Host-finding behavior of Strongyloides stercoralis infective larvae to sodium cation, human serum, and sweat.

The host-finding behavior of Strongyloides stercoralis infective larvae was examined by in vitro agarose assay method. As human body fluid contains 0.85% (ca 0.15 molar) NaCl, various concentrations of sodium chloride, from 0.5M to 0.01M (7 steps), were examined. Many larvae were attracted at concentrations between 0.5 and 0.05M of sodium chloride. The concentration of 0.05M attracted the most larvae. The concentration of 0.02M of sodium chloride showed greatly reduced larval attraction compared with 0.05M. Therefore, the threshold concentration was determined as 0.05M. Then, 0.05M of chemicals were examined in a further experiment. Chloride compounds (NaCl, KCl, CaCl2, MgCl2) were investigated. These chemicals are components of human body fluids. Distilled water was used as the control in all experiments. Only sodium chloride attracted the larvae. Next, alkaline compounds were examined [NaOH, KOH, Ca(OH)2, and Mg(OH)2]. Larvae accumulated only at the NaOH site. The results suggested that the Na cation is important for larval attraction. A high pH value did not influence attraction at all. Next, human serum was tested. The human serum used was from normal serum to 1:32 diluted sera by distilled water (7 steps). Hierarchical attraction was seen according to serum concentration. Next, human sweat was collected from a limited zone of chest skin where only eccrine glands were distributed. Non-diluted sweat attracted the most larvae. Sweat might act as one of the most probable factors for infection by this skin-penetrating nematode.

Comparative studies on the pathological findings and mortality in Schistosoma mansoni infected mice after treatment with artesunate and the current antischistosomal drugs.

The effect of artesunate (ART) on the pathology and mortality rate of in Schistosoma mansoni infected mice was comparatively studied with the current drugs of choice for the treatment of schistosomiasis mansoni: praziquantel (PZQ) and oxamniquine (OX). S. mansoni experimentally infected mice were treated at 9th week of infection with ART, PZQ or OX at an oral dosage of 300 mg kg(-1), 600 mg kg(-1) and 100 mg kg(-1), respectively. Untreated, infected mice and non-infected mice were added as controls. Samples of mice were sacrificed and examined for the pathological findings at 1 week, 1 month, and 3 months after treatment. At 1 week after treatment, both gross and microscopic lesions were observed. No significant differences were noted among the infected groups. Differences were observed at 1 month after treatment. The lesions decreased more rapidly in groups treated with PZQ and OX. At 3 months after treatment, there were significant differences in the pathological findings among groups. In the groups treated with PZQ and OX, the lesions were markedly reduced and rarely found, but they were clearly observed in the group treated with ART and in the untreated, infected group. High mortality was also recorded in the group treated with ART and in the untreated, infected group. Therefore, the treatment of S. mansoni infected mice at 9 weeks of infection with ART did not reduce the pathological findings or the mortality rate compared to treatment with the current recommended schistosomicides, PZQ and OX.

Therapeutic effect of subcurative dose praziquantel on Schistosoma mansoni infected mice and resistance to challenge infection after treatment.

The therapeutic effect of a subcurative dosage of praziquantel (PZQ) on Schistosoma mansoni infected mice and resistance to challenged worm infection after treatment were assessed and compared with conventional treatment using a curative dosage of PZQ. S. mansoni infected mice were treated with PZQ at a curative dosage (600 mg kg(-1)) or a subcurative dosage (300 mg kg(-1)) at 9 weeks after infection. Untreated mice and non-infected mice were added as controls. The therapeutic effect of the drug was evaluated in terms of the mortality of mice after treatment, and the parasitological and pathological findings in mice sacrificed at 1 week, 1 month, or 3 months after treatment. Another sample of mice was not killed but challenged with S. mansoni cercariae at 1 week, 1 month, or 3 months after treatment. Resistance to re-infection was evaluated by the extent of challenged worm reduction. In conclusion, there was no significant difference in mortality, or parasitological and pathological findings between mice treated with PZQ at the two dosages. However, resistance to challenged worm infection was more sustained in the group treated with subcurative dose PZQ, especially at 3 months after treatment.

The current situation regarding the establishment of national ethical guidelines for biomedical research in Thailand and its neighboring countries.

This study discusses the establishment of ethical guidelines for ethical review for biomedical research performed in Thailand, and to some extent, in neighboring countries. There are differences, from country to country, at national and institutional levels regarding guidelines for ethical review committees. Only a handbook issued by Mahidol University describes guidelines for human genetic research and on research dealing with reproductive technology. Both these areas require special consideration to avoid violating human dignity, rights, and confidentiality. This indicates that further efforts should be made to establish research guidelines and/or principles dealing with the human genome.

