Waterborne zoonotic helminthiases

Abstract This review deals with waterborne zoonotic helminths, many of which are opportunistic parasites spreading directly from animals to man or man to animals through water that is either ingested or that contains forms capable of skin penetration. Disease severity ranges from being rapidly fatal to lowgrade chronic infections that may be asymptomatic for many years. The most significant zoonotic waterborne helminthic diseases are either snail-mediated, copepod-mediated or transmitted by faecal-contaminated water. Snail-mediated helminthiases described here are caused by digenetic trematodes that undergo complex life cycles involving various species of aquatic snails. These diseases include schistosomiasis, cercarial dermatitis, fascioliasis and fasciolopsiasis. The primary copepod-mediated helminthiases are sparganosis, gnathostomiasis and dracunculiasis, and the major faecal-contaminated water helminthiases are cysticercosis, hydatid disease and larva migrans. Generally, only parasites whose infective stages can be transmitted directly by water are discussed in this article. Although many do not require a water environment in which to complete their life cycle, their infective stages can certainly be distributed and acquired directly through water. Transmission via the external environment is necessary for many helminth parasites, with water and faecal contamination being important considerations. Human behaviour, particularly poor hygiene, is a major factor in the re-emergence, and spread of parasitic infections. Also important in assessing the risk of infection by water transmission are human habits and population density, the prevalence of infection in them and in alternate animal hosts, methods of treating sewage an

HOOKWORM INFECTIONS OF SCHOOLCHILDREN IN SOUTHERN THAILAND

Abstract. A study of hookworm infections of schoolchildren was conducted in Nakhon Si Thammarat Province, southern Thailand. Of the 2,940 hookworms that were recovered from the children, almost all (99.9%), were Necator americanus, only three (0.1%) were identified as Ancylostoma duodenale, and all were female worms. An estimation of the worm burden of and the worm expulsion from the schoolchildren indicated there were 17 cases of light intensity hookworm infection. Fifteen cases (88.2%) expelled worms in numbers that corresponded with the worm burden that was estimated from the number of eggs per gram of feces. Two cases (11.8%) expelled more worms than predicted. In 16 moderate intensity cases, five (31.3%) expelled worms in a quantity that corresponding with the estimated worm burden. Eleven cases (68.7%) expelled fewer worms than predicted. All cases of heavy intensity infection expelled fewer worms than predicted

Taeniasis and Other Helminthic Infections in the Northern and Northeastern Border Provinces of Thailand

Abstract icroscopic stool examinations to diagnose taeniasis and other helminthic infections were performed in three provinces: Nan in the north, and Ubon Ratchathani and Khon Kaen in the northeast. In Nan, lowland communities and hill-tribe communities were treated separately. By Kato thick-smear technique, the results indicated similar prevalence (13-15%) of helminthic infections in all three provinces. In Nan, higher infection rates were found among lowland (34.9%) than hilltribe inhabitants (13.0%). The most significant contributors to the high infection rate were minute intestinal flukes (29.4%) in lowland Nan, whereas in the hill-tribe community, prevalence was very low (0.5%). Infections in the two northeastern provinces were mainly caused by Opisthorchis liver flukes (6-7%). Hookworm infection rates were 4-6% in all study areas. Taenia eggs were found in 2% of both Nan groups, 3.7% in Ubon Ratchathani and 0.9% in Khon Kaen. Other helminths found included Ascaris lumbricoides (4%), Enterobius vermicularis (0.5%) in Nan hill-tribe communities, Strongyloides stercoralis (about 1-2%), Trichuris trichiura in both northeastern provinces (< 1%), and A. lumbricoides in Ubon Ratchathani (< 1%). Thirteen cases positive for Taenia eggs were treated with 2 g niclosamide, and five bowel movements were observed immediately following cathartic administration. Eleven of these 13 cases had Taenia segments in their stool. Long-chain strobilae were commonly expelled in the first two bowel movements. The head portion, or scolex, was released in five cases during any of the five bowel movements. One case expelled two separate long-chain strobilae with two scolices. All Taenia worms found were identified morphologically as T. saginata, either by scolex or gravid proglottids

Sympatric Occurrence of Taenia solium, T. saginata, and T. asiatica, Thailand

We confirmed sympatric occurrence of Taenia solium, T. saginata, and T. asiatica in western Thailand. DNA analysis of morphologically identified T. saginata, in a dual infection with T. solium, indicated it was T. asiatica. To our knowledge, this report is the first of T. asiatica and a dual Taenia infection from Thailand

Evidence of hybridization between Taenia saginata and Taenia asiatica

There has long been a debate as to the specific status of the cestode Taenia asiatica, with some people regarding it as a distinct species and some preferring to recognize it as a strain of Taenia saginata. The balance of current opinion seems to be that T. asiatica is a distinct species. In this study we performed an allelic analysis to explore the possibility of gene exchange between these closely related taxa. In total, 38 taeniid tapeworms were collected from humans living in many localities including Kanchanaburi Province, Thailand where the two species are sympatric. A mitochondrial DNA (mtDNA)-based multiplex PCR tentatively identified those parasites as T. asiatica (n = 20) and T. saginata (n = 18). Phylogenetic analyses of a mitochondrial cytochrome c oxidase subunit 1 (cox1) gene and two nuclear loci, for elongation factor-1 alpha (ef1) and ezrin-radixin-moesin (ERM)-like protein (elp), assigned all except two individual parasites to the species indicated by multiplex PCR. The two exceptional individuals, from Kanchanaburi Province, showed a discrepancy between the mtDNA and nuclear DNA phylogenies. In spite of their possession of sequences typical of the T. saginata cox1 gene, both were homozygous at the elp locus for one of the alleles found in T. asiatica. At the ef1 locus, one individual was homozygous for the allele found at high frequency in T. asiatica while the other was homozygous for the major allele in T. saginata. These findings are evidence of occasional hybridization between the two species, although the possibility of retention of ancestral polymorphism cannot be excluded