Therapeutic efficacy of artesunate in Plasmodium vivax malaria in Thailand.

Our previous study showed that in vitro susceptibility of Plasmodium vivax to chloroquine has significantly decreased in Thailand within the past two decades. Thus, the evaluation of alternative antimalarials for treatment of vivax malaria is needed. The aim of this study was to examine parasitological and clinical efficacy of an artemisinin derivative (artesunate) for the treatment of vivax malaria in patients who were admitted to the Bangkok Hospital for Tropical Diseases. We randomly allocated patients aged 12-56 years to receive 3.3mg/kg (adult dose 200 mg) on the first day, and for the next four days each patient was given 1.65 mg/kg orally (adult dose 100 mg), total dose = 600 mg. After the five-day course of artesunate, primaquine was given: a single oral dose of 15mg for 14 days. A total number of 42 patients received treatment. All participants were followed up for 28 days. In all the cases, both parasitemia and fever were resolved rapidly; the mean fever clearance time and parasite clearance time, 14.6 and 36.7 hours, respectively, showed that therapeutic response to artesunate was better than that of chloroquine. The 14-day cure rate was 100%, but reappearance of parasitemia was seen in two patients on days 21 and 25 following treatment, respectively. These two cases of failure rate should be considered as true relapse rather than recrudescence, since the relapse interval in Southeast Asian vivax malaria according to recent findings seems to be 3 weeks after start of treatment, if primaquine is not given or an inadequate amount is given. In conclusion, artesunate might be useful in treatment of vivax malaria, causing a good blood schizontocidal effect. However, to prevent emerging resistance it should never be used alone.

Mapping soil-transmitted helminths in Southeast Asia and implications for parasite control.

Establishing the current status and distribution of soil-transmitted helminths is essential for developing and implementing parasite control. Although Southeast Asia is known to have a high prevalence of infection, a precise estimate of the total disease burden has not been fully described. Here, we use Geographical Information Systems (GIS) to collate and map recent published surveys on soil-transmitted helminth epidemiology and distribution for this region. Distinct geographical variation was observed, which is suggested to reflect climatic variation, as well as behavioral differences. However, for much of the region few data are available, and therefore it proved necessary to generate predictions of the distribution of soil-transmitted helminths using remotely sensed (RS) satellite sensor environmental variables. A significant finding was the importance of land surface temperature in influencing the distribution of Ascaris lumbricoides and Trichuris trichiura. Spatial analyses using RS satellite sensor data were then used to generate predictive maps of infection risk. This information provided the basis for an estimate of the population at risk of infection and the numbers requiring treatment. These applications of GIS and remote sensing provide a good basis for developing control of soil-transmitted helminths in the region.

A cross-sectional study of intestinal parasitic infections among schoolchildren in Nan Province, Northern Thailand.

A cross-sectional study of the prevalence of intestinal parasitic infections at eight schools in Bo Klau district and four schools in Chalerm Prakiet district, Nan Province, in January and February, 2001. A total of 1,010 fecal samples were examined using the formalin-ether sedimentation technique. Results revealed that the rate of helminthic infection was 60.0%, while protozoa accounted for 36.2% of infections; mixed infections were common, resulting in a total prevalence of both parasites of 68.1%. Helminthic parasites, listed by frequency of infections, were Ascaris lumbricoides (21.7%), hookworm (18.5%), Trichuris trichiura (16.3%), Opisthorchis viverrini (1.7%), Strongyloides stercoralis (0.9%) and Enterobius vermicularis (0.9%). The protozoal infections were Entamoeba coli (25.8%), Giardia lamblia (5.3%), Endolimax nana (2.5%), Entamoeba histolytica (1.4%), Blastocystis hominis (0.8%), Chilomastix mesnili (0.3%) and Iodamoeba bütschlii (0.1%). This study emphasizes the need for improved environmental hygiene ie clean water supplies and enhanced sanitation, in affected communities. Health promotion, by means of a school-based educational approach is recommended; regular check-ups should be implemented, and a continuos program of treatment should be considered.

Improvement of growth of Plasmodium falciparum fresh clinical isolates by using an established serum-free medium, GIT.