Gnathostoma infection in fish caught for local consumption in Nakhon Nayok Province, Thailand. II. Deasonal variation in swamp eels.

From August 2000 to August 2001, 1844 swamp eels (Monopterus albus) were purchased from several local markets in Nakhon Nayok Province, Thailand, and examined for the presence of Gnathostoma advanced third-stage larvae. The overall prevalence was 30.1% and the mean number of larvae/eel (infection intensity) was 10.0. The highest infection rate (44.1%) was found in August 2000 and the lowest (10.7%) in March 2001. The greatest mean number of larvae/eel (75.1) was found in August 2000, whereas the fewest (2.3) was in July 2001. It is suggested that the prevalence and intensity of infection decreased within two months after the end of the rainy season and started to rise again about two months after the next rainy season began. A total of 5,532 Gnathostoma larvae were recovered from 555 infected eels, with a maximum number of 698 larvae/eel. The highest rates of Gnathostoma infection according to eel body length and weight were 87.5% in the group 91-100 cm, and 100% in groups of 901-1100 g, respectively. There were significant correlations between eel body lengths and infection rates, body lengths and infection intensities; eel body weights were also significantly correlated with infection rates and infection intensities. It was noted that the longer/ heavier the eels were, the higher would be the infection rates and the greater the infection intensities. Tissue distributions of Gnathostoma larvae in the livers and muscles of swamp eels were as follows: 43.0% of the total number of larvae were found in the muscles and 57.0% were in the liver; 29.7, 51.7, and 18.6% were in the anterior, middle, and posterior parts, respectively; 35.1% were in the dorsal part, while 64.9% were in the ventral part; 9.0, 18.7, 7.4, 20.6, 33.1, and 11.2% were in the anterodorsal, mediodorsal, posterodorsal, anteroventral, medioventral and posteroventral parts, respectively. Of the 5,532 Gnathostoma larvae examined, 1101 (19.9%) were found to possess morphological variants or abnormal cephalic hooklets. The most common unusual feature was that there were few to numerous extra rudimentary hooklets below row 4 and between the 4 rows of hooklets (7.6%), the presence of a fifth row of hooklets (3.5%), abnormal hooklets in any of the 4 rows of hooklets (5.2%), spiral arrangement of the 4 rows of hooklets (1.8%), and larvae having only 3 rows of hooklets (0.3%).

Gnathostoma infection in fish caught for local consumption in Nakhon Nayok Province, Thailand I. Prevalence and fish species.

Between August 2000 and August 2001, 12,216 fish of 73 species were purchased from several local markets in Nakhon Nayok Province, Thailand, and examined for the presence of Gnathostoma larvae. Almost all species were fresh-water fish that had grown naturally, rather than raised commercially. Eight species were found to be infected with gnathostome larvae. The overall prevalence was 5.1% (626/12,216) and a total of 5,969 larvae was recovered. The highest rate of infection (30.1 %) was found in Monopterus albus (swamp eel). The rates in the remaining infected fish were as follows: Anabas testudineus (climbing perch) 7.7%, Channa striata (striped snake-head fish) 7.4%, Clarius macrocephalus (Gunther's walking catfish) 6.7%, Channa micropeltes (giant snake-head fish) 5.1%, Channa lucius (blotched snake-head fish) 4.0%, Clarius batrachus (Batrachian walking catfish) 1.4%, and Ompok krattensis (butter sheatfish) 0.6%. The mean number of larvae/fish was highest in swamp eels (10.0 larvae/eel), and the maximum number of 698 larvae was recovered from one eel. The body sizes of the recovered G. spinigerum advanced third-stage larvae were 2.70-5.10 mm in length (average, 3.97+/-0.50 mm) and 0.29-0.60 mm in width (average, 0.40+/-0.04 mm). The average number of cephalic hooklets of the larvae from rows 1 to 4 were 41.8+/-0.5 (range, 40-43), 43.6+/-0.6 (range, 42-45), 46.1+/-0.9 (range, 44-48) and 49.3+/-0.7 (range, 48-51), respectively.

Antioxidant enzyme levels in the erythrocytes of riboflavin-deficient and Trichinella spiralis-infected rats.

