Evaluation of mosquitoes, Aedes vexans, as biological vectors of porcine reproductive and respiratory syndrome virus

The objective of this study was to determine whether mosquitoes, Aedes vexans (Meigen), could serve as biological vectors of porcine reproductive and respiratory syndrome virus (PRRSV). Specifically, the study assessed the duration of viability and the site of PRRSV within mosquitoes, and evaluated whether PRRSV could be transmitted to a susceptible pig by mosquitoes following a 7- to 14-day incubation period after feeding on an infected pig. For the first experiment, a total of 100 mosquitoes were allowed to feed on a pig, experimentally infected with PRRSV (day 7 post-inoculation) and were then maintained alive under laboratory conditions. A set of 10 mosquitoes were collected at 0 hour (h), 6 h, 12 h, 24 h, 48 h, 72 h, 5 days (d), 7 d, 10 d, and 14 d post-feeding (pf). Samples of exterior surface washes, salivary glands, thorax carcasses, and gut homogenates were collected from each set of mosquitoes, and tested for PRRSV. Infectious PRRSV was detected by polymerase chain reaction and swine bioassay only from the gut homogenates of mosquitoes collected at 0 h and 6 h pf. For the second experiment, a total of 30 mosquitoes were allowed to feed on a pig, experimentally infected with PRRSV and the mosquitoes were then maintained under laboratory conditions. On each of day 7, 10, and 14 pf, a set of 10 mosquitoes were allowed to feed on a susceptible pig. Transmission of PRRSV to susceptible pigs did not occur, and PRRSV was not detected from the mosquitoes. These findings indicate that mosquitoes are not likely to serve as biological vectors of PRRSV.     

一种牦牛蚊蝇驱避剂作用效果观察

[目的]为了观察蚊蝇驱避剂对牦牛体表蚊蝇的趋避效果。[方法]选择10头成年牦牛,分为实验组和对照区,实验组使用驱避剂之后,观察比较牦牛体表蚊蝇数目,实验结束时采集牦牛血清检测谷草转氨酶和谷丙转氨酶水平。[结果]表明,实验组牦牛明显不良反应,体表蚊蝇明显少于对照组,蚊蝇趋避效果作用明显,两组牦牛血清谷草转氨酶和谷丙转氨酶水平无显著差异。[结论]说明牦牛蚊蝇驱避剂能效趋避蚊蝇,可以推广使用。     

蚊虫抗凝血活性物质研究进展

蚊虫在吸血过程中其唾液腺分泌一组抗凝血活性物质,这些物质不仅可干扰宿主的凝血反应和炎症反应,更是一组具有潜在药理活性的物质。本文对蚊虫抗凝血活性物质进行分类并从其特点、抗凝血作用原理、研究现状等方面进行综述,为该类物质的深入研究提供借鉴。     

Attraction of mosquitoes to domestic cats in a heartworm enzootic region

Heartworm disease is caused by a mosquito-borne parasite that can affect many different mammalian species and has worldwide distribution. The agent, Dirofilaria immitis (Leidy 1856), infect mainly dogs but feline infection have been frequently reported in the last decade. Feline heartworm infection is difficult to detect, therefore, low reported prevalence could reflect true low prevalence or poor diagnostic efficiency. As mosquitoes are known to be attracted differently by different mammalian species, mosquitoes were collected from both a cattery and a contiguous home located in a canine heartworm enzootic area in Niterói, state of Rio de Janeiro, Brazil. For 14 months, mosquitoes were collected weekly for genus identification, speciation when possible, and for individual blood meal identification. Culex species mosquitoes were the most captured and those most frequently found with feline blood meal, followed by Aedes species that, although captured in lower numbers, also fed on feline blood. While Culex species mosquitoes have been reported as potential secondary heartworm vectors for dogs and primary vectors for cats, the present results suggest that Aedes species mosquitoes may also be involved in feline heartworm transmission in a larger proportion than previously thought.     

