Clinical and Epidemiological Features of Imported Loiasis found in Beijing

Background Loiasis, a filarial disease primarily affecting rural populations in forested and adjacent savannah regions of central and west Africa, is rarely identified in China. There is a lack of comprehensive research on the clinical features of imported loiasis cases reported. The study aimed to enhance awareness of this rare parasitic disease. Methods Between July 2014 and July 2023, a retrospective survey was conducted in Beijing. All the patients’ epidemiological, clinical, and biological data, as well as their treatment and outcome, were gathered. Blood samples were analyzed for Loa loa detection using microscopy and molecular methods. Results Loiasis disease was diagnosed in 21 case reports who traveled to Africa. Most patients (95.2%) were male and their ages ranged from 24 to 53 years with the mean age of 38.19 ± 9.58 years. The vast majority of migrants (n=20; 95.2%) stayed for more than six months in their destination and worked outdoors. Calabar swelling (n=19; 90.5%) and pruritus (n=11; 52.4%) were the most common clinical presentation followed by pain (n=7; 33.3%) and skin rash (n=2; 9.5%). Adult worms were seen in the eyelid or subconjunctiva (n=2; 9.5%) and subcutaneous tissues (n=2; 9.5%). All patients had high eosinophil counts (> 0.52×10 9 /L), but only two cases had microfilariae in their blood and tested positive for filarial antigen. A section of adult worm was found in the skin lesional, surrounded by lymphocytes, plasma cells and eosinophils. All patients tested positive for L. loa -specific PCR. Phylogenetic tree of the ITS-1 region sequences clustered closely with that described L. Loa sequences endemic in Africa. All patients recovered after treatment with albendazole and diethylcarbamazine and had no recurrence of symptoms or eosinophilia. Conclusions Imported loiasis individuals have a distinct clinical profile, which is characterized by Calabar swelling and various non-specific symptoms (recurrent pruritus, pain and skin rash) along with predominant eosinophilia. Since most of them lack microfilariae in their blood, nucleic acid detection could be used as a diagnostic tool for hidden infection.