Potential vectors of malaria and their different susceptibility to Plasmodium falciparum and Plasmodium vivax in northern Brazil identified by immunoassay

During the period from May 1983 to July 1985 we conducted an epidemiological study to determine potential vectors of malaria in 6 districts in the state of Pará in northern Brazil. The examination of random human blood smears, prepared at the time of mosquito capture, indicated overall human infection rates of 16.7% and 10.9% for Plasmodium falciparum and P. vivax, respectively. Two immunoassays, the immunoradiometric assay (IRMA) and the enzyme-linked immunosorbent assay (ELISA), based on the use of species-specific antisporozoite monoclonal antibodies, were used to analyze a total of 9,040 field-collected Anopheles mosquitoes for plasmodial infection. P. falciparum sporozoite antigen was detected in A. darlingi at rates varying from 2.7% to 4.2%, and in small numbers of A. oswaldoi collected in 1 of the districts. In contrast, sporozoite antigen of P. vivax was found in A. darlingi, A. triannulatus, A. nuneztovari, and A. albitarsis at rates ranging from 0.9% to 12.0%. By dissection, sporozoites were found in the salivary glands of these same 4 species at rates ranging from 0.8% to 2.2%. The latter 3 species had not previously been implicated as malaria vectors of any significance in northern Brazil.     

Natural malaria infections in anophelines in Rondonia State, Brazilian Amazon

The use of an Immunoassay for the detection of Plasmodium falciparum and P. vivax circumsporozoite (CS) antigens in anophelines has recently incriminated other malaria vectors besides Anopheles darlingi in the Brazilian Amazon. In this study we analyzed 12,336 field-collected anophelines from endemic areas in Rondonia for plasmodial infection. Sixty-one specimens from 6 species were positive: 47 An. darlingi, 5 An. triannulatus, 4 An. albitarsis, 2 An. braziliensis, 2 An. strodei, and 1 An. oswaldoi. As concerns the species, 41 anopheles harbored P. falciparum and 20 were infected with P. vivax. An. darlingi was the most important local vector, as it was the one most frequently found infected and the only one clearly related to areas where malaria transmission was being recorded.     

Malaria vectors in areas of Plasmodium falciparum epidemic transmission in the Amazon region, Brazil

The main vectors of malaria in Brazil are Anopheles darlingi, An. aquasalis, and some species of the An. albitarsis complex, whereas others have questionable importance with regard to the disease transmission. To identify these vectors in the State of Pará, Brazil, in a high-prevalence P. falciparum area, 565 anophelines were captured and identified while the seasonal variation and daily biting activity were determined. Of the seven anopheline species (An. strodei, An. albitarsis s.l., An. rondoni, An. darlingi, An. triannulatus, An. oswaldoi, and An. nuneztovari), the plasmodia circumsporozoite protein (CSP) was detected in three of them, with a total infection rate of 6.2%. An. darlingi was the most prevalent species (22.4%), followed by An. albitarsis (5.2%) and An. rondoni (3.6%). An. rondoni was found to be infected for the first time, which was also confirmed through PCR. This result possibly represents a new malaria vector based on its highest frequency, biting and seasonal activities in the peak of malaria transmission.     

Affinity and diversity indices for anopheline immature forms

As for the entire Amazon Region, malaria continues to be a major health public problem in Roraima that presented an Annual Parasitic Index of 85.4 in 2005, the highest in Brazil. Information on anopheline breeding sites is an essential component in malaria control strategies. Aiming to contribute to the limited knowledge on anopheline immature forms in Roraima, collections and breeding site observations were performed in 10 breeding sites around the capital city Boa Vista. Collections were carried out in the rainy and dry season periods between April 2004 and January 2005. Breeding sites comprised natural and artificial water reservoirs. A total of 623 immature forms were collected belonging to Anopheles albitarsis s.l., An.triannulatus s.l., An. nuneztovari/dunhami, An. braziliensis, An. evansae, An. oswaldoi s.l., An. strodei and An. darlingi. An. albitarsis and An. braziliensis were the most frequently found species. Eight larvae of An. darlingi were found in only one breeding site located in the forest. An. triannulatus/An. nuneztovari and An. albitarsis/An. braziliensis were the pairs of species that mostly occurred together. Both pair of species displayed the highest affinity index what might indicate a high compatibility for the same breeding conditions and/or a synergistic co-occurrence. Species diversity index was higher for the dry season.     

