Mosquito abundance in a Dirofilaria immitis hotspot in the eastern state of Rio de Janeiro, Brazil.

Coastal lowlands in the state of Rio de Janeiro, Brazil, support high numbers of heartworm-infected dogs. Microfilariae of heartworm need to be ingested by a potencial mosquito vector in order to develop into infective larvae and infect a new host. Ochlerotatus taeniorhynchus and Ochlerotatus scapularis are the primary vector species in the coastal lowlands of metropolitan Rio de Janeiro; thus, the aim of this study was to investigate whether these two species were abundant enough at the heartworm hotspot in the eastern area of the state to be important to the local parasite's life cycle. The study was conducted at the Massambaba sandbank (22°55'45″S;42°18'51″W), where canine heartworm prevalence was 53.1%. Mosquitoes were captured monthly using two traps with CO2, as well as eventual human landing. A total of 6118 mosquitoes of 16 species were collected. Ochlerotatus taeniorhynchus (37.5%), Culex quinquefasciatus (19.3%), Oc. scapularis (18.2%), and Coquillettidia sp. (10.5%) were the most abundant species. The monthly variation in frequency was marked for Oc. scapularis and Cx. quinquefasciatus and steadier for Oc. taeniorhynchus and Coquillettidia sp. The abundance of the two Ochlerotatus species reaffirms that they are the primary natural vectors for D. immitis in the coastal Rio de Janeiro state lowlands.

Modeling the extrinsic incubation of Dirofilaria immitis in South America based on monthly and continuous climatic data.

The spread and recrudescence of dirofilariosis across several regions, either caused by Dirofilaria immitis or D. repens, responds to many factors. Building upon the temperature model by Slocombe et al. (1989), a number of studies have been performed to generate predictive models for dirofilariosis. These studies have demonstrated the length of transmission periods and the number of Dirofilaria generations supported throughout several regions of the world (either at large or at small-scale). The usual procedure have proved to be extremely time consuming, as it appears impractical when assessing potential transmission at large scale, such as at a country or large-scale level. Due to the increasing need to suggest standardized surveillance protocols and apply adequate preventive measures at national and regional levels, a model for calculation of Dirofilaria HDUs based on monthly data was adapted for large-scale regional use. The models proposed are based on both point data (meteorological stations) and interpolated climate data layers (WorldClim). Three different models (daily and monthly models based on point data, and monthly model based on continuous data) were developed and compared statistically. When compared with the results from the classical daily model, the monthly models proposed accurately predicted the locations were extrinsic incubation was possible. These models proved to be adequate for the regional analysis of the extrinsic incubation of D. immitis and, hence, the relative risk of transmission in South America. Further, these models confirm that favorable temperatures for heartworm transmission in South America are present in most of the countries. D. immitis extrinsic incubation follows a seasonal pattern in Argentina, Chile, Uruguay, eastern Paraguay and southeastern Brazil; while in northern half of South America (less than 25° S) transmission may occur year-round. Moreover, high risk areas suitable for dirofilariasis transmission are not geographically constant throughout the year. The validation procedures indicate that the predicted HDU and HG maps are good predictors of dirofilariosis potential distribution, but estimating dirofilariosis prevalences based on them might not be completely accurate. The resulting distribution and seasonal maps would be useful for heartworm prevention by chemoprophylaxis in different regions known to be endemic for canine dirofilariasis. The information here provided can be an important tool in veterinary public health, as well as a guide for future research.

Prevalence of Dirofilaria immitis infection in dogs from Celestun, Mexico, using polymerase chain reaction test.

The aim of this study was to determine the prevalence of Dirofilaria immitis in dogs and to analyze risk factors associated with infection at Celestun, a coastal locality in southeast Mexico. Blood samples were collected from 279 asymptomatic individuals between August 2007 and March 2008 and analyzed by polymerase chain reaction technique. The association between D. immitis infection and sex, age group, and distance of residence from a wetland of dogs was statistically analyzed. Prevalence of D. immitis infection was of 59.8%. Age of individuals (>2 years) was a risk factor for infection with D. immitis (odds ratio 2.49, confidence interval 1.47-4.23, p=0.001). In conclusion, Celestun can be considered a focus of D. immitis infection with high levels of transmission among the local dog population, as confirmed by the high prevalence reported and the association of age (dogs >2 years) as a risk associated with infection.

Epidemiology of canine heartworm in its southern distribution limit in South America: Risk factors, inter-annual trend and spatial patterns.