Role of insects in the transmission of bovine leukosis virus: potential for transmission by mosquitoes

Bovine leukosis virus (BLV) was transmitted to sheep in a simulated mechanical transmission experiment, using the following species of mosquitoes; Anopheles freeborni, A stephensi, A quadrimaculatus, and A albimanus. Mosquitoes were fed on blood taken from a BLV-infected cow with persistent lymphocytosis. Mouthparts and heads of mosquitoes were removed immediately after feeding, placed in RPMI 1640 medium, and inoculated subcutaneously into sheep. Nine sheep were inoculated with mouthparts and heads from 37 to 122 mosquitoes. Infection was determined serologically. Three monthly serum samples were collected from the sheep and were tested for the presence of antibodies to BLV, using the agar-gel immunodiffusion (AGID) test. Sera that were negative by AGID at 3 months were tested by radioimmunoassay. Results from radioimmunoassay agreed with those obtained by AGID. Four of the 9 sheep developed antibody to BLV. Sheep that seroconverted were inoculated with mouthparts and heads from as few as 54 mosquitoes.     

Mechanical transmission of porcine reproductive and respiratory syndrome virus by mosquitoes, Aedes vexans (Meigen)

The objective of this study was to determine whether porcine reproductive and respiratory syndrome virus (PRRSV) could be transmitted to naïve pigs by mosquitoes following feeding on infected pigs. During each of 4 replicates, mosquito-to-pig contact took place on days 5, 6, and 7 after PRRSV infection of the donor pig. A total of 300 mosquitoes [Aedes vexans (Meigen)] were allowed to feed on each viremic donor pig, housed in an isolation room. After 30 to 60 s, feeding was interrupted, and the mosquitoes were manually transferred in small plastic vials and allowed to feed to repletion on a naïve recipient pig housed in another isolation room. Prior to contact with the recipient pig, the mosquitoes were transferred to clean vials. Swabs were collected from the exterior surface of all vials, pooled, and tested for PRRSV. Separate personnel handled the donor pig, the recipient pig, and the vial-transfer procedure. Transmission of PRRSV from the donor to the recipient pig occurred in 2 out of 4 replicates. The PRRSV isolated from the infected recipient pigs was nucleic-acid-sequenced and found to be 100% homologous with the virus used to infect the donor pigs. Homogenates of mosquito tissues collected in all replicates were positive by either polymerase chain reaction or swine bioassay. All control pigs remained PRRSV negative, and PRRSV was not detected on the surface of the vials. This study indicates that mosquitoes (A. vexans) can serve as mechanical vectors of PRRSV.     

Culex annulirostris as a vector of Eperythrozoon ovis infection in sheep

Eperythrozoon ovis, a blood parasite of sheep, was transmitted from carrier lambs to susceptible lambs by the interrupted feeding of the mosquito Culex annulirostris. The circumstances of some of the transmissions were similar to those encountered in the field, in that carrier and susceptible lambs were exposed to a natural population of mosquitoes, while in another transmission an artificial means of containment of the mosquitoes was used. Infective E. ovis organisms were shown to be present in and/or on Cx. annulirostris for at least 14 hours by the inoculation of physiological saline-extracted material from macerated mosquitoes fed on E. ovis carrier lambs.     

First record of avian Plasmodium DNA from mosquitoes collected in the Yaeyama Archipelago, southwestern border of Japan

We studied the prevalence of avian Plasmodium in 509 mosquitoes of 9 species collected from the Ishigaki and Iriomote islands in the Yaeyama Archipelago, located southwest from the mainland of Japan. Two identical avian Plasmodium lineages were detected from Culex (Culiciomyia) nigropunctatus. Detected lineages were phylogenetically classified into different clade to avian Plasmodium lineages from birds and mosquitoes in the mainland of Japan but identical to a lineage detected from a resident bird, White-breasted Waterken (Amaurornis phoenicurus). This is the first detection of avian Plasmodium DNA from mosquitoes in the Yaeyama Archipelago and suggested that resident birds might have been infected with an avian Plasmodium lineage specific to the studied area and C. nigropunctatus could be the candidate vector mosquito species.     

Failure to propagate equine infectious anemia virus in mosquitoes and Culicoides variipennis.

