Black flies (Diptera: Simuliidae) attracted to humans and water buffalos and natural infections with filarial larvae,probably Onchocerca sp., in northern Thailand

Several Simulium species were investigated as to their biting habits and natural infections with filarial larvae at Ban Pan Fan, Chiang Mai Province, in northern Thailand. Female adults flies landing on or flighting around a human and a water buffalo were collected during the daytime from 06.00 to 19.00 hours on 22 June 2001. As a result, 217 S. nodosum, 86 S. asakoae and two S. nigrogilvum were obtained from a human attractant, and 416 S. nodosum, 25 S. nakhonense, 16 S. asakoae, four S. fenestratum and two S. nigrogilvum, from a water buffalo. The blood-feeding was confirmed only for S. nodosum and S. nigrogilvum on humans, and for S. nodosum and S. nakhonense on water buffalos. Dissections of these simuliids showed that S. nodosum was naturally infected with developing filarial larvae. Two types of microfilariae were distinguished but only one type of infective larvae. These larvae resembled Onchocerca suzukii, a parasite from a wild Japanese bovid, suggesting that an unknown Onchocerca species from ruminants was transmitted in Thailand. Infection rates with all stages of larvae and third-stage larvae were 2.3% (14/608) and 1.0% (6/608), respectively. This is the first report of natural infections of black flies with Onchocerca larvae in Southeast Asia, and the involved black fly species is shown to be not only anthropophilic but also zoophilic in this region.     

Setaria cervi: immunoprophylactic potential of glutathione-S-transferase against filarial parasite Brugia malayi

Glutathione-S-transferase (GST) has been detected in the adult female Setaria cervi, a bovine filarial parasite. The role of S. cervi GST antigen in inducing immunity in the host against Brugia malayi microfilariae and infective larvae was studied by in vitro antibody dependent cell mediated reaction as well as in situ inoculation of filarial parasites within a microchamber in Mastomys. The immune sera from glutathione-S-transferase immunized Mastomys promoted the adherence of peritoneal exudate cells to B. malayi microfilariae and infective larvae in vitro inducing 80.7 and 77.6% cytotoxicity, respectively in 72 h. In the microchambers implanted in the immunized Mastomys host cells could migrate and adhere to the microfilariae and infective larvae and induced 77.8 and 75% cytotoxicity to B. malayi microfilariae and infective larvae in 72 h, respectively. These results suggest that native GST from S. cervi is effective in inducing protection against heterologous B. malayi filarial parasite and thus has potential in immunoprophylaxis.     

Diel biting activity of Culex (Melanoconion) caudelli in Trinidad, West Indies

The diel biting periodicity of the arbovirus vector Culex (Melanoconion) caudelli Dyar and Knab (Diptera; Culicidae) in the Aripo-Wallerfield forest, Trinidad, was studied by collecting mosquitoes attracted to mouse-baited traps at 2-hourly intervals during eight 24 h periods. Biting females of Cx caudelli were collected during all night-time hours, 18.00-06.00 hours, with an overall unimodal pattern, i.e. one well-defined peak between 22.00 and 04.00 hours. This contrasts with previous reports that Cx caudelli is diurnally active. During the four moon phases, the period of peak biting activity varied from 22.00 to 24.00 hours at fullmoon, from 22.00 to 04.00 hours at first quarter, and from 24.00 to 02.00 hours at new moon and last quarter phases. The number of mosquitoes collected varied significantly with moon phases, the highest (152/24 h) being collected in the first lunar quarter and the lowest (71/24 h) in the last lunar quarter. Cloud cover and rainfall had no significant effect on the diel biting periodicity of Cx caudelli.     

