The American Journal of Tropical Medicine and Hygiene - Volume 3, Issue 5, September 1954

Thirty-five cases of P. vivax malaria occurred among a group of Camp Fire girls who attended the 1952 summer camp at Lake Vera, Nevada County, California. Nine of the cases experienced primary attacks 10 to 40 days after exposure. Twenty-six exhibited latent periods of 217 to 316 days. The probable source of these infections was traced to a recently returned Korean veteran.

The occurrence of this outbreak demonstrated the vulnerability of this country to the introduction of malaria from abroad when favorable circum-stances exist, and it provided an unusual opportunity to observe the natural history of the P. vivax strain of malaria in a nonimmune population living in a nonendemic area.

The investigation confirmed, extended, and elucidated the knowledge on latency and delayed primary attacks exhibited by certain strains of temperate zone malaria. The documentation of the incubation periods substantiated the observation that many P. vivax infections contracted in autumn may remain clinically latent for eight to nine months.

The outbreak of malaria at Lake Vera in Nevada County, California, in 1952 (Brunetti et al., 1953; Brunetti, 1953; Gray, 1953, 1953a; Fontaine, 1953) made it imperative that control measures be taken to prevent a recurrence of the disease in the following year. Not only was it desirable that the health of nearly 1,800 persons be protected, but the Oakland, Piedmont, Vallejo and Sacramento Councils of the Camp Fire Girls had a considerable investment in equipment and facilities at the four camps which would be jeopardized by a recurrence of the outbreak. In the absence of an effective local health department in this county and because of the wide area of the State from which the occupants of the four camps came, the State Department of Public Health initiated the epidemiological studies and the necessary control work.

After eight years of a nation-wide campaign against malaria in Venezuela, malaria has been eradicated over a large area. The criterion of cessation of malaria endemicity established in 1950 by the National Malaria Society of the U.S.A. has been adopted. This area, where almost half (49 per cent) of the population of Venezuela lives, is believed to be the largest area, within the tropical zone, of malaria eradication following residual insecticide spraying.

In this area of North-central Venezuela, within the Costa-Cordillera and Llanos geographic regions of the country, the intensity of malaria was as high as in the most malarious zones of tropical America. The incriminated vectors have been A. darlingi, the most important of the Neotropic Region, and A. albimanus and A. albitarsis. Highly endemic and epidemic malaria were found in sections of the area.

DDT, applied at the rate of 2 gm. per sq. meter every six months, has been the insecticide used. At the beginning, however, 1 gm. every three months and later every four months was employed. In some districts, after malaria transmission ceased, other insecticides have been utilized: chlordane against flies and BHC and dieldrin against triatomids.

After exhaustive epidemiological investigations, which may be compared favorably with some used in the more developed countries of the temperate zone, the following facts were established. In one area of about 20,000 sq. km. no primary indigenous case of malaria has been discovered during the last three years. In another area of about 160,000 sq. km. no primary indigenous case of malaria was observed, during the last two years, with the exception of 2 cases near the border of the area, which seems to indicate that here also malaria endemicity has entirely ceased.

Of the incriminated vectors, A. darlingi has been eliminated by DDT residual spraying and is apparently eradicated from most of the territory under discussion. But the population density of the other two vectors, A. albitarsis and A. albimanus, has not been affected by the insecticide. This indicates that in a tropical zone in the presence of efficient vectors, malaria may be eradicated by DDT residual spraying without vector eradication.

With this experience it is expected that malaria eradication from most of Venezuela will be attained in the near future. Only two exceptions to this generalization are considered probable. The first involves two small areas representing only 3.4 per cent of the territory previously malarious, where out-of-doors transmission is taking place which will require additional measures. The second includes those districts inhabited by some nomadic and rather wild Indian tribes, most of them in Amazonas, Apure, Bolívar and Delta Amacuro, which may have to wait for their incorporation to Venezuelan society before they can be freed from malaria.

On the greater part of the coast of British Guiana, close association has hitherto existed between hydrological bonification and hyperendemic malaria, except on the eastern coastlands. Residual DDT house spraying, as the sole means of control, brought about the elimination of A. darlingi and Ae. aegypti, and an economic technique of control maintenance by “strategic barrier” spraying was gradually developed.

In 1951, A. darlingi reappeared suddenly in small numbers on the eastern coastlands in the wake of artificial changes in conditions of physical and human ecology in a localised area. Prompt spraying of houses in the villages and along the path of invasion eliminated a potentially dangerous threat from A. darlingi-borne malaria in the district. This incident confirmed rather than weakened the principle of “strategic barrier” spraying in British Guiana.

TVA has used DDT extensively as a larvicide since 1945 and to a lesser extent as an adulticide during the period 1945–1950. It is still effective for use as a larvicide for control of A. quadrimaculatus on TVA lakes. Its use as a residual spray has been discontinued, and its effectiveness for this purpose is now highly questionable.

