The American Journal of Tropical Medicine and Hygiene - Volume s1-22, Issue 1, 1942

The close relationship between Tropical Medicine and Military Medicine is little appreciated by others than those immediately concerned with the health of the forces, except when periods of emergency require the expedition of men into the warm countries. At such times the special problems in sanitation, public health, and clinical medicine achieve an unaccustomed dignity and importance, secondary only to the major strategic plans of the General Staffs. This relationship, moreover, is more than one of mutual responsibility. It is one of common origin. Sir Patrick Manson is frequently referred to as the “father of tropical medicine” because he initiated the era of clinical and scientific investigation. In point of fact both fields of medicine may be said to originate from the experiences of the British Army in the Crimea and in India in the middle of the last century. And both Tropical Medicine and Military Medicine have a common parent.

Plague is a satisfactory disease to speak or to write about. Its history may be traced and is fairly well known. But first and foremost, it is spectacular. The mere name of the sickness brings fear and by contrast with “influenza,” which in India destroyed in a few days more lives than the plague in as many years, the word “The Plague” is emotionally colorful. Its biology has been studied and, to a certain extent, its epidemiology has been explained with considerable success. Moreover, the most pessimistic can hardly doubt that, until civilization completely disintegrates, bubonic plague will never cause the havoc it did 500 or even 300 years ago. But, in another sense, the subject appears quite unsatisfactory when after a brief period of enthusiasm the initiated analyzes deliberately the known and unknown in plague. In spite of all the details accumulated in the published records unfortunately read by a relatively few, nobody can answer the great question as to why epidemics or pandemics occur.

No general scientific effort had ever been made to determine the exact character of the snake population in Central America, with the exception of Costa Rica, until July, 1924. Therefore very little definite scientific knowledge of the species of snakes responsible for snake-bite accidents had been recorded. Brazil was apparently the only country in the tropics of the western hemisphere that had made significant progress in the study of its venomous snakes. A great stimulus was given the subject in 1924 by Dr. W. E. Deeks, General Manager of the United Fruit Company's Medical Department, and since then considerable progress has been made in a Central American snake census and in promoting the manufacture of antivenin.

During my service in his organization while at Tela, Honduras, C. A., a plan was launched for a snake census of the coastal plain in use by the fruit growers.Snake accidents had never been a subject of great importance in these plantations yet occasional tragic accidents did occur and we were not prepared to offer modern treatment nor did we have scientific information regarding the species of snakes responsible for the accident.

• 1.  The malaria survey in Cuba, which is planned eventually to include the whole island, has been completed now in Pinar del Río Province and the data are reported here.
• 2.  In the Province of Pinar del Río 16,855 children have been examined for splenomegaly and 7,407 for malaria parasites. The results of the latter examinations show a significantly higher frequency of children with malaria parasites among those with splenomegaly than in the spleen negative group.
• 3.  Plasmodium vivax and Plasmodium falciparum are well distributed throughout the area. The former occurs almost twice as frequently as the latter.
• 4.  The endemicity of malaria is moderate in those portions of the counties of Mantua, Guane, Consolación del Sur, San Luis, and Viñales which lie in the low coastal plain. In the remainder of the province the malaria problem is one of light endemicity, with recurring epidemics when conditions are unusually favorable to the breeding of anophelines capable of transmitting the disease.
• 5.  Five species of anopheline mosquitoes have been encountered in the area. These are: A. albimanus, A. crucians, A. grabhami, A. vestitipennis, and A. atropos.
• 6.  A study of the distribution of these anophelines in the area confirms the fact that A. albimanus is present in far greater numbers in the coastal plain area, where most malaria was encountered. The season of maximum prevalence of this mosquito coincides with the malaria transmission season. It is known to be a malaria vector, and it is reasonable to conclude that it is the important malaria vector in Pinar del Río Province.

• 1.  The malaria survey of Cuba has now been extended to Havana Province and the data collected there are recorded.
• 2.  The results of the examination of 19,188 children for splenomegaly and 9,982 for malaria parasites are presented and analyzed.
• 3.  Except possibly in two municipalities in the province, the incidence of endemic malaria at the present time is, as a whole, quite low. With the exception of small, localized foci which are related to the special anopheline problems of one of the three types described, the problem of endemic malaria in this province is inconsiderable.
• 4.  The peculiar conditions of soil and subsoil which account for the lack of malaria in the province are described.
• 5.  Four species of anophelines, A. albimanus, A. crucians, A. vestitipennis and A. grabhami, have been encountered in the area surveyed.
• 6.  It is concluded that such endemic malaria as is found in this province is caused by A. albimanus.

Patients infected with Plasmodium vivax exhibit a wide difference in their infectiousness for Anopheles quadrimaculatus.

Based on the infection resulting in anophelines, patients have been distinguished as “good” and “poor” infectors. These have not in general differed markedly in gametocyte densities, except that on only a few occasions were the higher densities observed in the “poor” infectors.

The qualitative and quantitative infection of the mosquitoes infected on patients of either category, varies directly with the gametocyte density, although at any given density the qualitative infection arising from a feed on a “poor” infector will more likely be lower than that resulting from an application to a “good” infector of comparable density.

Although gametocyte densities in “good” infectors have tended to be slightly higher than in “poor” infectors, the most striking difference lies in the parity of the sexes in the “good” infectors, and deficiency of males in the “poor” infectors.

Although the data submitted abundantly establish these relationships, gametocyte density is not a reliable guide to the probable resulting qualitative infection of mosquitoes.

It is possible that varying proportions of susceptible and refractory mosquitoes in different lots affect the qualitative infection of any lot, particularly when the gametocyte density is low.