Transmission of Onchocerca volvulus and prospects for the elimination of its vector, the blackfly Simulium neavei in the Mpamba-Nkusi focus in Western Uganda

The transmission of Onchocerca volvulus Leuckart (Spirudida: Onchocercidae) and the prospects of Simulium neavei Roubaud (Diptera: Simuliidae) vector elimination through ground larviciding were investigated in the Mpamba-Nkusi focus, western Uganda. Transmission levels and the initiated vector elimination activities were assessed to supplement the ongoing ivermectin mass distribution programme. Searches for breeding sites, adult fly catches, dissection of flies, river treatment with temephos (Abate) and a review of annual ivermectin treatment data were conducted. High levels of crab infestation with S. neavei sensu stricto immature stages were recorded; 57.9% and 100% for the Mpamba and Nyabugando river systems, respectively. The mean numbers of larvae/pupae per crab were 3.6 +/- 0.5 in the Mpamba and 20.6 +/- 1.8 in the Nyabugando systems. Pre-intervention mean biting densities were 39 and 32 flies/(man day) in 2001 and 2002, respectively, and an annual biting rate in 2001 of > 14 000. The bimodal biting pattern of S. neavei s.s. consisted of two peaks; one in the morning (09.00-10.00 hours) and one in the afternoon (14.00-15.00 hours) with a mid-day lull in biting. The infection/infective rates were 13.3%/2.8% and 16.6%/2.9% in the dissected parous flies from the Mpamba and Nyabugando river systems, respectively. Out of approximately 1000 parous flies, 129 and 109 were found to be harbouring infective larvae of Onchocerca volvulus in their heads from the Mpamba and Nyabugando river systems, respectively. In spite of the > 10 years of ivermectin treatment, at a mean coverage of 71.3%, infection remained relatively high. Ground larviciding with temephos (Abate) initiated in June and October 2002 had a significant impact. In the Mpamba river system there was a significant (P < 0.001) reduction in positive crabs from 57.9% in 2001 to 0.06% in 2003 and a decrease in the mean number of larvae/pupae per crab from 3.6 +/- 0.5 in 2001 to 0.0007 +/- 0.0001 (P < 0.002) in 2003. Similarly, in the Nyabugando river system, a significant (P < 0.001) reduction in crab infestation from 100% in 2001 to 0.06% in 2003 and a decrease in the mean number of larvae/pupae per crab from 20.6 +/- 1.8 in 2001 to 0.06 +/- 0.03 in 2003. Drastic reductions were observed in the mean number of biting flies from 3 flies/h in 2001 to 0 flies/h in 2003 and the annual biting rates fell from 14,235 flies/year in 2001 to only 730 flies/year in 2003. These data suggest that substantial progress towards the goal of S. neavei s.s. vector elimination has been made and this will enhance the ongoing ivermectin treatment in this isolated focus.     

Evidence that sulfisoxazole, an antibacterial sulfonamide, can adversely affect the development of Brugia pahangi in Aedes aegypti mosquitoes

The average number of infective larvae recovered from Brugia pahangi-infected Aedes aegypti was approximately one-half that recovered from the controls after the former group of infected mosquitoes had ingested a 1.0% solution of sulfisoxazole diolamine (SXZ) in 10% sucrose-water for 4 consecutive days, beginning 4 days after infection. Most of the filarial larvae from the SXZ-treated mosquitoes were small and sluggish compared with those from the controls. There was no increased mortality of mosquitoes that ingested 1.0% SXZ in sugar-water for 4 days. Average filarial larval burdens were not decreased in mosquitoes that ingested a solution of 10(-6) M methotrexate (MTX), a potent dihydrofolate reductase inhibitor, in sugar-water for 4 days, beginning 4 days after infection. The distributional pattern of larval burdens in mosquitoes that ingested combined 1.0% SXZ and 10(-6) M MTX in sugar-water for 4 days closely resembled that seen in mosquitoes that had imbibed 1.0% SXZ only. Average filarial larval burdens were not decreased in mosquitoes with 4-day-old B. pahangi infections that fed upon jirds which received intraperitoneal injections of SXZ (2 g/kg) and MTX (1 mh/kh), alone and in combination, 1 hr previously. Survival of the mosquitoes that fed upon the drug-treated hosts was unaffected, as was the hatchability of their eggs and subsequent growth and development of the mosquito larvae.     

