Lots Of Mosquitoes Research Articles

Young, at Work in the Fields

Most young farmworkers in California are migrants from Mexico, especially the south of the country, where many people share an indigenous culture and language. Ricardo Lopez, living in a van with his grandfather in a store parking lot in Mecca, a tiny farmworker town in the Coachella Valley, says working as a migrant without a formal home was no surprise: This is how I envisioned it would be working here with my grandpa and sleeping in the van. It's hot at night, and hard to sleep well. There are a lot of mosquitoes, very few services, and the bathrooms are very dirty. At night there are a lot of people here coming and going. You never know what can happen; it's a bit dangerous. But my grandfather has a lot of experience and knows how to handle himself. With the money I earn I'm going to help my mother and save the rest. I'll be attending college in the fall at Arizona Western College--my first year. I want to have a good job, a career. I'm not thinking of working in the fields. Not at all. I look at how hard my grandfather has worked. I don't want to do field work for the rest of my life because it's so hard and the pay is so low. Lopez describes the reality for farmworkers in California in a way that gives tangible meaning to the facts and numbers describing farmworker life. There are about 120,000 indigenous Mexican farmworkers in California. Counting the 45,000 children living with them, that is a total of 165,000 people. They are the most recent migrants from Mexico. They speak twenty-three languages, come from thirteen different Mexican states, and have rich cultures of language, music, dance, and food that bind their communities together. Lorena Hernandez, working in a blueberry field outside of Fresno, in California's San Joaquin Valley, came from Oaxaca with her aunt after getting pregnant as a teenager. Now she wonders if life will have more to offer to a young indigenous woman than field labor: They pay six dollars a bucket picking blueberries, and each has to weigh twelve pounds. This is my second year doing this work. Since I don't have much experience, I can only pick fifteen or sixteen buckets a day. Those with more experience can do twenty. After a day picking blueberries, my hands feel tired and hurt a lot. But they don't give us gloves because they say they will damage the fruit. I don't really have friends, just acquaintances from work. Most who are my age don't have a child, like I do, so they go out on the weekend. Since I have a daughter, I don't go out. So my coworkers share their stories with me because I just stay at home. I really don't have a vision of my own future yet. I went to school in a small town in Oaxaca, Mexico, and I left when I was fifteen years old. I don't think I'll ever return to school because of my age. My job will be working in the fields. I would love to go back to school, but it's too late for me. Maybe one day. The indigenous immigrant community is very young. The typical age of someone crossing the border today is about twenty years old, and the average age of all California farmworkers is twenty-one. Many young people, even children, work in the fields. On average, Mexican farmworkers in California have only six years of school, but younger Mexicans tend to have more education than older migrants. [ILLUSTRATION OMITTED] Javier Mondar, son of a single Mixtec mother, lives in Santa Maria. Growing up, he traveled with his family as they migrated with the crops. He finished high school in spite of the obstacles, and went on to university to get skills to fight discrimination against indigenous people. Yet he was also the victim of discrimination himself and recognizes that, within his own community, his sexuality was not easily accepted: [ILLUSTRATION OMITTED] I grew up in a farmworking family--so working in the fields is everything I ever knew. …

The Nigerian I/CDC Strain of Plasmodium ovale in Chimpanzees

The chimpanzee is the only animal host currently available that can support the development of the human malaria parasite Plasmodium ovale. Thirty-one infections with the Nigerian I/CDC strain were induced in splenectomized chimpanzees. Maximum parasite counts ranged from 1,240 to 127,224/microliters. Infections were transient and unpredictable. Anopheles stephensi, Anopheles gambiae, Anopheles freeborni, and Anopheles dirus mosquitoes were infected by feeding through parafilm membranes on heparinized blood containing gametocytes; each species supported development to sporozoites in the salivary glands. Mean oocyst counts per infected mosquito ranged from 1 to 85.1; 21.7% of infected lots of mosquitoes averaged > 20 oocysts per positive mosquito gut. One infection was induced via the bites of infected An. gambiae. The prepatent period was 16 days.

Arbovirus activity in southern Arizona. Isolations of virus and observations of sentinel chickens.