These observations also suggest that the gametocytes of “poor” infectors are inferior, perhaps in vitality, to those produced in “good” infectors.

In the area selected for this investigation, which included two scattered communities in the cocoa growing districts of Tamana Reserve, four species of Anopheles were found: A. bellator, A. oswaldoi, A. mediopunctatus, and A. nimbus. A. mediopunctatus and A. nimbus were rare and A. oswaldoi could be collected with regularity, but none of these species is abundant enough, under present conditions, to be involved in the transmission of malaria in this highly malarious area of Trinidad. A. bellator, the predominant species, was present in great numbers.

A. bellator attacked man viciously, literally swarming about people during the hours when the females became active. Although attracted to cows and donkeys, it seemed to prefer the blood of man to that of animals. A. oswaldoi fed readily on man, but appeared to be associated primarily with animals, especially cattle.

A. bellator will attack man throughout the afternoon, especially on dark days and in the shade of the forest, but the real flight begins at about 5:30 p.m., and continues until about 8:00 p.m., with the peak occurring between 6:30 and 7:00 p.m. The species becomes active early in the morning also, between four and six-thirty o'clock, but the morning flight is light as compared with the evening flight.

A. bellator will feed on man both indoors and out of doors. It will enter houses, and even bed nets, in search of human blood, but it attacks more readily out of doors or under the roofs of cocoa-drying or similar sheds without walls. The females do not remain in houses after feeding, but return immediately to their jungle resting places.

The larvae of A. bellator were found only in Bromeliaceae, and of four species of bromeliads examined, the larvae were collected from two: a species of Wittmackia, and one of Gravisia. Gravisia is the chief A. bellator producing bromeliad in Trinidad.

Experimental infections of A. bellator were obtained twice, and proved that the species is very susceptible to at least one of the species of Plasmodium causing human malaria. Oöcysts were found in two of four A. oswaldoi that fed on a P. vivax gametocyte carrier.

Three of 725 “wild” A. bellator were found to be naturally infected with Plasmodium; one had a single mature oöcyst on the stomach wall, another had infected salivary glands, and the third had nine small oöcysts on the stomach wall.

The evidence presented confirms the conclusion of De Verteuil, that A. bellator is the vector of malaria in the interior cocoa growing districts of Trinidad.

Information has been presented to show that amebiasis surveys conducted in different geographical locations in the Western Hemisphere are too few and too fragmentary to provide a complete demographic picture of the infection. For many areas no surveys have been undertaken; for many others the data are based on unrepresentative groups of the population or too few persons have been examined to provide significant statistics. Moreover, most surveys have employed a single technic on a single stool specimen; hence the positive cases reported constitute only a fraction of the true incidence in the particular area.

In spite of the discrepancies pointed out, there is substantial evidence that amebiasis exists in an appreciable portion of the population of the Western Hemisphere, from Central West Canada (52° 30′ N. latitude) to the Strait of Magellan (52° S. latitude); that it is much more intensely endemic in the American tropics than in the temperate zones; and that in areas like the United States the incidence figure may possibly average as high as 20 per cent, or double that of previously accepted estimates.

The food handlers at a professional school in Philadelphia, Pa. were examined annually for intestinal protozoa for the seven years, 1932–39. Of the 190 persons examined, 50 were older, more permanent employees, who were examined on successive years an average of 3.2 times per person. The 140 student helpers were examined an average of 1.4 times per person. Methods were the same as for the survey of 1060 freshmen at the same institution.

Incidences were higher for the employee group, when single (first) examinations alone are compared, for Blastocystis, Total Protozoa, Endolimax, Endamoeba coli, Dientamoeba, Chilomastix and Enteromonas. The student group had an incidence of 10.7 per cent for E. histolytica as compared with 8 per cent for the employees after one examination. On one (first) examination the 140 students showed higher incidences for Total Protozoa, Endolimax, Endamoeba coli, E. histolytica, and Giardia, but lower for Dientamoeba as compared to the 1060 freshmen who were examined only once.

The incidences derived from 3.2 examinations of the employee group are considerably higher than for the first examination alone in respect to most of the items in the list. The added percentages for 1.4 examinations of the students in comparison with one examination alone are relatively slight. Of the 6 infections with E. histolytica detected in the employee group, four were found at the first examination, one at the fourth and one at the fifth. All of the 15 infections with this species discovered in the students were found at the first examination.

Persons found infected with E. histolytica were treated to eliminate the infection and in this connection daily examinations were made just before, during, and following, treatment. These additional examinations revealed very few additional infections.

The carriers of E. histolytica revealed no more gastro-intestinal symptoms than the others.

All six of the carriers of E. histolytica among the employees and one among the students lived in or near Philadelphia. The remainder came from homes in various parts of Pennsylvania and from other states.

The use of permanent fixed and stained slides added greatly to the number of positives for Endolimax, Endamoeba histolytica, Dientamoeba, Iodamoeba, and Enteromonas.

Mr. President, Dr. Rozeboom, Members of the Society:

I consider it a distinct privilege that, as Chairman of your Committee, I am allowed to present to Dr. Lloyd E. Rozeboom, the Society's new Award for research in the field of tropical medicine, which is known as the Bailey K. Ashford Award.

As you know, this award, which was made possible through the generosity of Eli Lilly & Company, is being presented this year for the first time. It consists of travel expense to and from the meeting, $1,000.00 and a bronze medal. According to the requirements established by the donors, it is to be given annually to “a citizen of the United States, less than 35 years of age, in recognition of demonstrated research in the field of tropical medicine, taking into consideration independence of thought and originality.”