ELISA检测云南按蚊环子孢子蛋白的评价

目的　采用酶联免疫吸附测定(ELISA)技术检测疟疾媒介按蚊环子孢子蛋白(CSP),评价ELISA用于云南疟疾媒介按蚊传疟效能调查的可行性。　方法　现场捕获疟疾媒介按蚊经产蚊,每只蚊镜检3叶唾腺子孢子感染率,ELISA检测另3叶唾腺CSP;用含间日疟原虫配子体的患者血人工喂饲微小按蚊,11d后同法镜检唾腺子孢子感染率及ELISA检测唾腺CSP。在种植场捕获8种按蚊(微小按蚊、中华按蚊、多斑按蚊、迷糊按蚊、可赫按蚊、带足按蚊、菲律宾按蚊和须喙按蚊 )各龄成蚊,ELISA检测唾腺CSP。　结果　①现场捕获经产蚊1010只,镜检唾腺子孢子阳性7只,阳性率为0.69%;ELISA检测唾腺CSP阳性8只,阳性率为0.79%;其中6只蚊两项检测均为阳性,阳性率为0.59%。两法比较,差异无显著性意义(P>0.05)。②人工感染36只微小按蚊,镜检唾腺子孢子阳性27只,阳性率为75.0%;ELISA检测唾腺CSP阳性29只,阳性率为80.6%;其中有26只蚊两项检测(Pv2 10CSP)均阳性,阳性率为72.2%。两法比较,差异无显著性意义(P>0.05)。③种植场捕获8种按蚊各龄成蚊4675只,ELISA检测唾腺CSP阳性11只,阳性率为0.24%;其中Pv210阳性9只,Pf2A10阳性2只;微小按蚊、中华按蚊和多斑按蚊ELISA检测阳性     

斑面按蚊体内柏氏疟原虫子孢子感染能力的实验研究

目的 研究斑须按蚊体内柏氏疟原子虫孢子的感染能力。方法 收集并计数感染后不同时间蚊唾液腺内子孢子数;收集感染后第20天蚊胃部、体腔和唾液腺内的子孢子及感染后第34天唾液腺内的子孢子,按不同的子孢子量分组经尾静脉注入小鼠体内,检查各实验组小鼠疟原虫感染状况。结果 1.感染后第14天,在唾液腺内发现子孢子。子孢子的密度在第20天出现一小峰,第30天达高峰,而后迅速下降。2.经尾静脉注入30个子孢子即可在小鼠体内检出红内期疟原虫。3.唾液腺及体腔内的子孢子均可使小鼠感染疟疾。4.感染后第34天唾液腺内的子孢子未能使小鼠感染疟疾。结论 不同发育时期唾液内的子孢子感染力具有差异,成熟囊合子内的子孢子尚需进一步分化、成熟才能获得感染能力。     

Identification of malaria species by ELISA in sporozoite and oocyst infected Anopheles from western Kenya

Enzyme-linked immunosorbent assays (ELISAs) for the circumsporozoite (CS) antigens of Plasmodium falciparum, P. malariae, and P. ovale were used to identify species of sporozoite and oocyst infections detected by dissection in Anopheles gambiae s.1. and An. funestus collected in western Kenya. ELISAs identified 92.5% of 1,113 salivary gland infections; Plasmodium species infections included 79.4% P. falciparum, 3.2% P. malariae, 1.7% P. ovale, and 2 or more Plasmodium species were detected in 15.7% of the Anopheles in which the species of parasite was identified. Identification was more likely with greater numbers of sporozoites observed in dissections, increasing from 65% ELISA positivity in mosquitoes with 1-10 sporozoites in their salivary glands to 96% in mosquitoes with over 1,000 sporozoites. ELISAs detected CS antigen in 66% of 294 Anopheles that by dissection had oocysts but uninfected salivary glands. Of 112 Anopheles with a single species of Plasmodium detected in the salivary glands, 29 (25.9%) had 1 or more additional species detected in the midgut, indicating a high potential for multiple infections. Similar proportions of Plasmodium species were found in An. gambiae s.1. and An. funestus.     

Malaria transmission at a new irrigation project in Sri Lanka: the emergence of Anopheles annularis as a major vector.