Anthropophilic blackflies (Diptera: Simuliidae) and onchocerciasis transmission in southwest Ethiopia

Abstract. From May 1984 to May 1985, the transmission of onchocerciasis by blackflies (Dipteria: Simuliidae) was studied around Gilgel Ghibe and Gojeb rivers in southwest Ethiopia. The predominant anthropophilic species of Simulium at both localities were S.(Edwardsellum) damnosum sensu law and S.(Lewisellum) ethiopiense. Some S.(Anasolen) dentulosum also landed on human bait at Gilgel Ghibe river.
Dissections of S. damnosum from Gilgel Ghibe and Gojeb revealed mean parous rates of 92% (n = 18,291) and 84% (n = 9530), respectively. S. ethiopiense from Gilgel Ghibe and Gojeb showed mean parous rates of 53% (n = 322) and 93% (n = 14), respectively. Of the parous S. damnosum , 1.3% at Gilgel Ghibe and 0.5% at Gojeb harboured infective third-stage larvae (L3) of Onchocerca volvulus (or morphologically indistinguishable from it). Unknown filariae of animal origin, indicative of zoophily, were found in 0.3% and 0.7% of Simulium damnosum complex females from Gilgel Ghibe and Gojeb, respectively. S. ethiopiense harboured developing (L,) larvae only, with 7.7% infection rate in both localities. In contrast, S. dentulosum did not harbour any filaria larvae. The annual infective biting rate (AIBR) and transmission potential (ATP) of the S. damnosum complex at Gilgel Ghibe river were 858 and 5478, respectively. The AIBR and ATP of S. damnosum s.I. at Gojeb river were 519.5 and 1963, respectively. These results emphasize the predominant role of the S. damnosum complex in the transmission of O. volvulus in southwest Ethiopia     

African Program for Onchocerciasis Control (APOC): Onchocerca volvulus transmission by Simulium damnosum s. l. in two regions of the Central African Republic

Entomological baseline data were collected in the villages of Zinga and Boali-Falls in Central African Republic (CAR) in view of the long term impact assessment of community-directed treatment with ivermectin (CDTI). Morphological determinations revealed that flies caught in both sites belong to the sub-group Sou/Sq. In Boali, the nuisance was relatively high with biting rates averaging 243 bites/man/day, with a parous rate of 61.6% and a crude annual transmission potential (ATP) of 8,259 infective larvae/man/year; and the average number of infective larvae per 1,000 parous flies was 177. In Zinga, the mean biting rate was 191 bites/man/day, with a parous rate of 51.6%, a crude ATP of 3,422, and 86 infective larvae per 1,000 porous flies. In conclusion, the vectorial capacity and the entomological indices recorded are characteristic of high onchocerciasis transmission zones. However, some of the infective larvae found, maybe of animal origin, need identification to better determine the real level of endemicity.     

Cell-mediated immunity in experimental filariasis: lymphocyte reactivity to filarial stage-specific antigens and to B- and T-cell mitogens during acute and chronic infection.

To study immunological responses in chronic filarial infections, a model utilizing inbred Lewis rats infected with Brugia pahangi was developed. Microfilaria were found in the bloodstream of over 90% of the rats by 16 weeks of infection. Using in vitro lymphocyte blastogenesis, cell-mediated immune responses of blood, splenic, and mesenteric node lymphocytes were followed during 1.5 years of infection. Lymphocyte responses to antigen prepared from infective stage filarial larvae were detectable in the early weeks of infection, whereas responses to microfilarial antigen only developed late as microfilaremia waned. Lymphocyte responses to antigen from adult filaria vacillated during the infection. With the mitogens, phytohemagglutinin, pokeweed mitogen, and bacterial lipopolysaccharide, periods of B and T-cell hyporesponsiveness were demonstrable. Between 16 and 36 weeks of infection node lymphocytes from many rats were unresponsive to all mitogens and antigens. The model of B. pahangi in inbred rats offers advantages for immunological studies of filarial infections.     

