Effectsof malaria infeetioninanophele stephensi

Transcription

1 The JapanSociety Society ofmedical of Medical Entomology and Zoology (Jpn.J.Sanit.Zoal Vol. 42 No.2 p ) Effectsof malaria infeetioninanophele stephensi mosquitoes on passage through a wide-mesh net" Takeshi KuRiHARA"*TetsushiKiKucm"' and Kazuyo DePartment of MedicaJ Zoology. Teikyo UniversitySchool of ltabashi-ku Tokyo I73 JaPan (Received: December ) IcHIMoR[** Medieine Keywords: Plasmodium yoelii nigeriensis activity cage test wide-meshanopheles net. stephensi infectedmosquitoes reduced Abstract: The effects of Plasmodium infeetionupon the behaviour of vector mosquitoes were examined by the cage-test rnethod. AnoPhelesstephensi parasitized with Plasmodium yeeliinigeriensis had reduced ability to passthe wide-mesh net barrier.the reduction was particularly remarkable when there was no air-flow in the test cages. It is suspected that in some of these mosquitoes the receptor for chemicals from a bloodsource may malfunction under a windless condition. The effects of Ptasmodium infectionupon the behaviour and other lifefunctionsof mosquito vectors have been the subject of intensivestudies in recent years.gad et al. (1979) reported that the rnortality of Ano- Phele stephensi infectedwith P. beghei was higherthan in nonmal blood-fedmosquitoes. Klein et al. ( ) also found a deterioration effect on the longevity of An. dirusinfectedwith P. cynomolgi. The reduction of flightactivity of An. stephensi was reported when these mosquitoes were parasitized with P. cynomolgi (Schiefer et al. 1977) and with P. yoelii (Rowland Boersma 1988). Ressignol et al. ( ) found that P. gallinaceum sporozoite- infected Aedes aegypti were impaired in locatingblood vessels but the bitingrate was greater than noninfected mosquitoes. The present paper describesthe results of tests of the ability of An. stephensi to pass a barrierafter parasitization with P. yoelii * This work was supported in part by a grant from Sumitomo Chemical Co Ltd. "* Mwt X sutaptfi -mufitt: reptsc\k\ut Kthth\SZ (+173MfiasutfiXrmes )141 nigeriensis. The method called the "cagetesti' utilizes a wide-mesh net and cages and as reported earlier is useful in determining the behaviouralresponses of mosquitoes when facedwith a physicalbarrier or with insecticides et al ). The (Kurihara sarne apparatus was adopted to examine the influence of malaria parasiteson mosquito behaviour particularlywhen on their way to access a blood source. MATERIALs AND METHoDs The mosquitoes u'sed were the BEECH strain of An stephensi. These were maintained and examined in an insectariumat 23-25aC80% RH and with 16:8 (hr. L:D) phetoperiod. Adult mosquitoes were reared in a cm cage on a 10% sucrose solution P. yoelii nigeriensis N67 strain was preserved in liquid nitrogen. Te infect An. stephensi with the parasite white miee were infected with 107 parasitized erythrocytes. Other details on the mosquitoes and parasites were as previously describedby one of the authors (Ichimori 1989). Three days after inoculation an infectedmouse was chosen NII-Electronic Library Service

2 The JapanSociety Society of Medical Entomology and Zoology 142 fer the mosquitoes to feed on thereby being the source of infection A batch of mosquitoes of both sexes emerging on the same day was kept in a cage for 5 days to allow time formating. They were then dividedintotwo 300 females groups.approximately of group A were exposed to a 6B week old rnouse which had a parasitaemia of 5-20% and gametocytaemia of OOl- 1% in red blood cells. These mosquitoesengorged with infected blood were separated and allowed to layeggs on Day 5 after feedingand then served forthe cagetest at 3p.m. of Day 10. Group B fed on unparasitized (=non-infected) mice were simultaneously treated in the same manner as a noninfected control group. The cage-test apparatus was composed of two wire cages ( cm) each with two round ho]es and a piece of wide-mesh net. The