Malaria transmission was studied in a newly irrigated area of the Mahaweli project in the dry zone of Sri Lanka. Observations were performed for a three-month period following the northeast monsoon. Parasitemia in the population varied from 20.2% in February to 7% in May, and infection was due to both Plasmodium falciparum and P. vivax. Night catches of mosquitoes collected with human bait included a high proportion of Anopheles annularis. Mosquitoes containing sporozoites in the salivary glands were identified by an enzyme-linked immunosorbent assay. Anopheles culicifacies, An. annularis, and An. aconitus were all implicated as vectors in the area. The highest entomologic inoculation rate, 0.12 infected bites/hr, was observed with An. annularis and P. vivax in March. We suggest that a change in the ecosystem from dry zone forest to irrigated cultivated land is the cause of the increased prevalence of An. annularis in this area and its emergence as a major vector of malaria.     

Anopheles barbirostris/campestris as a probable vector of malaria in Aranyaprathet,Sa Kaeo Province

As a result of dramatic increase in malaria cases in Sa Kaeo Province from 666 cases in 1995 to 4,381 in 1997, a brief entomological study was carried out during January 1998 to December, 1999 in Pa Rai subdistrict where most malaria cases were reported. Of fourteen species of mosquitos found, only Anopheles barbirostris group was the most abundant species throughout the year. Adult identification was not able to confirm species within An. barbirostris group, particularly between An. barbirostris and An. campestris because of morphological resemblance. Therefore, the barbirostris group captured in this study is reported to be either An. barbirostris or An. campestris. The seasonal prevalence of barbirostris/campestris was bimodal in distribution (September and November) and coincided well with malaria occurrence in this area. Human landing collections revealed high adult densities with 20 bites/person-night for mean indoor density and 53.5 bites/person-night for mean outdoor density. The biting peak was during 21.00-24.00 hours. Among 223 barbirostris/campestris dissected for oocysts and sporozoites only one gut from the outdoor collection in November was infected with oocysts. There were no sporozoites detected in salivary glands of all mosquitos collected. This appears to indicate that in the absence of major vectors local species may serve as potential transmitters of malaria in Thailand.     

云南湄公河流域上游河谷地区疟疾媒介传疟作用研究

目的通过观察蚊媒季节消长、嗜血习性、叮咬行为和疟疾子孢子率以研究出它们在云南湄公河上游河谷地带传疟作用的关系. 方法村内采取诱蚊灯和人工诱捕方法捕蚊;现场采取显微镜解剖蚊虫的方法观察唾腺子孢子,实验室采用ELISA技术检测蚊虫体内环子孢子蛋白(CSP). 结果村内共捕获16种按蚊.现场显微镜解剖7种按蚊,1 010只经产蚊中,发现了7只唾液腺感染子孢子;ELISA方法检测现场捕回的8种按蚊,5 154只各龄期蚊中,发现11只环子孢子蛋白阳性蚊.微小按蚊、中华按蚊、多斑按蚊子孢子阳性率(包括ELISA环子孢子蛋白阳性和镜检唾腺子孢子感染蚊)分别是0.37%、0.22%、0.32%, 昆虫接种率分别估算为9.82、3.97、2.69.这些蚊媒叮咬活动起始于黄昏,并整夜有活动,但微小按蚊夜间活动高峰出现于子夜,中华按蚊和多斑按蚊的高峰则在2100之前.它们的人血指数都在80%以上. 结论以上结果显示微小按蚊、中华按蚊和多斑按蚊是湄公河上游河谷地带的重要传疟媒介.     

Malaria vector incrimination in three rural riverine villages in the Brazilian Amazon

Vector incrimination studies were conducted from April 2003 to February 2005 at three riverine villages 1.5 km to 7.0 km apart, along the Matapi River, Amapa State, Brazil. A total of 113,117 mosquitoes were collected and placed in pools of 相似文献   

Unravelling the relationships between Anopheles darlingi (Diptera: Culicidae) densities, environmental factors and malaria incidence: understanding the variable patterns of malarial transmission in French Guiana (South America)

Anopheles darlingi, one of the main malaria vectors in the Neotropics, is widely distributed in French Guiana, where malaria remains a major public-health problem. Elucidation of the relationships between the population dynamics of An. darlingi and local environmental factors would appear to be an essential factor in the epidemiology of human malaria in French Guiana and the design of effective vector-control strategies. In a recent investigation, longitudinal entomological surveys were carried out for 2-4 years in one village in each of three distinct endemic areas of French Guiana. Anopheles darlingi was always the anopheline mosquito that was most frequently caught on human bait, although its relative abundance (as a proportion of all the anophelines collected) and human biting rate (in bites/person-year) differed with the study site. Seasonality in the abundance of human-landing An. darlingi (with peaks at the end of the rainy season) was observed in only two of the three study sites. Just three An. darlingi were found positive for Plasmodium (either P. falciparum or P. vivax) circumsporozoite protein, giving entomological inoculation rates of 0·0-8·7 infectious bites/person-year. Curiously, no infected An. darlingi were collected in the village with the highest incidence of human malaria. Relationships between malaria incidence, An. darlingi densities, rainfall and water levels in the nearest rivers were found to be variable and apparently dependent on land-cover specificities that reflected the diversity and availability of habitats suitable for the development and reproduction of An. darlingi.     

