Importance of Aedes albopictus in veterinary medicine

To assess the role of Aedes albopictus in transmission of filarial nematodes of veterinary importance, researches were carried out in different geographical areas. In Italy a first research was performed to study the susceptibility of Ae. albopictus to Dirofilaria repens, D. immitis and Setaria labiatopapillosa. The development of L3 larvae was longer than in other species of mosquitoes but Ae. albopictus could be a suitable vector of filariae. To understand the role of Ae. albopictus in the natural transmission of Dirofilaria and to assess the risk for animal and human health, in 2000, 2001 and 2002 another study was carried out in the town of Padua. A total of 2,534 Ae. albopictus were caught on human-attracted mosquitoes. Specific primers and sequencing identified filarial DNA as D. immitis; Ae. albopictus was proved a natural vector of D. immitis. Similar results were confirmed in Central Italy also for D. repens. The presence of Ae. albopictus increased the probability of transmission of canine and human dirofilariosis in urban environment and it could change the epidemiology of dirofilariosis, in particular for what concern the time of biting and the risk season. These aspects must be considered to outline a correct prophylaxis.     

Susceptibility of mosquitoes in central Taiwan to natural infections of Dirofilaria immitis

From October 1997 to September 1998, 3085 Culex quinquefasciatus (Say) (Diptera: Culicidae), 584 Cx. tritaeniorhynchus (Giles) (Diptera: Culicidae), 392 Cx. annulus (Theobald) (Diptera: Culicidae), 374 Aedes albopictus (Skuse) (Diptera: Culicidae) and 102 Armigeres subalbatus (Coquillet) (Diptera: Culicidae) were collected and examined for Dirofilaria immitis (Leidy) (Spirurida: Filariidae) infection. However, only Cx. quinquefasciatus and Ae. albopictus were infected, with a prevalence of 4.28% and 3.74%, respectively. The intensity of D. immitis found in Ae. albopictus (3.43 larvae/mosquito) was higher than that found in Cx. quinquefasciatus (2.89 larvae/mosquito). After being fed with canine blood containing 7500 microfilariae (mf) per mL, Cx. quinquefasciatus ingested approximately two times as many mf as Ae. albopictus (mean of 31.73 in comparison to 16.47). However, almost three times as many third-stage infective larvae developed in Ae. albopictus as in Cx. quinquefasciatus (mean of 3.25 as compared with 1.10), with a vector efficiency index (VEI) of 19.73 and 3.47, respectively. The results showed that Cx. quinquefasciatus and Ae. albopictus served as natural vectors of D. immitis in central Taiwan. Although Ae. albopictus was more efficient for heartworm transmission, Cx. quinquefasciatus may play a more prominent role on the transmission of dirofilariasis in central Taiwan.     

Critical review of the vector status of Aedes albopictus

The mosquito Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae), originally indigenous to South-east Asia, islands of the Western Pacific and Indian Ocean, has spread during recent decades to Africa, the mid-east, Europe and the Americas (north and south) after extending its range eastwards across Pacific islands during the early 20th century. The majority of introductions are apparently due to transportation of dormant eggs in tyres. Among public health authorities in the newly infested countries and those threatened with the introduction, there has been much concern that Ae. albopictus would lead to serious outbreaks of arbovirus diseases (Ae. albopictus is a competent vector for at least 22 arboviruses), notably dengue (all four serotypes) more commonly transmitted by Aedes (Stegomyia) aegypti (L.). Results of many laboratory studies have shown that many arboviruses are readily transmitted by Ae. albopictus to laboratory animals and birds, and have frequently been isolated from wild-caught mosquitoes of this species, particularly in the Americas. As Ae. albopictus continues to spread, displacing Ae. aegypti in some areas, and is anthropophilic throughout its range, it is important to review the literature and attempt to predict whether the medical risks are as great as have been expressed in scientific journals and the popular press. Examination of the extensive literature indicates that Ae. albopictus probably serves as a maintenance vector of dengue in rural areas of dengue-endemic countries of South-east Asia and Pacific islands. Also Ae. albopictus transmits dog heartworm Dirofilaria immitis (Leidy) (Spirurida: Onchocercidae) in South-east Asia, south-eastern U.S.A. and both D. immitis and Dirofilaria repens (Raillet & Henry) in Italy. Despite the frequent isolation of dengue viruses from wild-caught mosquitoes, there is no evidence that Ae. albopictus is an important urban vector of dengue, except in a limited number of countries where Ae. aegypti is absent, i.e. parts of China, the Seychelles, historically in Japan and most recently in Hawaii. Further research is needed on the dynamics of the interaction between Ae. albopictus and other Stegomyia species. Surveillance must also be maintained on the vectorial role of Ae. albopictus in countries endemic for dengue and other arboviruses (e.g. Chikungunya, EEE, Ross River, WNV, LaCrosse and other California group viruses), for which it would be competent and ecologically suited to serve as a bridge vector.     