cages were placed side by side with a net stretched between the two holes. One cage served as a release cage centaining hungry mosquitoes of either greup A or B and the other as a bait cage centaining a mouse. Mosquitoes were able to pass through the netting easily and feed on the baitanirnal ifthe mesh size was greater than 6mm (Kurihara et al. 1989). After release the mosquitoes w'ere Ieft overnight and were recovered from each cage at 10am and the number of livingand dead fed or unfed was recorded. Live insectswere immediately dissectedto determine the number of oocysts present. Each experiment had 34 replications and a total of 13 experiments was carried out through 4 series or fer4 batchesof mosquitoes. The percentage of oocysts present(=% infected) was similar in each series ranging from 40-65%. The firstand second series were cornpared for their ability to pass through the nets of differentsize mesh. In the firstseries test cages were placed so that they were exposed to an intermittent side flowof air from the room air-conditioning. In the second series the cages were placed so that the directionof air-flow was from bait to release cage and velocity of the air-flow was measured at O.15mlsec. The third series was conducted to deterrninemosquito ability to pass through the 6mm mesh net under a cendition where the cages were JpnJSanit.Zool. completely coverd with a transparent plastic sheet thus avoiding any influenceof breeze. For comparison partiallycovered cages were also tested both ends of which were opened and air allowed te pass Iike a wind tunnel from the baitto the release cage Then in series 4 the passage rate at "witheut net" was also tested. In all these experiments the analysis was made mainly on the mosquitoes passingthreugh the net'' that is itwas based on the number recovered in the bait cage and the number engorged found inthe release cage er (No ṛecovered in bait cage + No. engorged found in release cage) 1 No. released REsuLTs In all the experiments using the net the rate of passage ef oocyst-present mosquitoes in group A was always lower than that of oocyst-absent insects regard]ess the size of mesh or whether covered by the plasticsheet. Out of 9 experiments the differencein 4 of them was shown to be statistically significant. Even ifno net was interposed the same results were obtained (Tables1 and 2). The difference of passage rate between oocyst-present and -absent mosquitoes was however not always extreme. In series 1 the cages were placed in side air-flow and the differeneewas remarkable But in series 2 in the headwind positionțhe difference was almost negligible To withdraw the wind factor the cages were completely covered with a sheet and passage was studied in series 3 and 4. The rate of oocyst-present mosquitoes in group A of the covered cages was then clearly lower than oocyst-absent ones In contrast oocyst-present mosquitoes in a partially covered condition in group A demenstratedslightly lower passagethan the oocyst-absent ones but there was no significant difference. The effect of mesh size on % passing varied No clear tendency was observed among the differentmesh sizes in series 1 and 2. Incidentally the passage rate of oocyst-absent insectsin group A did not greatly differfrom group B Higher rates were found in 5 experiments and lower rate in 4 experiments. In series 3 and 4 the effect of complete [:% NII-ElectronicMbraryService Library Service