The effect of Brugia pahangi infection on survival of susceptible and refractory species of the Aedes scutellaris complex

Life table statistics were used to examine the survival functions of filarial susceptible and refractory species of the Aedes scutellaris (Walker) group of mosquitoes, following infection with high and moderate doses of Brugia pahangi (Buckley & Edeson). Survivorship curves and hazard function curves were generated, and the median survival times and the proportions of mosquitoes surviving beyond the extrinsic incubation period of the parasite were determined. In the susceptible populations of Aedes polynesiensis Marks, Ae. pseudoscutellaris (Theobald) and Ae.tabu Ramalingam & Belkin a dose-response relationship was detected between parasite load and mortality. This relationship was characterized by a significant reduction in the proportions of infected female mosquitoes surviving at days 1 and 9 postinfection, reduction in the median survival times and an increase in the hazard rates as the infectious dose increased. The survival of the refractory species, Ae.alcasidi Huang and Ae.katherinensis Woodhill was not significantly affected by the infection. A positive correlation between microfilaraemia in the vertebrate host and parasite load in the susceptible mosquito populations was also observed. Regression analysis of the number of parasites recovered from susceptible mosquitoes at the time of death showed that mosquitoes at highest risk of dying harboured from 11.6 to 19.4 infective larvae when fed on a gerbil with sixty-five microfilariae per 20 microliters blood; this resulted in 34.4-40.2% mortality by day 9 postinfection. A mean number of 32.6-46.9 infective larvae was observed when these populations were exposed to a gerbil with a microfilaraemia of 150 mf/20 microliters and resulted in 72.8% to 80% mortality in these populations. Viable infective larvae were recovered from infected mosquitoes up to 50 days postinfection.     

A 43-kDa circulating filarial antigen fraction of Wuchereria bancrofti in immunoprophylaxis against Brugia malayi in jirds

A 43 kiloDaltan (kDa) antigen fraction (CFA₂-6) isolated from microfilaraemic plasma of bancroftian filarial patients showed selective reactivity with sera samples collected from endemic normals. Antibodies raised against this antigen showed a strong reactivity with the surface of Brugia malayi infective larvae as well as microfilariae. Similar antigenic determinants were detected in the parasite extracts, but not in the excretory–secretory products. Further analysis was done on the immunoprophylactic potential of CFA₂-6 in inducing immunity against Brugia malayi in Meriones unguiculatus (jird) in vivo. A strong protective response of approximately 84% was observed against the development of the filarial parasite in the jirds immunized with CFA₂-6. The immunized jirds also showed a significant clearance (87%) of microfilariae inoculated intravenously. Approximately 65% of infective larvae failed to survive in jirds transferred with anti-CFA₂-6 serum compared to the jirds transferred with sera from the control jirds. Passive transfer of anti-CFA₂-6 antibody to the jirds followed by intravenous inoculation of microfilariae resulted in the reduction of 77% of circulating microfilariae. This study suggests that the 43-kDa CFA₂-6 could stimulate a strong protective immune response against infective larvae and microfilariae in experimental animals.     

