Malaria and anaemia at different altitudes in the Muheza district of Tanzania: childhood morbidity in relation to level of exposure to infection

Parallel monthly surveys of children aged 6-71 months were conducted in the Muheza district of Tanzania. The aim was to compare highland villages, where the mean, annual entomological inoculation rate (EIR) for malaria is 34 and mean annual prevalences of parasitaemia range from 33%-76%, with culturally similar villages of the lowlands, where the mean EIR is 405 and prevalences of parasitaemia range from 80%-84%. The total survey population could be divided into six geographical subgroups, which can be arranged in order of increasing prevalence of parasitaemia. The prevalences of dense parasitaemia, of febrile malaria, and of anaemia all increased in the same order across this series of groups, the trends being statistically significant. The results of previous studies have indicated a paradoxical effect whereby children in regions with a lower exposure to malarial infection suffer, in the long term, a higher incidence of severe attacks of malaria. In the present study there was no sign of any such paradoxical inverse relationship between the level of exposure and the prevalence of malarial illness or anaemia. However, child mortality rates are similar in the highlands and lowlands, as are the median ages of children admitted to hospital. Overall, the present findings indicate that, for the populations studied, an artificial reduction in EIR would be beneficial, even in the long term, with regard to the chronic effects of malaria. This does not necessarily conflict with previous studies reporting opposite conclusions with regard to the incidence of severe,acute effects.     

The effect of DDT spraying and bed nets impregnated with pyrethroid insecticide on the incidence of Japanese encephalitis virus infection

A retrospective investigation was conducted to evaluate the effectiveness of DDT residual indoor spraying and bed nets impregnated with pyrethroid insecticide for Japanese encephalitis control in southern Henan province, China. DDT residual indoor spraying had no effect on the incidence of Japanese encephalitis, but it was greatly reduced after the introduction of pyrethroid-impregnated bed nets. Only a small effect on outdoor biting densities of Culex tritaeniorhyncus was found, although the number of mosquitoes resting inside bed nets decreased markedly after the introduction of bed net impregnation.     

Factors limiting the domestic density of Triatoma infestans in north-west Argentina: a longitudinal study

Reported are the environmental and demographic risk factors associated with the domestic infestation and density of Triatoma infestans in three heavily infested rural villages in Santiago del Estero Province, Argentina. In a one-factor unadjusted analysis, the number of T. infestans captured per person-hour was associated significantly and negatively with the use of domestic insecticides by householders, type of thatch used in the roofs and the age of the house; and positively with the following: degree of cracking of the indoor walls and presence of hens nesting indoors. In one model, using multiple linear regression and a backward stepwise elimination procedure, most of the variation in the overall abundance of T. infestans was explained by insecticide use and the presence of hens nesting indoors; in another model using the same procedure it was explained by insecticide use, bug density in 1988 and previous spraying with deltamethrin in 1985. Variations in bug density per capture stratum (household goods, beds, walls and roof) were explained by the bug density in other strata and by one or two of the following risk factors: hens nesting indoors, type of roof, presence of cracks in the walls and number of people living in the house. Bug density might be locally controlled by the availability of refuges in the roofs and walls, by the presence of hens nesting indoors and by the use of domestic insecticides. Certain local materials, such as a grass known as simbol, could be successfully used in rural housing improvement programmes aimed at reducing the availability of refuges for insects in the roof.     

Bed nets for the prevention of malaria and anaemia in pregnancy

A prospective comparison of the antimalarial efficacy of bed nets was conducted with 341 pregnant women living in a mesoendemic malarious area of the Thai-Burmese border. Women in 3 adjacent study sites were allocated at random to receive either a single size permethrin-impregnated bed net (PIB), a non-impregnated bed net (NIB), or to a control group who used either their own family size non-impregnated bed net (FNIB) or no net. In one study site, but not the other 2, PIB significantly reduced parasite densities and, together with FNIB, reduced the incidence of malaria in pregnancy from 56% to 33% (relative risk = 1.67, confidence interval = 1.07-2.61, P = 0.03, allowing for parity). Anaemia proved a more sensitive marker of bed net antimalarial efficacy than parasite rates. The incidence of anaemia (haematocrit < 30%) at all study sites was significantly lower at delivery in the PIB (27%) and FNIB groups (21%) than in the NIB group (41%) or those using no net (56%). This suggests that a significant proportion of the malaria in pregnancy in this mesoendemic area was sub-patent. Both patent Plasmodium falciparum parasitaemia and anaemia were associated with a reduction in birth weight. Infant mortality was high (16%) and strongly associated with prematurity, low birth weight and maternal anaemia. PIB were well tolerated and had no apparent adverse effect on the pregnancy or infant development. Although the overall effect of bed nets on patent parasitaemia was marginal, they were associated with a significant reduction in maternal malaria-associated anaemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determinants of dengue 2 infection among residents of Charters Towers, Queensland, Australia

