Strongyloidiasis in northern Vietnam: epidemiology, clinical characteristics and molecular diagnosis of the causal agent

Abstract

Background: Strongyloidiasis is a health problem in Vietnam, but appropriate information is still limited. The aim of this study was to determine the prevalence, geographical distribution, epidemiological aspects, symptoms and other health indicators of Strongyloides stercoralis infections in patients from 27 provinces of northern Vietnam attending the Hanoi Medical University Hospital during 2016 and 2017.

Methods: Blood samples of 2000 patients were analyzed for S. stercoralis infection with an IgG ELISA test. Seroprevalence was analyzed by gender, age group, locality of origin (rural or urban areas) and symptoms. Stools from the seropositive patients were examined for the detection of worms which were subsequently used for species identification by morphology and rDNA ITS1 sequencing.

Results: A seroprevalence of 20% was detected, showing an increasing prevalence from young to older age groups but without significant gender difference. Seroprevalence was higher in rural areas than in urban areas, both in general and individually in all provinces without exception, and lower in the mountainous areas than in the large valley lowlands. The follow-up of the 400 patients showed eosinophilia in 100% of cases, diarrhoea in 64.5%, digestion difficulties in 58.0%, stomachache in 45.5%, stomach and duodenal ulcers in 44.5%, itching in 28.0% and fever in 9.5%. The prevalence of symptoms and signs were also higher in older age groups than in younger age groups. Worms were detected in stools of 10.5% of the patients. Sequencing of a 501-bp nuclear ribosomal DNA ITS1 fragment allowed for the verification of infection by Strongyloides stercoralis.

Conclusions: To our knowledge, this study is the largest survey of human strongyloidiasis in Vietnam so far and the first molecular identification of this nematode species in this country. Long-term chronicity may probably be usual in infected subjects, mainly in the older age groups.

Keywords: Diagnosis; Epidemiology; Geographical distribution; ITS1 sequence; Strongyloides stercoralis; Symptomatology; Vietnam.

Fig. 1

Maps of Vietnam showing political division in provinces. a Location of Vietnam in Southeast Asia, showing areas where human strongyloidiasis has been previously analyzed in the country: Ho Chi Minh city (seroprevalence of 18.2%), Dak Lak in rural central highlands (42.4%), Hue in the central coast area (29.9%) and Hanoi city where the Medical University Hospital receiving the patients studied is located. b Distribution of urban and rural areas of northern Vietnam where the patients live. c Geographical map of northern Vietnam showing seroprevalences (in parentheses) according to the 27 provinces analyzed (for province names see corresponding numbers in Table 2)

Fig. 2

Rhabditiform larva collected from stools of an infected patient from northern Vietnam. Note the rhabditoid oesophagus on the left

Fig. 3

Skin lesions found in Vietnamese patients showing two creeping eruptions (a, b) of the type of cutaneous larva migrans

Fig. 4

Seroprevalence and symptoms found in strongyloidiasis patients from northern Vietnam related to the age group

Fig. 5

Alignment of ITS1 sequences, including Strongyloides stercoralis from Vietnam (Sster-VN) and from other countries (Sster1 to Sster7). (.) = same nucleotide as in the first sequence

Fig. 6

Phylogenetic tree based on ITS1 sequence data including Strongyloides stercoralis from Vietnam (VN) and from other countries, together with other human-infecting nematode species available on GenBank

Fig. 7

Mean monthly values of climate factors influencing the external cycle of Strongyloides stercoralis in (i) Hanoi city representing the northern Vietnam area studied and where the Medical University Hospital receiving the patients studied is located; (ii) Ho Chi Minh city in southern Vietnam lowland; (iii) Hue in the central coast area; and (iv) Dak Lak province in rural south-central highlands