3 The JapanSociety Society of MedicalEntomology Entomology andzoology Zoology Vol. 42 No Table 1 Rate ef passage thteugh the net: Summary of 3 replications of each experiinent of series 1 and 2. MosquStoes in series 1 were exposed to a side air-flow and series 2 to a headwind Groups A and B were fed simultaneously on an infectedmouse and non-infected mouse respectively. Group A (%) Oocyst(+) Oocyst <-) Group B (%) 1. With 6mm net Witheut net 20.0*:**10 3*** **57. 1**100 ss With 6mmnet O O L8 Without 11 mm net net * Significant differenceat 5% level from oocyst-absent mosquitees " Significantdifferenceat 5% - level from "without net" Table 2 Rate of passage through the net: Summary of 4 replications of each experiment of two batches of mosquitoes series 3 and 4. Greups A and B were fed sirnultaneously on an infected and non-infected mouse respectively. tt... tt t tt.. 3 'cages coveied Cornpletely Partially Oocyst<+) IS.7*:*** 67.3 Group A (%) Oocyst (-) O Group B (%) Cages covered Completely Completely Partially Partially and without net and without net ' Significantdifferencefrem oecyst-absent. '*' Signifieantdifferencefrom partiallycovered. *' Sig 17.8****** ". 8*45.e**77. 7 nificant 47.2** ** 937 differencefrom `[without net." 6L P..i cover and partial cover was cempared. Oocyst-presentmosquitoes showed significantly lower passing rate at complete cover but oocyst-absent insectsshowed no significant differencebetween complete and partial. When the net was removed the passagerate of mosquitoes increased greatly both in oocyst-present and -absent in series 1 and 4 but in series 2 no clear differencewas observed. Through all these series the rise in passing rate caused by removal of the net was much prominent in oocyst-present mosquitoes than -absent ones but the rate did not attain the level of non-infected insects (Tables 1 and 2). Comparison was also done among the group A mosquitoes those successful in ing the pass- net vs. others which failedto pass. The rate of oocyst-present mosquitoes succeeding in passing was much lower than those failingin the 9 experiments. Geometric mean number of oocysts in the former rnosquitoes was also much lessthan in the latter with one exception (Table3). Rate of blood feedingin each experiment was calculated based en the number of mos- NII-Electronic Library Service

4 The JapanSociety Society ofmedical of Medical Entomology and Zoology 144 Jpn.J. Sanit. Zool Table 3 Geometricmean numbers of oocysts (m) and % oocyst-present mosquitoes in those fed on an infected mouse (=group A) calculated for mosquitoes passing through the net and those failingto pass through With 6 mm net Without net With 6mm net S mm net 11 mm net Without net Complete cover aomplete Complete cover ancl without net Partial and without net Succeededto pass m % oocy$t (+) O O O Failed to pass m %oocyst (+) 33.3*42.8* * *406* O ' Significantdifferencefrom "failing to pass." Table 4 Rqte of blood feeding based on the nurnber of mosquitoes entering the baitcage in each experiment Groups A and B were fed simultaneously on an infected and non-infected mouse respectively Group A (%) Oocyst {+)Ooeyst (-) Group B (%) L With 6mm net Without net With 6mrn net 11 mm net Without net Complete cover Complete cover Complete and without net Partlal and without net O A O quitoes entering the bait cage ( =passing the net barrier)(table 4). The comparison was being made in the oocyst-present vs. -absent insectsof group A. Among the 9 experiments using the net a higher feeding rate in oocystpresent was observed in 4 experiments a lower rate in 4 experirnents and the same rate in 1. It seems that the infected mosquitoes which succeeded to passhave similar ability to feed on blood as the uninfected ones. Non was any clear differencefound in the rate of group B mosquitoes and in the rate `Cwithout net" interposed. NII-Electronic Mbrary Library Service