Dengue fever is caused by one of the four serotypes of the dengue virus and is transmitted by the urban mosquito Aedes aegypti. In 1993, the city of Charters Towers in the tropical north of Australia experienced an epidemic caused by the dengue 2 virus. A cross-sectional sample of 1,000 people was assessed for determinants of recent symptomatic dengue infection. After exclusion of people with prior exposure to dengue 2, a study group of 797 persons, including 196 patients with recent infection, were evaluated. Stepwise logistic regression analysis identified four determinants of infection: the presence of a case of dengue fever within two residential blocks (odds ratio (OR) = 3.61, 95% confidence interval (CI) 2.56-5.10), house screening (OR = 0.60, 95% CI 0.40-0.89), the presence of a water tank within two residential blocks (OR = 1.51, 95% CI 1.02-2.22), and the use of knockdown insecticide (OR = 1.75, 95% CI 1.22-2.51). Classification and Regression Tree analysis identified a group of 152 individuals in whom the prevalence of dengue infection was 50%. These people lived within two blocks of a suspected dengue fever case, did not have house screening, and used knockdown sprays. If dengue had not occurred within two residential blocks, there were no additional factors that significantly influenced the prevalence of dengue fever. Control of dengue epidemics should involve attempts to geographically contain the spread of infection, use of house screening, and the removal of mosquito breeding sites such as water tanks.     

Malaria transmission in the rural zone of Niakhar, Senegal

The anopheline bioecology and the malaria transmission were studied from January to December 1995 in three villages of the sahelian rural area of Niakhar, Senegal. This area of 29000 inhabitants, has been for several decades, a regional observatory for population and health. The three methods used for collecting mosquitoes were the collection at larval stages, the all night human biting collection, and the pyrethrum spray catch in houses during afternoons. The anophelines collected were, by numerical importance: Anopheles arabiensis, An. rufipes, An. gambiae, An. pharoensis, An. funestus and An. coustani. In the An. gambiae complex, An. arabiensis represented 97% of man biting females and 98% of half gravid resting females (difference not significant); the other reminding species of this complex was always An. gambiae. These two species belonging to the An. gambiae complex were responsible for the totality of the transmission. The anthropophilic index, obtained from half gravid indoor resting An. gambiae s.l., was 83%. The annual biting rate of An. gambiae s.l. varied from 512 to 1558 bites per man per night, depending on the villages. Vectors were observed all year long but their densities were low during the dry season. Vector population presented a notable increase due to the rains, with a maximum of about 10 bites per man per night in September or at the beginning of October; during September the biting rate represented 48% of the annual biting rate. The sporozoitic index of An. gambiae s.l., obtained by ELISA revealing the circumsporozoite protein, was 1.6% for human biting females and 1.8% for half-gravid resting females (difference not significant). Plasmodium falciparum was the only plasmodial species observed among infected anophelines. The annual transmission in the vo villages representative of the Niakhar area were 9 and 12 bites of infected anophelines per man, occurring mainly from August to October. In the third village, not representative of the area regarding permanent breeding places, the transmission was 26 bites of infected anopheline per man per year. These results were discussed in the Senegambian and sahelian contexts.     

Convulsions with malaria: febrile or indicative of cerebral involvement?

Evaluation of 446 infants and young children (6 months to 5 years olds) with malaria parasitaemia showed a significant relationship (P < 0.05- < 0.001) (a) between coma and age, pattern of convulsions, haematocrit, and blood glucose, and (b) between the severity of parasitaemia and risk of convulsions, prevalence of hepatosplenomegaly, and severe anaemia. No significant relationship was observed between convulsions and temperature or haematocrit. Comatose children were older and had a higher prevalence of repeated convulsions, severe anaemia, and hypoglycaemia than non-comatose children. Convulsions, hepatosplenomegaly, and severe anaemia were more prevalent in children with moderate-severe parasitaemia. It is concluded that convulsions with malaria are more often a manifestation of cerebral dysfunction rather than being simply febrile in nature. All forms of cerebral dysfunction in malaria, including repeated convulsions, should be managed as being clinical manifestations of cerebral malaria.     