Natural infection of Aedes trivittatus (COQ) with Dirofilaria immitis in central Iowa.

Juveniles identified as Dirofilaria immitis were recovered from Aedes trivittatus and Anopheles punctipennis collected CO2-baited CDC light traps in Ames, Iowa, during 10 days in July and August 1975. Ae. trivittatus composed 58.7% of the mosquitoes collected, and D. immitis was recovered from 18 of 393 (4.6%) dissected and from 7 of 31 pools (911 mosquitoes; 0.77%). Approximately 1.0% of the Ae. trivittatus collected harbored infective-stage juveniles, and as many as 27 were recovered from a single mosquito. This is the first report of Ae. trivittatus supporting the development of D. immitis. An. punctipennis was the only other species infected, with 2 of 468 harboring first-stage juveniles. The data suggest that Ae. trivittatus probably is the principal vector of D. immitis in central Iowa.     

Are Aedes albopictus or other mosquito species from northern Italy competent to sustain new arboviral outbreaks?

The Asian tiger mosquito Aedes albopictus (Skuse) (Diptera: Culicidae), native to Southeast Asia, has extended its geographical distribution to invade new temperate and tropical regions. This species was introduced in 1990 to Italy and has since become the main pest in urban settings. It was incriminated as a principal vector in the first European outbreak of chikungunya virus (CHIKV) in the province of Ravenna (Italy) in 2007. This outbreak was associated with CHIKV E1-226V, efficiently transmitted by Ae. albopictus . The occurrence of this outbreak in a temperate country led us to estimate the potential of Ae. albopictus to transmit CHIKV and dengue virus (DENV), and to determine the susceptibility to CHIKV of other mosquito species collected in northern Italy. Experimental infections showed that Ae. albopictus exhibited high disseminated infection rates for CHIKV (75.0% in Alessandria; 90.3% in San Lazzaro) and low disseminated infection rates for DENV-2 (14.3% in San Lazzaro; 38.5% in Alessandria). Moreover, Ae. albopictus was able to attain a high level of viral replication, with CHIKV detectable in the salivary glands at day 2 after infection. In addition, the other three mosquito species, Anopheles maculipennis Meigen, Aedes vexans vexans (Meigen) and Culex pipiens L., showed variable susceptibilities to infection with CHIKV, of 0%, 7.7% and 0–33%, respectively. This information on vector competence is crucial in assessing the risk for an outbreak of CHIKV or DENV in Italy.     

Growth characteristics of the veterinary vaccine candidate ChimeriVax-West Nile (WN) virus in Aedes and Culex mosquitoes