Laboratory-colonized mosquitoes, Culex tarsalis, aedes aegypti, Culiseta inornata, and Anopheles free-borni, and the biting gnat, Culicoides variipennis, were exposed to equine infectious anemia virus. Exposure to the virus was by intrathoracic inoculation for mosquitoes and by oral ingestion of an infective blood meal through a membrane for C variipennis. After various intervals, groups of 15 to 20 insects were homogenized and inoculated into susceptible ponies. Positive immunodiffusion test results were used as criterion for equine infectious anemia infection in ponies. Virus was not detected in the 4 species of mosquitoes at 3, 6, 12, and 18 days after inoculation, or in C variipennis at 6, 8, 12, 14, 21, and 26 days after oral exposure to the virus.     

Isolation of bluetongue and epizootic hemorrhagic disease viruses from mosquitoes collected in Indonesia.

Three viruses isolated from anopheline mosquitoes in Indonesia have been identified as bluetongue and epizootic hemorrhagic disease viruses. Another virus isolate showed no relationship to other orbiviruses tested and should be regarded as a new virus; the name Golok is proposed for it. The mosquitoes were collected in 1980 and 1981 in a program designed to isolate flaviviruses infecting humans. It is apparent that such collections of arthropods which feed on large mammals could be screened for other viruses which may infect domestic livestock.     

Molecular survey of Dirofilaria immitis and Dirofilaria repens by direct PCR for wild caught mosquitoes in the Republic of Korea

Adult mosquito collections using New Jersey light traps and Black-hole light traps were conducted to determine the potential vectors and the relative mosquito infection rates of Dirofilaria immitis and Dirofilaria repens in Gyeonggi and Gangwon Provinces, Republic of Korea, 2005. Dirofilaria spp. were confirmed by polymerase chain reaction (PCR) using species-specific primers for D. immitis and D. repens. Minimum field infection rates (MFIR) [MFIR = (number infected pools/total number of mosquitoes) x 1000] of 12 pools/2059 total number mosquitoes (5.8) and 21 pools (10.1) of the wild caught mosquitoes were positive by PCR for D. immitis and D. repens, respectively. Dual infections of both D. immitis and D. repens were detected by PCR in eight pools (3.9). Anopheles sinensis sensu lato (includes An. sinensis s.s., An. pullus, An. kleini, An. belenrae, and An. lesteri), An. sineroides, Aedes vexans nipponi, Culex pipiens and Armigeres subalbatus were found to be infected and are potential vectors of D. immitis and D. repens in Korea. Infections observed in mosquitoes represent potential health risks for domestic animal and human populations.     

First report of Wolbachia from field populations of Culex mosquitoes in south-western Nigeria

Recent reports on finding Wolbachia-strain infections in field mosquito species in some West African countries and the potential for developing these as disease vector biocontrol tools have prompted a search for Wolbachia in mosquitoes within the study area. Using a completely randomised design, mosquito traps were set at different locations in a rural and an urbanised community. One hundred and eighty (180) mosquitoes were trapped and pooled on the basis of genus, sex and site of collection, because there have been no earlier reports of Wolbachia isolated from Nigeria. Twenty pools, made up of not more than ten mosquitoes per pool, were homogenised and analysed for Wolbachia-specific DNA. Mosquitoes were trapped within Ede (urbanised community) and Akoda (rural community). Genomic DNA was extracted from trapped mosquito samples and used as a template in a PCR reaction. The Wolbachia sp. specific 16S rRNA gene was amplified, sequence analysis of PCR products was performed and a chromatogram of the sequence was subjected to Basic Local Alignment Search Tool analysis to identify the Wolbachia sp. This sequence was subsequently submitted to GenBank with accession number MK127541. The first evidence of the presence of the endosymbiont, Wolbachia in field-caught mosquitoes is hereby documented. The homology of this strain of Wolbachia bears similarities to those reported recently from other parts of West Africa and forms a single clade with a Wolbachia sp. from Mali, with a strong bootstrap support of 99%. This finding of a Wolbachia strain in mosquitoes at Ede could form the basis for more searches for diverse strains of Wolbachia in Nigeria.     

