The American Journal of Tropical Medicine and Hygiene - Volume 18, Issue 5, September 1969

The concept of nation-wide or even global eradication of malaria originated from the findings that 1) interruption of transmission of the four species of plasmodia infecting man throughout large areas was possible with indoor residual spraying with DDT, and 2) malaria parasites usually disappear spontaneously from infected persons in less than 3 years, permanently interrupting transmission. From this standpoint three types of malaria may be considered: 1) responsive, when the vectors die after alighting on a sprayed surface for sufficient time, carrying with them malaria parasites that may be within their bodies, thereby interrupting transmission; 2) refractory, when due to a natural or acquired behavior of the mosquitoes, or to resistance to the insecticide, some of the vectors may survive the application of the insecticide; and 3) inaccessible, when due to cultural patterns or to the state of mind of the affected populations it is not possible to spray dwellings. Only responsive malaria is now eradicable; fortunately it is extensive, and current successes prefigure further benefits. Eradication of refractory malaria must be deferred, with few exceptions, but the disease can be reduced by adequate application of residual insecticides. Inaccessible malaria must await profound changes in cultural patterns or states of mind, but fortunately the affected populations are small and frequently isolated, and the required changes may not be far away.

Therefore, eradication of malaria must at present be considered unstable, regional, and temporary. Until malaria disappears from the world there are risks of losing what has been accomplished in a given country. That more than one-third of the population of former malarious areas lives in zones where the disease has been eradicated, and that another third inhabits regions under eradication programs, constitute a great achievement. Slow progress, however, in the rest of the world indicates that further efforts should be made, particularly in financing the relevant programs in the developing countries. It is also of great importance to delimit the areas where malaria, because of being refractory or inaccessible, will not be soon eradicated. Changes in strategy are necessary—general public-health activities in hyperendemic areas are not effective in the presence of malaria; the funds they use might be better designated for efficient indoor residual spraying. On the other hand, simple control programs should be regarded with more enthusiasm in countries that are at present unable to undertake eradication, as the insecticide represents the best method to improve health in the highly endemic areas.

As the maintenance phase will be long-lasting, it is essential that the work performed be simple and of low cost. I advise that the malaria-eradication service be transformed, after the objective is achieved, into a vector-borne-diseases control service, which would maintain eradication while producing benefits in other fields.

The incorporation of sodium (1-14C) acetate into the blood lipids of normal ducks and ducks infected with Plasmodium lophurae was studied. After incubation, the cells and plasma were separated, their total lipids extracted, and the lipid classes were separated by thin-layer chromatography. Individual lipid classes were examined for radioactivity by liquid-scintillation spectrometry. Activity was found in the phospholipids, sterols, free fatty acids, triglycerides, and sterol esters of both normal and infected blood cells and plasma. An additional class, monodiglycerides, was found to be active in the parasitized cells. The free fatty acids of both normal and infected plasma contained most of the activity found in their total lipids. The phospholipid fractions of normal and parasitized blood cells possessed most of the 14C activity. Parasitized blood cells demonstrated greater incorporation of 14C into their lipids than did plasma or normal blood cells.

Two intra-uterine deaths from placental and systemic leishmanial parasitism occurred in offspring of a multiparous marmoset bred with a mate of her own subspecies, Saguinus fuscicollis lagonotus. Trypanosomes resembling Trypanosoma cruzi were found in maternal but not in paternal blood. The morphologic identification of a T. cruzi-like trypanosome associated with leishmanial forms in fetal placental endothelium and trophoblasts suggests that this embryonic death is an example of Chagas' placentitis, previously reported only in man. The widespread infection in the other abortus is an example of so-called congenital Chagas' disease. The histopathological features of these congenital infections and the cellular reactions of the marmosets to the organism indicate that this small laboratory primate has potential for studying the pathogenesis and therapy of this disease. This presence of T. cruzi-like infections in a marmoset breeding colony suggests the need for precautions against accidental infection by animal handlers.

The indirect hemagglutination (IHA) test for the detection of antibodies in amebic infection has proved to be sensitive and specific. It would be advantageous to have a stable, uniform preparation of sensitized erythrocytes available for use at any time. Erythrocytes were treated with glutaraldehyde, tanned and sensitized with Entamoeba histolytica antigen and used in the IHA test. Serum from uninfected persons and from patients with amebic colitic and liver abscess were used to ascertain the sensitivity and stability of the treated erythrocytes as compared with sensitized untreated erythrocytes. The sensitivity of the glutaraldehyde-treated erythrocytes in the detection of E. histolytica antibody was comparable to that of fresh erythrocytes. Treated sensitized cells were stable, when stored at -70°C, for 6 months.