5 The JapanSociety Society of Medical Entomology and Zoology Vol. 42 No DlscussloN The present experiments demonstrated that malaria-infected mosquitoes were impairedin their ability to access a blood source. Many of these mosquitoes were unable to pass through the net barrierunlike healthy mosquitoes This phenomenon was also supported by the fact that the rnosquitoes successfully passing through the net had a lower densityof oocysts than those failingto get through. Mosquitoes passing through were mainly oocyst-absent ones and those failing to pass were usually oocyst-present. It is suspected that the malaria parasitedestroys some part of the normal mechanism functioning to guide the approach to a host. How the parasiteinterferes with the mosquito's is of interest. From the present ebservatiens we can state that infectedmosquitoes were as aggressive in feedingon blood as uninfected ones as deterrnined by the rate of those successful in entering the bait cage. We may thus assume that various processes occur on arrival in the vicinity of a source for those mosquitoes aggressively wanting to feed.in small laboratory experiments however the processmay differsomewhat compared (Gillies 1980). But even in a cage-test mosquitoes must locatethe bloodsource and then rnust move toward it.to detectthe source night-feeding mosquitoes should be stimulated by airborne chemicals which emanate from the hostbody It was clear that oocyst-present mosquitoes were not as active as oocyst-absent enes and the non-infected B grouppanicularlyunder the conditions of lessmovement of air. Even ifthe net barrierwas removed and a way te aceess the b]oodsource fullyopened their passage rate did not attain the level of noninfectedinsectswhen cages were completely covered. Infected mesquitoes it seems were unable to activate the sensor to detectthe blood source due to there being lessmovement of air The rate was also remarkably lower than when cages were only partia]ly cevered Consequently itappeared as though they were not much concerned about a blood source even though itwas located inan easily 145 accessible spot. In contrast in the case of a partiallycovered cage 77.7% of infected mosquitoes reached the nearby blood source. Does a certain receptor in a mosquito infected with a malaria parasitecurtail the host-findingfunctionin some way particularlyunder a windless conditien? The impairmentof kineticfunctioning was also doubted as a rnechanism of deterioration by a parasiteṭhe passagerate of infected mosquitoes when the net was rernoved was higher but this increasephenomenon also happened in the uninfected mosquitoes. Thus the blockage of movernent by the net was seen inboth eocyst-present and -absent mosquitoes. It was reported earlier that mos- could easily fly through the net if quitoes the mesh size was larg enough. With smaller mesh size a more complicated activity was necessary for the mosquitoes: they rested on the net for an average of 23 sec and then walked through it(itohet al. 1986). This is a kinetichandicap not only for damaged but also for healthy mosquitoes too. Therefereat the present stage kineticdeterioration was not well dernonstrated. However the rise in passing rate when the net was removed was somewhat more in oocyst-present meequitoes than prominent in -absent ones. Therefore it is suspected that the kineticdamage may net have occurred so conspicuously in the infected population. Reduced flightcapability by parasitization with Ptasmodium was demonstrated by Rowland and Boersma (1988) and by Schieferet at (1977)Țhey explained that infectedmosquitoes had reduced flight capabilitysuch as distance and duration.the equipment used in the present cage-test may well have been too small in size to evaluate their kineticfunction In any event the existence of lessactive is significant insects due to parasitization epidemiologically. The reduced ability of mosquitoes after becoming infected means limitation to their natural transmission activity.if such reduction occurs in nature modified frequenciesof biting and transmission may have important epidemiological implications. It is possible these mesquitoes will hesitateto enter a tear in a mosquito net ( :bed-net) or a crack in the wall. This reaction enhances the effect of the wide mesh NII-Electronic Library Service

