Temporal and spatial patterns of aquatic macrophyte diversity in the Upper Paraná River floodplain / Padrões temporais e espaciais da diversidade de macrófitas aquáticas na planície de inundação do Alto Rio Paraná

Although the importance of long-term data has been emphasized by ecologists in recent years, little is known about how communities may change over time. In this study, we describe the general patterns of aquatic macrophyte diversity in the Paraná River floodplain observed during six years of study. Temporal changes in community composition were also evaluated. Data on the presence or absence of aquatic macrophytes were collected between March 2002 and March 2008, in six lakes associated with three rivers. Different analytical strategies were used to evaluate the dynamics of aquatic macrophyte communities between the different systems in the floodplain. The composition of aquatic macrophytes differed among the rivers, mainly with respect to the different vegetation life forms (floating, submersed, emergent and rooted with floating stems). The temporal similarity of species composition during the six years and the beta-diversity index indicated that the month-to-month species turnover was, in general, lower in the connected lakes, which are directly influenced by the river. Probably the water level fluctuation is a selective force that contributes to maintaining diversity or richness. Our findings indicated the importance of abiotic characteristics and connectivity of the lakes in determining macrophyte composition and community stability over a long time frame.

Estudos utilizando ampla escala temporal ainda são escassos na ecologia, mesmo considerando sua importância no estudo de comunidades. Esse trabalho teve como objetivo principal descrever padrões gerais sobre a diversidade de macrófitas aquáticas na planície de inundação do Alto Rio Paraná utilizando uma ampla escala temporal (seis anos de estudo). Mudanças na composição das comunidades ao longo do tempo também foram avaliadas. Dados de presença ou ausência de macrófitas foram obtidos entre Março de 2002 e Março de 2008 em seis lagoas associadas a três rios na planície de inundação. Diferentes técnicas foram utilizadas para avaliar a dinâmica das comunidades de macrófitas aquáticas entre os diferentes ambientes. De maneira geral, a composição das comunidades foi dissimilar entre os diferentes rios, principalmente considerando os diferentes grupos funcionais de macrófitas (flutuante livre, submersa, emergente e enraizada com folha flutuante). A similaridade temporal na composição de espécies e o índice de diversidade beta indicaram que a substituição de espécies ao longo dos meses foi, de maneira geral, menor nas lagoas conectadas ao rio principal. Provavelmente, a flutuação no nível da água representa uma pressão seletiva que ajuda a manter a diversidade de espécies nas lagoas diretamente influenciadas pelo rio. Os resultados desse estudo indicaram a importância das características abióticas e da conectividade das lagoas na composição e estabilidade temporal das comunidades de macrófitas aquáticas na planície de inundação do Alto Rio Paraná.

Possibility of false-positive detection for sporozoites in mosquitos (Diptera: Culicidae) by nested polymerase chain reaction using Plasmodium yoelii genomic DNA.

Anopheles stephensi Liston and An. saperoi Bohart and Ingram infected with the rodent malaria parasite Plasmodium yoelii nigeriense. They were examined 12 and 19 days after blood feeding for sporozoites in head with anterior thorax (HT) and oocysts in abdomen with posterior thorax (AB) by light microscopy and by the nested polymerase chain reaction (nested PCR-based on the amplification of the sequences of the small subunit ribosomal RNA gene). The detection rate of parasite DNA by nested PCR in HT samples 12 days after blood feeding was similar to that by microscopic method. However, in HT samples 19 days after blood feeding, the rate by the PCR method was higher than that by the microscopic method. The incidence of sporozoites in salivary glands of infected mosquitos for 12 days after blood sucking was examined by the PCR method. Parasite DNA in HT of Aedes albopictus Skuse (a non vector for the rodent malaria) as well as An. stephensi and An. saperoi was detected for up to 4 days after feeding on mouse with the rodent malaria parasites. The results indicate that when the PCR method is used for detection of sporozoites of human malaria in mosquitos collected in the field, there are possibilities of including false-positive data for mosquitos that have just or recently fed on human blood infected with malaria (erythrocytic form).