In 1999 West Nile (WN) virus was introduced to North America where this flavivirus has spread rapidly among wildlife (especially birds) transmitted by various species of mosquitoes (Diptera: Culicidae). Increasing numbers of cases and deaths among humans, horses and other domestic animals require development of effective vaccines. 'ChimeriVax-West Nile(vet)' is being developed for use as a veterinary vaccine to protect against WN infection. This chimeric virus contains the pre-membrane (prM) and envelope (E) genes from the wild-type WN NY99 virus (isolated from a flamingo in New York zoo during the 1999 WN epidemic) in the backbone of yellow fever (YF) 17D vaccine virus. Replication kinetics of ChimeriVax-WN(vet) virus were evaluated in mosquito cell culture (Aedes albopictus C6/36), in WN vector mosquitoes [Culex tritaeniorhynchus Giles, Cx. nigripalpus Theobald and Cx. quinquefasciatus Say (Diptera: Culicidae)] and in YF vectors [Aedes aegypti (L) and Ae. albopictus (Skuse)], to determine whether these mosquitoes become infected through feeding on a viraemic vaccine, and their potential infectivity to transmit the virus. Growth of ChimeriVax-WN(vet) virus was found to be restricted in mosquitoes, compared to WN virus in Ae. albopictus C6/36 cells. When inoculated intrathoracically, ChimeriVax-WN(vet) and YF 17D viruses did not replicate in Cx. tritaeniorhynchus or Cx. nigripalpus; replication was very restricted compared to the wild-type WN virus in Cx. quinquefasciatus, Ae. aegypti and Ae. albopictus. When fed on hanging drops with ChimeriVax-WN(vet) virus (7.7 log10 PFU/mL), none of the Culex mosquitoes became infected; one Ae. albopictus and 10% of the Ae. aegypti became infected, but the titre was very low and virus did not disseminate to head tissue. ChimeriVax-WN(vet) virus had a replication profile similar to that of the attenuated vaccine virus YF 17D, which is not transmitted by mosquitoes. These results suggest that the natural mosquito vectors of WN and YF viruses, which may incidentally take a bloodmeal from a vaccinated host, will not become infected with ChimeriVax-WN(vet) virus.     

First report of the oriental mosquito Aedes albopictus on the West African island of Bioko,Equatorial Guinea

The invasive oriental mosquito Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) was detected on Bioko Island for the first time in November 2001. It was found to be well established breeding in artificial containers at Planta, near Malabo, the capital of Equatorial Guinea. Associated species of mosquito larvae were Aedes aegypti (L.), Ae. africanus (Theobald), Culex near decens Theobald, Cx. duttoni Theobald, Cx. quinquefasciatus Say, Cx. tigripes De Grandpré & De Charmoy, Eretmapodites quinquevittatus Theobald and Mansonia africana (Theobald). This is the third tropical African country to be invaded by Ae. albopictus, which has recently spread to many parts of the Americas and Europe--with vector competence for dengue, yellow fever and other arboviruses. In the Afrotropical environment, it will be interesting to monitor the ecological balance and/or displacement between introduced Ae. albopictus and indigenous Ae. aegpyti (domestic, peri-domestic and sylvatic populations).     

Four species of mosquito as possible vectors for Dirofilaria immitis piedmont rice-fields

Wild mosquitoes were allowed to feed, during two nights, on a heartworm-infected dog with a very high microfilaraemia (72,000 and 78,000 microfilariae/ml just prior to be allocated in the live trap). A heartworm-free dog was used as control bait in the second night. Engorged mosquitoes (Aedes caspius, Anopheles maculipennis s.l., Culex modestus, and Cx pipiens) were kept under laboratory conditions, artificially fed until day 10 post-infection (PI) and then dissected for the presence of Dirofilaria immitis larvae. Mortality of Ae. caspius and Cx modestus was significantly higher than controls on day 3 PI (89.4 and 80.3%, respectively), but survival rates were similar in the following period. Third-stage larvae were observed from day 12 to 17 PI in the four mosquito species studied. However, vector efficiency was significantly higher in Ae. caspius which produced 102 (73.9%) of the 138 infective larvae found. Although less efficient vectors, the other 3 species may contribute to D. immitis transmission in the study area due to their abundance (Cx modestus) or higher resistance to the negative effects of infection (An. maculipennis s.l., Cx pipiens). As far as Cx pipiens is concerned, this mosquito, which luckily fed the least frequently on the dog, confirmed to act as powerful vector in iperendemic areas. The risks for veterinary and medical health, related to the zoo-antropophylic host-feeding pattern of the studied species, are discussed.     