The inhibitory effect of a combination of imidacloprid and permethrin on blood feeding by mosquitoes in dogs raised under outdoor conditions

Combinations of imidacloprid and permethrin were frequently used to control harmful arthropod of companion animals. The inhibitory effects on blood-feeding activity of mosquitoes in dogs raised under outdoor conditions were evaluated by using combination of 10% (w/v) of imidacloprid and 50% (w/v) of permethrin as spot-on form. Dogs in the treated group received the combination imidacloprid/permethrin spot-on. After treatment, dogs in the control and treated groups were kept separately from the evening (17:00) to the morning of the following day (09:00) in two different kennels installed outdoors to mimic realistic dog-raising conditions. Mosquitoes in the kennels were collected by light traps placed in the kennels and a sweep net to determine evidence of blood feeding, and for species identification. Mosquitoes were collected at Days 5, 3 and 1 before agent treatment, and the Day of treatment, and Days 3, 7, 14, 21, 28, 35 and 42 after treatment. The percentages of blood-fed mosquitoes measured at Days 0, 3, 21, 28 and 42 after treatment were statistically significantly lower (p<0.01) in the treated group than in the control group. The most commonly collected mosquito, Culex tritaeniorhynchus, revealed statistically significant lower percentages (p<0.01) of blood-fed mosquitoes in the treated group than in the control group at the Day of treatment, and Days 3, 7, 21, 28 and 42 after treatment. It appeared that the test agent was effective in inhibiting blood feeding by adult female mosquitoes, and the efficacy lasts for 42 days after treatment under outdoor conditions.     

Aedes albopictus is a natural vector of Dirofilaria immitis in Italy

Investigations were carried out in Padova town (Veneto region, NE Italy) to define the actual role of Aedes albopictus in the natural transmission of Dirofilaria nematodes, and to assess the risk that its presence might represent for veterinary and medical health. During summer 2000-2002 daytime captures of human-attracted mosquitoes were carried out in three areas of the town. The presence of filarial parasites in mosquitoes was evaluated by PCR, and sequencing confirmed species assessment. DNA extraction was performed separately on pools of the insect abdomen and thorax-head, to discriminate between Dirofilaria infected/infective specimens. A total of 2721 mosquitoes were caught and A. albopictus was the most abundant species (2534). Filarial DNA was found in 27.5% (19/69) of the abdomen pools formed with mosquitoes collected in summer 2000, and in 11.1% (16/144) and 4.9% (6/123) thorax-head pools coming from samplings 2001 and 2002, respectively. Filarial DNA was belonging to D. immitis and all studied areas harboured infective specimens. These results prove A. albopictus as natural vector of D. immitis in Italy. Moreover, they support the hypothesis that the presence of the mosquito could affect the transmission pattern of canine heartworm disease in urban environment and, considering the aggressive anthropophylic behaviour of the species (30-48 bites/h) proven in Padova town, could enhance the circulation of filarial nematodes from animals to humans.     

West Nile virus in the United States (1999-2005)

The accidental introduction of West Nile Virus into New York City from the Old World in 1999 resulted in an epidemic in humans, horses, and birds that swept to the west coast in just 3 years. The virus is transmitted by infective mosquitoes among susceptible native birds, which serve as amplifying hosts. Clinical disease occurs in humans and horses, but not enough virus is produced in their blood to infect other mosquitoes; therefore, humans and horses are considered dead-end hosts. Humans can best protect themselves by remaining indoors during periods of high mosquito activity and/or by using recommended repellents. Effective vaccines are available for horses.     

Assessment of the efficacy of a single dose of a recombinant vaccine against West Nile virus in response to natural challenge with West Nile virus-infected mosquitoes in horses

OBJECTIVE: To determine the onset of immunity after IM administration of a single dose of a recombinant canarypox virus vaccine against West Nile virus (WNV) in horses in a blind challenge trial. ANIMALS: 20 mixed-breed horses. PROCEDURE: Horses with no prior exposure to WNV were randomly assigned to 1 of 2 groups (10 horses/group). In 1 group, a recombinant canarypox virus vaccine against WNV was administered to each horse once (day 0). The other 10 control horses were untreated. On day 26, 9 treated and 10 control horses were challenged via the bites of mosquitoes (Aedes albopictus) infected with WNV. Clinical responses and WNV isolation were monitored for 14 days after challenge exposure; antibody responses against WNV after administration of the vaccine and challenge were also assessed in both groups. RESULTS: Following challenge via WNV-infected mosquitoes, 1 of 9 treated horses developed viremia. In contrast, 8 of 10 control horses developed viremia after challenge exposure to WNV-infected mosquitoes. All horses seroconverted after WNV challenge; compared with control horses, antibody responses in the horses that received the vaccine were detected earlier. CONCLUSIONS AND CLINICAL RELEVANCe: In horses, a single dose of the recombinant canarypox virus-WNV vaccine appears to provide early protection against development of viremia after challenge with WNV-infected mosquitoes, even in the absence of measurable antibody titers in some horses. This vaccine may provide veterinarians with an important tool in controlling WNV infection during a natural outbreak or under conditions in which a rapid onset of protection is required.     

