation in Liberia. Approximately 90 per cent of these nodules were located in the pelvic region.
• 2.  Microfilariae were demonstrated in 278 or 39.9 per cent of 696 Africans examined by both skin biopsy and scarification smears, which was higher than any single method of diagnosis employed.
• 3.  Nodules containing O. volvulus occurred in a significant number of cases in the absence of demonstrable microfilariae on skin biopsy and scarification smears. The highest prevalence of onchocerciasis was demonstrated by combining skin biopsies, scarification smears, and palpation for nodules.
• 4.  Microfilariae of W. bancrofti and A. perstans occasionally occurred in skin biopsies, especially in patients from the Coast where the prevalence of wuchereriasis was much higher.
• 5.  Small nebulae and other minute corneal opacities occurred with greater frequency among individuals with onchocerciasis than in those without this infection. Ocular pathology attributable to this disease was not severe enough nor common enough in the groups examined in Liberia to make it a public health problem. Onchocerciasis should, however, be considered in the differential diagnosis of ocular pathology in the individual case.
• 6.  Onchocerciasis was most common in the tribes from the interior of Liberia. The Kpelle, Gola, Mendi, and Gbandi tribes especially had a high rate of infection, whereas, among the Kru, Vai, and coastal Bassas it was much lower.

Eight patients having advanced filarial elephantiasis were treated with cortisone. Initial treatment consisted of 100 mgm. daily in divided doses, over a period of 30 days or longer. Dosage was then lowered stepwise over several days before discontinuance. Six patients had a marked response to treatment, with diuresis followed by reduction or disappearance of induration. One patient's response could not be assessed; his case was complicated by concurrent arteriosclerotic heart disease. The other treatment failure was in a patient with verrucous skin changes involving penis and scrotum. Such skin changes, which were also seen to a minor degree in other patients, were unaffected by cortisone.

In five of the six patients, although induration reappeared or increased following discontinuance of therapy, improvement persisted during the entire period of observation. This period varied from about seven to ten months. Retreatment with smaller doses of cortisone for short periods as relapse occurred seemed beneficial.

In the one patient with microfilaremia prior to treatment, the number of microfilariae in the circulating blood increased markedly during treatment, then diminished again as induration reappeared. Biopsies before and after treatment in one patient showed no effect on the elephantoid tissue itself. Diuresis and increase in microfilaremia suggest that the action of cortisone is to reduce the inflammatory blockage of the lymphatics.

All available evidence indicates that the admonitions of Moses not to eat the flesh of swine and that of public-health officials to cook pork until it is well done have not been followed. In the United States, reports of various samples of the population reveal zoologic infections of Trichinella spiralis of from 10 to 20 per cent. There is sufficient evidence to warrant the conclusion that such infections have produced no clinical manifestations.

In spite of the many-times repreated warnings about the thorough cooking of pork and even laws forbidding the feeding of raw garbage to hogs, zoologic trichinosis in hogs and man persists. Accordingly, other means of controlling parasitism by this worm have been suggested, and prominent among them is the suggestion of Gould, Gomberg and Bethell (1954) that pork intended for consumption be irradiated. Aside from the cost and difficulty of establishing this process in the country, the question must be raised as to whether the low grade of the zoologie infection in question actually is not beneficial, conferring an immunity on the public and even the hogs to such an extent that the development of clinical symptoms, heavy infections and even death often is precluded.