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.

[Occurrence of Mansonella ozzardi (Nematoda, Onchocercidae) in riverine communities of the Purus river, Boca do Acre municipality, Amazonas State, Brazil]. / Ocorrência da Mansonella ozzardi (Nematoda, Onchocercidae) em comunidades ribeirinhas do rio Purus, Município de Boca do Acre, Amazonas, Brasil.

The study aimed to estimate the prevalence of Mansonella ozzardi and calculate the parasitic infection rate in simuliid blackflies. The research was conducted in communities on the Purus River, Boca do Acre municipality, Amazonas State, Brazil. Prevalence was measured using the thick smear method. Captured blackflies were dissected to verify the parasitic infection rate. M. ozzardi prevalence was 27.30% (77/282). The study showed higher prevalence in men (31.97%) than women (22.22%), farmers (48.99%), and individuals in the 38-47 (60.00%), 48-57 (66.66%), and 58-67-year age brackets (75.00%). Microfilaremia was higher in individuals 58 to 67 years of age (average= 58.41 mf/40 microl), men (41.44 mf/40 microl), and farmers (49.94 mf/40 microl). Only the simuliid Cerqueirellum amazonicum was found infected with a parasitic infection rate of 0.98%.

Ocorrência da Mansonella ozzardi (Nematoda, Onchocercidae) em comunidades ribeirinhas do rio Purus, Município de Boca do Acre, Amazonas, Brasil / Occurrence of Mansonella ozzardi (Nematoda, Onchocercidae) in riverine communities of the Purus river, Boca do Acre municipality, Amazonas State, Brazil

Este estudo teve o objetivo de estimar as prevalências de Mansonella ozzardi e calcular taxa de infecção parasitária nos simulídeos. O trabalho foi realizado em comunidades ribeirinhas do rio Purus, Boca do Acre, Amazonas, Brasil. As prevalências foram obtidas por meio do método de gota espessa de sangue obtido por porção digital. Os simulídeos coletados foram dissecados para estimar a taxa de infecção parasitária. A prevalência de M. ozzardi foi de 27,3 por cento (282/77). Foram observadas maiores prevalências nos homens (31,97 por cento) que nas mulheres (22,22 por cento), nos agricultores (48 por cento) e nos indivíduos entre: 38-47 (60 por cento), 48-57 (66,66 por cento) e 58-67 (75 por cento). A microfilaremia foi maior nos indivíduos entre 58-67 anos (média = 58,41mf/40µL), sexo masculino (41,44mf/40µL) e nos agricultores (49,94mf/40µL). Somente o simulídeo Cerqueirellum amazonicum foi encontrado infectado com taxa de infecção parasitária de 0,98 por cento.

The study aimed to estimate the prevalence of Mansonella ozzardi and calculate the parasitic infection rate in simuliid blackflies. The research was conducted in communities on the Purus River, Boca do Acre municipality, Amazonas State, Brazil. Prevalence was measured using the thick smear method. Captured blackflies were dissected to verify the parasitic infection rate. M. ozzardi prevalence was 27.30 percent (77/282). The study showed higher prevalence in men (31.97 percent) than women (22.22 percent), farmers (48.99 percent), and individuals in the 38-47 (60.00 percent), 48-57 (66.66 percent), and 58-67-year age brackets (75.00 percent). Microfilaremia was higher in individuals 58 to 67 years of age (average= 58.41mf/40µl), men (41.44mf/40µl), and farmers (49.94mf/40µl). Only the simuliid Cerqueirellum amazonicum was found infected with a parasitic infection rate of 0.98 percent.

The invasion of the midgut of the mosquito Culex (Culex) quinquefasciatus Say, 1823 by the helminth Litomosoides chagasfilhoi Moraes Neto, Lanfredi and De Souza, 1997.

The Litomosoides chagasfilhoi helminth was studied as a model for microfilaria invasion of the midgut of Culex quinquefasciatus mosquito, vector of Wuchereria bancrofti helminth, causative agent of the human filariasis. Histology and transmission and scanning electron microscopy were utilized to show the topography of mosquito midgut invasion by the helminth. An analysis of midguts dissected at different time points after a blood meal demonstrated that the microfilariae interacted and crossed the peritrophic matrix and the midgut epithelium of C. quinquefasciatus. The microfilariae invaded preferentially the mosquito abdominal midgut and the invasion process occurred between 2 and 3h after the blood feeding. In some cases, microfilariae caused an opening in the midgut that separated the epithelial cells, while in others cases, the worms caused the detachment of cells from the epithelium. Ultimately, L. chagasfilhoi crossing activity appeared to damage the midgut. It was also observed that the microfilariae lost their sheaths during their passage through the fibrous material of the peritrophic matrix, before they reached the midgut epithelium. Since the exsheathment process is necessary for the continuity of larvae development, it seems that the passage through the peritrophic matrix is an important step for the parasite's life cycle. This experimental model revealed details of the interaction process of helminthes within the vector midgut, contributing to the knowledge of factors involved in the vector competence of C. quinquefasciatus as a vector of filariasis.