The erythrocyte antioxidant enzyme levels of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) of riboflavin-deficient and Trichinella spiralis-infected rats were investigated. The rats were deprived of riboflavin at the 8th week of the experiment. At that time, the erythrocyte glutathione reductase activity coefficient (EGR AC), as an indicator of riboflavin status, was > or = 1.30 in rats fed a riboflavin-deficient diet and T. spiralis-infected rats fed a riboflavin-deficient diet showed no biochemical sign of riboflavin deficiency. At the 12th week of the experiment, the levels of catalase, SOD and GSH-Px were significantly lower in the riboflavin-deficient, T. spiralis-infected, and combined riboflavin-deficient and T. spiralis-infected, rats, compared to the control group. This may have been due to an increase in free oxygen radicals caused by riboflavin deficiency and parasitic infection.

Case report: intraocular gnathostomiasis in Vietnam.

This is the report of the first case of intraocular gnathostomiasis diagnosed in Vietnam. The disease progressed in two months in two distinct phases: in the first phase, the patient had swellings, which appeared at different times and in different locations, on his face--this phase lasted around one month; the second phase was the embedding of the parasite in the vitreous cavity of the right eye and uveitis. Surgical extraction of a living Gnathostoma larva was carried out. Based on morphological, histological criteria, the larva may have been an atypical third-stage of Gnathostoma spinigerum.

Gnathostoma infection in Nakhon Nayok and Prachin Buri, Central Thailand.

Gnathostoma infection in Nakhon Nayok and Prachin Buri Provinces, Central Thailand, was investigated. The prevalence and intensity of infection of swamp eels were determined; dog fecal samples and fresh-water copepods were examined for evidence of infection. The overall prevalence of eel infection was 38.1% (117/307) in Nakhon Nayok and 24.0% (74/308) in Prachin Buri--the former rate being significantly higher than the latter. Most of the positive Nalkhon Nayok eels (53.8%) harbored only 1-9 larvae; only one eel bore more than 50 larvae. In Prachin Buri, 67.6% of the positive eels harbored 1-9 larvae; again, only one eel bore more than 50 larvae. The mean number of 11.0 +/- 10.4 larvae/eel in Nakhon Nayok was not significantly different from that of Prachin Buri (9.3 +/- 11.4). A total of 1,292 gnathostome larvae were recovered from 307 eels in Nakhon Nayok. Of these, 52.3% had accumulated in the liver and 47.7% had spread throughout the muscles. In eels from Prachin Buri, 50.6% and 49.4% of the total of 688 larvae (from 308 eels) were found in the liver and muscles, respectively. The larvae preferred encysting in ventral of muscles rather than dorsal part; they preferred the middle portion to the anterior and posterior portions. The average length of gnathostome larvae recovered from Nakhon Nayok eels was 4.0 +/- 0.5 mm (range 2.5-5.1 mm) and the average body width was 0.40 +/- 0.05 mm (range 0.29-0.51 mm). Those from eels in Prachin Buri were 3.9 +/- 0.5 mm (range 2.2-5.1 mm) and 0.34 +/- 0.05 mm (range 0.20-0.48 mm), respectively. The mean body length and width of the larvae from eels in Nakhon Nayok were significantly greater than those of the larvae from eels in Prachin Buri. In Ban Phrao, Nakhon Nayok, none of the first 44 fecal specimens examined was positive. Of the second (68) and the third (70) specimens, one (1.5%) and two (2.9%) samples were positive. However, six months after the third fecal collection, no eggs were found. In Tha Ngam, Prachin Buri, no eggs were found in all three batches (109, 115, and 100 fecal samples). A cyclops survey of 4,000-5,000 crustacea from each of two areas (Ban Phrao and Tha Ngam) found no evidence of natural cyclops infection.

Fish as the natural second intermediate host of Gnathostoma spinigerum.

Gnathostomiasis is a helminthic disease most frequently occurring in Thailand. Human infections are usually found to be caused by Gnathostoma spinigerum, although five species of the genus Gnathostoma exist in Thailand, and three of these are capable of infecting man. In Thailand, 47 species of vertebrates--fish (19), frogs (2), reptiles (11), birds (11) and mammals (4)--have been reported to serve naturally as the second intermediate (and/or paratenic) hosts of G. spinigerum. Of these, fish, especially swamp eels (Monopterus albus), were found to be the best second intermediate/paratenic hosts: they had the highest prevalence rate and the heaviest infection intensity. However, the scientific names of these fish have been revised from time to time. Therefore, for clarity and consistency, we have summarized the current scientific names of these 19 species of fish, together with their illustrations. We describe one additional fish species, Systomus orphoides (Puntius orphoides), which is first recorded as a naturally infected second intermediate host of G. spinigerum.