Study on the sequential tsetse-transmitted Trypanosoma congolense, T. brucei brucei and T. vivax infections to African buffalo, eland, waterbuck, N'Dama and Boran cattle

Susceptibility of African buffalo, eland, waterbuck, N'Dama and Boran cattle to sequential Glossina morsitans centralis-transmitted infections of Trypanosoma congolense, T. brucei brucei and T. vivax was compared, and their possible role as reservoirs of these parasites for G. moristans centralis, G. pallidipes, G. austeni, G. brevipalpis and G. longipennis determined. The buffalo, eland, waterbuck and N'Dama controlled T. congolense parasitaemias and were able to prevent anaemia. By contrast, one Boran became severely anaemic whilst the other controlled parasitaemia and anaemia. When the above five species of Bovidae were rechallenged with T. brucei brucei they showed persistent parasitaemias but did not develop anaemia. The buffalo died of other causes. When the remaining four bovids were rechallenged with T. vivax they became infected with mixed T. vivax/T. b. brucei parasites. Eland, waterbuck and N'Dama controlled parasitaemias and anaemia whereas the Boran became anaemic. Cyclical development of T. congolense occurred in G. moristans centralis when fed on the bovid hosts, with buffalo being infective for tsetse flies for a much longer period. There was no relationship between the levels of T. congolense parasitaemia in the bovid hosts and the resultant infection rates in tsetse flies. Glossina m. centralis was more susceptible than G. pallidipes to T. brucei brucei whilst G. austeni the least; G. brevipalpis and G. longipennis were refractory to the mature infection. Again there was no relationship between T. brucei brucei parasitaemia levels in the hosts and infection rates in the flies. Glossina m. centralis and G. pallidipes showed mixed T. brucei brucei/T. vivax infections whilst G. austeni, G. brevipalpis and G. longipennis became infected with T. vivax alone. Tsetse flies showed higher T. vivax infection rates when fed on the hosts with high parasitaemias than thosewith low parasitaemias. Thus trypanotolerant African buffalo, eland, waterbuck, N'Dama as well as some trypanosusceptible Boran cattle can serve as reservoirs of single or mixed trypanosome infections for tsetse flies. This study has also shown that the Ag-ELISA on the sera from the five bovid hosts had low sensitivity and species-specificity. Examinations of thin wet blood films and buffy coats with a phase-contrast microscope were not sensitive enough to detect the parasites on all occasions. Xenodiagnosis using mice for T. brucei brucei and T. congolense infections, and tsetse flies for all the three trypanosome species were most sensitive for the detection of trypanosome infections in the bovid hosts.     

Extended field trial of deltamethrin WDP for control of malaria at Jagdalpur, Madhya Pradesh, India

The synthetic pyrethroid, deltamethrin 2.5% wdp, was evaluated at a dosage of 25 mg/sq m in a group of villages of tribal area around Jagdalpur, District Bastar (Madhya Pradesh). Study was carried out in three consecutive years from 1986 to 1988 with a total of five rounds of deltamethrin spray covering a population of approximately 10,000. The suspension of deltamethrin wdp was white in colour, odourless, non-irritant and the deposits were faintly visible on the surface of wall. A total of 3848 kg of 2.5% deltamethrin wdp was consumed during the trial. Insecticide was found effective in keeping the adult vector density An. culicifacies to a very low level for a period of 14-16 wks. Both anopheline and culicine mosquitoes were affected by the spray. The trial confirmed its long residual effectiveness from 15 to 16 wks on both mud and cement plastered surfaces. Deltamethrin spray shortened the average life span of vector mosquitoes. Observations indicated that insecticide although has an excito-repellent effect on mosquitoes, thus forcing exodus from treated area but with poor survival. Partial impact of deltamethrin spray was observed on the larval population confirm this. Deltamethrin spray did not exhibit any fumigant effect on mosquitoes. Significant decline in SPR from 17.93 to 4.26% was observed in areas sprayed with deltamethrin as compared to the comparison area. Similarly, SfR showed 81% reduction in experimental area while the control area showed increase by 42 per cent. No ill-effect of spray was noticed on the inhabitants, spray personnels, animal population and other non-target organisms of the area. The acceptability of the deltamethrin spray was found to be very high.     

