Abstract
Rodents constitute the largest and most successful group of mammals worldwide. Brown rats (Rattus norvegicus) are one of the most common rodent species, and they serve as intermediate hosts of Hydatigera taeniaeformis. Although there have been a few studies reporting on the presence of the larval form of H. taeniaeformis (strobilocercus fasciolaris) in brown rats worldwide, little information is available on the genetic characterization of this parasite, with no molecular data from China. Therefore, from April 2014 to March 2016, this study was carried out to understand the prevalence and genetic characters of strobilocercus fasciolaris in brown rats captured in Heilongjiang Province in northeastern China. The livers of brown rats were collected and examined for the presence of cysts. Each cyst was identified based on morphological observation: the larvae with the naked eye and the scolexes under a microscope. The results were confirmed by polymerase chain reaction (PCR) and sequencing of the cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 4 (nad4) genes. At the investigated sites, 11.8% (13/110) of the brown rats were infected with strobilocercus fasciolaris. Based on sequence analysis, there were 10 and six haplotypes regarding the cox1 and the nad4 loci, with 24 and 42 polymorphic sites, respectively (degree of intraspecific variation: 0.3%–4.4% and 0.6%–4.7%, respectively). Twelve nucleotide sequences (six of the 10 at the cox1 locus and all six at the nad4 locus) have not previously been described. Base differences in three of the six novel cox1 gene sequences and five of the six novel nad4 gene sequences caused amino acid changes. Phylogenetic analyses of the cox1 and nad4 gene sequences based on neighbor-joining and Bayesian inference trees indicated that all the strobilocercus fasciolaris isolates belonged to Hydatigera taeniaeformis sensu stricto (s.s.). This is the first report on the genetic characterization of strobilocercus fasciolaris in brown rats in China. The findings of novel cox1 and nad4 nucleotide and amino acid sequences may reflect the region-specific genetic characterization of the parasite. The data will be useful to explore the biological and epidemiological significance of the intraspecific variation within H. taeniaeformis s.s.
Highlights
Taeniidae is one of the most important families of the order Cyclophyllidea, which contains most of the zoonotic parasites of medical significance
Thirteen of the 110 brown rats (11.8%) were confirmed to be infected with strobilocercus fasciolaris in the livers based on morphological observation and by sequence analysis of the partial cox1 and nad4 genes
The prevalence of 11.8% was lower than that reported in brown rats in the Philippines (100%) (Claveria et al, 2005), India (36.0%) (Singla et al, 2008), Korea (33.8%) (Lee et al, 2016), Serbia (29.9%) (Kataranovski et al, 2010), and Grenada, West Indies (29.6%– 67.6%) (Chikweto et al, 2009; Sharma et al, 2017)
Summary
Taeniidae is one of the most important families of the order Cyclophyllidea, which contains most of the zoonotic parasites of medical significance. H. taeniaeformis is found in the small intestine of cats and other felids, which are the definitive hosts. They acquire the parasitic infection by consuming the livers of rats and mice (the intermediate hosts) infected with the larval form of H. taeniaeformis (strobilocercus fasciolaris) (Singla et al, 2008; Moudgil et al, 2016). Several human cases have been documented: strobilocercus fasciolaris infection in the liver of a 77-year-old man from Czechoslovakia (Sterba and Barus, 1976) and H. taeniaeformis infection in the small intestine of individuals from Argentina, Japan and Sri Lanka (Sterba and Barus, 1976; Ekanayake et al, 1999; Hoberg, 2002)
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