In the present study, we have tried to establish continuous cultures of fresh clinical isolates of P. falciparum by using a serum-free medium, GIT. To examine the ability of GIT to support the parasite growth, the growth of various P. falciparum isolates including two laboratory strains of P. falciparum, FCR3 and K1 was compared in both of GIT and RPMI 1640 medium supplemented by 10% human serum (RPMI-HS). Growth rates of various P. falciparum expressed as fold increases were compared in GIT and RPMI-HS, and the maximum growth rates of P. falciparum were 72 in GIT and 35 in RPMI-HS during the culture for 8 days. Growth rate of the clinical isolates varied individually in both culture media, with average growth rates of parasites being 15.9 in GIT and 8.8 in RPMI-HS, respectively (not significant). Growth rates of FCR3 and K1 strains were 28.0 and 6.6 in GIT, and 10 and 7.5 in RPMI-HS. After 30 days culture of P. falciparum in GIT, 9 of 12 clinical isolates still continuously propagated but other three isolates disappeared. Despite variation of the P. falciparum isolates in their abilities to multiply in GIT, our experiments suggested that GIT is useful for culture of fresh clinical isolates of P. falciparum that are derived from geographically distinct areas as well as laboratory strains used commonly in laboratory research.

A new type of advanced third-stage larvae of the genus Gnathostoma in freshwater eels, Fluta alba, from Nakhon Nayok, central Thailand.

Five advanced third-stage larvae of a newly identified type of genus Gnathostoma were collected from freshwater eels, Fluta alba, which were purchased at a market in Nakhon Nayok, central Thailand. The most remarkable characteristic of the newly identified larvae was the larger body size compared with any other larva of Gnathostoma spp. They were also distinguishable from other species by the shape of their hooklets, which branched in a complex manner at the base: this had not been previously observed in any other larval Gnathostoma. The newly described larvae had an average number of 44.5, 45.0, 49.0 and 55.1 hooklets on the head-bulb from the first to the fourth rows, respectively, which were comparable to those of larval G. spinigerum. However, the average number of nuclei in each intestinal cell was 2.21 and fewer than those of the larvae of G. spinigerum. These results suggest that the new type of larvae belong to either G. vietnamicum, G. malaysiae, or constitute a new species of the genus Gnathostoma.

Gnathostomiasis in Thailand: a survey on intermediate hosts of Gnathostoma spp. with special reference to a new type of larvae found in Fluta alba.

To clarify current status of gnathostomiasis in Thailand, a survey on intermediate hosts has been carried out at various localities since 1987. It was found that Fluta alba (Fresh water eel) as well as Channa striata (snake-headed fish) might be important in playing a role of transmitting the infection either among humans or reservoir animals. During the three years from 1987 to 1989, larvae of Gnathostoma spinigerum were found in 80-100% of F. alba obtained from markets in Nakhon Nayok, with a maximum recovery of 2,582 larvae per eel. Among larvae found in these eels, five were peculiar in possessing four rows of hooklets with complicated branches at the base. Epithelial cells of the intestine of these larvae contained 1-2 nuclei. These observations indicate that the larvae are different from those of reported species of Gnathostoma from Thailand including G. spinigerum, suggesting a possibility of the advanced third-stage larvae of G. malaysiae.

Preparation of monoclonal antibody against Angiostrongylus cantonensis antigen.

Monoclonal antibodies (MAb) against A cantonensis were produced through fusion of immunised spleen cells from BALB/c mice with NS-1 myeloma cells at a ratio of 10:1. The successful fusion rate on the 3rd day of fusion was 90.1%. Ten MAb were characterised, six of which were IgG1 and the remaining four were IgG2a, IgG2b, IgM and IgA respectively. Among 6 IgG1 MAb, four were A. cantonensis-specific, of which three reacted to adult worm antigen only and one reacted to both adult worm and juvenile worm antigens. Two other IgG1 MAb showed cross-reaction with other helminthic antigens of Toxocara canis. Ascaris suum. Paragonimus westermani, Dirofilaria immitis, Anisakis Spp, Gnatostoma Spinigerum and Clonorchis sinensis.

Genetic control of immune responses to Schistosoma japonicum.

The mouse IgE antibody response to S. japonicum antigen (Sj) was found to be under control of a gene(s) linked to the major histocompatibility complex. In some strains but not all among low responders, however, T cell responsiveness to Sj could be demonstrated by the induction of carrier effect as well as by proliferation response. Resistance to reinfection with a large dose of S. japonicum cercariae was demonstrated in most strains examined, except C57BL/6, irrespective of the immune responsiveness. Further studies will be needed to elucidate whether genetically regulated immune responses may affect susceptibility to or pathogenesis of schistosomiasis japonica in the mouse.