Mass chemotherapy with diethylcarbamazine for the control of bancroftian filariasis: a twelve-year follow-up in Northern Trinidad, including observations on mansonella ozzardi

A microfilaria survey was conducted in Trinidad in 1992, 12 years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined using thick blood smears and a membrane filtration technique. They included 104 who had participated in the mass chemotherapy campaign in 1980. No Wuchereria bancrofti microfilariae were detected among 66 percent of the population examined. In 1980, 86 of 592 persons examined were found to be infected with W. bancrofti, 140 with Mansonella ozzardi and 44 with mixed infections, while in 1992, only M. ozzardi infections persisted despite treatment with DEC-C. Of the 104 persons reexamined 12 years later, 46 had M. ozzardi, of which five were new cases, but none had W. bancrofti. During both the 1980 and 1992 surveys, low microfilariae rates for M. ozzardi were observed among those 19 years of age or younger. Of the 302 persons newly examined in 1992, 29 were infected with significantly (P<0.001) more males (79.3 percent) than females (20.9 percent) being microfilaremic. The combined results showed similar prevalence rates for M. ozzardi from 23.3 percent to 21.6 percent in 1980 and 1992. Nuclepore membrane filtration and thick blood films were very efficient in demonstrating the presence of microfilariae. The usefulness of these methods and spaced treatment using DEC-C are also discussed (AU)

Mass chemotherapy with diethylcarbamazine for the control of bancroftian filariasis: a 12-year follow-up in North Trinidad including observations on mansonella ozzardi microfilaraemia - abstract

A microfilaria survey was conducted in Blanchisseuse, North Trinidad in 1992 twelve years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined, including 104 who had participated in the mass-chemotherapy campaign in 1980. No W. bancrofti microfilarie were detected among 66 percent of the population examined. In 1980, 86 persons were found with W. bancrofti, 140 with M. ozzardi and 44 with mixed infections while in 1992 only Mansonella ozzardi infections persisted despite DEC-C treatment. From the 104 persons re-examined, 46 persons had M.ozzardi, of which 5 were new cases but none had W. bancrofti infections in 1992. During both the 1980 and 1992 surveys, low microfilariae rates of M.ozzardi were observed among the 1-4, 5-9 and 10-19-year age groups. From the 302 persons examined in 1992, 29 were infected, with significantly (p<0.001) more males (79.3 percent) than females (20.7 percent) being microfilaraemic. The combined results showed similar prevalence rates of M.ozzardi from 23.3 percent to 21.6 percent in 1980 and 1992, respectively. A good correlation was found between the results observed from Nucleopore membrane filtration and thick blood films. The usefulness of thes methods and spaced treatment using DEC-C is also discussed (AU)

Filariasis in Amerindians of Western Guyana with observations on transmission of Mansonella ozzardi by a Similium species of the amazonicum group

In order to conduct experimental infection studies on Mansonella ozzardi in local haematophagos Diptera, volunteers infected with this parasite were identified during a microfilaria survey of four Amerindian villages in the Pakaraima Mountains of Western Guyana, near the Brazilian border. M. ozzardi microfilariae were detected in blood smears from 8-21 percent of persons examined. They were also found in skin snips from 8/73 persons all of whom were positive by blood smear examination. No Onchocerca volvulus microfilariae were detected. Dipetalonema perstans infections were found in three of four villages but prevalence rates were only 1-8 percent. Man-baited catches of haematophagous Diptera made at the onset of the dry season in one of the villages yielded only three Simulium species. After the flies were engorged on infected volunteers, M. ozzardi larvae developed to the infective stage in 6-7 days in the most abundant species, a member of the Simulium amazonicum group. Man-biting rates of up to 156 per 15-minute period were recorded for this species in midday collections along riverbanks near one of the villages. Developing filariae, including infective larvae of M. ozzardi, were also found in wild-caught flies. It was concluded that this Simulium species is a vector of M. ozzardi in the study area (Summary)

Parasitological and clinical studies of Wuchereria Bancrofti and Mansonella Ozzardi in coastal North Trinidad, West Indies

A parasitology and clinical survey of Wuchereria bancrofti and Mansonella ozzardi was conducted in Blanchisseuse, an isolated rural community of 650 people in coastal north Trinidad. W. bancrofti microfilariae were found in 15 percent of the resident population and the prevalence was higher in males (19 percent) than in females (12 percent). Microfilaraemias were undetected in children under 5 years of age but 12 percent of children and adolescents between 5 and 19 years of age were positive. Microfilaraemias were most common in males aged 40-59 years (34 percent) and in females in the same age group (21 percent). Whereas geometric mean microfilaria densities were generally higher in females than in males under 40 years old, in the older age groups the pattern was reversed, the difference being especially pronounced in the over sixties. There were more than twice as many males with M. ozzardi microfilariae (35 percent) than there were females (15 percent). The prevalence was low in children and young adults but increased with age thereafter. In the older age groups microfilaria densities followed a similar trend. Genital signs compatiable with lymphatic filarial disease were seen in 29 percent of males; these included hydrocoele (15 percent) and elephantiasis of the scrotum (1 percent). Most signs were seen in persons over 50 years of age. Six per cent of females had lymphoedema of the leg(s), and in four cases (2.3 percent) this had progressed to elephantiasis. A positive association was found between M. ozzardi microfilaraemia and clinical history of articular pain (p<0.001). The findings suggest that both filarial species are some public health significance in at least one rural area in Trinidad, and they provide a basis for the development of a lymphatic filariasis control strategy in the community (AU)