Transmission intensity and the patterns of Onchocerca volvulus infection in human communities.

We focus on possible constraints upon Onchocerca volvulus establishment in humans in relation to exposure rates to infective larvae (L3) as measured by the annual transmission potential (ATP). We use mathematical and statistical modeling of pre-control west African (savanna), Mexican, and Guatemalan data to explore two hypotheses relating human infection to transmission intensity: microfilarial (mf) loads either saturate with increasing ATP or become (asymptotically) proportional to the ATP. The estimated proportion of L3 developing into adult worms ranged from 7% to 0.3% (low and high intensity areas, respectively). Relationships between mf prevalence and both mf and transmission intensity were nonlinear and statistically similar between west Africa (Simulium damnosum s.l.) and Meso America (S. ochraceum s.l.). This similarity extended to the relationship between mf intensity and ATP. The critical biting rates for onchocerciasis introduction and persistence (which depended on vector competence and host preference), were approximately 10-fold higher in settings where onchocerciasis is transmitted by S. ochraceum than in those where the vector is S. damnosum. A role for focal vector control in Mexico and Guatemala, in addition to nodulectomy and ivermectin, is suggested.

Bancroftian filariasis in Maceio, state of Alagoas, Brazil: Observations on Culex quinquefasciatus after blood feeding on individuals with different densities of microfilariae in the peripheral blood stream.

Females of laboratory-reared Culex quinquefasciatus were allowed to take blood meals on individuals with low (1-100 microfilariae/ml of peripheral blood), moderate (101-500 microfilariae/ml), and high (> 500 microfilariae/ml) microfilaremia. The mosquitoes ingested 1.39-3.80 microl of blood and infective third-stage (L3) larvae were first recorded 13-14 days after the infecting blood meal. The number of microfilariae ingested by mosquitoes was proportional to the density of microfilariae in the peripheral blood of the human subjects, but with a concentration factor of up to 6.5 times the expected number. Survival of mosquitoes was not influenced by the density of microfilariae in the peripheral blood of infected individuals. Infectivity indices were proportional to microfilaremia in human subjects. The number of L3 larvae/female (intensity of infection) was not influenced by individual microfilaremia. The highest vector efficiency and the best experimental infection index were recorded in mosquitoes that blood fed on individuals with moderate microfilaremia. The results are discussed in relation to the transmission on Bancroftian filariasis in the study area.

Mast cell distribution in nodules of Onchocerca volvulus from untreated patients with generalized onchocerciasis.

Onchocercomata with a defined worm population were analysed to elucidate the distribution of mast cells. Nodules with live females were classified according to the presence or absence of microfilariae. Immunohistochemical staining was performed using antibodies specific for mast cells or IgE. Mast cells appeared singly or in diffuse accumulations perivascularly and in inflammatory infiltrates between adult Onchocerca volvulus and in the capsular area. No mast cells were detected in cystic parts. Only few, scattered mast cells were found in the fibrous zone around the adult worm. They were increased with stronger infiltration and hence, related to the inflammatory cells. Mast cells were never localized directly at adult worms or microfilariae. A correlation of the mast cell distribution to the occurrence of eosinophils was observed regarding higher numbers of mast cells and eosinophils in nodules with microfilariae-producing females. Nodules with single males revealed higher numbers of mast cells than nodules with non-producing females, although both contained very few eosinophils. Onchocercomata with dead worms contained significantly more mast cells than those with live filariae. In conclusion, the localization and frequency of mast cells is contingent on the vitality and productivity of the worms and therefore, indirectly and directly on the release of O. volvulus antigens.

Studies on the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae in paired samples of capillary and venous blood from Recife, Brazil.

We examined the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae (mf) and determined the effect of these parasite properties on the accuracy of blood filming and filtration methods for diagnosis of bancroftian filariasis in the endemic area of Recife, Brazil. Microfilariae in both venous and capillary blood exhibited a nocturnal periodicity pattern with a relatively high amplitude. Overall, capillary blood contained approximately 1.25 times the number of mf present at the same time in the same volume of venous blood. However, the ratio of mf present in capillary and venous blood varied over a 24-hour period, so that the fewest mf were present in the capillary bed of the skin at the time when biting activity of the local Culex vector is the lowest. Twenty or 60 microliters blood films did not reliably detect carriers with fewer than 100 or 60 mf/ml venous blood, respectively, and were thus inadequate for the identification of low density mf carriers. In contrast, all carriers with > 1 mf/20 or 60 microliters blood smear at night could be identified during daytime hours by filtration of 1 micromilligram venous blood.

Density-dependent processes in the transmission of human onchocerciasis: intensity of microfilariae in the skin and their uptake by the simuliid host.

