Parasites & Vectors - Latest Articles

Low-temperature threshold for egg survival of a post-diapause and non-diapause European aedine strain, Aedes albopictus (Diptera: Culicidae)

Stephanie Thomas — 2012-05-23T00:00:00Z

Background: The interplay between global warming and invasive arthropods in temperate zones is of utmost interest in terms of the potential expansions of vector-borne diseases. Up to now, investigations on the recent establishment of mosquito vectors have focused on temperatures during their phases of activity. However, cold temperatures may also act as a strong ecological constraint. Projected changes in winter climate indicate an increase of mean minimum temperatures of the coldest quarter, less frequent days with frost and a shorter frost-season in Europe at the end of the century. Nevertheless, single cold extremes are also expected to persist under warming scenarios, which have a strong impact on reproduction success. Methods: Here, the temperature constraints of European Aedes lbopictus eggs, which had passed through a diapause, compared to non-diapausing eggs were examined systematically under controlled laboratory conditions. One tropical strain of each species (Ae. albopictus and Ae. aegypti) was used in the comparison. Results: The lower temperature threshold tolerated by the European eggs of Ae. albopictus which have undergone a diapause, was -10degreesC for long term exposures (12 and 24h) and -12degreesC for 1h exposure. Non-diapausing eggs of European Ae. albopictus were found to hatch after a -7degreesC cold treatment (8, 12 and 24h exposure). Both tropical aedine species only tolerated the long term treatment at -2degreesC. Neither Ae. albopictus nor Ae. aegypti eggs hatched after being exposed to -15degreesC. Survival was mainly influenced by temperature (F = 329.2, df = 1, p < 0.001), whereas the duration of the cold treatment only significantly influenced the hatching response at the thermal limits of survival (F = 5.6, df = 1, p = 0.031) but not at 0degreesC (F = 0.1, df = 1, p = 0.730). Hatching success after the cold treatment was significantly increased in European eggs, which have undergone a diapause compared to non-diapausing eggs (F = 14.7, df = 3, p < 0.001). Conclusions: Here, low temperature thresholds for aedine mosquito egg survival were detected. The compilation of risk maps for temperate regions can substantially be improved by considering areas where an establishment of a vector population is unlikely due to winter conditions.

Evidence of mosquito-transmitted flavivirus circulation in piedmont, north-western Italy

Francesco Cerutti — 2012-05-22T00:00:00Z

Background: Flavivirus is a highly heterogeneous viral genus that includes important human pathogensand several viral strains with unknown zoonotic potential. Mosquito-borne flaviviruses havebeen isolated and characterized in Northern Italy: West Nile virus and Usutu virus weredetected in mosquitoes and in different host species and recent studies provided evidenceabout the circulation of "insect Flavivirus" strains. Methods: In order to clarify the diffusion and the distribution of the mosquito-transmitted flavivirusesin Italy, we analyzed Culex and Ochlerotatus mosquitoes collected in 2009 and 2010 in anarea divided evenly between hills and plains and where the landscape is dominated by mixedagricultural patches, rice fields, deciduous tree forests, and urban environments. Eachmosquito pool was tested for the presence of Flavivirus strains and we characterized positivesamples by genetic sequencing. Results: Positive mosquito pools revealed low infection prevalence, but suggested a continuouscirculation of both Usutu virus and insect Flavivirus. Interestingly, phylogenetic analysesbased on NS5 gene partial sequences showed a closer relationship among new Usutu virusstrains from Piedmont and the reference sequences from the Eastern Europe, with respect toItalian samples characterized so far. Moreover, NS5 gene phylogeny suggested that mosquitoflaviviruses found in Italy could belong to different lineages. Conclusions: Our results contribute to a wider point of view on the heterogeneity of viruses infectingmosquitoes suggesting a taxonomical revision of the Mosquito-borne Flavivirus group.