Persistence of Ehrlichia phagocytophila infection in lambs in relation to clinical parameters and antibody responses

Five lambs were infected experimentally with Ehrlichia phagocytophila and examined regularly during the next six months. The lambs all had recurrences of parasitaemia at various times but had a fever on only 21 per cent of these occasions. A reduced number of leucocytes was observed in all the lambs for at least eight weeks. All the lambs were still infected four months after inoculation with E phagocytophila. After six months, blood from four of the five lambs was infective when inoculated into susceptible lambs.     

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The present study investigated the influence of dietary protein on the intensity of parasitaemia, degree of anaemia and erythropoietic responses, in sheep experimentally infected with Trypanosoma congolense and given either a high protein diet (116 g digestible crude protein [DCP] per day) or a low protein diet (51.5 g DCP per day). It was observed that infected and control animals on the high protein diet grew at similar rates while infected animals on the low protein diet experienced marked retardation of growth compared with their uninfected controls. Dietary protein had no influence on the degree of anaemia that followed infection. Measurement of blood volumes revealed that low protein infected group had significantly lower mean circulating red cell volume than their controls. Ferrokinetic measurements indicated that plasma iron turnover rates (PITR) and 59Fe incorporation rates were higher in the high protein infected group than in the low protein infected group, although these differences were not significant. These observations indicate that infected animals on a high protein tended to show greater enhancement of erythropoietic activity that infected animals on low protein diet.     

Evaluation of methods of insecticide application for control of smokybrown cockroaches (Dictyoptera: Blattidae)

The insecticide components of a previously developed integrated pest management system for smokybrown cockroaches, Periplaneta fuliginosa (Serville), were tested individually and at reduced application rates in 4 separate trials over 2 yr. A 2-bait combination (pellet and gel baits) did not significantly reduce cockroach abundance more than a single constituent bait alone. A targeted spray of trelamethrin was significantly less effective than a 2-bait combination. Residual activity of insecticides was determined with American cockroaches, P. americana (L.), in a laboratory bioassay. Chlorpyrifos wettable powder remained active < 12 d in the field, after which time its activity was not different from an experimental control (no insecticide residues), whereas chlorpyrifos pellet and hydramethylnon paste baits retained initial activity for > 27 d. Nematodes [Steinernema carpocapsae (Weiser)] applied as a spray solution did not effect the abundance of smokybrown cockroaches, and no cockroaches were recovered that exhibited nematode infection. Time needed to apply various insecticide treatments did not differ substantially (15-25 min per house), even for lower application rates.     

Anopheles arabiensis and An. gambiae chromosomal inversion polymorphism, feeding and resting behaviour in relation to insecticide house-spraying in Tanzania

Differential responses of the mosquitoes Anopheles arabiensis and An. gambiae sensu stricto to house-spraying with DDT or lambda-cyhalothrin were evaluated in relation to chromosomal inversion polymorphism, feeding and resting behaviour of these malaria vectors in Tanzania. Blood-fed mosquitoes from pit traps outdoors, exit traps on windows and indoor-resting catches were identified cytogenetically and the chromosomal inversion frequencies compared between samples and species. Their outdoor-resting behaviour was assessed by a mark-release-recapture experiment and by determining the proportion of freshly blood-fed individuals in exit traps. The source of bloodmeals was analysed by an ELISA method. Endophagic females of An. arabiensis were more likely than those of An.gambiae to exit from a house on the night of blood-feeding. Only in one out of three villages was there evidence that chromosomally distinct individuals within a species had different preferences for resting sites. There were indications, but not conclusive evidence, that mosquitoes caught indoors or outdoors had a tendency to return to the same type of resting site. In villages sprayed with either insecticide, the mean age of the vector populations was greatly reduced, compared with those in the unsprayed villages. An.arabiensis females exited from DDT sprayed houses after blood-feeding, whereas with lambda-cyhalothrin those exiting were mostly unfed and there was a decline in the human blood index. The excitorepellency of DDT was perceived as a disadvantage, whereas lambda-cyhalothrin apparently had more impact on malaria transmission by An.arabiensis.     