The transmission success of Onchocerca volvulus is thought to be influenced by a variety of regulatory or density-dependent processes that act at various points in the two-host life-cycle. This paper examines one component of the life-cycle, namely, the ingestion of microfilariae by the simuliid vector, to assess the relationship between intake of larvae and the density of parasites in the skin of the human host. Analysis is based on data from three areas in which onchocerciasis is endemic and includes published information as well as new data collected in field studies. The three areas are: Guatemala (Simulium ochraceum s.l.), West and Central Africa (savanna members of the S. damnosum complex), and South Venezuela (S. guianense). The data record experimental studies of parasite uptake by flies captured in the field and fed to repletion on locally infected subjects who harboured varying intensities of dermal microfilarial infection. Regression analyses of log transformed counts of parasite burdens ingested by the flies plotted against log transformed counts of microfilariae per mg of skin revealed little evidence for saturation in parasite uptake by the flies as the intensity in the human host increased. There was a positive and highly significant rank correlation between both variables for the three blackfly species. In an alternative analysis a model was fitted to data on prevalence of flies with ingested microfilariae (mff) versus dermal mean intensities. The model assumed an overdispersed distribution of the number of mff/fly and a given functional relationship between intake and skin load. The results of both approaches were consistent. It is concluded that parasite ingestion by the vector host is not strongly density dependent in the three geographical areas and ranges of dermal loads examined. It therefore appears that this transmission process is of reduced importance as a regulatory mechanism in the dynamics of parasite population growth.

Transplacental transmission of Wuchereria bancrofti in Haitian women.

To document the occurrence of transplacental transmission of microfilariae and to determine how frequently it occurred, umbilical cord blood samples and placental tissues were collected from 22 microfilaria-positive women in an area with endemic Wuchereria bancrofti. Microfilaria (mf) counts in the women ranged from 1 to 3,820 mf/ml. Microfilariae were detected in 2 placenta samples and a single cord blood sample. The positive cord blood sample and 1 of the positive placenta samples came from the same woman; no microfilariae were found in a finger prick sample taken from the infant 3 wk after delivery. Our results suggest that microfilariae cross the placenta in less than 10% of pregnancies of microfilaria-positive mothers. Furthermore, the microfilaria count of the mother does not seem to influence directly whether microfilariae are present in the placental blood pool. Although actual transfer of microfilariae to the fetus may occur infrequently, exposure to parasite antigens occurs with much greater frequency. The effect of in utero exposure to either microfilariae or parasite antigens may render newborns tolerant and explain why children born to infected mothers are almost 3 times more likely to become infected than are children born to uninfected women.

Mantenimiento in vitro de microfilarias / In vitro maintenance of microfilariae

Con el propósito de hacer estudios inmunológicos de los productos metabólicos de microfilarias, se realiza el mantenimiento in vitro de las mismas. Se trabaja con 3 especies de filarias humanas: Wuchereria bancrofti, Dipetalonema perstans, Loa loa y con una filaria canina, Dirofilaria immitis. Se utilizan en los primeros 20 estudios, 2 medios de cultivo, 2 pH y 2 temperaturas diferentes. De esta primera experiencia se escogen las mejores condiciones para realizar la segunda fase del trabajo. El tiempo de sobrevivencia establecido, teniendo en cuenta la no utilización de suplementos en el medio, está en correspondencia con el objetivo del trabajo

[Lymphatic filariasis in Haiti. Results of treatment with diethylcarbamazine in the town of Limbe]. / Filariose lymphatique en Haiti. Résultats du traitement par le diéthylcarbamazine dans la ville du Limbe.

In the town of Limbe, in Haiti, 16,8% of the inhabitants show W. bancrofti microfilariae in their blood taken by finger prick between 8.00 and 10.00 p.m. From those positive patients, 208 have received a cure of DEC at the dosage of 6 mg/kg/day during ten days. The control of the therapeutic efficacity among 190 patients, after three and a half months of this cure, shows a negativity of 72%. The positives patients show a very low parasitic charge (MfD50 = 1.9). If the secondary effects are frequent (83.7%), they are often benign and temporary.

[Absence of response of Mansonella ozzardi microfilaria in the diethylcarbamazine provocation test]. / Défaut de réponse des microfilaires Mansonella ozzardi au test de provocation par le diéthyl-carbamazine.

One hundred and twelve inhabitants of an area endemic for M. ozzardi received 20 cmm capillary blood samples by finger prick before and 30 minutes after the ingestion of 100 mg of diethylcarbamazine citrate. No significant variations in microfilaremia were detected. Thus, a provocative dose of DEC would not appear to be helpful in sampling for mansonellosis in Haiti.

Early formation of the nodule in Guatemalan onchocerciasis.

Thirty-eight nodules containing adults of Onchocerca volvulus were removed from 36 patients who had no detectable microfilariae in skin snips. Worms were digested from nodules in collagenase solution, maintained alive in vitro, and the number, sex, and state of fecundity were recorded. A total of 48 female and 8 male worms were recovered; 39 females were in the nodules without the presence of a male. Eleven females (22.9%) had microfilariae in utero or produced microfilariae in vitro; seven of these were found together with males in the nodules while four were not. No nodules were found around male worms unless a female was also present. These observations indicate that the nodule forms only around female worms and that mating probably occurs before or early during nodule formation. Furthermore, the production of microfilariae by the the female is not essential for nodule formation since many nodules contained non-fecund, living females.