Detection of Leishmania infantum DNA mainly in Rhipicephalus sanguineus male ticks removed from dogs living in endemic areas of canine leishmaniosis

Laia Solano-Gallego — 2012-05-21T00:00:00Z

Background: Sand flies are the only biologically adapted vectors of Leishmania parasites, however, apossible role in the transmission of Leishmania has been proposed for other hematophagousectoparasites such as ticks. In order to evaluate natural infection by Leishmania infantum inRhipicephalus sanguineus ticks, taking into account its close association with dogs, 128 adultR. sanguineus ticks removed from 41 dogs living in endemic areas of canine leishmaniosiswere studied. Methods: Individual DNA extraction was performed from each tick and whole blood taken from dogs.Dog sera were tested for IgG antibodies to L. infantum antigen by ELISA and L. infantumreal-time PCR was performed from canine whole blood samples and ticks. Results: Leishmania infantum PCR was positive in 13 ticks (10.1%) including one female, (2.0%) and12 males (15.2%), and in only five dogs (12.2%). Male ticks had a significantly higherinfection rate when compared to female R. sanguineus. The percentage of L. infantumseroreactive dogs was 19.5%. All but two PCR positive dogs were seroreactive. Leishmaniainfantum PCR positive ticks were removed from seropositive and seronegative dogs with avariety of PCR results. Conclusions: This study demonstrates high prevalence of L. infantum DNA in R. sanguineus ticks removedfrom L. infantum seropositive and seronegative dogs. The presence of L. infantum DNA wasdetected mainly in male ticks possibly due to their ability to move between canine hosts andfeed on several canine hosts during the adult life stage. Additional studies are needed tofurther explore the role of R. sanguineus ticks and in particular, male adults, in both theepidemiology and immunology of L. infantum infection in dogs in endemic areas.

Population genetic structure of Ascaridia galli re-emerging in non-caged laying hens

Johan Höglund — 2012-05-20T00:00:00Z

Background: The poultry roundworm Ascaridia galli has reappeared in hens kept for egg production inSweden after having been almost absent a decade ago. Today this is a frequent intestinalnematode parasite in non-caged laying hens. The aim of this study was to investigate thegenetic diversity (Fst) in A. galli collected from different poultry production sites in southernSweden, to identify possible common routes of colonization. Methods: Adult parasites (n = 153) from 10 farms, including both broiler breeder parents and layinghens, were investigated by amplified restriction fragment length polymorphism analysis(AFLP). Worms from a Danish laying hen farm were also included for comparison. Most ofthe farms were represented by worms from a single host, but on two farms multiple samplesfrom different hosts were assessed in order to study flock variation. Results: A total of 97 fragments (loci) were amplified among which 81% were variable alleles. Theaverage genetic diversity was 0.13 (range = 0.09-0.38), which is comparable to other AFLPstudies on nematodes of human and veterinary importance. Within-farm variation showedthat worms harboured by a single hen in a flock covered most of the A. galli genetic variationwithin the same flock (Fst = 0.01 and 0.03 for two farms). Between-farm analysis showed amoderate population genetic structure (Fst = 0.13), along with a low mutational rate but highgene flow between different farms, and absence of strong genetic selection. Network analysisshowed repeated genetic patterns among the farms, with most worms on each farm clusteringtogether as supported by high re-allocation rates. Conclusions: The investigated A. galli populations were not strongly differentiated, indicating that theyhave undergone a genetic bottlenecking and subsequent drift. This supports the view that theinvestigated farms have been recently colonized, and that new flocks are reinfected uponarrival with a stationary infection.

Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and manmade aquatic habitats

Louis Gouagna — 2012-05-19T00:00:00Z

Background: Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present atlow altitudes in remote areas in Reunion Island. Little attention has been paid to theenvironmental conditions driving larval development and abundance patterns in potentialhabitats. Two field surveys were designed to determine whether factors that discriminatebetween aquatic habitats with and without An. arabiensis larvae also drive larval abundance,comparatively in man-made and naturally occurring habitats. Methods: In an initial preliminary survey, a representative sample of aquatic habitats that would beamenable to an intensive long-term study were selected and divided into positive andnegative sites based on the presence or absence of Anopheles arabiensis larvae.Subsequently, a second survey was prompted to gain a better understanding of biotic andabiotic drivers of larval abundance, comparatively in man-made and naturally occurringhabitats in the two studied locations. In both surveys, weekly sampling was performed torecord mosquito species composition and larval density within individual habitats, as well asin situ biological characteristics and physico-chemical properties. Results: Whilst virtually any stagnant water body could be a potential breeding ground for An.arabiensis, habitats occupied by their immatures had different structural and biologicalcharacteristics when compared to those where larvae were absent. Larval occurrence seemedto be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly,the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI[0.3-0.7]) was significantly lower than that recorded in naturally occurring ones (0.74,95%CI [0.5-0.8]). Such differences may be accounted for in part by varying pressures thatcould be linked to a specific habitat. Conclusions: If the larval ecology of An. arabiensis is in general very complex and factors affectingbreeding site productivity sometimes not easy to highlight, our results, however, highlightlower populations of An. arabiensis immatures compared to those reported in comparablestudies conducted in the African continent. Overall, this low larval abundance, resulting fromboth abiotic and biotic factors, suggests that vector control measures targeting larval habitatsare likely to be successful in Reunion, but these could be better implemented by takingenvironmental variability into account.

Spinosad: a biorational mosquito larvicide for use in car tires in southern Mexico

Carlos Marina — 2012-05-19T00:00:00Z

Background: Car tires are important habitats for mosquito development because of the high densitypopulations they can harbor and their presence in urban settings. Water in experimental tireswas treated with one of three insecticides or an untreated control. Aquatic invertebrates weresampled at weekly intervals. Eggs, larval and pupal samples were laboratory-reared toestimate seasonal fluctuations in Aedes aegypti and Ae. albopictus abundance. Results: Spinosad treatments at 1 or 5 ppm (mg a.i./liter) provided 6-8 weeks of effective control ofAe. aegypti, Ae. albopictus, Culex quinquefasiatus and Cx. coronator larvae, both in the dryseason and the rainy season when mosquito populations increased markedly in southernMexico. Spinosad continued to provide partial control of larvae for several weeks after initialrecolonization of treated tires. The larvicidal performance of VectoBac 12AS (Bacillusthuringiensis var. israelensis) was relatively poor with one week of complete control ofAedes spp. larvae and no discernible control of Culex spp., whereas the duration of larvicidalactivity of 1% temephos mineral-based granules was intermediate between those of VectoBacand spinosad treatments. Populations of chironomids, ostracods and Toxorhynchites theobaldiwere generally reduced in spinosad and temephos treatments, but were similar in control andVectoBac treatments. Conclusion: The present study is the first to report spinosad as an effective larvicide against Cx.coronator, which is currently invading the southern United States. These results substantiatethe use of spinosad as a highly effective mosquito larvicide, even in habitats such as unusedcar tires that can represent prolific sources of adult mosquitoes.

Trapping of Rift Valley Fever (RVF) vectors using Light Emitting Diode (LED) CDC traps in two arboviral disease hot spots in Kenya