Development of a novel sticky trap for container-breeding mosquitoes and evaluation of its sampling properties to monitor urban populations of Aedes albopictus

Collection methods currently used for large-scale sampling of adult Stegomyia mosquitoes (Diptera: Culicidae) present several operational limitations, which constitute major drawbacks to the epidemiological surveillance of arboviruses, the evaluation of the impact of control strategies, and the surveillance of the spreading of allochthonous species into non-endemic regions. Here, we describe a new sticky trap designed to capture adult container-breeding mosquitoes and to monitor their population dynamics. We tested the sampling properties of the sticky trap in Rome, Italy, where Aedes (Stegomyia) albopictus is common. The results of our observations, and the comparison between sticky trap catches and catches made with the standard oviposition trap, are presented. The sticky trap collected significantly larger numbers of Ae. albopictus females than any other Culicidae species representing >90% of the total catches. A maximum of 83 An. albopictus females was collected in a single week. A high correlation (Pearson correlation coefficient r= 0.96) was found between the number of females and the number of eggs collected by the traps. The functional relationship between the number of eggs and the number of adult females was assessed by major axis regression fitted to log(1 +x)-transformed trap counts as y= 0.065 + 1.695x. Trap samples significantly departed from a random distribution; Taylor's power law was fitted to the trap samples to quantify the degree of aggregation in the catches, returning the equations s(2)= 2.401 m(1.325) for the sticky trap and s(2)= 13.068 m(1.441) for the ovitrap, with s(2) and m denoting the weekly catch variance and mean, respectively, indicating that eggs were significantly more aggregated than mosquitoes (P < 0.0001). Taylor's power law parameters were used to estimate the minimum number of sample units necessary to obtain sample estimates with a fixed degree of precision and sensitivity. For the range of densities encountered in our study area during the Ae. albopictus breeding season, the sticky trap was more precise and sensitive than the ovitrap. At low population densities (c. < 0.1 mosquito/trap), however, the ovitrap was more sensitive at detecting the presence of this species. Overall, our results indicate that our new model of sticky trap can be used to sample Ae. albopictus females in urban environments, and, possibly, other container-breeding Stegomyia mosquitoes (e.g. Aedes aegypti). The technical properties of the new trap are discussed with respect to its possible application in monitoring the population dynamics of container-breeding mosquitoes, in studying their bionomics, and in vector surveillance and, possibly, control.     

Accidental importation of the mosquito Aedes albopictus into the Netherlands: a survey of mosquito distribution and the presence of dengue virus

Abstract.  In the summer of 2005, the Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae) was found for the first time in the Netherlands. It was collected on the premises of several horticultural companies that import the ornamental plant Dracaena sanderiana (Sparagalus: Dracaenaceae [Agavaceae]), known as Lucky bamboo, from southern China, an area endemic for this mosquito species and for arboviruses transmitted by this vector. Here we report the results of a 1-year survey of the distribution and vector status of Ae. albopictus in Lucky bamboo nurseries in the Netherlands (July 2006–June 2007). As it had been established previously that the presence of this species was linked to the import of Lucky bamboo, the survey was conducted only on sites owned by relevant import companies. In total, 569 adult Ae. albopictus were collected with mosquito traps from 15 of the 17 (88%) glasshouses used by Lucky bamboo importers, none of which were found to be infected with dengue virus. On two occasions there was evidence that Ae. albopictus had escaped from the glasshouses, but, overall, there was no evidence that a population had become established in the greenhouses or elsewhere.     

Presence of Dirofilaria repens and an insect immunocyte (plasmatocyte) in a human subcutaneous nodule, induced by a mosquito bite.