Abstract This study was undertaken to define the nature and extent of arbovirus activity in the environment of Tucson, Arizona; especial interest was centered in the prevalence of arthropod-borne encephalitis. Field collections of mosquitoes, ticks, birds, and small mammals were made in the selected study areas along the valleys of the Santa Cruz River and the Rillito in or near Tucson. Flocks of sentinel chickens were maintained during the hot seasons in the same areas. The virus of St. Louis encephalitis (SLE) was isolated 12 times from mosquitoes in three separate summer seasons. The virus of Western encephalitis (WE) was recovered in the summer of 1966 in three different lots of mosquitoes. The results of serologic tests on the chickens maintained as sentinels in the study areas confirmed that active transmission of SLE and WE viruses had occurred during the summers that the isolations had been obtained. There was a relative scarcity of Culex tarsalis in the areas studied. The explanation for this is not clear. As a result of this study it appears clear that arthropod-borne encephalitis poses a continuing threat to the population of southern Arizona.

Studies on the Transmission of Simian Malarias II. Transmission of the H Strain of Plasmodium knowlesi by Anopheles balabacensis balabacensis

Five species of anopheline mosquitoes were examined in regards to their susceptibility to infection with the strain of Plasmodium knowlesi. Anopheles balabacensis balabacensis, Anopheles freeborni, Anopheles maculatus, and Anopheles stephensi were readily infected to the oocyst stage but only in the first-named species were salivary glands heavily infected. Only A. quadrimaculatus failed to become infected. Transmission of this parasite to Alacaca mulatta monkeys was obtained by the bites of A. b. balabacensis mosquitoes on two occasions. The extrinsic incubation periods in these lots of mosquitoes were 12 and 13 days and the prepatent periods in the infected monkeys were 8 and 7 days, respectively. The usefulness of the malaria parasites of nonhuman primates as laboratory models for the study of pathology, physiology, immunity, and drug response has been well established. Some of these species have been easily adapted to laboratory transmission with a variety of anophelines while considerable difficulty has been encountered in finding a suitable laboratory vector for others. Plasmodium knowlesi is one of the monkey parasites which has proven most difficult to adapt to routine laboratory transmission. The development of this parasite in mosquitoes to the point of sporozoite-positive salivary glands has been demonstrated in Anopheles annularis (Singh et al., 1949), in A. atroparvus (Weyer, 1937; Hawking et al., 1957), in A. aztecus (Gamrnham et al., 1957), and in A. stephensi (Singh et al., 1949; Hawking and Mellanby, 1953; Hawking et al., 1957; Garnham et al., 1957). The parasite has been passaged through mosquitoes to susceptible monkeys by the intravenous inoculation of dissected infected salivary glands and/or guts by several workers. The mosquitoes used for this purpose included A. stephensi (Singh et al., 1949; Garnham et al., 1957; Hawking and Mellanby, 1953; Hawking et al., 1957), A. annularis (Singh et al., 1949), A. aztecus (Gamham et al., 1957), and A. atroparvus (Hawking et al., 1957). None of these investigators reported attempts to transmit the infection through the bite of infected mosquitoes, and to our knowledge such natural transmission has not been reported elsewhere. The present report is concerned with the Received for publication 20 March 1967. susceptibility of five species of Anopheles to Plasmodium knowlesi and the transmission of this parasite by the bite of Anopheles balabacensis balabacensis. MATERIALS AND METHODS The P. knowlesi used was isolated from a naturally acquired human infection (Chin et al., 1965) and had been passaged by blood to humans and Macaca mulatta monkeys. It has been designated by us as the H strain. Malaria-free M. mulatta monkeys from North India were used throughout the course of these experiments. In Al. mulatta monkeys parasitemias of P. knowlesi develop to extremely high levels and the infection is usually fatal if not treated. The Anopheles quadrimaculatus mosquitoes were the Q-1 strain which was obtained from Technical Development Laboratories, CDC, Savannah, Georgia. The A. freeborni (F-1 strain) were from Marysville, California and have been maintained in the laboratory since 1944. The A. stephensi were from Delhi, India and were obtained from the London School of Hygiene and Tropical Medicine, London, England in 1963. The A. maculatus were obtained from the Institute for Medical Reearch, Kuala Lumpur, Malaysia in 1964 and have been maintained in our laboratory since then. The A. balabacensis balabacensis colony was originally from Thailand and was recently obtained from the Walter Reed Army Institute of Research, Washington, D. C. through the courtesy of Col. W. D. Tigertt and Major J. E. Scanlon. The mosquitoes most often used in the experiments were A. freeborni and the susceptibility of the others was, in each case, compared with this species. After the infective feeding, six to 43 specimens of each species were examined for oocysts. Only when A. freeborni was found to be infected were the results used in determination of the comparative susceptibility of the anopheline species. The details of the procedures used in this study are presented in the first report in this series (Collins et al., 1966).