Antigen for the indirect hemagglutination test was made from locally isolated strains of Entamoeba histolytica. These strains were associated with a Klebsiella sp. strain. The antigen was prepared by washing and treating the amebae with formalin-NH4-OH-Polysorbate 80 and was then subjected to sonic distintegration. The ameba-immobilization test was modified and stadardized for the purpose of this study. Sixteen patients with amebic liver abscess, 13 with amebic hepatitis, three with intestinal and hepatic amebiasis, three with acute intestinal amebiasis, 11 with chronic intestinal amebiasis, 32 with varying nonamebic conditions, and 27 apparently healthy persons were included in the study. Positive results of 75, 54, 36, 16, and 4% by the indirect hemagglutination test and 88, 62, 45, 13, and 0% by the ameba-immobilization test were obtained in cases of amebic liver abscess, amebic hepatitis, chronic intestinal amebiasis, miscellaneous-disease group, and apparently healthy individuals, respectively. All three cases of intestinal and hepatic amebiasis and all three cases of acute intestinal amebiasis were positive by both the tests. These results suggest that both these tests can be used as useful adjuncts for the diagnosis of amebiasis.

An epidemic of a chronic wasting disease, caused by a previously unknown nematode. Capillaria philippinensis, was discovered to be occurring along the northwest coast of Luzon. Philippines. A study was undertaken to elucidate by epidemiologic methods the possible mode of spread of the new disease, intestinal capillariasis, in Pudoc West, the site of the first cases and the most heavily infected village. A census of the village was conducted and the date of onset of capillariasis determined by interview for each case. Stool surveys were done of the entire village and individual families followed more closely for occurrence of new cases. Thirty-two percent of the population and capillariasis during the 2½ years since the beginning of the epidemic. The fatality rate in males was 35%, 19% in females. An analysis of initial cases within households revealed that most were males, usually between the ages of 20 and 49, suggesting a relation between initial infection and occupation. The distribution of age and sex in subsequent cases and the general population were similar. In addition, the pattern of spread within families and within the village also suggested a direct mode of transmission of the disease.

A total of 45 injections of guinea-pig kidney extract positive for Forssman antigen (0.1 mg nitrogen per injection) was administered to mice 21 days before infection and until 65 days after infection by Puerto Rico strain Schistosoma mansoni cercariae. Infected mice were killed on days 70 to 76 after infection, and parasitemia was determined. Pigment content, measured by total-iron determination, noted in pooled liver samples and adult worm pairs, increased significantly (p, <0.001) in mice receiving kidney extracts, as compared with normal and experimental control animals. Infected mice receiving extract showed similar increases in the percentage of nonviable eggs. The injection of extract alone into normal mice produced no apparent effects. The results suggest that guinea-pig kidney extract positive for Forssman antigen alters the metabolism of S. mansoni adults in mice.

Salmonella organisms were sought in five Costa Rican cattle abattoirs whose products are approved for export to the United States. No Salmonella were found in samples of cattle feces. From one sample of meat, Salmonella saint paul was isolated. Five samples of meat from each of two slaughterhouses yielded multiple isolations of other enteric bacteria. Swabs taken from equipment, floors and walls, and workers' clothing in the five abattoirs were all negative for Salmonella spp. From floor-drain swabs collected from four of the five plants, Salmonella group E1 was isolated. Fecal samples from workers in two of the five plants were tested for Salmonella spp.; there were seven isolations from one plant and none from the others.

A method for survey of natural waters and soils for Pseudomonas pseudomallei was devised, and it was tried in sampling a tin-mining pool area near Kuala Lumpur, Malaysia. The method consisted of intraperitoneal inoculation of weanling hamsters with either 2.0 ml of natural waters, or 1.0 ml of supernatant fluid from sedimented suspensions of soil. Subsequent cultural study was made only of animals dying after inoculation. A differential bacteriologic medium was used, composed of nutrient agar with 3% glycerol and 1:200,000 crystal violet added. The method is sensitive: fewer than 10 organisms regularly killed hamsters. The method is fast: average time of death was 3 days after inoculation, with a range of 2 to 5 days for 96% of animals.

