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Necator americanus and Ancylostoma duodenale are the two most important species of human hookworm, and occur in sympatry over much of their distribution. The specific diagnosis of hookworm infections is central to control. Diagnosis currently relies on the detection of hookworm eggs in human faeces and/or the specific identification of larvae by 'copro-culture' combined with microscopic examination. However, the eggs of the two species are morphologically indistinguishable, and the procedure of copro-culture is tedious and time-consuming to carry out. To work toward overcoming these limitations, a molecular approach utilizing genetic markers in the first internal transcribed spacer (ITS-1) of ribosomal DNA (rDNA) was established. The ITS-1 sequences of both hookworm species were determined, and specific oligonucleotide primers designed to regions of major sequence difference between the species were evaluated in polymerase chain reaction (PCR). Using a range of control samples, the primers allowed the specific identification of as little as 10 pg DNA of A. duodenale or N. americanus. The findings indicate clearly the potential for specific PCR to confirm the identity of eggs from faeces and larvae from the environment or host tissues. This should have important implications for studying fundamental aspects relating to anthelmintic efficacy and the epidemiology of hookworms.

The population dynamics and production of cercariae of Schistosoma japonicum in Oncomelania hupensis are reported. The experiments covered the whole life span of positive snails and different intervals of cercariae shedding. The results indicated that two patterns of the dynamics of cercariae shedding had been found in the life span of positive snails. The first was a long-time interval (4-7 days) and progressive decline pattern. The cercariae shedding of positive snails lasted 18-19 weeks in males and for 32-33 weeks (once a week). The second was a short-time interval (1-3 days) and continued release pattern. The cercariae shedding of positive snails lasted for 20-36 days (every day shedding). Shedding cercariae stimulate cercariae development.

Thirteen enzymes encoded by 16 loci of six population of Oncomelania hupensis in Zhejiang, China, were investigated by means of starch gel electrophoresis. Ten loci (AO, 6PGD, ME, AKP, OCT-1, HBDH-1, HBDH-2, XDH, MDH and MPI) were monomorphic and 6 loci (OCT-2, PGI, AAT, PGM-1, PGM-2 and ACP) were polymorphic. Three enzymes (OCT, HBDH and PGM) were encoded by 2 loci. The results indicated that there were allozyme variations in two subspecies, O.h. hupensis and O.h. fausti in Zhejiang, China. Nei's multilocus genetic distances (D) between subspecies ranged from 0.167 to 0.265. Minor genetic distances were detected between populations of the same subspecies. The results indicated that the enzyme acid phosphatase (ACP) is a possible marker to measure the degree of susceptibility of O. hupensis to S. Japonicum.