Taenia solium, Taenia saginata, Taenia asiatica, their hybrids and other helminthic infections occurring in a neglected tropical diseases' highly endemic area in Lao PDR

Abstract

Most part of Southeast Asia is considered endemic for human-infecting Taenia tapeworms; Taenia solium, T. saginata, and T. asiatica. However, until now there was no report of the occurrence of human cases of T. asiatica in Lao PDR. This study, conducted in Savannakhet Province, Lao PDR, microscopically examined a total of 470 fecal samples by Kato Katz method and found 86% of people harboring at least one helminth. Hookworms were detected in 56% of the samples besides Opisthorchis like eggs (42%), Trichuris trichiura (27%), Ascaris spp. (14%), and Taenia spp. (4%) eggs. Serology for cysticercosis showed 6.8% positives with results varying from 3% to 14.3% in Ethnic School students and Kalouk Kao village respectively. Species-specific PCR targeting mitochondrial DNA (mtDNA) of 28 tapeworms, recovered from 16 patients, revealed T. solium (n = 2), T. saginata (n = 21), and T. asiatica (n = 5). Two patients were confirmed to be coinfected with T. saginata and T. asiatica, indicating the endemicity of the 3 human Taenia in Lao PDR. However, nucleotide sequencing of a nuclear DNA gene, DNA polymerase delta ( pold) revealed that all the tapeworms identified as T. asiatica using mtDNA had T. saginata type allele at pold locus, demonstrating that they are not “pure T. asiatica” but the hybrid descendants between the two species, confirming the wide distribution of hybrids of T. saginata/ T. asiatica in Southeast Asia. The high prevalence of several helminthic NTDs in east Savannakhet area even with conventional control measures indicates the importance to establish wide and multifaceted health programs to sustainably improve the quality of life of the populations living in these communities.

Author summary

Southeast Asian Countries are endemic for several foodborne and soil-transmitted helminths occurring in different levels and areas, depending on environmental and cultural conditions. This study aimed to study the soil-transmitted helminths (STHs) and foodborne parasites in Savannakhet Province of Lao PDR, bordering with Vietnam. We found people infected with hookworms, roundworms, whipworms, intestinal/liver flukes, and tapeworms. We also detected antibodies against cysticercosis, an infection caused by eating the eggs of Taenia solium, the pork tapeworm. Focusing on human tapeworm infection, using molecular techniques based on mitochondrial DNA, we detected the three species of human tapeworms T. solium, T. saginata and T. asiatica. Interestingly, when we checked the same material using nuclear gene markers we noted that T. asiatica found in the region were the hybrid descendants of T. saginata and T. asiatica. The causes of hybridization may include people harboring different tapeworm’s species at the same time, allowing the exchange of genetic material but, the consequences of this hybridization are unknown including the seriousness of disease in people. Despite the deworming programs, there is a high prevalence of STHs and foodborne parasites in east Savannakhet area, therefore wide and sustainable health programs are an urgent task to improve the quality of life of the people living in the area.