The relationship between anthropometric indicators of nutritional status and malaria infection among youths in Khammouane Province, Lao PDR.

We assessed anthropometric indicators of the nutritional status among children and adolescents in Khammouane Province in the Lao PDR and examined the relation between malnutrition and malaria infection. The survey was conducted from July to August 1999 using a sample of 309 youths aged 2 to 18 years. Malnutrition was categorized as stunting (below -2 Z scores height-for-age) and wasting (below -2 Z scores weight-for-height). The prevalence of stunting and wasting were 45.1% and 9.2%, respectively, which were classified by WHO as "very high" prevalence. Compared with the results of previous national surveys in Lao PDR, similar prevalence was shown. The prevalence of wasting in youths with P. falciparum infection was 17%, significantly higher than those of not infected (4%). On the other hand, P. vivax infection was not associated with any indicators of malnutrition. In conclusion, this study showed that the nutritional status in youths was poor and P. falciparum infection was associated with acute malnutrition.

Community control studies on Strongyloides infection in a model island of Okinawa, Japan.

The community control program for Strongyloides infection was conducted by fecal examination and subsequent treatment of the population on a model island (Kume Island) in Okinawa, Japan, for 5 years from 1993 to 1997. More than 1,200 persons, accounting for 17% to 20% of the persons subjected, received fecal examinations each year. The positive rate in 1993 was found to be 9.7% (133/1,374). The positive rate decreased to 6.5% (95/1,468) in 1994, then 4.8% (60/1,245) in 1995, 2.2% (27/1,225) in 1996 and 2.7% (33/1,217) in 1997 through treatment with albendazole or ivermectin on the positive persons detected each year. Among the positive persons detected after operation of the control program, more than 70% were newly detected persons who did not receive an examination in the previous year or were falsely-negative in the previous examination. The low enforcement of procuring fecal examinations, as well as low sensitivity of fecal examination, might have had an effect on the relatively gradual decrease in the prevalence rate, in spite of the high efficacy of the treatment. The results indicate that continuation of the control program for several years is needed to effectively reduce the prevalence of the parasitic infection in the community.

Comparative studies on the efficacy of three anthelminthics on treatment of human strongyloidiasis in Okinawa, Japan.

A study was undertaken to compare the efficacy of three drugs in the treatment of uncomplicated strongyloidiasis in Okinawa, Japan. Two hundred and eleven patients with confirmed Strongyloides stercoralis infection were given either ivermectin, 6 mg in a single dose, albendazole, 400 mg/day for 3 days or pyrvinium pamoate, 5 mg/kg/day for 3 days. For each treatment, the same regimen was repeated once 2 weeks later. Efficacy was evaluated at 2 weeks, 6 months and 12 months after the second course of treatment. Each follow-up examination included a parasitological examination of z stool specimens, using the agar-plate culture method. Coprological cure was obtained in 65 of the 67 patients treated with ivermectin (97.0%), in 65 of the 84 patients treated with albendazole (77.4%) and only in 14 of the 60 patients who were given pyrvinium pamoate (23.3%). The cure rates were lower in males and in the patients with concurrent HTLV-1 infection. An epidemiological feature of Strongyloides infection in recent Okinawa might allow workers to evaluate the exact efficacy of the treatment for an extended period, over a year, without the possibility of reinfection from the environment.

An epidemiological study on Opisthorchis viverrini infection in Lao villages.

The prevalence of liver fluke, Opisthorchis viverrini, infection in rural and urban communities was studied in Khammouane Province in Lao PDR. The infection was the commonest among the villagers examined, showing the positive rates of 52.9% and 55.0% in two rural communities and 60.7% in an urban community, respectively. The infection rate reached up to 20% or more within 4 years after birth and increased with age to a plateau in the age group over 20 years. The highest prevalence rate was over 80% in the age group of 35-54 years. The age-related patterns of infection in males and females were almost the same, although there were some sex-related differences by village and by age group. Infection with Opisthorchis viverrini appears to be a serious public health problem strongly associated with the frequent eating habit of raw fish in low land Laos.