The Gambian National Impregnated Bednet Programme: evaluation of the 1994 cost recovery trial

Following the success of a controlled trial of insecticide-impregnated bednets in reducing mortality in children. The Gambia started a National Impregnated Bednet Programme (NIBP) in 1992. The objectives of this programme were to introduce impregnated bednets into all primary health care (PHC) villages and to establish a system of cost recovery over a three-year period. During the initial phase of the programme, when insecticide was given out free, a high uptake was achieved. However, after small user charges were introduced in 1993, coverage dropped to a low level. In 1994, different systems of insecticide distribution and permethrin formulations were tried in an attempt to improve coverage. A nationwide cross-sectional survey carried out during the 1994 rainy season measured coverage by distribution channel, as well as the knowledge, attitudes and practices of health workers and villagers during the intervention. Overall, only 16% of bednets were impregnated in 1994, compared to 80% when the insecticide was offered free of charge in previous years. Lack of money was the major reason given by villagers for not impregnating their bednets in 1994. Use of impregnated bednets was higher in areas where the sale of permethrin emulsion by village health workers was supplemented by the sale of insecticide in individual packages through shops. In villages where insecticide was distributed free to women with small children through governmental mother and child health (MCH) services, higher levels of coverage were achieved among women and young children than in villages where other distribution systems were used. We conclude that the sale of insecticide through the private sector may increase bednet impregnation rates in African communities, and that the free distribution of insecticide through MCH services may be an effective way of targeting young children, the group most at risk of malaria.     

Insecticide barrier spraying for the control of sand fly vectors of cutaneous leishmaniasis in rural Guatemala

An initial evaluation of insecticide barrier spraying directed against sand fly vectors of cutaneous leishmaniasis was done in a nonclimax forested area with heavy undergrowth in Peten, Guatemala. A 100 m-wide swath of vegetation was sprayed once with a 1:3 mixture of cyfluthrin insecticide and a palm oil carrier using back-pack sprayers to simulate a central cantonment area in one site while another site remained as an untreated control. Prior to spraying and throughout 87 days post-treatment, sand fly populations were monitored at both sites with light traps set at ground and canopy levels at 50-m intervals radiating out from the centers of the cantonments, 150-m in the four cardinal directions. A total of 2,876 female sand flies were captured, representing 16 species. Three species, Brumptomyia galindoi, Lutzomyia panamensis, and Lu, ovallesi, comprised 70% of the total collection. The single insecticide barrier significantly reduced sand flies from reaching the cantonment area for more than 80 days, while sand fly populations outside the treated cantonment and in the untreated (control) cantonment remained high (52 sand flies in the treated cantonment versus 235 sand flies in the untreated cantonment).     

Mortality of urban and rural young children with cerebral palsy in Bangladesh

In January 1994 mass antibiotic prophylaxis was undertaken in the contiguous villages of Deir el-Asad and B'ine in northern Israel (combined population of 11600) in response to a prolonged outbreak of serogroup B meningococcal infection with an overall annual rate of 37.4 cases of infection per 100000 residents. The average case fatality rate in the villages was 23% compared with 11% in Israel during the same period. Neisseria meningitidis group B was identified in 9 of 13 (69%) cases. Seven of these were subtype P1.7,16. The persistence of the outbreak with its accompanying public reaction prompted the establishment of an intervention programme that included antibiotic prophylaxis for the whole community with monitoring for pharyngeal carriage of meningococci in a stratified sample of the population. The objectives were to achieve a reduction of carriage of the outbreak strain and to reduce morbidity and mortality. A total of 1036 pharyngeal swabs were taken 1 day before and 6 weeks after treatment. Antibiotic prophylaxis was administered in one dose: children under 5-years-old received ceftriaxone i.m.; all others received oral ciprofloxacin. Overall, 96% of the population received treatment. The carriage rate was 8.3% prior to treatment (three serogroup B:14:P1.7,16), and 1.3% afterwards (one serogroup B:14:P1.7,16). The intervention failed to eradicate carriage of the putative outbreak strain, or to reduce the incidence and fatality rates in the villages. The outbreak finally terminated in late 1996. Public health professionals should bear this experience in mind when faced with prolonged, localized, nonexplosive outbreaks of meningococcal disease associated with low carriage rates of the outbreak strain.     