Evaluation of a membrane (Nuclepore) filtration method using capillary blood for the detection of microfilariae

The efficacy of a membrane (Nuclepore) filtration technique using capillary blood (100 mm 3) for the detection of blood-circulating microfilariae was investigated during a prevalence survey for Wuchereria bancrofti and Mansonella ozzardi in north Trinidad by comparing results thus obtained with results from conventional thick smear preparations (25mm3) and from membrane (Nuclepore) filtration of venous blood (1 ml). Prevalence rates of W. bancrofti were 14 percent by thick smear, 17 percent by filtration of capillary blood and 6 percent by filtratioon of venous blood. For M. ozzardi the corresponding rates were 27 percent, 29 percent and 31 percent. A total of 389 persons was examined by all three methods. Microfilaria detection rates for both of the filtration techniques were significantly higher than by thick smear preparation, with the exception of results for M. ozzardi obtained by filtration of capillary blood. There was no significant difference between the number of positive persons detected by filtration of capillary blood and filtration of venous blood. Significantly higher microfilaria densities per unit volume of blood were recorded by thick smear preparation and filtration of capillary blood than by filtration of venous blood. Whereas results for the two capillary blood techniques were similar. In the detection of low density microfilaraemias, membrane filtration of capillary blood provides a practical and sensitive alternative to venous blood filtration and has the additional advantage of capilary blood collection rather than venepuncture.(AU)

Transmission of the human filarial parasite Mansonella ozzardi by Culicoides phlebotomus (Williston) (Diptera: Ceratopogonidae) in coastal north Trinidad

Between June 1976 and November 1977, man-baited and truck-trap collections of Haematophagous Diptera were made on the foreshore of Las Cuevas Bay, north Trinidad, close to a fishing village where Mansonella ozzardi infections are prevalent in man. Culicoides phlebotomus (Will.) predominated in all collections, forming 96.1 percent of the total catch. Analysis of blood-meals from engorged C. phlebotomus collected by truck trapping at sunset indicated frequent feeding on mammals, with feeds on man comprising 47 percent of those identified. Filarial larvae were found in 0.8 percent of 6767 females of C. phlebotomus captured on man, and five (0.08 percent) had infective larvae of M. ozzardi. Similarly, 1.3 percent of 7028 females obtained by truck trapping were infected, including nine (0.13 percent) with infective larvae. Growth rates of M. ozzardi in C. phlebotomus were determined by experimental infection and were used to estimate daily survival rates of wild-caught females of C. phlebotomus based on filarial growth stages found in them. The daily survival rate varied from 85 to 95 percent in flies 1-3 days after infection to 69 percent in flies six days after infection. It was estimated that a person spending one hour on the beach every morning would receive 38 infective bites from C. phlebotomus per annum. (AU)

The prevalence and distribution of Mansonella ozzardi in coastal north Trinidad, W. I

A day blood smear survey for Mansonella ozzardi in the north coast communities of Trinidad recorded a prevalence of 4.8 percent in 4,488 persons examined. Prevalence rates were highest in the four western-most communities, where the vector, Culicoides phlebotomus, is a severe nuisance problem. Prevalence rates increased with age and were higher in males than in females. Mean microfilaria densities were low in both sexes up to 50 years of age but in older males the density increased with age. Wuchereria bancrofti infections were detected in five of the ten communities surveyed. (AU)

Infections with Dipetalonema perstans and Mansonella ozzardi in the Aboriginal Indians of Guyana

Blood surveys conducted among the aboriginal Indians (Amerinds) in the interior of Guyana revealed that Dipetalonema perstans or Mansonella ozzardi, or both, occurred in approximately 12 percent of the persons examined, D. perstans being more common and widely distributed. It was found in Amerinds in all of the districts surveyed and in persons of other than aboriginal stock living in the interior of the country. M. ozzardi, in contrast to D. perstans, had a low prevalence and a very limited geographic distribution. It was found among Amerinds in the Pakaraima Mountains of the Mazaruni-Potaro and Rupununi Districts and in the North West District, but was absent from many areas in which it had been found at the turn of the century. M. ozzardi occurred more frequently mixed with D. perstans than as a pure infection. The geographic distribution of each species in the various administrative districts of the country is presented. (AU)

Filariasis in Suriname / Filariasis in Suriname

After an introduction of the concept of 'filaria', the different forms of filaria parasitic on man are briefly summed up. The morphological and physiological characteristics of W. bancrofti are discussed, and the symptoms caused by this worm. After pointing out the necessity for the population of Paramaribo to submit themselves to an examination of filaria, the organization of the department for the prevention of filaria is briefly described and the results of the examination of 50.861 inhabitants. It appeared that 24.2 per cent of the examined population of Paramaribo is infected with W. bancrofti; besides, it was observed that the blood of 88.2 per cent of the sufferers from elephantiasis contained no microfilariaemie; possible explanations are given for this latter phenomenon. The Creole population group appears to be most strongly infected. The results of the polyclinical treatment with Hetrazan are stated, namely, a disappearance and long absence of the microfilariaemie. Other sanitary measures are also stated. Finally the presence of F. ozzardi and A. perstans in the blood of the Amerindians living in the savannah zone is referred to.(AU)