Plasmodium ovale infections detected by PCR assay in Lao PDR.

Plasmodium ovate infection was demonstrated in 5 out of 143 inhabitants in a village in Lao PDR by blood microscopy and PCR assay. Although the specimen confirmed to be positive for P. ovale by microscopical examination was only one, the target sequences in the 18S rRNA genes of malaria parasite detected in all of the five cases were consisted with those of P. ovale by the PCR assay. This is the first report concerning the presence of so many cases with P. ovale infection in Lao PDR.

An epidemiological survey on intestinal parasite infection in Khammouane Province, Lao PDR, with special reference to Strongyloides infection.

To estimate the current prevalence of intestinal helminth infection in Lao PDR, a parasitological survey was conducted in three villages in Khammouane Province in December 1996, with special reference to Strongyloides infection. A total of 669 fecal samples were collected in the villages and examined by agar-plate culture method and Kato-Katz thick smear method. Intestinal helminths were demonstrated in 82% of the samples as follows: Ascaris lumbricoides (30.5%), Trichuris trichiura (23.7%), hookworm (28.8%), Strongyloides stercoralis (19.0%), Enterobius vermicuralis (3.4%), Opisthorchis viverrini (56.7%) and Taenia sp (3.0%). The infection rates of S. stercoralis were 27.5% and 18.4% in two rural villages, but only 9.4% in an urban village. The highest prevalence rate of Strongyloides infection was obtained in the age group from 20 to 29 years old, although the infection rate already reached 10% in the age group under 10 years old. The prevalence was consistently higher in male subject than females in almost all age groups.

Current status of malaria infection in a southeastern province of Lao PDR.

In Khammouane, a southeastern province in Lao PDR, active case detection (ACD) surveys for malaria infection on the villagers in three villages were conducted four times from December, 1995 to August, 1996. The malaria infection was demonstrated in 5.3-10.5% of the villagers throughout the year in 2 villages located in mountainous forest, but the infection was rarely observed in the other village located in the plain along the Mekong River, in which only 4 malaria cases were detected in August, 1996. Although the positive rate of malaria parasites among the villagers was not so significantly different in the rainy season compared with the dry season, the intensity of infections (ie parasitemia) was significantly higher in the rainy season. More than 90% of the positive villagers were children under 15 years old. Most infections were due to Plasmodium falciparum.

Collection of anopheline mosquitos in three villages endemic for malaria in Khammouane, Lao PDR.

Anopheline mosquito collections were made during the months of May and June (dry season) and August (rainy season), 1996 at villages, Nakham, Namdik and Hinboon Neua in Khammouane Province. Larval collections were also made in 3 slow running streams around Nakham villages in May 1996. Altogether, 3,549 adult females consisting 19 Anopheles species were collected by 3 nights of human and 6 animal bait traps and 3 resting collections. Among them, Anopheles vagus (19.75%), An. philippinensis (15.02%), An. nivipes (11.55%), An. pallidus (11.27%), An. peditaeniatus (8.34%), An. kochi (8.00%) and An. barbirostris (7.27%) were predominant species. The immatures of An. barbirostris, An. minimus, An. maculatus sensu lato, and An. culicifacies were found in the streams of Nakham. It is noteworthy that An. minimus, An. dirus and An. maculatus sensu lato, which are well known malaria vectors in Thailand, were recorded for the first time in this area.

Prevalence of intestinal parasitic infection among children in two villages in Lao PDR.

The prevalence of intestinal parasitic infection among 128 children under 15 years old in two villages in Khammouane Province, southeastern Lao PDR, was investigated. Overall prevalence of helminth infection was 77.3%; the prevalence was 64.8% in children under 6 years, 88.5% in those aged 6-10 years and 81.8% in the age group above 11 years. The prevalent helminths found in the subjects were Ascaris lumbricoides (48.4%), Trichuris trichiura (43.8%), hookworm (37.5%) and Opisthorchis viverrini (37.5%). Intestinal protozoan infection was demonstrated in 14.1%; Giardia lamblia was the most prevalent (8.6%) protozoan species.