It is well known that the nematode Dirofilaria repens is transmitted to humans by vector mosquito bite. Examination of a fine needle aspiration biopsy drawn from a month-old nodule on the chest of a woman, residing in Garlasco, province of Pavia, Northern Italy, revealed the presence of not only one immature female of D. repens, but also some scattered cells that we believe to be mosquito's blood cells, plasmatocytes (immunocytes). We presume that plasmatocytes were carried into the bite wound with the mosquito's hemolymph that had oozed from a rupture in its mouthparts during feeding. Because Aedes albopictus recently colonized certain areas in the above region, we suspect that the nodule resulted from the bite of this mosquito.     

Analysis of the potential for survival and seasonal activity of Aedes albopictus (Diptera: Culicidae) in the United Kingdom.

The international trade in used tires, coupled with the ability to lay non-desiccating eggs, has enabled Aedes albopictus (Skuse) (Diptera: Culicidae) to travel and establish on new continents, including North, Central, and South America, the Caribbean, Australasia, Africa, and Europe. Concerns have been raised over its potential role in the transmission of arboviruses and Dirofilaria nematodes. Following importation into northerly latitudes, photoperiodically-induced egg diapause enables establishment of Ae. albopictus, and a number of abiotic factors determine the subsequent seasonal activity. The United Kingdom (U.K.) imports over 5 million used tires annually, and this seems the most likely route by which Ae. albopictus would be imported. The anthropophilic and container-breeding nature of Ae. albopictus could cause an urban human biting nuisance and the potential for involvement in (human and veterinary) disease transmission cycles needs to be assessed. This paper addresses the likelihood for importation of Ae. albopictus into the U.K. and assesses, using a Geographic Information Systems (GIS)-based model, the ability for Ae. albopictus to establish, and the likely seasonal activity. It also reviews its possible role as a potential disease vector in the U.K. The model predicts that abiotic risk factors would permit establishment of Ae. albopictus throughout large parts of lowland U.K., with at least four to five months of adult activity (May-September), being more prolonged in the urban centers around London and the southern coastal ports. Pre-emptive surveillance of possible imported Ae. albopictus, through a targeted approach, could prevent the establishment of this exotic mosquito and mitigate any subsequent human and animal health implications for the U.K., either now or in the future.     

Potential vectors of West Nile virus following an equine disease outbreak in Italy

In the late summer of 1998, an outbreak of equine encephalomyelitis due to West Nile virus (WNV) occurred in the Tuscany region of central Italy. The disease was detected in 14 race horses from nine localities in four Provinces: Firenze, Lucca, Pisa and Pistoia. The outbreak area included Fucecchio wetlands (1800 ha), the largest inland marsh in Italy, and the adjacent hilly Cerbaie woodlands with farms breeding horses. To detect potential vectors of WNV, entomological surveys of Fucecchio and Cerbaie were undertaken during 1999-2002 by collecting mosquito larvae from breeding sites and adult mosquitoes by several methods of sampling. Among 6023 mosquitoes (Diptera: Culicidae) collected, 11 species were identified: Aedes albopictus (Skuse), Ae. vexans (Meigen), Anopheles atroparvus Van Thiel, An. maculipennis Meigen s.s., An. plumbeus Stephens, Culex impudicus Ficalbi, Cx. pipiens L., Culiseta longiareolata Macquart), Ochlerotatus caspius (Pallas), Oc. detritus (Haliday) and Oc. geniculatus (Olivier). In Fucecchio marshes, Cx. impudicus predominated with seasonal peak densities in spring and autumn: its greatest abundance during early spring coincides with arrival of migratory birds from Africa. In Cerbaie hills, Cx. pipiens predominated with peak population density in late summer. No viruses were isolated from 665 mosquitoes processed. These findings, plus other data on Italian mosquito bionomics, suggest a possible mode of WNV transmission involving the most abundant Culex in the Fucecchio-Cerbaie areas. Culex impudicus, being partly ornithophilic, might transmit WNV from migratory to non-migratory birds during springtime; Cx. pipiens, having a broader host range, would be more likely to transmit WNV from birds to horses and, perhaps, to humans by late summer.     