Susceptibility of two karyotypic forms of Anopheles aconitus (Diptera: Culicidae) to Plasmodium falciparum and P. vivax

Four laboratory-raised colonies of two karyotypic forms of Anopheles aconitus, i.e., Form B (Chiang Mai and Phet Buri strains) and C (Chiang Mai and Mae Hong Son strains), were experimentally infected with Plasmodium falciparum and P. vivax using an artificial membrane feeding technique and dissected eight and 12 days after feeding for oocyst and sporozoite rates, respectively. The results revealed that An. aconitus Form B and C were susceptible to P. falciparum and P. vivax, i.e., Form B (Chiang Mai and Phet Buri strains/P. falciparum and P. vivax) and Form C (Chiang Mai and Mae Hong Son strains/P. vivax). Comparative statistical analyses of the oocyst rates, average number of oocysts per infected midgut and sporozoite rates among all strains of An. aconitus Form B and C to the ingroup control vectors, An. minimus A and C, exhibited mostly no significant differences, confirming the high potential vector of the two Plasmodium species. The sporozoite-like crystals found in the median lobe of the salivary glands, which could be a misleading factor in the identification of true sporozoites in salivary glands were found in both An. aconitus Form B and C.     

Malaria vectors in the Brazilian amazon: Anopheles of the subgenus Nyssorhynchus

Various species of Anopheles (Nyssorhynchus) were studied in the Amazon with the objective of determining their importance as malaria vectors. Of the 33 known Anopheles species occurring in the Amazon, only 9 were found to be infected with Plasmodium. The different species of this subgenus varied both in diversity and density in the collection areas. The populations showed a tendency towards lower density and diversity in virgin forest than in areas modified by human intervention. The principal vector, An. darlingi, is anthropophilic with a continuous activity cycle lasting the entire night but peaking at sunset and sunrise. These species (Nyssorhynchus) are peridomiciliary, entering houses to feed on blood and immediately leaving to settle on nearby vegetation. Anopheles nuneztovari proved to be zoophilic, crepuscular and peridomiciliary. These habits may change depending on a series of external factors, especially those related to human activity. There is a possibility that sibling species exist in the study area and they are being studied with reference to An. darlingi, An. albitarsis and An. nuneztovari. The present results do not suggest the existence of subpopulations of An. darlingi in the Brazilian Amazon.     

The number of sporozoites produced by individual malaria oocysts

Mature oocysts of Plasmodium falciparum and P. vivax from western Thailand were separated from the midguts of Anopheles dirus by collagenase digestion, and the number of sporozoites contained in each was counted. For 26 P. vivax oocysts, the mean count was 3, 688 (range 1, 954-5, 577) and for 14 P. falciparum, the mean count was 3, 385 (range 1, 359-4, 554); a single P. cynomolgi oocyst contained 7, 521. Counts were not significantly correlated with oocyst density, oocyst age, or identity of the examiner. There may have been strain differences in fecundity, particularly between P. falciparum lines maintained in vitro. Mosquitoes receiving a second, uninfected blood meal seven days after feeding on P. vivax-infected volunteers developed no additional sporozoites per oocyst, but had salivary glands 3.4 times as infected. By calculation, more than 20% of P. vivax sporozoites released from oocysts subsequently invade the salivary glands.     

Capture-recapture studies with the South American malaria vector Anopheles darlingi, Root

A capture-recapture experiment was undertaken in October 1987, in the Jaru district of Rondonia, Brazil, with the malaria vector Anopheles darlingi. On two consecutive nights, 160 blood-fed, 78 unfed biting and 81 unfed resting mosquitoes were released. Recapture rates of 12-19% and survival rates of 0.59-0.57 per oviposition cycle were obtained for all releases, indicating that blood-feeding was not an obstacle for this population, which had a high vectorial capacity. Two A. darlingi were collected 7.2 km from the release site nine days after release. In contrast, recapture rates for 259 anophelines of nine other species released were only 2.3%. These other species also had a limited flight time and range in comparison with A. darlingi, which indicates that the latter is the only malaria vector of importance in this part of Brazil.     