In the TVA control program, chemical control measures have always been considered as supplementary, principal reliance being placed on environmental or naturalistic control methods. However, insecticides have been invaluable in the development of the program. They have served well pending the establishment of satisfactory environmental controls. There is a continuing need for efficient larvicidal measures for use when emergency situations arise and as a part of the regular control program to obtain the maximum benefit from water level management schedules. All control measures are frequently subjected to critical evaluation as to their economy and effectiveness under current conditions and changes made as might be indicated. DDT larvicidal measures are under close scrutiny at present because of the possibility of development of resistance. Concurrently, investigations of new insecticidal materials are underway so that a satisfactory substitute for the DDT larvicide will be available if needed.

The relative susceptibility of Anopheles quadrimaculatus and two strains of A. albimanus (Panama and Florida Keys strains) to three strains of Plasmodium vivax was determined. The strains of vivax included a U. S. strain (St. Elizabeth), a New Guinea strain (Chesson), and vivax of Korean origin.

In all cases A. quadrimaculatus showed a high degree of susceptibility, while the two strains of albimanus either were completely non-susceptible, as in the Korean vivax, or became infected only occasionally and at a very low rate.

The infectivity of Korean vivax to A. quadrimaculatus, and transmission through that species, confirms the possibility of establishment of malaria from that area in this country.

The effects of a whole-milk diet, and of a normal diet supplemented with yeast known to be a rich source of p-aminobenzoic acid, were tested in nine African children infected with P. falciparum or P. malariae or with both species. The results demonstrate that within the conditions of the experiment neither a milk diet, nor the addition of yeast to a normal diet, influence the malaria parasite density or the clinical manifestations of human malaria. These findings are at variance with those reported by investigators working with malaria species infecting rats and monkeys.

Pyrimethamine has no unpleasant taste. Some babies were given crushed tablets with a drink of water to wash them down. No toxic effect was noted. Of the 47 who received weekly doses regularly, twelve revealed the gametocytes of P. falciparum in their blood films for two to six weeks. Blood films on all of the 134 regular people were negative at the end of the experiment. No clinical symptoms or relapse occurred during the 18 weeks of suppressive treatment in any of the treated people after the first 3 weeks, when all became free from asexual forms. This appears to be a very good drug for suppressive use if continued weekly. We get the same result with chloroquine but pyrimethamine is easier to administer.

One thousand and twenty Hondurans were treated for acute malaria with a single oral dosage of either amodiaquin (Camoquin), chloroquine (Aralen), hydroxychloroquine (Plaquenil) or pyrimethamine (Daraprim). In general, clinical response was excellent, treatment failures were few, relapses were infrequent, drug toxicity was negligible. The results with pyrimethamine were not equal to the results obtained with the three 4-aminoquinolines. Obviously, it is of great advantage to have several antiplasmodial agents that can be used in single oral dosage for mass treatment.

In cultures of E. histolytica-organism t and E. histolytica-A. aerogenes the production of carbon dioxide, measured in Eldredge-tubes, was greater than could be calculated on the basis of glucose disappearing and lactate produced. The results appear to indicate that some glucose which could not be measured was derived by diffusion from the solid phase of the medium, and from fragmentation of rice flour with hydrolysis of the starch thus liberated. The possibility that some of the carbon dioxide may have been derived from protein and/or fat could not be ruled out. The excess of carbon dioxide in cultures with amebas over that produced by the respective bacterial symbionts without amebas was attributed to production of sugar by the amebas and utilization thereof by the bacterium but some of the gas may have been produced by the amebas.

Lactate, pyruvate, and 3-phosphoglyceric acid provided substrates for growth of A. aerogenes in pure culture, but in cultures of E. histolytica-A. aerogenes there were factors that could not be analyzed.

E. histolytica was shown to produce amylase which finds its way into the medium by unknown pathways. Amylase was demonstrated in overlay removed from cultures of E. histolytica-organism t when growth of organisms was inhibited by toluene. Quantitative data on activity of amylase were obtained from extracts of precipitates by acetone of ameba-harvests. The best extracts showed a specific activity of 48.4 units of amylase per milligram of protein. The activity was highest in the presence of sodium chloride, and optimum activity occurred somewhere between pH 5 to 6.

A new synthetic amebicidal drug, Camoform has been described. Preliminary results indicate an apparent cure rate of 85 per cent among a small series of twenty individuals.

The antibiotic Puromycin produced from a species of Actinomyces, Streptomyces albo-niger, was tested for its trypanocidal properties against Trypanosoma equiperdum, T. equinum, T. evansi, T. rhodesiense, T. gambiense, and T. congolense infections in mice. The data presented in this report show that when treatment with Puromycin was begun approximately four hours after inoculation with these species of Trypanosoma all except T. congolense were prevented from developing. Administration of the drug four days prior to inoculation with trypanosomes did not prevent infections from progressing. When treatment was initiated at the height of infection the drug had a strong suppressive effect against all species except T. congolense. This effect was greater against those of the evansi group, T. equiperdum, T. evansi and T. equinum, than those of the brucei group, T. rhodesiense and T. gambiense. It is encouraging that this antibiotic has this powerful effect against these trypanosome infections.