6 The Japan Society Sooiety of Medioal Medical Entomology and Zoology 146 net curtain method impregnated with insecti. c 量 de It was previouslydemonstrated by Kurihara et al.(1986 ) tbat the net curtain reduced the number of mosquitoes reaching the blood source. Even after reduction of the insecticidal effect a certain levelof pro tection from infected mosquitoes isexpected. Incidentally rate of a similar passage oocyst present mosquitoes to noninfected mosquitoes was observed in a part and 3. It is therefore possible of series 2 to create a certain wind condition which may induce inverselyexciting the infected mosquitoes It is still not clear whether the reduction in passage rate is attributable to the growth stage of the oocysts : ookinate development epithelial damage oocysts and sporo growing zoite migration (Maicr et al 1987 ). We found that some mice bittenby group A mosquitoes in the present experiments showed parasitaemia soon after the cage tests ; thus. Our we cannot overlook any possibility studies are continuing. REFERENCES Gad A.M W.A.Maier and G.Piekarski(1979 ) : Pathology of Anopheles stephensi after infection with Pltsmodium berghei らerghei tenkunde 60 : Z.P α rα 豆一 Gillies M.T. ( 1980 ) : The role of carbon dioxide in host 一丘 nding by mosquitoes (Diptera ; Culici dae) Areview.BuU.Entomol.Res :.70: Ichimori K. ( 1989 ) : Corre 二 ation of mosquito size blood meal size and malarial oocyst 1Pn.1.SanitZoo 乙 4 刈 D : production. Itoh T. G.Shinjo and T.Kurihara (1986 ) : Studieson wide nlesh netting impregnatedwith 三 nsecticides against Culex mosquitoes. ノ.Am. Mosq.Control Assoc.2 : Klein T.A り B.A.Harrison R.G.Andre R.E Whitlnire and I.Inlao (1982 ) : Deterlmental cffects of Pla Fmodium cynomolgi infections the longevityof 1{nopheles d ぎ rus.mosq.new. s 42 : KleinT.A.B.A.Harrison.S.Grovc 丿 S.V. Dixon and R.G.Andre (1986 ) : Cerrelation Qf survival rates of 1tnophetes dirus A ( Diptera : Culicidae) with different infection densitiesof Piasmodium.BullW cynomolgi.h.0 リ 64; Kurihara T. K Fujita and T Suzuki ( 1985 ) : Insecticide treatrllent of wide mesh net curtain for vect r control and the effect upon behaviour responses o 正 adult mosquitoes. ノpn.1.Sanit. Zoot.36 : ( in Japanese ). Jpn.J.Sanit.ZooL Kurlhara T. K Ichimori C F.Gurtis and M I. Hossain ( 1989 ) Behavioural : studies in thc lab rat ry.ln : Ap ρ ropriate Techn 1 gy in Ve tor Control ( ed Gurtis C.F. ) pp GRC PressBoca RatQn Florida Kurihara T. K.Kamimura and R Arakawa (1986 ) : Pヒenothrin impregnationof wide mesh net for protection from bitingmosquitoes. pn. ノ.Sanit.Zool 37 : Kurihara T and T.Umino (1987 ) : The effects ohnsecticides on the behaviourqf female mos quitoes under the laboratory conditions. ノ pn. ノ. sanit.z ol り 38 : ( in Japanesewith Eng lish summary ). Maier W.A H.Becker Feldman and H M Seitz ( 1987 ) : Pathology of infected malaria rnosquitoes.parasitol.today : Rossigno1 P A. J.M.C.Ribeiro and A.Spielman (1984 ) : Increased intradermal probing time in spqrozoite infected mosquitoes. Am. ノ.TroP し 4ed.H ッ g 33 : Rossigno1 P.A. J.M.C.Ribeiro and A.Spielmal1 (1986 ) : Increased biting rate and reduced fer tility in sporozeite infected mosquitoes. 4m. ノ. : rop.med.hyg. 35. 丿 : Rowland M.and E.BDersma (1988 ) : Changes in the spontaneous Hight activity of the mosquito Anopheles stephensi by parasitizationwith the rodent maiaria Plasm dium yoetii.parasitol 9 } 97 : SchieferB A R A.Ward and B.E Eldridge (1977 ) : Plasmodium cynomolgi ; Effects of malaria infectionon laboratoryhight perform. ance of Anophele stephensi mosquitoes.exp. Parasitol.41 ; 摘 室内試験でみられた Ptasm dium yoetii ni.geriensis に感染された AnoPheles 要 b tephensi の吸血源接近の行動 マラリア媒介蚊が病原体をとりこんだために 未感 染の蚊に比して その寿命を短縮したり行動の束縛を うけたりすることは 少ないというのが従来の報告と しては多かった. 近年この点についてネズミマラリアなどを供しての実験で いくつかの異論がみられる. われわれは An.stePhensi にネズミマラリアの一種 P. yoelii nigeriensis を吸血によりとりこませた. そ の 5 日後に産卵させ 10H 後にケージテスト法で 障 害物である網を越してベイトのマウスに接近し吸血する状況を調べた. その結果オーシスト保有の蚊は 非保有の蚊と比べて 網目サイズの大小にかかわらず 網を越して接近する率が低いことを見いだした. とく にテストの装置をビニール布でおおって外気を遮断す ると 6mm メッシュの網を越える率が著しく低率に なることが明らかになった. 本原虫感染が媒介蚊の吸 血源感知の能力や接近飛翔に影響をもたらしていると考えられる. NII-Electronic N 工工一 Eleotronio Library Service