First record of Anopheles (Anopheles) costai Fonseca & Ramos, 1939 in Espírito Santo State, Brazil

Field collections of immatures and adults of Culicidae were carried out in the Rio Doce Valley, Espírito Santo State, aiming to increase knowledge on the anopheline species of that region. Considering all Culicidae species collected, among other anopheline it is noteworthy the presence of Anopheles darlingi, An. oswaldoi and An. costai. Regarding to An. darlingi, responsible for malaria outbreak in the low lands in that state, it was expected to confirm its presence in the area. The register of specimens of An. costai in the field collections is relevant, increasing the geographical distribution of the species and representing better knowledge of the Series Arribalzagia of the subgenus Anopheles.     

Inability of Plasmodium knowlesi sporozoites to invade Anopheles freeborni salivary glands

Oocysts of Plasmodium knowlesi developed normally on the gut of the mosquito Anopheles freeborni, rupturing and releasing sporozoites at 10-14 days post-infection. Subsequently, however, sporozoites were never found in this mosquito's salivary glands. Heterologous transplants of whole salivary glands from uninfected An. freeborni and An. dirus, a completely susceptible mosquito, into the abdomens of insects heavily infected with mature oocysts were done. Sporozoites failed to infect An. freeborni glands implanted in An. dirus but did enter An. dirus glands implanted in An. freeborni. These experiments suggest that P. knowlesi sporozoites are unable to recognize An. freeborni glands.     

Role of the prevalent Anopheles species in the transmission of Plasmodium falciparum and P. vivax in Assam state, north-eastern India

In north-eastern India, Anopheles minimus, An. dirus and An. fluviatilis are considered the three major vectors of the parasites causing human malaria. The role in transmission of the other Anopheles species present in this region is not, however, very clear. To examine the vectorial role of the more common anopheline mosquitoes, the heads and thoraces of 4126 female Anopheles belonging to 16 species (collected using miniature light traps set in human dwellings in a foothill village in the Jorhat district of Assam state) were tested, in ELISA, for the circumsporozoite proteins (CSP) of Plasmodium falciparum or the VK-210 and VK-247 polymorphs of P. vivax. Sixty-five pools of head-thorax homogenates, representing 10 different species of Anopheles, were found reactive, giving an overall minimum prevalence of infection (MPI) of 1.58%, with a 95% confidence interval (CI) of 1.21%-2.0%. Among the CSP-reactive pools of mosquitoes, 31% were positive only for P. falciparum, 45% only for P. vivax VK 247, 6% only for P. vivax VK 210, and 18% for both P. falciparum and P. vivax VK 247. The results indicate that not only the proven vector, An. minimus s.l. (MPI = 0.71%), but also several species of Anopheles previously considered unimportant in the epidemiology of malaria, especially An. aconitus (MPI = 3.95%), An. annularis (MPI = 5.8%), the An. hyrcanus group (MPI = 0.48%), An. kochi (MPI = 1.28%), the An. philippinensis-nivipes complex (MPI = 0.94%), and An. vagus (MPI = 3.87%), are important vectors in the foothills of Assam.     

Bionomics of Anopheles minimus and its role in malaria transmission in Thailand

The bionomics of Anopheles minimus, one of the main malaria vectors in Thailand, were conducted in Pakchong district, Nakhon Ratchasima province, from January 1984 to June 1985. The prevalence of An. minimus was influenced by monthly rainfall, relative humidity, temperature and wind velocity, with a major peak of density from September to November. An. minimus preferred to feed on animal rather than on human, tended to bite human more outdoors than indoors, and thus exhibiting zoophilic and exophilic behaviour. The biting activity of the mosquitoes on animal exhibited high densities throughout the night in all seasons, whereas on human they tended to be an early evening biter in the dry cool season, and early morning biter in the wet season, and thus increasing the chance of man-vector contact. The life expectancy of An. minimus varied from month to month, ranging from 2.7 to 11.5 days, with the longest longevity during the dry cool season. The natural malaria infection rate of this species was very low. Out of 1,518 dissected guts, only 0.4% were found infected with oocysts. There were no sporozoites detected in the 1,560 dissected salivary glands.