All states in West Malaysia except the island state of Penang were sampled for the distribution of Pseudomonas pseudomallei in the water and soil, as determined by hamster inoculation. The terrain from which samples were taken was classified into several categories among which were primary forest, secondary forest, wet rice fields, and recently cleared areas. Isolations of P. pseudomallei were obtained from all states sampled and from all types of terrain. There were striking differences, however, in the low rate of isolation from surface water of forested lands (0.8 to 3.2%) and the high rate of isolation from wet rice fields and fields of newly planted oil palm (14.5 to 33.3%). Results of this investigation and other recent studies indicate that P. pseudomallei is a normal inhabitant of the soil and water. There is no evidence to suggest that this microorganism requires the rat or any other animal as a maintenance host.

A total of 1,592 serum specimens from Army recruits and other selected population groups in Malaysia were examined for the presence of Pseudomonas pseudomallei antibodies with a hemagglutination (HA) test. The percentage of serum specimens with an HA-antibody titer of 1:40 or greater ranged from 1.9 to 15.8. The highest prevalence of antibodies was found in persons residing in rice-growing areas.

The prior observation that Rickettsia-like microorganisms could be propagated from the blood of a patient with trench fever directly on blood agar received confirmation by further isolations of rickettsiae on cell-free media from the blood of two volunteers infected with a Mexican strain of Rickettsia quintana. The first volunteer was infected by scarification with saline suspensions of body lice, randomly collected in México City, in whose feces R. quintana had been seen. Infective blood from this patient was inoculated subcutaneously into the second volunteer. Both volunteers contracted typical clinical trench fever. The etiology of their infection was confirmed by xenodiagnostic louse-feeding. R. quintana was propagated from the blood of both volunteer patients directly on blood agar. Lice inoculated with the microorganisms so cultivated showed a typical histologic picture of exclusively extracellular rickettsiae in the lumen of their gut.

A Mexican strain of Rickettsia quintana isolated directly on blood agar from a volunteer trench-fever patient and passaged exclusively on this medium induced typical clinical trench fever in two of three volunteers. The etiology of their infection was established by xenodiagnosis as well as by recovery of the rickettsiae from their blood directly on blood agar. The recovered microorganisms produced typical extracellular infection in lice after intrarectal inoculation. The numbers of rickettsiae circulating in the peripheral blood of the two infected volunteers at various intervals after onset of disease were quantified. Both infected volunteers had antibodies in low titer, which reacted with a complement-fixing antigen prepared from a European strain of R. quintana cultivated on blood agar. The experiments established that the microorganisms propagated on cell-free media from the blood of trench-fever patients were R. quintana.

In a field trial of trachoma vaccine in young children in Saudi Arabia, conjunctival scrapings were taken from 1,093 vaccinated and 1,056 control children before the start of the study and at 6-month intervals thereafter. The scrapings were examined in a direct immunofluorescent test with fluorescein-conjugated anti-lymphogranuloma venereum serum with appropriate controls to ensure specificity of the strain. Total numbers of inclusions on each slide were counted. The microbiological conversion rates from negative to positive or the reverse were analyzed in children receiving one of three dosages of vaccine together with quantitative counts of inclusions. No effect of the vaccines was found on the microbiological attack rates of trachoma over intervals of 6, 12, 18, or 24 months. However, a highly significant reduction in inclusions was observed in vaccinated children compared with controls 6 months after primary inoculation. This beneficial effect was not found at the later examinations. Clinical observations in this same vaccine field trial were published earlier; a beneficial clinical response was seen only after administration of the middle dosage of vaccine. In contrast, the microbiological assessment of these vaccines indicated that a significant reduction of inclusions followed administration of vaccines containing the least or the most amount of antigen. We suggest that the microbiological intensity of the disease and presumably the contagiousness of the vaccinated persons were reduced by these vaccines thereby raising the possibility of eventual interruption of the transmission cycle of the disease.

The number of currently catalogued arbovirus serotypes has increased dramatically from 34 in December 1949 to 228 in January 1969. Techniques involving inoculation of suckling mice principally, and tissue cultures to a lesser extent, provided the key to unlock a Pandora's box of arboviruses, especially in tropical areas, whenever serologic research stations were established between 1950 and the present.