池塘养殖环境下滇池金线鲃仔稚鱼的食性转化与生长

2008年3月—2009年3月,把35 000尾滇池金线鲃(Sinocyclocheilus grahami)仔稚鱼分别饲养于3个池塘进行对比饲养研究。密度分别是：P1为208尾/m3;P2为167尾/m3;P3为41尾/m3。饲养期间采用相同的管理措施。每天数据收集采用：在仔鱼孵化后的5～16 d的每天8:00和18:00从每个育苗池中捞取5～8尾仔鱼进行测量分析。仔鱼开口30ｄ后,每月从培育池各捞取15尾,测量全长和体重。研究发现,滇池金线鲃仔鱼的开口时间为孵化后的5ｄ,混合营养期3～5 d,这与初孵的滇池金线鲃仔鱼的全长和卵黄囊较大有关。在容易造成仔鱼大量死亡的混合营养期,通过采用浆状物—轮虫—人工混合饲料的方式,大幅度提高了滇池金线鲃仔稚鱼的存活率,孵化一年后的滇池金线鲃稚鱼存活率可达82.7%。经过一周年的饲养,滇池金线鲃稚鱼的体重由(0.027±0.01) g（0.003~1.22）增长到(8.83±0.54) g（3.7~16.7）,月均增重为0.73 g;全长由(15.8±0.30) mm（11.5~20.0）增长到(91.6±1.67)mm（75.0~16.0）,全长月均增长6.32 mm。滇池金线鲃稚鱼全年全长的增长呈线性相关,y=9.82+7.05 month（R2=0.989 1）;全年体重的增长呈指数关系,y=0.0158 month2.54（R2=0.993 9）。     

Identification of 38kDa Brugia malayi microfilarial protease as a vaccine candidate for lymphatic filariasis

A FPLC purified 38kDa protease (Bm mf S-7) isolated from B. malayi microfilarial soluble antigen was identified. It showed pronounced reactivity with sera collected from 'putatively immune' asymptomatic and amicrofilaraemic individuals residing in an endemic area for bancroftian filariasis. Further the immune protective activity of Bm mf S-7 antigen was evaluated in susceptible hosts, jirds (Meriones unguiculatus) against B. malayi filarial infection. The antigen showed 89% cytotoxicity against mf and 87-89% against infective (L3) larvae in in vitro antibody dependent cellular cytotoxicity Assay (ADCC) and in situ micropore chamber methods. Bm mf S-7 immunized jirds after challenge infection showed 81.5% reduction in the adult worm burden. The present study has shown that, the 38kDa microfilarial proteases (Bm mf S-7) could stimulate a strong protective immune response against microfilariae and infective larvae in jird model to block the transmission of filariasis. Analysis of IgG subclasses against Bm mf S-7 revealed a significant increase in IgG2 and IgG3 antibodies in endemic normals. Lymphocyte proliferation to Bm mf S-7 was significantly high in endemic normal group as compared to that in clinical and microfilarial carriers. Significantly enhanced levels of IFN-gamma in the culture supernatant of PBMC of endemic normals followed by stimulation with Bm mf S-7 suggest that the cellular response in this group is skewed towards Th 1 type.     

Suppression of parasitemia in rodent filariasis (Litomosoides carinii) by immunization with BCG and microfilaria. I. Intracutaneous inoculation of BCG

After intracutaneous inoculation of BCG and challenge by subcutaneous injection of infective larvae of Litomosoides carinii, the parasitaemia of the filarial infection in cotton rats remains significantly lower when BCG and larvae are applied in the region of the same popliteal and ileal lymph nodes. However, when the infective larvae are directed to other regional lymph nodes (Ln cubitales and axillares), the depression of microfilaraemia is missed. The worm load (recovery rate) and the expulsion of microfilariae by the adult worms are not influenced by the BCG inoculation. Obviously BCG stimulates the lymphatic tissue unspecifically, and the infective larvae produce the first antigen contact, which is boostered by the microfilariae at the onset of patency. When the intracutaneous BCG inoculation is combined with specific antigen stimulation by simultaneous injection of blood microfilariae in the region of the same lymph nodes, the microfilaraemia of the challenge infection disappears completely or remains extremely low.     