Transmission of a New Strain of Plasmodium cynomolgi to Man

Transmission of a New Strain of Plasmodium cynomolgi to Man

The Infectivity of Native Malarias in South Carolina to Anopheles Quadrimaculatus 1

Summary and Conclusions In a field study in South Carolina, Anopheles quadrimaculatus mosquitoes were applied to native cases of malaria in Negroes to determine the infectivity of such malaria cases. Of 142 feedings upon Plasmodium falciparum patients, 21 showed infections. Of 12,606 mosquitoes dissected, 2.5 per cent were infected. These infections developed normally in the mosquito and in one out of two trials transmission was successful. The majority of the mosquito infections occurred during the months of October through January. Mosquitoes kept at outside temperatures during October and November became infected. One patient remained infective to mosquitoes over an 8-month period. Of the 25 patients showing gametocytes, 64 per cent infected mosquitoes. The gametocyte densities resulting in infections were relatively low, none being over 90 per cmm. Thirteen of the infections resulted when the gametocytes were fewer than 10 per cmm. Patients with asymptomatic parasitemias infected mosquitoes at about the same rate as did those who were symptomatic. As the asymptomatic group is considerably larger than the other, it is concluded that the former is mainly responsible for the transmission of malaria. There were 14 feedings upon P. malariae. Four cases showed gametocytes of a low density at feeding and three lots of mosquitoes were infected. Of 586 mosquitoes dissected, 1.7 per cent were infected. Of nine feedings upon P. vivax, none became infected nor were gametocytes present. It is concluded that the patient with an asymptomatic parasitemia, usually with a relatively low gametocyte density, is the important factor in the transmission and maintenance of P. falciparum and P. malariae malaria in the area studied.

The Clinical Reaction in Vivax Malaria as Influenced by the Consecutive Employment of Infectious Mosquitoes 1

The problem of sporozoite dosage as a factor in determining the duration of the incubation period and clinical attack with vivax malaria is of considerable interest. Its exact solution awaits the discovery of a satisfactory menstruum for the suspension and dilution of sporozoites mechanically removed from the salivary glands. We have already presented some data bearing on this subject (1, 2), and consider that the highly confirmatory character of the present supplemental material justifies its submission. It may reasonably be inferred that, if mosquitoes are consecutively applied to several subjects, without a replenishment of their supply of sporozoites, the numbers in their glands will gradually be depleted, and the last patient to whom they are applied will be inoculated with a much smaller number of sporozoites than was received by the first patient. On different occasions, in connection with the performance of immunity observations (usually heterologous), we have applied various lots of mosquitoes in a consecutive manner, in order to demonstrate that the patient whose immunity was being tested actually received an infectious dose of sporozoites.

Vernal Vivax Activity in Persons Simultaneously Inoculated with Plasmodium Vivax and Plasmodium Falciparum 1

In two recent papers (1, 2) we reported successful simultaneous inoculations with Plasmodium vivax and Plasmodium falciparum. In the first paper the clinical experience of each of the two patients was presented at length. In each case the attacks represented a succession of reactions produced by each species of parasite acting independently, rather than a reaction produced through the joint agency of the two species. Furthermore, the initial attack in each instance was produced by P. falciparum. The second report dealt only with the results of inoculations made by different lots of mosquitoes maturing infections with two species of parasite either simultaneously or consecutively, and did not relate the subsequent clinical experiences of the five patients who were successfully inoculated with both species of parasite. The results are of sufficient interest to justify the present report.For the details of the inoculations we refer to table 2 of the second report cited.

