Distribution of 'promoter' sandflies associated with incidence of classic Kaposi's sarcoma.

The patchy geographical distributions of classic Kaposi's sarcoma (KS) and human herpesvirus type 8 (HHV-8), better known as Kaposi's sarcoma-associated herpesvirus (KSHV) remain unexplained. It has been proposed that certain species of bloodsucking insects ('promoter arthropods') promote the reactivation of HHV-8/KSHV and facilitate both HHV-8/KSHV transmission and KS development. This hypothesis was tested by sampling the presence and density of human-biting Diptera with CDC light traps in two areas of Sardinia with contrasting incidence rates of classic KS. In total, 11,030 specimens (99.9% sandflies and 0.1% mosquitoes) belonging to 10 species were collected from 40 rural sites. Five of these species are considered to be possible promoter arthropods because of the irritation their bites cause: Phlebotomus perniciosus Newstead; Phlebotomus perfiliewi Parrot (Diptera: Psychodidae); Aedes berlandi Seguy; Culiseta annulata (Schrank) and Culex theileri Theobald (Diptera: Culicidae). Five species are probable 'non-promoters' because their bites are not particularly irritating: Culiseta longiareolata (Macquart); Culex pipiens s.l.; Anopheles algeriensis Theobald; Anopheles maculipennis s.l., and Anopheles plumbeus Stephens. A significant correlation was found between the geographical distribution of promoter arthropods and incidence rates of KS (Spearman's r = 0.59,P < 0.01). Promoter arthropods were more likely to be caught in areas with cutaneous leishmaniasis and a past high prevalence of malaria, and in areas of limestone, acid volcanic soil and cereal cultivation. The study supports the association between promoter arthropods and classic KS, which may explain the geographic variability of KS and HHV-8/KSHV, and highlights the links with a number of variables previously associated with the incidence of KS.

Blood-feeding preferences of Aedes albopictus (Diptera: Culicidae) in urban and rural settings within the province of Rome, Italy.

We here report the results of field trials carried out in Rome with the aim to obtain data on the feeding behaviour of Aedes albopictus, in relation to different availability and abundance of putative hosts. Human Blood Index values were found higher than 75% in urban areas, where humans represented the most abundant hosts, and lower than 60% in rural areas, where host alternative to humans were frequent. The overall results confirm the generalist feeding-behaviour shown by this species in its original range of distribution and highlighting its high potential as vector of human pathogens in urban areas of Italy.

Assessing the impact of density dependence in field populations of Aedes aegypti.

Although many laboratory studies of intra-specific competition have been conducted with Ae. aegypti, there have been few studies in natural environments and none that examined density dependence in natural containers at normal field densities. Additionally, current mathematical models that predict Ae. aegypti population dynamics lack empirically-based functions for density-dependence. We performed field experiments in Tapachula, Mexico, where dengue is a significant public health concern. Twenty-one containers with natural food and water that already contained larvae were collected from local houses. Each container was divided in half and the naturally occurring larvae were apportioned in a manner that resulted in one side of the container (high density) having four times the density of the second side (low density). Larvae were counted and pupae were removed daily. Once adults emerged, wing span was measured to estimate body size. Density had a significant impact on larval survival, adult body size, and the time taken to transition from 4(th) instar to pupation. Increased density decreased larval survival by 20% and decreased wing length by an average of 0.19 mm. These results provide a starting point for a better understanding of density dependence in field populations of Ae. aegypti.

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.

Distribution of mosquito species in areas with high and low incidence of classic Kaposi's sarcoma and seroprevalence for HHV-8.

The 'promoter-arthropod' hypothesis, which postulates that exposure to the bites of certain species of haematophagous arthropods is an environmental risk cofactor linked to human herpes virus 8 (HHV-8) and Kaposi's sarcoma, was investigated in the Po River valley, northern Italy. The presence and density of adult female mosquitoes (Diptera: Culicidae) was determined by CDC light trap catches in two adjacent districts, at variance with respect to Kaposi's sarcoma incidence and HHV-8 seroprevalence. A total of 3910 specimens belonging to 11 species was collected in 34 rural sites (six municipalities) representative of the two districts. Five of these species are considered to be possible 'promoters' because of the irritation their bites cause humans: Aedes vexans (Meigen) and Ae. caspius (Pallas) (87% of sampled promoters), Culex modestus Ficalbi, Culiseta annulata (Schrank) and Coquillettidia richiardii (Ficalbi). Six are probable 'non-promoters': Cx. pipiens s.l., Cx. martinii Medschid, Anopheles claviger (Meigen), An. maculipennis s.l., An. plumbeus Stephens and Uranotaenia unguiculata Edwards. The density of promoters by site was correlated with the incidence rates of Kaposi's sarcoma at the district level (Pearson's r = 0.33, P = 0.06) and at the municipal level (r = 0.50, P< 0.01). Similar correlations emerged for non-promoters (r = 0.48, P< 0.01 and r = 0.42, P = 0.01, respectively). The density of promoters was higher than that of non-promoters in sites with livestock (odds ratio, OR = 2.8, 95% CI 2.2-3.6) and in municipalities with Kaposi's sarcoma cases (OR = 2.5, 95% CI 1.7-3.5). The study provides additional evidence of the association between the density of some mosquito species and Kaposi's sarcoma.