Vector competence of Culex quinquefasciatus say from different regions of Brazil to Dirofilaria immitis

The vector competence of Culex quinquefasciatus from five localities in Brazil to Dirofilaria immitis was evaluated experimentally. Females from each locality were fed on an infected dog ( approximately 6 microfilariae/microl blood). A sample of blood fed mosquitoes were dissected approximately 1 h after blood meal. These results demonstrated that all had ingested microfilariae (mean, 4.8 to 24.6 microfilariae/mosquito). Fifteen days after the infected blood meal, the infection and infective rates were low in all populations of Cx. quinquefasciatus. The mean number of infective larvae detected in the head and proboscis of these mosquitoes was 1-1.5. The vector efficiency, the number of microfilariae ingested/number of infective larvae, was low for all populations of Cx. quinquefasciatus. However, the survival rate for all populations was high (range 50-75%). The survival rate of Aedes aegypti assayed simultaneously for comparison was low (24.7%), while the vector efficiency was much higher than for Cx. quinquefasciatus. These data suggest that the vector competence of all assayed populations of Cx. quinquefasciatus to D. immitis in Brazil is similar and that this species is a secondary vector due to its low susceptibility. Nevertheless, vector capacity may vary between populations due to differences in biting frequency on dogs that has been reported in Brazil.     

Suppression of Brugia malayi (sub-periodic) larval development in Aedes aegypti (Liverpool strain) fed on blood of animals immunized with microfilariae

Preliminary studies were carried out to investigate the role of filarial specific antibodies, raised in an animal model against the filarial parasite, Brugia malayi (sub-periodic), in blocking their early development in an experimental mosquito host, Aedes aegypti (Liverpool strain). In order to generate filarial specific antibodies, Mongolian gerbils, Meriones unguiculatus, were immunized either with live microfilariae (mf) of B. malayi or their homogenate. Mf were harvested from the peritoneal cavity of Mongolian gerbils with patent infection of B. malayi and fed to A. aegypti along with the blood from immunized animals. Development of the parasite in infected mosquitoes was monitored until they reached infective stage larvae (L3). Fewer number of parasites developed to first stage (L1) and subsequently to L2 and L3 in mosquitoes fed with blood of immunized animals, when compared to those fed with blood of control animals. The results thus indicated that filarial parasite specific antibodies present in the blood of the immunized animals resulted in the reduction of number of larvae of B. malayi developing in the mosquito host.     

Simuliid blackflies (Diptera: Simuliidae) and ceratopogonid midges (Diptera: Ceratopogonidae) as vectors of Mansonella ozzardi (Nematoda: Onchocercidae) in northern Argentina

Mansonella ozzardi, a relatively nonpathogenic filarial parasite of man in Latin America, is transmitted by either ceratopogonid midges or simuliid blackflies. In the only known focus of the disease in north-western Argentina the vectors have never been incriminated. This study investigated the potential vectors of M. ozzardi in this area. The only anthropophilic species of these Diptera families biting man at the time of the investigation were Simulium exiguum, S. dinellii, Culicoides lahillei and C. paraensis. Using experimentally infected flies S. exiguum and both species of Culicoides allowed full development of microfilariae to the infective stage, with C. lahillei being a more competent host than S. exiguum. Based on these data, biting rates and natural infectivity rates it is probable that at the begininning of the wet season C. lahillei is the main vector of M. ozzardi and both C. paraensis and S. exiguum secondary vectors. Additionally, it was found that a single dose of ivermectin was ineffectual in eradicating M. ozzardi from infected individuals in this area.     

