Toxocara canis of canids is a parasitic nematode (ascaridoid) that infects humans and other hosts, causing different forms of toxocariasis. This species of Toxocara appears to be the most important cause of human disease, likely followed by Toxocara cati from felids. Although some studies from Malaysia and China have shown that cats can harbor another congener, T. malaysiensis, no information is available about this parasite for other countries. Moreover, the zoonotic potential of this parasite is unknown at this point. In the present study, we conducted the first investigation of domestic dogs and cats for Toxocara in Vietnam using molecular tools. Toxocara malaysiensis was identified as a common ascaridoid of domestic cats (in the absence of T. cati), and T. canis was commonly found in dogs. Together with findings from previous studies, the present results emphasize the need to explore the significance and zoonotic potential of T. malaysiensis in Vietnam and other countries where this parasite is endemic and prevalent in cats.
This paper presents the first reported use of 18S rRNA gene sequence to determine the phylogeny of Brugia pahangi. The 18S rRNA nucleotide sequence of a Malaysian B. pahangi isolate was obtained by PCR cloning and sequencing. The sequence was compared with 18S rRNA sequences of other nematodes, including those of some filarial nematodes. Multiple alignment and homology analysis suggest that B. pahangi is closely related to B. malayi and Wuchereria bancrofti. Phylogenetic trees constructed using Neighbour Joining, Minimum Evolution and Maximum Parsimony methods correctly grouped B. pahangi with other filarial nematodes, with closest relationship with B. malayi and W. bancrofti. The phylogeny of B. pahangi obtained in this study is in concordance with those previously reported, in which the 5S rRNA gene spacer region and cytochrome oxidase subunit I (COI) sequences were used.
Laboratory strain of the Malaysian Culex quinquefasciatus was susceptible to Wuchereria bancrofti. Thirty three percent of the Cx. quinquefasciatus that fed on W. bancrofti patient were infective after 12-14 days. There is a possibility for W. bancrofti to occur in the urban areas of the Malaysia in the near future.
Strongyloides stercoralis infection is prevalent worldwide and can cause lifelong infection in immunocompetent individuals, and potentially death in immunosuppressed patients. The diagnosis is hindered by the low sensitivity of microscopic examination, thus making serology an important complementary test to improve the detection rate. However, there were reports that some Strongyloides-infected individuals were negative with specific IgG and IgG4 assays, and other helminth infections were positive with commercial Strongyloides IgG-ELISAs. Thus, there is a need to develop better serodiagnostic methods for strongyloidiasis. We investigated the diagnostic potential of IgE-ELISAs using Strongyloides larval lysate. Sera from two groups infected with Strongyloides served as the positive reference, that is, 1) positive by commercial IgG-ELISAs and IgG4 rapid test, and stool samples positive by microscopy and/or PCR (group IA; n = 20); and 2) negative by IgG-ELISAs and IgG4 rapid test, but stool samples were PCR positive (group IB sera; n = 11). Sera from another two groups served as negative reference (controls), that is, 1) infected with other parasites (group II; n = 73) and 2) healthy donors (group III; n = 22). Results showed a 100% diagnostic sensitivity in detecting sera from groups IA and IB. The latter group of individuals probably had early infection because their IgG and IgG4 assays were negative. The optical density values of group IB sera were also significantly lower than those of group IA (P < 0.003). The IgE-ELISA was 100% specific when tested against sera from groups II and III. This study highlights the diagnostic potential of IgE-ELISA using larval lysate to detect strongyloidiasis, especially those with probable early infection.
Random amplification of polymorphic DNA (RAPD) was used to analyse genomic DNA from virgin females and males of Brugia malayi, with a view to identifying sex-specific differences predicted by an XX/XY system of chromosomal sex determination. A product of 2338 bp, amplified with the arbitrary primer 5' GTTGCGATCC 3', was obtained exclusively from males. Primers based on the sequence of this product amplified a DNA fragment of the expected size from each of two independent isolates of B. malayi (from Malaysia and Indonesia) by PCR. No reaction product was obtained from the closely related species Brugia pahangi. In a genetic cross between B. malayi males and B. pahangi females, F1 hybrid microfilariae were PCR-positive, indicating that the locus is paternally-inherited. Southern blotting demonstrated that the target sequence resides in the high molecular weight fraction of genomic DNA, confirming that it is of chromosomal, rather than mitochondrial, origin. Sequencing of the locus revealed significant similarity with members of a family of reverse transcriptase-like genes in Caenorhabditis elegans. In-frame stops indicate that the gene is non-functional, but multiple bands of hybridisation in Southern blots suggest that the RT sequence may be the relic of a transposable element. Multiple repeats of the dinucleotide AT occurred in another region of the sequence. These varied in number between the two isolates of B. malayi in the manner of a microsatellite, surprisingly the first to be described from the B. malayi genome. Because of its association with the Y chromosome, we have given the locus the acronym TOY (Tag On Y). Identification of this chromosome-specific marker confirms the XX/XY heterogametic karyotype in B. malayi and opens the way to elucidation of the role of Y in sex determination.