Multiplication of the Virus of Equine Encephalomyelitis in Surviving Mosquito Tissues

Evidence for the multiplication of insect-transmitted viruses in the insect host has now been obtained in three instances. Holt and Kintner (1931), using the feeding method of St. John, Simmons and Reynolds (1930), were able to pass dengue virus through three, but not through five, successive lots of mosquitoes. Using essentially the same method, Merrill and Ten Broeck (1934) passed western strain equine encephalomyelitis virus through more than ten successive lots of mosquitoes, and showed that the virus multiplied and retained all its characteristics. Merrill, Lacaillade and Ten Broeck (1934) found that Aedes sollicitans infected with the eastern strain of equine encephalomyelitis virus contained more virus five days after the infective feed than just after it. Whitman (1937), using mice for titration, has recently shown that yellow fever virus multiplies in Aedes aegypti. His work contradicts the earlier negative results of Davis, Frobisher and Lloyd (1933), obtained with titration in monkeys.

Comparative Effects of the Blood of Different Species of Vertebrates on Egg-Production of Aëdes Aegypti Linn

Summary and Conclusions Aedes aegypti feeds on the blood of many species of animals, including man. The object of these experiments was to determine whether there exist significant differences in the nutritive values of the blood of different species of warm- and cold-blooded vertebrates, when fed to Aedes aegypti, using egg-production as the criterion. The number of eggs produced per milligram of blood ingested served as the basis on which to compare the relative values of the various diets. The quantity of blood ingested was determined by weighing the mosquitoes before and after feeding. A uniform group of imagines for use in experiments was obtained by carefully rearing and selecting the larvae, pupae, and adults. All the mosquitoes used were produced under similar conditions and selected in a similar manner. All of these mosquitoes had access to sugar solution in addition to blood, but on sugar solution alone no eggs were produced. In several preliminary observations mosquitoes which had ingested blood-meals from man invariably produced fewer eggs than those which had ingested blood-meals from any of several species of laboratory animals. Very little or no difference was found in the value for egg-production of blood from different human individuals, nor from one individual obtained at different times in relation to the time of ingestion of food by the host. An experiment to obtain data with which to determine more definitely the comparative effects on egg-production of blood from different species of animals appeared to be indicated. Seven lots of mosquitoes were prepared and each lot was fed on the blood of a different species of animal. Records were obtained of the quantity of blood ingested and the number of eggs produced for each of two successive blood-meals by each individual mosquito in each of the seven lots. The results from the 23 to 28 mosquitoes in the different lots were treated statistically. The essential data are summarized in table 1, and the results of the analysis in table 2. The conclusions may be expressed as follows: The blood of different species of animals differs in its effect on egg-production of Aedes aegypti. Significantly greater numbers of eggs are produced on the blood of turtle, frog, canary, rabbit, and guinea pig, than on the blood of man and of monkey, and significantly greater numbers of eggs on the blood of guinea pig, and of frog, than on the blood of canary. The difference in the effect of the blood of man and of monkey on egg-production is probably not significant. The difference in the effect of the blood of rabbit, guinea pig, and frog, on egg-production is probably not significant. The difference in the effect of the blood of turtle and of rabbit on egg-production is probably not significant. The difference in the effect of the blood of turtle and of guinea pig, turtle and frog, canary and turtle, and canary and rabbit, in each case, is probably significant, but is questioned. The writer wishes to acknowledge his indebtedness to Dr. Francis M. Root, now deceased, under whose direction this work was started, and to Dr. Robert W. Hegner and Dr. Justin Andrews under whose guidance it was continued, for their helpful criticism and suggestions.

CONCERNING SOME PHILIPPINE MOSQUITOES

In connection with the work on the Philippine mosquitoes carried on by the authority of the Surgeon-General, U.S. Army, and “for and with the co-operation of the Medical Corps, U.S.A.,” a lot of mosquitoes recently received from Cottabato, Mindanao, P.I., makes it possible to describe a new Myzomyia; to state definitely all the differences between Stegomyia scutellaris, Walker, and the variety Sumarensis, Ludlow; and to make a small correction in the description of Myzorhyncus pseudobarbirostris, Ludlow.