There is no question that the in vitro dye test of Sabin and Feldman (1948) is a very useful tool for the study of Toxoplasma infections. The results obtained in different laboratories in the United States have been, in general, consistent, as indicated by “blindfold” comparative tests. However, there are indications in reports from other countries that the test, still relatively unstandardized, may yield surprisingly low titers in cases of toxoplasmosis (Westphal, 1951). Standardization of the test has been attempted by Beverly and Beattie (1952) on the basis of the number of parasites present in the peritoneal exudates used in each particular run. In our own routine performance of the test in this Laboratory, we have encountered instances of interference or inhibition of the dye test reaction, the analysis of which has yielded information of considerable importance relative to standardization. It is the purpose of this paper to describe this phenomenon and present evidence bearing on its elucidation.

A characteristic feature of dermatology of the New World is the endemic pemphigus of the central part of South America. Any studies relative to this striking type of skin reaction should be of interest to those in tropical medicine, for there are many problems of epidemiology, differential diagnosis and therapy, all related to dermatology in the tropics. Since this is the most extensive, most active, and perhaps only focus of endemic pemphigus in the world, there are still those outside of Brazil who doubt the relationship of the pemphigus of Brazil to pemphigus seen elsewhere in the world. Since no one knows what pemphigus is, one can argue only about clinical features. For those who actually work with the cases in Brazil, there is no doubt about the morphological relationships to pemphigus.

The classification of true pemphigus today is considered by Lever (1953) to be:

• 1)  pemphigus vulgaris malignus
• 2)  pemphigus vegetans
• 3)  pemphigus foliaceus
• 4)  pemphigus erythematosus (Senear-Usher)

Epidemiologic observations in Polynesia suggested that Aedes polynesiensis Marks served as a natural vector of dengue in that area. This mosquito species was shown to be capable of transmitting dengue from monkey to monkey in the laboratory. A hemagglutination-inhibition test was used to demonstrate the occurrence of the infection in the experimental monkeys.

A study of 452 cases of murine typhus fever occurring in Southwest Georgia from January, 1945, to January, 1953, showed a seasonal peak of rural cases during the summer but an even distribution of urban cases throughout the year. Incidence rates were about twice as high in rural as in urban areas, and about eight times greater in the white than in the colored race. Age-specific incidence rates were low in childhood, rising to a peak during the fourth and fifth decades. Farmers and their families made up 70 per cent of the cases studied. The mean titer of the Weil-Felix test was high in the first week and then rapidly declined, whereas the mean titer of the complement fixation test reached a peak during the second week and remained high over the next 50–60 weeks after which it slowly declined. In cases treated with aureomycin, there was a consistent lowering of mean titers for the complement fixation test, but very little effect on the Weil-Felix titers was demonstrated.

Eight species in two genera of Triatominae have been tested as vectors of plague. The plague bacilli were found to remain infective in Triatoma protracta (Uhler) for 3 days at 30°C., but were negative on the fifth day when the bugs were injected as an aqueous suspension into guinea pigs and mice.

Four adult Triatoma phyllosoma pallidipennis (Stål) in 2 different groups transmitted plague by interrupted feeding; i.e., first feeding on an infected mouse and then feeding on a healthy mouse. These transmissions were probably due to contaminated mouth parts. Thirteen similar feedings were negative using 5 other species of Triatoma.

Triatoma protracta and Mestor megistus (Burmeister) infected with Trypanosoma cruzi Chagas and Pasteurella pestis (Lehman and Neumann) were fed to mice; 4 positive plague infections resulted one of which was pneumonic; 3 mice were negative. Thirteen other tests with plague-infected Triatominae fed to mice failed to transmit P. pestis through the gastrointestinal tract, but produced 3 pneumonic cases.

Triatoma platensis Neiva was the only species to yield plague positive feces out of 17 specimens tested.

Soil studies carried out with specimens collected on the Isthmus of Panama yielded isolates of Histoplasma capsulatum, Allescheria boydii and Microsporum gypseum. This constitutes the first record of the occurrence of these three human pathogenic molds in the soil of tropical America. The techniques used in the recovery of these fungi are outlined, and the implication of the findings are discussed.

An improved antigen for the complement-fixation test has been prepared by extracting desiccated adult schistosomes with anhydrous ether in the cold (-15 to -18°C.) prior to final extraction with buffered salt solution. Preliminary extraction with ether markedly reduced a tendency of the antigen to react with syphilitic serum without appreciably altering its capacity to fix complement specifically with serum from schistosome-infected individuals.

Sera from persons infected with S. mansoni or S. japonicum could not be differentiated on the basis of their capacity to react with antigens from the homologous and heterologous parasites.

The complement-fixation test is discussed from the point of view of its value in the diagnosis of schistosomiasis.