A model for the dynamics of human lymphatic filariasis

In this paper, Bryan Gren fell, Edwin Michael and David Denham review the appropriateness of feline filariasis as a model of the population dynamics of human lymphatic filarial infection and disease. Because of the longevity of infection and our inability to measure the adult parasite population in humans, research in filariasis is particularly dependent on the use of laboratory animal models. We demonstrate that Brugia pahangi infection patterns in the cat closely parallel those of Brugia and Wuchereria in humans. Although primary infections in 'susceptible' cats are long-lived, repeatedly infected animals show evidence of concomitant immunity which prevents the establishment of later cohorts of infective larvae. Furthermore, there is some evidence from macro filarial length distributions of 'stunting' of adult worms during long-term repeat infections. Cats can also show an 'acute' response that spontaneously eliminates infections, and this appears to be due to a combination of intrinsic and dynamic mechanisms. As in humans, pathology in cat filariasis develops as a sequel to the asymptomatic microfilaremic state, largely as a result of re-expression of immunity. The relationship between macro filarial burdens and microfilariae in blood is positive but portrays a high degree of variability. The cat model provides an important tool for elucidating the relationships between infection, immunity and disease dynamics in lymphatic filariasis, and we conclude by suggesting directions for further work in this area.     

A combination of two Brugia malayi filarial vaccine candidate antigens (BmALT-2 and BmVAH) enhances immune responses and protection in jirds

In this study filarial recombinant protein or DNA vaccine constructs encoding BmALT-2 and BmVAH as single or as cocktail antigens were evaluated. Male jirds were immunized intramuscularly with DNA vaccine constructs or were immunized intraperitoneally with protein vaccine. The single and bicistronic DNA constructs induced substantial interferon-γ responses in spleen cells; antigen-specific responses were higher following immunization with the bicistronic cocktail construct and evoked a significant protective response of 57% in jirds challenged with Brugia malayi that was similar in the antibody-dependent cellular cytotoxicity (ADCC) assay and micropore chamber experiment. The cocktail protein vaccines induced a mixture of IgG2a (Th1) and IgG1 (Th2) responses with 80% protective response when challenged with B. malayi infective larvae. However, the single protein vaccine rALT-2 induced Th2 (IgG1/IgG3) with a 70% protective response and rVAH induced Th1 (IgG2a) with a lower proliferative response with 60% protection following challenge with B. malayi infective larvae. These results suggest that filarial cocktail protein vaccines are able to elicit substantial immune and protective responses when compared with single antigen vaccination in suitably vaccinated jirds.     

The prevalence of Stephanofilaria sp. in buffalo fly, Haematobia irritans exigua, in Central Queensland

Abstract  Buffalo fly ( Haematobia irritans exigua ) infestations of cattle are associated with characteristic lesions, the initial cause of which has been attributed to a filarial nematode of the genus Stephanofilaria , for which the fly acts as a vector. Survey work in the 1980s estimated the prevalence of microfilaria in female buffalo fly in Queensland at 2.91%. Since then no information has been published and the current prevalence of microfilarial infection in buffalo fly is not known. Buffalo fly were collected from four geographically distinct sites in Central Queensland in mid-summer 2004 and were dissected to estimate Stephanofilaria sp. infection rates . Larval stages of the nematodes were recovered from female flies from all four sites and the percentage of female flies from which nematodes were recovered ranged from 29% to 57%. The average number of larvae recovered from infected female flies ranged from 1.25 to 1.75. Whereas no infected male flies were found from Sites 2–4, larvae were recovered from 43% of male flies collected at Site 1. This high prevalence of filarial infection in buffalo flies implies a correspondingly high level of transmission to cattle in Central Queensland.     

Cytotaxonomy, morphology and ecology of the Simulium nobile species group (Diptera: Simuliidae) in Thailand

The polytene chromosomes of 512 larvae of the Simulium nobile species group collected from 16 stream sites in northern, central and southern Thailand were examined. Band-by- band comparisons relative to the established standard chromosome map for the subgenus Simulium distinguished the 2 species of this group, S. nobile and S. nodosum. The differences are mainly due to the position of the nucleolar organizer, pseudochromocenter, and fixed and polymorphic inversions. S. nobile is a monomorphic species, while S. nodosum is a polymorphic species. The morphology of these taxa is described based on the gill filaments and the color of the antennae and female genitalia. S. nobile is distributed in southern Thailand at low altitudes, whereas the distribution of S. nodosum is in the north at higher altitudes.