Susceptibility of Laboratory Rodents to Trichinella papuae

Members of the genus Trichinella are small nematodes that can infect a wide range of animal hosts. However, their infectivity varies depending on the parasite and host species combination. In this study, we examined the susceptibility of 4 species of laboratory rodents, i.e., mice, rats, hamsters, and gerbils to Trichinella papuae, an emerging non-encapsulated Trichinella species. Trichinella spiralis and Trichinella pseudospiralis were also included in this study for comparison. Fifteen animals of each rodent species were infected orally with 100 muscle larvae of each Trichinella species. Intestinal worm burden was determined at day 6 and 10 post-inoculation (PI). The numbers of muscle larvae were examined at day 45 PI. The reproductive capacity index (RCI) of the 3 Trichinella species in different rodent hosts was determined. By day 6 PI, 33.2-69.6% of the inoculated larvae of the 3 Trichinella species became adult worms in the small intestines of the host animals. However, in rats, more than 96% of adult worms of all 3 Trichinella species were expelled from the gut by day 10 PI. In gerbils, only 4.8-18.1% of adult worms were expelled by day 10 PI. In accordance with the intestinal worm burden and the persistence of adults, the RCI was the highest in gerbils with values of 241.5+/-41.0 for T. papuae, 432.6+/-48 for T. pseudospiralis, and 528.6+/-20.6 for T. spiralis. Hamsters ranked second and mice ranked third in susceptibility in terms of the RCI, Rats yielded the lowest parasite RCI for all 3 Trichinella species. Gerbils may be an alternative laboratory animal for isolation and maintenance of Trichinella spp.

Molecular Detection of Ancylostoma duodenale, Ancylostoma ceylanicum, and Necator americanus in Humans in Northeastern and Southern Thailand

The 2 principal species of hookworms infecting humans are Necator americanus and Ancylostoma duodenale. Case studies on zoonotic hookworm infections with Ancylostoma ceylanicum and/or Ancylostoma caninum are known mainly from Asian countries. Of these 2 zoonotic species, only A. ceylanicum can develop to adulthood in humans. In the present study, we report a molecular-based survey of human hookworm infections present in southern and northeastern Thailand. Thirty larval hookworm samples were obtained from fecal agar plate cultures of 10 patients in northeastren Thailand and 20 in southern Thailand. Partial ITS1, 5.8S, and ITS2 regions of the ribosomal DNA genes were amplified using PCR. The amplicons were sequenced, aligned, and compared with other hookworm sequences in GenBank database. The results showed that, in Thailand, N. americanus is more prevalent than Ancylostoma spp. and is found in both study areas. Sporadic cases of A. ceylanicum and A. duodenale infection were seen in northeastern Thailand.

Evaluation of IgG4 Subclass Antibody Detection by Peptide-Based ELISA for the Diagnosis of Human Paragonimiasis Heterotrema

A synthetic peptide was prepared based on the antigenic region of Paragonimus westermani pre-procathepsin L, and its applicability for immunodiagnosis for human paragonimiasis (due to Paragonimus heterotremus) was tested using an ELISA to detect IgG4 antibodies in the sera of patients. Sera from other helminthiases, tuberculosis, and healthy volunteers were used as the references. This peptide-based assay system gave sensitivity, specificity, accuracy, and positive and negative predictive values of 100%, 94.6%, 96.2%, 100%, and 88.9%, respectively. Cross reactivity was frequently seen against the sera of fascioliasis (75%) and hookworm infections (50%). Since differential diagnosis between paragonimiasis and fascioliasis can be easily done by clinical presentation and fascioliasis serology, this cross reaction is not a serious problem. Sera from patients with other parasitoses (0-25%) rarely responded to this synthetic antigen. This synthetic peptide antigen seems to be useful for development of a standardized diagnostic system for paragonimiasis.