Although most of the recently described arboviruses have been designated by the town, district, or geographic location such as a river valley from which the specimens yielding the new prototypes were isolated, difficulties regarding nomenclature have persisted with some older arboviruses that were named for the symptoms that they induced in man or domestic animals. Following the leadership of Smithburn and Haddow in 1944, who designated the recently isolated non-yellow fever virus, Bunyamwera, after the location in the African forest from which this agent was recovered from mosquitoes, most arbovirologists have applied geographic names to isolates of new arbovirus serotypes.

During the summer of 1964 and the spring and summer of 1965, California encephalitis group viruses were isolated from six pools of boreal Aedes mosquitoes collected in and near Rochester (54°N, 113°W), Alberta, Canada. Mosquitoes were collected by aspiration, by sweep-netting, and with a CO2-baited cone trap. Collections were placed on Dry Ice and shipped to Madison, Wisconsin, for identification and isolation of virus. Aedes mosquitoes accounted for 97% of 16,453 mosquitoes examined for virus. Snowshoe hare virus of the California group was isolated from three pools of Aedes communis group, and one pool of Aedes stimulans group. Jamestown Canyon virus of the California group was isolated from one pool of A. communis and from a pool of Aedes spp. The minimum vector-infection rate was 0.40 isolates per 1,000 Aedes spp. mosquitoes in 1964, 0.46 isolates per 1,000 A. communis group mosquitoes in 1965, and 0.33 isolates per 1,000 A. stimulans group mosquitoes in 1965.

This is an introduction to seven papers reporting the results of arbovirus studies conducted in the central Ohio-Mississippi Basin from 1964 through 1967. Several arboviruses were isolated, but the focus was on St. Louis encephalitis virus. Evidence of disease in human population groups was procured through liaison with practicing physicians and official health agencies. Mosquitoes and birds were collected, as well as limited numbers of ectoparasites and small mammals. Suckling white Swiss mice were used in all attempts to isolate virus. Subsequent identification of isolates was usually based upon results of complement-fixation and neutralization tests. The latter technique (NT) and the hemagglutination tests were used in serologic surveys.

Culex tarsalis and members of the Culex pipiens complex are important vectors of St. Louis encephalitis virus (SLE). In the western part of the United States where C. tarsalis is the primary vector, long-term observations have included nonepidemic as well as sporadic epidemic years. Before the present report and in regions where C. pipiens complex is the vector, studies were limited to outbreaks of encephalitis. This paper is based on field and laboratory studies that were focused on rural McLeansboro, Illinois, during 1964–1967 and on the metropolitan area of St. Louis, Missouri, during 1966–1967. In each of the years, SLE virus was isolated from pools of C. pipiens complex collected in both areas. At less frequent intervals, the virus was encountered in specimens from birds. Sparse rainfall and periods of sustained high temperatures were related to the SLE virus activity in mosquitoes. Although virus was regularly detected, overt disease in man was limited to 1964 in McLeansboro and to 1966 in St. Louis. Nevertheless, the potential threat of epidemics exist. This threat could be reduced through elimination of sites of mosquito-breeding by the installation of adequate treatment and transport systems for sewage.

Flanders virus was isolated from multiple pools of Culex pipiens complex and Culex restuans mosquitoes collected during 1965–1967 at several localities in the Ohio-Mississippi Basin. In this region, the virus was detected earlier in the mosquito-breeding season than was St. Louis encephalitis virus. Moreover, the presence of Flanders virus was not related to the hot and dry weather that appeared to favor SLE virus. As a result of studies in McLeansboro, Illinois, 14 strains of Flanders virus were isolated from blood taken from birds collected in 1967 during the period when isolation rates were highest in mosquito pools. Mosquito-bird-mosquito transmission cycles were active, but there was no evidence that human residents were infected.

A focus of activity of Cache Valley virus was located in the Lake Mermet Conservation Area of southern Illinois as a result of field and laboratory studies conducted during 1964–1967. During each of the 4 years, multiple virus strains were isolated from Anopheles quadrimaculatus mosquitoes collected from resting places in the trunks of several trees. A close association apparently existed in this natural habitat between that mosquito and the virus. Although the vertebrate host was not identified, the results of mosquito host-preference study and results of antibody surveys suggest that cattle may be involved in cycles of Cache Valley virus.