Ecological Surveillance for West Nile in Catalonia (Spain), Learning from a Five‐Year Period of Follow‐up

To enhance early detection of West Nile virus (WNV) transmission, an integrated ecological surveillance system was implemented in Catalonia (north‐eastern Spain) from 2007 to 2011. This system incorporated passive and active equine surveillance, periodical testing of chicken sentinels in wetland areas, serosurveillance wild birds and testing of adult mosquitoes. Samples from 298 equines, 100 sentinel chickens, 1086 wild birds and 39 599 mosquitoes were analysed. During these 5 years, no acute WNV infection was detected in humans or domestic animal populations in Catalonia. WNV was not detected in mosquitoes either. Nevertheless, several seroconversions in resident and migrant wild birds indicate that local WNV or other closely related flaviviruses transmission was occurring among bird populations. These data indicate that bird and mosquito surveillance can detect otherwise silent transmission of flaviviruses and give some insights regarding possible avian hosts and vectors in a European setting.     

河南省猪场蚊虫中Ⅰ、Ⅲ型乙型脑炎病毒的分离及鉴定

用Vero细胞对2010年河南省采集的猪舍蚊虫标本进行病毒分离,对新分离的乙型脑炎病毒（JEV）进行分子生物学鉴定,并对其PrM基因进行克隆、测序及病毒进化分析。结果显示,从采集的蚊虫标本中分离到1株基因Ⅰ型JEV（HN10-1）和1株基因Ⅲ型JEV（HN10-2）。结果表明,河南省同时存在Ⅰ、Ⅲ2种基因型JEV的传播和流行。     

A sensitive polymerase chain reaction based assay for the detection of Setaria digitata: the causative organism of cerebrospinal nematodiasis in goats, sheep and horses

A sensitive PCR assay for the detection of Setaria digitata has been developed. Two oligonucleotide primers (17 nt) were designed from a previously cloned and characterized tandemly arranged repetitive sequence of Setaria digitata. Using these primers, it was possible to amplify small quantities (100 fg) of S. digitata genomic DNA. A simple procedure, using proteinase K and non-ionic detergent NP 40, was followed to process the host blood samples and mosquitoes harbouring L3 larvae. The sensitivity of the polymerase chain reaction based assay surpasses the microscopic detection and the previously reported oligonucleotide based chemiluminescent detection of microfilariae in infected host blood samples and L3 larvae in mosquitoes.     

Mosquito collection in endemic areas of Japanese encephalitis in Hokkaido, Japan

A study was conducted during 1985 and 1986 to evaluate the roles of mosquito species as possible vectors of Japanese encephalitis (JE) virus in Hokkaido. The number of Culex tritaeniorhynchus was very low among the four pig farms where outbreaks of abortion caused by JE virus were observed in swine populations. At one farm near Sapporo, only one Cx. tritaeniorhynchus was found among a total of 510 mosquitoes collected during the survey period from July to October 1985, even when JE virus activity among sentinel pigs was revealed by seroconversion. At another farm in the south, no individuals of this mosquito species were found among 987 mosquitoes collected at the time of the outbreaks of abortion. Cx. pipiens pallens, Anopheles species, Aedes vexans nipponii, and Ae. japonicus were predominant over Cx. tritaeniorhynchus. Cx. tritaeniorhynchus, almost a solve vector species of JE virus in the southern part of Japan, is probably not a vector of the virus in Hokkaido. The collected mosquitoes (2,332 from 1985 and 1,403 from 1986) were processed for virus isolation but no JE virus was isolated. More extensive field studies are necessary to provide further information on the role of mosquito species other than Cx. tritaeniorhynchus in the transmission of JE virus in the northern limits of its range including Hokkaido.