Distribution and seasonality of Culex (Melanoconion) caudelli, a vector of arboviruses in Trinidad

Seasonal and spatial distributions of the arbovirus vector mosquito Culex (Melanoconion) caudelli Dyar and Knab (Diptera: Culicidae) in the Aripo-Wallerfield forest, Trinidad, were studied by collecting mosquitoes attracted to mouse-baited traps in forest, ecotone and savannah, one day per week throughout the year, 98% of the Cx caudelli mosquitoes were collected during the wet season, with a significant positive correlation between rainfall and mosquito catch. The reverse occurred during the dry season. Cx caudelli displayed a preference for the ecotone where 67% were collected, while 32% and 1% were collected in the forest and savannah respectively.     

Population Genetics of Aedes albopictus (Diptera: Culicidae) Invading Populations, Using Mitochondrial nicotinamide Adenine Dinucleotide Dehydrogenase Subunit 5 Sequences

Aedes albopictus (Skuse) (Diptera: Culicidae), the Asian tiger mosquito indigenous to Asia, now an invasive species worldwide, is an important vector for several arboviruses. Genetic analysis using the mitochondrial nicotinamide adenine dinucleotide dehydrogenase subunit 5 (ND5) gene was carried out in populations from Cameroon (n = 50), Hawaii (n = 38), Italy (n = 20), the continental United States, Brazil, and its native range. Data for Brazil, the continental United States, and the native range was obtained from Birungi and Munstermann (2002). Direct sequencing was used to identity unique haplotypes. The limited phylogeographic partitioning of haplotypes with low levels of sequence divergence in both Cameroon and Hawaii was consistent with the population structure of Ae. albopictus in the United States and Brazil. Four new haplotypes were identified from the samples from Cameroon and Hawaii, adding to previously described haplotypes. Hawaii shared a haplotype with Cameroon that was unique to these two regions. Hawaii also had higher overall haplotype diversity than seen in previous continental United States, Brazil, or native range populations. Hawaiian, Cameroon, and Italian populations did not share haplotypes with Brazil, which validates the earlier mitochondrial DNA studies indicating a separate introduction of this species into Brazil.     

Evaluation of vector competence for West Nile virus in Italian Stegomyia albopicta (=Aedes albopictus) mosquitoes

West Nile virus (WNV) is a zoonotic arboviral pathogen transmitted by mosquitoes in a cycle that involves wild birds as reservoir hosts. The virus is responsible for outbreaks of viral encephalitis in humans and horses. In Europe, Culex pipiens (Diptera: Culicidae) is considered to be the main vector of WNV, but other species such as Stegomyia albopicta (=Aedes albopictus) (Diptera: Culicidae) may also act as competent vectors of this virus. Since 2008 human cases of WNV disease have been reported in northeast Italy. In 2011, new areas of southern Italy became involved and a first outbreak of WNV lineage 1 occurred on the island of Sardinia. On the assumption that a potential involvement of St. albopicta in WNV transmission cannot be excluded, and in order to evaluate the competence of this species for the virus, an experimental infection of an St. albopicta laboratory colony, established from mosquitoes collected in Sardinia, was carried out. The results were compared with those obtained in a colony of the main vector Cx. pipiens. The study showed St. albopicta collected on Sardinia to be susceptible to WNV infection, which suggests this Italian mosquito species is able to act as a possible secondary vector, particularly in urban areas where the species reaches high levels of seasonal abundance.     

Organization of a cloned repetitive DNA fragment in mosquito genomes (Diptera: Culicidae).