This study was aimed at understanding some aspects of the canine heartworm epidemiology in the southern distribution limit of the parasite in South America. With this objective, 19,298 blood samples of owned dogs from 65 localities of 13 municipalities of Buenos Aires Province were tested for Dirofilaria immitis circulating microfilariae and/or female antigens. The overall heartworm prevalence was 1.63% by microhematocrit tube technique (n=19,136), 3.65% by modified Knott (n=713), and 14.41% by antigen test kit (n=118). Microfilaremic dogs showed a median of 1933 microfilariae per millilitre (q1=375, q3=5625, n=100). Male dogs belonging to breeds of short hair and large size recorded significantly higher prevalences than the other categories. Also, the prevalence increased significantly with the age and only dogs younger than 12 months were not found infected. A clear decreasing trend of the annual prevalence was observed during the whole study period, from 3.91% in 2001 to 1.17% in 2006. D. immitis-infected dogs were detected in 32 localities of 9 municipalities (prevalence range: 0.2-6.7%). Generalized linear models were used to assess associations between heartworm prevalence and environmental variables. The resulting significant models were univariate and included variables related with soil cover and human population density. The best model predicted maximum heartworm prevalences around middle values of bare soil cover, and lower at high and low covers. According to our analyses, canine heartworm infection in urban temperate Argentina could be described as relatively low, endemic, and spatially heterogeneous. Host and environmental factors affecting heartworm transmission at local level were identified and discussed.

Incrimination of the mosquito, Aedes taeniorhynchus, as the primary vector of heartworm, Dirofilaria immitis, in coastal Yucatan, Mexico.

Mosquito collections were carried out on microfilaraemic dogs, positive for Dirofilaria sp., for 18 consecutive nights in the coastal town of Celestún, Yucatan, southeast Mexico, during the rainy season (August) of 2007. A total of 292 female mosquitoes representing 12 species of dipteran Culicidae were collected: Anopheles albimanus (Wiedemann); Anopheles crucians (Wiedemann); Anopheles pseudopunctipennis (Theobald); Culex coronator (Dyar & Knab); Culex interrogator (Dyar & Knab); Culex nigripalpus (Theobald); Culex quinquefasciatus (Say); Culex salinarius (Coquillett); Aedes aegypti (Linnaeus); Aedes scapularis (Rondani); Aedes sollicitans (Walker), and Aedes taeniorhynchus (Wiedemann). Aedes taeniorhynchus and Cx. quinquefasciatus were the species found most commonly feeding on the dogs. Filarial nematodes were observed by microscopy in nine of the mosquito species collected; however, third-instar larvae were only observed in Ae. taeniorhynchus and An. crucians. Of 76 Ae. taeniorhynchus specimens found positive for Dirofilaria sp. by dissection, 14 were confirmed to be positive for Dirofilaria immitis (Leidy) by polymerase chain reaction (PCR). The resulting infection rate for D. immitis confirmed by PCR (6.2%) is higher than any infection rate for Ae. taeniorhynchus previously reported from the Americas.

Ochlerotatus taeniorhynchus: a probable vector of Dirofilaria immitis in coastal areas of Yucatan, Mexico.

Mosquito collections were done on microfilaremic dogs, positive for Dirofilaria immitis (Leidy), for 15 consecutive nights in Celestun, Yucatan, southeastern Mexico, during January 2007. In total, 275 mosquitoes (3 male and 272 female) of five species were collected: Ochlerotatus taeniorhynchus (Wiedemann), Ochlerotatus sollicitans (Walker), Culex quinquefasciatus Say, Culex interrogator (Dyar & Knab), and Aedes aegypti (L.). Oc. taeniorhynchus was the species most frequently collected, and it had the highest rate of feeding success and the highest attack rates. First (L1) and third (L3) instars of Dirofilaria were observed in all mosquito species collected except for Ae. aegypti: 23 of 223 Oc. taeniorhynchus, three of 40 Cx. quinquefasciatus, and one of six Oc. sollicitans and one of one Cx. interrogator were infected with Dirofilaria (10.3% of total examined mosquitoes). This is the first report of Dirofilaria (presumably D. immitis) isolation from wild-caught mosquitoes in Mexico. Results imply that D. immitis can develop from microfilaria to infective L3s in Oc. taeniorhynchus, Cx. quinquefasciatus, and Oc. sollicitans, but L3s (infectious) were only recovered in heads of Oc. taeniorhynchus. Thus, Oc. taeniorhynchus can be considered a potential vector of dirofilariasis in Celestun, because infective L3 Dirofilaria were found in the vicinity of the mouthparts, and this mosquito has a strong association with microfilaremic dogs in this study area.

Comparative studies on the biology and filarial susceptibility of selected blood-feeding and autogenous Aedes togoi sub-colonies.

