Background: Rapid diagnostic tests (RDTs) are used widely in the diagnosis of malaria. Although the effectiveness of RDTs for malaria has been described in many previous studies, the low performance of RDT particularly for Plasmodium ovale malaria in traveller has rarely been reported. Methods: This was a retrospective cohort study conducted on Japanese travellers diagnosed with malaria at the National Center for Global Health and Medicine between January 2004 and June 2013. The diagnosis of malaria was confirmed by microscopic examination, RDT, and polymerase chain reaction in all patients. The RDTs used in our study were Binax NOW Malaria (Binax Inc., Scarborough, Maine, USA) (BN) and SD Malaria Antigen Pf/Pan (Standard Diagnostics Inc., Korea) (SDMA). We compared the sensitivity of the RDTs to P. ovale malaria and Plasmodium vivax malaria. Results: A total of 153 cases of malaria were observed, 113 of which were found among Japanese travellers. Nine patients with P. ovale malaria and 17 patients with P. vivax malaria undergoing RDTs were evaluated. The overall sensitivity of RDTs for P. ovale malaria and P. vivax malaria was 22.2% and 94.1%, respectively (P < 0.001). The sensitivity of SDMA for P. ovale malaria and P. vivax malaria was 50% and 100%, respectively. The sensitivity of BN for P. vivax malaria was 90.0%, but it was ineffective in detecting the cases of P. ovale malaria. Conclusions: The sensitivity of RDTs was not high enough to diagnose P. ovale malaria in our study. In order not to overlook P. ovale malaria, therefore, microscopic examination is indispensable.

Background: Rapid diagnostic tests (RDTs) have widely been used in the diagnosis of malaria. Although the effectiveness of RDTs for malaria has previously been described in many reports, the low performance of RDTs particularly for Plasmodium ovale malaria in travellers have rarely been reported. Methods: This was retrospective cohort study conducted among Japanese travellers who were diagnosed with malaria at the National Center for Global Health and Medicine between January 2004 and June 2013. Diagnosis of malaria by microscopic examination, RDT, and polymerase chain reaction were performed for all the patients. The RDTs used in our study were Binax NOW Malaria (Binax Inc., Scarborough, Maine, USA) (BN) and SD Malaria Antigen Pf/Pan (Standard Diagnostics Inc., Korea) (SDMA). We compared the sensitivity of the RDTs of P. ovale malaria with that of Plasmodium vivax malaria. Results: A total of 153 cases of malaria were observed, of which 113 patients were Japanese travellers. Nine patients with P. ovale malaria and 17 patients with P. vivax malaria performing RDTs were evaluated. The overall sensitivity of RDTs for P. ovale malaria was 22.2% and that for P. vivax malaria was 94.1% (P < 0.001). The sensitivity of SDMA for P. vivax malaria was 100% and that for P. ovale malaria was 50%. The sensitivity of BN for P. vivax malaria was 90.0%; however, it was unable to detect the cases of P. ovale malaria. Conclusions: The sensitivity of RDTs was not high enough to diagnose P. ovale malaria in our study. Thus, microscopic examination is indispensable not to overlook P. ovale malaria.

We encountered a probable case of loiasis in a returned traveler from Central Africa. A 52-year-old Japanese woman presented to our hospital complaining of discomfort in her eyes and skin. She reported having frequently visited Central Africa over many years and having been extensively exposed to the rainforest climate and ecosystem. Although no microfilariae were found in her blood, there was an elevated level of IgG antibodies against the crude antigens of Brugia pahangi, which have cross-reactivity with Loa loa. She was treated with albendazole for 21 days, after which the antigen-specific IgG level decreased and no relapse occurred.

We encountered a probable case ofloiasis in a returned traveler from Central Africa. A 52-year-old Japanese womanpresented to our hospital complaining of discomfort in her eyes and skin. She reportedhaving frequently visited Central Africa over many years and having been extensivelyexposed to the rainforest climate and ecosystem. Although no microfilariae werefound in her blood, there was an elevated level of IgG antibodies against thecrude antigens of Brugia pahangi,which have cross-reactivity with Loa loa.She was treated with albendazole for 21 days, after which the antigen-specificIgG level decreased and no relapse occurred.

Objective: Monitoring the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants is important due to concerns regarding infectivity, transmissibility, immune evasion and disease severity. We evaluated the temporal and regional replacement of previous SARS-CoV-2 variants by the emergent strains, Alpha and Delta. Methods: We obtained the results of polymerase chain reaction screening tests for variants conducted in multiple commercial laboratories. Assuming that all previous strains would be replaced by one variant, the new variant detection rate was estimated by fitting a logistic growth model. We estimated the transmission advantage of each new variant over the pre-existing virus strains. Results: The variant with the N501Y mutation was first identified in the Kinki region in early February 2021, and by early May, it had replaced more than 90% of the previous strains. The variant with the L452R mutation was first detected in the Kanto-Koshin region in mid-May, and by early August, it comprised more than 90% of the circulating strains. Compared with pre-existing strains, the variant with the N501Y mutation showed transmission advantages of 48.2% and 40.3% in the Kanto-Koshin and Kinki regions, respectively, while the variant with the L452R mutation showed transmission advantages of 60.1% and 71.9%, respectively. Discussion In Japan, Alpha and Delta variants displayed regional differences in the replacement timing and their relative transmission advantages. Our method is efficient in monitoring and estimating changes in the proportion of variant strains in a timely manner in each region.