The influence of supplementation with cotton seed cake on the resistance of Ugandan goats to primary and secondary challenges with Trypanosoma congolense and on their response to treatment

The present study investigated the influence of supplementation with cotton seed cake on the resistance of the Small East African breed of goats to primary and secondary challenges with Trypanosoma congolense and on their response to chemotherapy with diminazene aceturate. The supplemented group received 300 g of cotton seed cake per day in addition to about 500 g of fresh napier grass which was available to the unsupplemented group. It was observed that the supplemented infected (SI) group tended to sustain higher intensities of parasitaemia than the unsupplemented infected (USI) group particularly during the primary challenge and both groups showed longer prepatent periods to secondary challenge than to primary challenge. Infection caused a significant reduction in the rate of live body weight gain in the USI group compared with the unsupplemented control (USC) group whilst the SI group grew at the same rate as the supplemented control (SC) group. This effect was observed both during primary and secondary challenges. Following primary challenge, both infected groups developed similar degrees of anaemia, but the packed red cell volume (PCV) levels in the SI group improved towards the end of the first challenge and were also significantly higher than those of the USI group during the second challenge. After treatments at 56 and 126 days after infection (DAI), the greatest response was observed in PCV values. The response of the SI group was superior to that of the USI group and by 4 weeks after treatment the PCV values of the SI and SC groups were similar while those of the USI group were significantly lower than those of the USC group. It is concluded that supplementation with cotton seed cake plays an important role in the rate of live weight gain, and rate of recovery from anaemia produced by trypanosome infection in goats.     

Absence of seasonal variation in malaria parasitaemia in an area of intense seasonal transmission

Parasitological surveys carried out in two villages of the Kilombero district of Tanzania indicated a very high prevalence of Plasmodium falciparum parasitaemia throughout the year (all ages mean prevalence = 69.2%) and a low, unstable prevalence of P. malariae (all ages mean prevalence = 4.5%). Fevers (temperature > or = 37.5 degrees C) in both children and adults showed irregular changes in prevalence over time, but there was no seasonal pattern. Neither was there seasonal variation in either P. falciparum parasite prevalence or parasite densities. This was despite marked seasonality in vectors caught in CDC light-traps and in estimated sporozoite inoculations determined by ELISA. The estimated mean annual inoculation rate was extremely high, over 300 infectious bites per person per year, the main vectors being members of the A. gambiae complex and Anopheles funestus. There was considerable variation between houses but even in houses with relatively low mosquito numbers the inoculation rate was sufficient to maintain a maximal P. falciparum prevalence. Heterogeneities in exposure cannot explain why the parasite prevalence is not always 100%. In areas of such high transmission, parasitaemias are likely to be determined mainly by the interaction of schizogony and anti-blood stage immunity, since parasites arising from new inoculations generally comprise only a small proportion of the total in the circulation. In any one individual, this will lead to periodic fluctuations in levels of parasitaemia. These are unlikely to show a close relationship to either seasonal variation in inoculations or to differences between households in the local inoculation rate.     

The role of Leptotrombidium scutellare in the transmission of human diseases

OBJECTIVE: To investigate the role of Leptotrombidium (L.) scutellare in the transmission of hemorrhagic fever with renal syndrome (HFRS) and tsutsugamushi disease of autumn-type. MATERIALS AND METHODS: Four criteria were used to ascertain this mite as transmitting vector of disease: (1) epidemiological evidence; (2) natural infection of pathogen; (3) ability to transmit pathogen via biting; (4) ability to transfer pathogen via transovarian route. RESULTS: The results indicated that L. scutellare was the dominant species of chigger mite on rats. Its seasonal distribution was correlated with the incidence of these two diseases. This mite could be naturally infected by HFRS virus (HFRSV) and Rickettsia tsutsugamushi (Rt) and the mite could transmit HFRSV and Rt to vertebrates by biting and to its offspring via transovarian transmission. CONCLUSIONS: These results have proved that L. scutellare can be a transmitting vector of HFRS and tsutsugamushi disease of autumn-type.     

Learning to cope with biting flies: Rapid NMDA-mediated acquisition of conditioned analgesia.

A 30-min exposure to intact biting flies (stable flies) induced an opioid-mediated analgesia in fly-naive male deer mice, whereas exposure to either altered biting flies whose biting mouthparts were removed or nonbiting house flies had no significant effects. However, mice that were previously exposed to intact stable flies for 30 min exhibited significant analgesia when exposed 24–168 hr later to stable flies whose biting parts were removed, but not to nonbiting house flies. Administration of the specific N-methyl-D-aspartate (NMDA) antagonist NPC 12626 to fly-naive mice before exposure to intact flies, although not significantly reducing the analgesic response, blocked the subsequent conditioned analgesia. Naloxone, which blocked the intact biting fly-induced analgesia, did not alter the acquisition of the conditioned analgesic response to the altered stable flies. This demonstrates an NMDA-mediated acquisition of conditioned analgesia to a natural aversive stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)