Blood-feeding and autogenous sub-colonies were selected from a laboratory, stock colony of Aedes togoi, which was originally collected from Koh Nom Sao, Chanthaburi province, Southeast Thailand. Comparative biology and filarial susceptibility between the two sub-colonies (blood-feeding: F11, F13; autogeny: F38, F40) were investigated to evaluate their viability and vectorial capacity. The results of comparison on biology revealed intraspecific differences, i.e., the average egg deposition/gravid female (F11/F38; F13/F40), embryonation rate (F13/F40), hatchability rate (F11/F38; F13/F40), egg width (F11/F38), wing length of females (F13/F40), and wing length and width of males (F11/F38) in the blood-feeding sub-colony were significantly greater than that in the autogenous sub-colony; and egg length (F11/F38) and width (F13/F40), and mean longevity of adult females (F11/F38) and males (F13/F40) in the blood-feeding sub-colony were significantly less than that in the autogenous sub-colony. The results of comparison on filarial susceptibility demonstrated that both sub-colonies yielded similar susceptibilities to Brugia malayi [blood-feeding/autogeny = 56.7% (F11)/53.3%(F38), 60%(F13)/83.3%(F40)] and Dirofilaria immitis [blood-feeding/autogeny = 85.7%(F11)/75%(F38), 45%(F13)/29.4%(F40)], suggesting autogenous Ae. togoi sub-colony was an efficient laboratory vector in study of filariasis.

[Mosquitoes potential vectors of canine heartworm in the Northeast Region from Brazil]. / Mosquitos vetores potenciais de dirofilariose canina na Região Nordeste do Brasil.

INTRODUCTION: In some coastal districts of São Luís, capital of the state of Maranhão, Brazil, the prevalence of Dirofilaria immitis is more than 40% in house dogs. Natural potential vectors, as found in other areas of Northeastern Brazil, are unknown. The aim of this study was to identify probable vectors of the disease. METHODS: Mosquito catches were performed at a coastal, district Olho d'Agua, in S. Luís, to look for local potential vectors. Captures were carried out monthly, from March 1996 to May 1997, outdoors, having a man and a dog as baits. Mosquitoes were dissected for D. immitis larvae. RESULTS: A total of 1,738 mosquitoes belonging to 11 species were collected. Culex quinquefasciatus, the only species collected every month, was more frequently in the dry season. It accounted for 54.5% of the total, followed by Aedes albopictus (20. 3%), Ae. scapularis (11%) and Ae. taeniorhynchus (11%). D. immitis larvae were detected in 0.1% of the Cx. quinquefasciatus dissected (L3 in the Malpighian tubules) and 0.5% of the Ae. taeniorhynchus (L2 in the Malpighian tubules). CONCLUSION: Ae. taeniorhynchus and Cx. quinquefasciatus are considered natural potential vectors of the canine heartworm in São Luís. The role of Cx. quinquefasciatus as primary vector of D. immitis, however, needs further evaluation.

Human pulmonary dirofilariasis: a review.

The authors presented a detailed summary of the geographical distribution, clinical and pathological aspects of human pulmonary dirofilariasis. Although benign, this zoonosis, of which Dirofilaria immitis is the major etiological agent, represents a medical problem since it produces symptoms which may be confused with neoplasia and thus may subject patients to unnecessary thoracic surgery. Of 229 cases cited in the literature, only 17 were reported in Brazil, despite the existence of highly favorable conditions for the transmission of this infection in man. Thus it may well be that this parasitic infection remains underdiagnosed. Finally, the importance of a differential diagnosis between dirofilariasis and pulmonary neoplasia is emphasized in cases where there is a solitary subpleural nodule ("coin lesion") present. In addition, the development and improvement of modern immunological diagnostic techniques are essential to distinguish this benign disease from other pathological conditions and thus avoid unnecessary surgery. These techniques may reveal the true prevalence of this parasitic infection in our environment.

Dirofilariose pulmonar: relato de um caso / Pulmonary dirofilariasis: a case report

Os autores apresentam o caso de um paciente de 60 anos, sexo masculino, que após ter apresentado um episódio de dor torácica desenvolveu quadro de tosse e expectoraçäo. A radiografia simples de tórax mostrou um nódulo solitário em projeçäo do lobo superior direito, sem calcificaçäo, que persistiu inalterado após dez dias do desaparecimento dos sitnomas. Outros exames como tomografía computadorizada, teste de Mantoux, pesquisa de BAAR no escarro e broncoscopia näo acrescentaram nenhuma informaçäo, permenecendo o diagnótico anterior de foco pneumônico. A punçäo transparietal näo permitiu obter-se o diagnóstico definitivo. Foi, entäo, realizada toracotomia e o exame histopatológico do nódulo retirado revelou granuloma com necrose e larvas de Dirofilaria immitis. Os autores discutem os aspectos etiopatogênicos diagnósticos e terapêuticos desta rara afecçäo pulmonar