David Tchouassi — 2012-05-19T00:00:00Z

Background: Mosquitoes' response to artificial lights including color has been exploited in trap designs forimproved sampling of mosquito vectors. Earlier studies suggest that mosquitoes are attractedto specific wavelengths of light and thus the need to refine techniques to increase mosquitocaptures following the development of super-bright light-emitting diodes (LEDs) which emitnarrow wavelengths of light or very specific colors. Therefore, we investigated if LEDs canbe effective substitutes for incandescent lamps used in CDC light traps for mosquitosurveillance, and if so, determine the best color for attraction of important Rift Valley Fever(RFV) vectors. Methods: The efficiency of selected colored LED CDC light traps (red, green, blue, violet, combinationof blue-green-red (BGR)) to sample RVF vectors was evaluated relative to incandescent light(as control) in a CDC light trap in two RVF hotspots (Marigat and Ijara districts) in Kenya. Infield experiments, traps were baited with dry ice and captures evaluated for Aedes tricholabis,Ae. mcintoshi, Ae. ochraceus, Mansonia uniformis, Mn. africana and Culex pipiens,following Latin square design with days as replicates. Daily mosquito counts per treatmentwere analyzed using a generalized linear model with Negative Binomial error structure andlog link using R. The incidence rate ratios (IRR) that mosquito species chose other treatmentsinstead of the control, were estimated. Results: Seasonal preference of Ae.mcintoshi and Ae. ochraceus at Ijara was evident with a biastowards BGR and blue traps respectively in one trapping period but this pattern waned duringanother period at same site with significantly low numbers recorded in all colored trapsexcept blue relative to the control. Overall results showed that higher captures of all specieswere recorded in control traps compared to the other LED traps (IRR < 1) although onlysignificantly different from red and violet. Conclusion: Based on our trapping design and color, none of the LEDs outcompeted the standardincandescent light. The data however provides preliminary evidence that a preference mightexist for some of these mosquito species based on observed differential attraction to theselight colors requiring future studies to compare reflected versus transmitted light and theincorporation of colored light of varying intensities.

Review of 'External parasites of small ruminants. A practical guide to their prevention and contro' by Peter Bates

Olivier Sparagano — 2012-05-19T00:00:00Z

It is always risky to write a book trying to review such a broad topic on ectoparasites bringingnecessarily an update and some new information. Considering the number of internationalexperts who apparently helped to share their knowledge I was hoping to read about the latesttrials and epidemiological results.

Elevation of dopamine level reduces host-seeking activity in the adult female mosquito Aedes albopictus

Yuki Fukumitsu — 2012-05-10T00:00:00Z

Background: Mosquito-borne viruses are transmitted to human hosts via blood-feeding behavior of female mosquitoes. Female mosquitoes seek a host to take blood meals (host-seeking behavior). In order to prevent virus infections, it is important to understand how they modulate host-seeking behavior. Dopamine (DA) in the central nervous system acts as a neuromediator that regulates a variety of behaviors in insects. In female mosquitoes, host-seeking behavior increases when DA levels in the head decline after emergence. However, it remains unclear whether DA directly modulates host-seeking behavior in female mosquitoes. The aim of this study was to examine whether changes in DA levels in the head affects host-seeking activity in the adult female mosquito Aedes albopictus (Ae. albopictus).FindingsWe compared host-seeking behavior in one group of emerging female adults treated with L-beta-3,4-dihydroxyphenylalanine (L-DOPA), the precursor of DA, (L-DOPA group), with that in an untreated control (control group) after confirming elevation of head DA in L-DOPA group by using high-performance liquid chromatography. The content of head DA in L-DOPA group significantly remained higher than that in controls on all days examined. The host-seeking activity in the control group showed a gradual increase over the 6-day experimental period. In contrast, there was no such increase in the host-seeking activity in the L-DOPA group. Therefore, the host-seeking activity of L-DOPA group was significantly lower than that of the controls between day 3 and 6 post-emergence. Conclusion: Our results indicate that elevation of DA level reduces host-seeking activity in adult female mosquito Ae. albopictus.

Pet roundworms and hookworms: A continuing need for global worming

Donato Traversa — 2012-05-10T00:00:00Z

Ascarids and ancylostomatids are the most important parasites affecting companion dogs and cats worldwide, in terms of diffusion and risk for animal and human health. Different misconceptions have led the general public and pet owners to minimize the importance of these intestinal worms. A low grade of interest is also registered among veterinary professions, although there is a significant merit in keeping our guard up against these parasites. This article reviews current knowledge of ascarids and ancylostomatids, with a special focus on pathogenicity, epidemiology and control methods in veterinary and human medicine.