Malaria is an insect-borne disease transmitted by Anopheles mosquitoes or the importation of Plasmodium-infected blood, posing a serious threat to human health and life safety. This study aims to analyze the incidence of malaria in Qingdao at various stages from 1949 to 2021, to collate the control measures taken at different epidemic stages to assess the effectiveness of malaria control, and to identify a set of malaria control strategies suitable for Qingdao, while providing Chinese experience for other countries or cities in their malaria elimination efforts. A retrospective survey was used to collect information on malaria cases, control measures and prevention and control effects in Qingdao from 1949 to 2021, and to evaluate malaria control strategies and measures in Qingdao. 704 155 cases have been reported from 1949 to 2021, with three epidemic peaks: the incidence rate was 1715.9/100 000 in 1961, 1409.7/100 000 in 1965, and the most severe case occurred in 1972, with an incidence rate of 1635.6/100 000 and a case count exceeding 90 000. Throughout the various stages of malaria epidemics, Qingdao has effectively eliminated indigenous malaria by implementing diverse preventive and control measures. Since the last indigenous case of Plasmodium vivax was reported in 2002, all locally reported cases have been imported, mainly by returning migrant workers from Africa. This study examines a range of malaria prevention and control strategies and interventions that are appropriate for Qingdao. These measures have enabled Qingdao to successfully eliminate malaria and maintain malaria-free status for more than 20 years. These measures can also serve as a reference for similarly situated cities in Africa and Southeast Asia.

Trichinellosis is an important zoonotic parasitic disease worldwide and is principally caused by ingesting animal meat containing Trichinella infective larvae. Aspartyl aminopeptidase is an intracytoplasmic metalloproteinase that specifically hydrolyzes the N-terminus of polypeptides free of acidic amino acids (aspartic acid and glutamate), and plays an important role in the metabolism, growth and development of organisms. In this study, a novel T. spiralis aspartyl aminopeptidase (TsAAP) was cloned and expressed, and its biological properties and roles in worm growth and development were investigated. The results revealed that TsAAP transcription and expression in diverse T. spiralis stages were detected by RT-PCR and Western blotting, and primarily localized at cuticle, stichosome and intrauterine embryos of this nematode by immunofluorescence test. rTsAAP has the enzymatic activity of native AAP to hydrolyze the substrate H-Glu-pNA. There was a specific binding between rTsAAP and murine erythrocyte, and the binding site was localized in erythrocyte membrane proteins. Silencing of TsAAP gene by specific dsRNA significantly reduced the TsAAP expression, enzymatic activity, intestinal worm burdens and female fecundity. The results demonstrated that TsAAP participates in the growth, development and fecundity of T. spiralis and it might be a potential target molecule for anti-Trichinella vaccines.

In previous studies, a Trichinella spiralis serine protease (TsSP) was identified in excretion/secretion (ES) products from intestinal infective L1 larvae (IIL1) using immunoproteomics. The complete cDNA sequence of TsSP gene was 1372 bp, which encoded 429 amino acids with 47.55 kDa. The TsSP was transcribed and expressed at all T. spiralis life cycle phases, as well as mainly located at the cuticle and stichosome of the parasitic nematode. Recombinant TsSP bind to intestinal epithelial cells (IEC) and promoted larva invasion, however, its exact function in invasion, development and reproduction are still unknown. The aim of this study was to confirm the biological function of TsSP during T. spiralis invasion and growth using RNA interference (RNAi) technology. The results showed that on 1 day after electroporation using 2.5 µM siRNA156, TsSP mRNA and protein expression of muscle larvae (ML) was suppressed by 48.35 and 59.98%, respectively. Meanwhile, silencing of TsSP gene by RNAi resulted in a 61.38% decrease of serine protease activity of ML ES proteins, and a significant reduction of the in vitro and in vivo invasive capacity of IIL1 to intrude into the IEC monolayer and intestinal mucosa. When mice were infected with siRNA 156-transfected larvae, adult worm and muscle larva burdens were decreased by 58.85 and 60.48%, respectively. Moreover, intestinal worm growth and female fecundity were evidently inhibited after TsSP gene was knockdown, it was demonstrated that intestinal adults became smaller and the in vitro newborn larval yield of females obviously declined compared with the control siRNA group. The results indicated that knockdown of TsSP gene by RNAi significantly reduced the TsSP expression and enzymatic activity, impaired larvae intrusion and growth, and lowered the female reproductive capacity, further verified that TsSP might participate in diverse processes of T. spiralis life cycle, it will be a new prospective candidate molecular target of anti-Trichinella vaccines.