High Prevalence of Haplorchiasis in Nan and Lampang Provinces, Thailand, Proven by Adult Worm Recovery from Suspected Opisthorchiasis Cases

Opisthorchiasis, a risk factor for cholangiocarcinoma in humans, is of public health importance in Thailand. The Annual Surveillance Reports from Nan and Lampang Provinces, Thailand, for the year 2011 showed an opisthorchiasis prevalence of over 70% by recovery of eggs in the feces. This study investigated whether most cases are actually due to minute intestinal flukes (MIF) rather than Opisthorchis viverrini, as the eggs of both can hardly be differentiated by morphology. Fifty and 100 cases from residents in Nan and Lampang, respectively, had stools positive for eggs initially assumed to be those of O. viverrini. Each patient was given praziquantel at 40 mg/kg in a single dose. After 2 hr, 30-45 ml of the purgative magnesium sulfate was given, and stools were collected up to 4 times sequentially. The stools were examined for adult worms by simple sedimentation. It was found that 39 of 50 cases (78.0%) from Nan Province had Haplorchis taichui, with intensities ranging from 5 to 1,250 with an average of 62 worms/case. Taenia saginata (7 cases) and Enterobius vermicularis (1 case) were other helminths recovered as the co-infectants. In Lampang Province, H. taichui was recovered from 69 cases (69.0%). The number of flukes recovered ranged from 1 to 4,277, with an average of 326 worms/case. Four cases had Phaneropsolus bonnei, and 10 T. saginata as the co-infectants. Adult specimens of O. viverrini were not recovered from any stool. Clearly, MIF infection, especially haplorchiasis, is more common in northern Thailand. These findings should encourage the Public Health Office to employ more specific tools than Kato's method for surveillance of opisthorchiasis in Thailand.

OBSERVATION ON EXSHEATHMENT OF GNATHOSTOMA SPINIGERUM LARVA AND ITS PENETRATION THROUGH THE STOMACH WALL OF CYCLOPS

The mechanisms of Gnathostoma spinigerum larval exsheathment have been investigated. In our finding, after exposure to several proteases and chemicals, the sheath was shown as non-cuticle in nature and did not contain chitin by the use of Calcofluor dye. It appeared to be the first time that the process of penetration was live demonstrated, captured and followed in a single cyclops. It was found that the minimum time required for penetration into the body cavity through the stomach wall of the cyclops after ingestion of sheathed larvae was as early as 10 min. However it is still unclear whether, the mechanisms of exsheathment and penetration are enzymatic, mechanical or combined. Chiang Mai MedBull 2005;44(2):79-83.

OCCURENCE OF THERMOTOLERANT NAEGLERIA AND ACANTHAMOEBA IN SOME NATURAL WATER SOURCES IN CHIANG MAI

The free-living amoebae (FLA),Naegleria fowleri and Acanthamoeba spp. are ubiquitousin nature. Some thermotolerant FLA cause fatal human infections and the most importantsources of infection are in water. To determine the occurrence of thermotolerant FLA insome natural water sources around Chiang Mai, a total of 56 surface water and bottomsoil samples were collected from 28 water sources: water-loggedfi elds, ditches alongthe Chiang Mai-Lampang Superhighway, paddyfi elds, fi sh farms and large ponds. Thesediments of samples were cultured at 37 °C and thermotolerance was tested at 42 °C, withsubcultured amoebae.Naegleria and Acanthamoeba were morphologically differentiated,based on pseudopodia. Forty of the 56 samples (71.4%) yielded amoebae at 37 °C, and16 thermotolerant positive samples (28.6%) were further identifi ed at 42 °C. The thermotolerantpositive samples were recovered from all pH ranges of 5.0-8.5 and temperatureranges of 25-35 °C. Samples from the water-loggedfi elds gave the highest positive rate(75%), followed by those from paddyfi elds (50%), ditches (25%), large ponds (16.7%)andfi sh farms (15%). The number of thermotolerant positive samples obtained from watersamples (62.5%) was higher than that from soil samples (37.5%). Among 16 thermotolerantpositive samples, 6 (37.5%) were identifi ed as Naegleria spp., 3 (18.8%) as Acanthamoebaspp., 5 (31.3%) as a mix of both species, and 2 were unidentifi ed. High prevalenceof thermotolerant amoebae in the paddyfi elds and ditches indicated a health risk for localpeople.Chiang Mai Medical Journal 2009;48(3):117-124.