The structure and genomic organization of a cloned 5.2-kb repetitive DNA fragment, H-85, isolated from the Aedes albopictus genome have been examined. In situ hybridization of the 3H-labeled H-85 DNA to the meiotic and mitotic chromosome preparations of Ae. albopictus shows that the sequences homologous to H-85 DNA are dispersed throughout the length of all three pairs of chromosomes. A similar pattern of in situ hybridization appears in Aedes seatoi, Aedes flavopictus, and Aedes aegypti. The study shows that the arrangement of sequences in the cloned 5.2-kb fragment is rare in the Ae. albopictus genome. Dot-blot hybridization reveals that the sequences homologous to H-85 DNA are present in 12 species of mosquitoes examined, belonging to six genera in subfamilies Culicinae ad Anophelinae. The H-85 sequences are also present in the genome of Mochlonyx velutinus of the nematocerous family Chaoboridae, earlier proposed as the ancestor of the mosquito family Culicidae. Although the sequences homologous to H-85 DNA are present in different species of mosquitoes, they have diverged in their structure and organization. The cloned 5.2-kb fragment is composed of elements of different and independently evolving repetitive DNA families.     

Filarial susceptibility and effects of Wolbachia in Aedes pseudoscutellaris mosquitoes

The mosquito Aedes pseudoscutellaris (Theobald), a member of the Aedes (Stegomyia) scutellaris complex (Diptera: Culicidae), is an important vector of subperiodic Wuchereria bancrofti (Cobbold) (Spirurida: Onchocercidae), causing human lymphatic filariasis, on South Pacific islands. Maternal inheritance of filarial susceptibility in the complex has previously been asserted, and larval tetracycline treatment reduced susceptibility; the maternally inherited Wolbachia in these mosquitoes were suggested to be responsible. To investigate the relationship of these two factors, we eliminated Wolbachia from a strain of Ae. pseudoscutellaris by tetracycline treatment, and tested filarial susceptibility of the adult female mosquitoes using Brugia pahangi (Edeson & Buckley). Filarial susceptibility was not significantly different in Wolbachia-free and infected lines of Ae. pseudoscutellaris, suggesting that the Wolbachia in these mosquitoes do not influence vector competence. Crosses between Wolbachia-infected males and uninfected females of Ae. pseudoscutellaris showed cytoplasmic incompatibility (CI), i.e. no eggs hatched, unaffected by larval crowding or restricted nutrient availability, whereas these factors are known to affect CI in Drosophila simulans. Reciprocal crosses between Ae. pseudoscutellaris and Ae. katherinensis Woodhill produced no progeny, even when both parents were Wolbachia-free, suggesting that nuclear factors are responsible for this interspecific sterility.     

Seasonal prevalence of third-stage larvae of Dirofilaria immitis in mosquitoes from Florida and Louisiana

Heads of 109,597 mosquitoes collected during 1996 and 1997 from Gainesville, Florida (1996, n = 39,131; 1997, = 34,209), Bartow, Florida (1996, n = 12,000; 1997, n = 12,000), and Baton Rouge, Louisiana (1996, n = 12,257) were tested by a polymerase chain reaction and Southern hybridization-based test for the presence of third-stage larvae of the canine heartworm Dirofilaria immitis. Mosquito heads were pooled (1-200 heads) by month, locality, and species for testing. The test used was species specific for D. immitis and was capable of detecting DNA from a single larva in a pool of 200 mosquito heads. Specificity for the third larval stage was achieved by probing only mosquito heads. One or more D. immitis-infected mosquito heads were detected in each month of the year from Barrow in both 1996 and 1997. No infected mosquito heads were detected from Gainesville or Baton Rouge in December, January, February, or March. These results are in general agreement with previous sentinel dog and model prediction studies that showed heartworm transmission in the warm temperate Gulf coast region of the United States to be seasonal rather than continuous as previously believed.     

Nine more cases of human infections by Dirofilaria repens diagnosed in Italy by morphology and recombinant DNA technology

Dirofilariosis is a mosquito-borne disease of carnivors due, in Italy, to Dirofilaria repens and D. immitis species which are sympatric in many areas. Nine more cases of human infection are here reported, detected in Italian patients living in northern regions (where D. immitis and D. repens are largely present), in Tuscany (where D. repens is more frequent than D. immitis), and in Sicily (where D. immitis is present only sporadically). The nematodes surgically removed (7 female and 2 male specimens) have been identified by a PCR-based method and by morphology as D. repens. Morphological, clinical, and epidemiological data of these human infections are discussed.