Human Alveolar Echinococcosis Prevalence Research Articles

A regressive analysis of the main environmental risk factors of human echinococcosis in 370 counties in China.

Echinococcosis is a natural focal, highly prevalent disease in China. Factors influencing the spread of echinococcosis are not only related to personal exposure but also closely related to the environment itself. The purpose of this study was to explore the influence of environmental factors on the prevalence of human echinococcosis and to provide a reference for prevention and control of echinococcosis in the future. Data were collected from 370 endemic counties in China in 2018. By downloading Modis, DEM and other remote-sensing images in 2018. Data on environmental factors, i.e., elevation, land surface temperature (LST) and normalized difference vegetation index (NDVI) were collected. Rank correlation analysis was conducted between each environmental factor and the prevalence of echinococcosis at the county level. Negative binomial regression was used to analyze the impact of environmental factors on the prevalence of human echinococcosis at the county level. According to rank correlation analysis, the prevalence of human echinococcosis in each county was positively correlated with elevation, negatively correlated with LST, and negatively correlated with NDVI in May, June and July. Negative binomial regression showed that the prevalence of human echinococcosis was negatively correlated with annual LST and summer NDVI, and positively correlated with average elevation and dog infection rate. The prevalence of human cystic echinococcosis was inversely correlated with the annual average LST, and positively correlated with both the average elevation and the prevalence rate of domestic animals. The prevalence of human alveolar echinococcosis was positively correlated with both NDVI in autumn and average elevation, and negatively correlated with NDVI in winter. The prevalence of echinococcosis in the population is affected by environmental factors. Environmental risk assessment and prediction can be conducted in order to rationally allocate health resources and improve both prevention and control efficiency of echinococcosis.

Assessment of a 10-year dog deworming programme on the transmission of Echinococcus multilocularis in Tibetan communities in Sichuan Province, China

Human alveolar echinococcosis (AE) is considered a neglected zoonotic disease by the World Health Organization (WHO). The causative pathogen, Echinococcus multilocularis, lives as an adult tapeworm in the intestinal tract of canines. AE was identified as an emerging public health issue in Tibetan communities of Shiqu County 20 years ago. On St. Lawrence Island, Alaska (USA), in the 1980s peri-domestic transmission of E. multilocularis was controlled by regular deworming of owned dogs over a 10-year period. In Tibetan communities, on the Tibetan Plateau, control of E. multilocularis transmission is challenging due to the continental setting, complex epidemiology, disease ecology, geography, and socio-cultural factors. However, a control programme based on deworming owned dogs using praziquental (PZQ) has been carried out since 2006. Assessment was conducted in townships where baseline data were available 10 years prior. Purging of dogs by oral administration of arecoline was used to measure E. multilocularis prevalence, trapping small mammals around communities was employed to assess the change in infection of pikas and voles, and analysis of human AE abdominal ultrasound-based data was used to understand the change in prevalence in the past decade. In all three evaluated townships, the E. multilocularis prevalence in owned dogs was significantly (P < 0.01) reduced from 7.23% (25/346) during 2000–2003 to 0.55% (1/181) in 2016. Human AE ultrasound-based prevalence (adjusted for age and sex) in five evaluated townships decreased significantly (P < 0.01) from 6.25% (200/3,198) during 2000–2002 to 3.67% (706/19,247) during 2015–2017. The 2016 prevalence of E. multilocularis metacestodes in small mammal intermediate hosts was not significantly different from the prevalence in 2008. The control programme was effective in reducing E. multilocularis infection in owned dogs and human AE prevalence, but did not significantly impact infection in wildlife intermediate hosts.

Human cystic and alveolar echinococcosis in the Tibet Autonomous Region (TAR), China.

Human cystic echinococcosis (CE) is known to be endemic in the Tibet Autonomous Region (TAR), China; however, there is relatively little data from hospital records or community prevalence studies, and the situation regarding occurrence of human alveolar echinococcosis (AE) is unclear. Here we review the available reports about human echinococcosis in the seven prefectures of TAR. In addition, two pilot studies by mass screening using ultrasound (with serology) were undertaken (2006/7) in Dangxiong County of Lhasa Prefecture (north central TAR) and Dingqing County of Changdu Prefecture (eastern TAR). In Dangxiong County a prevalence of 9.9% (55/557) for human CE was obtained but no human AE cases were detected. By contrast, in Dingqing County (N= 232 persons screened), 11 CE cases (4.7%) and 12 AE cases (5.2%) (including one mixed CE and AE case) were diagnosed by ultrasound. Hospital records and published reports indicated that CE cases were recorded in all of seven prefectures in Tibet Autonomous Region, and AE cases in four prefectures. Incidence rates of human CE were estimated to range from 1.9 to 155 per 100,000 across the seven prefectures of TAR, with a regional incidence of 45.1 per 100,000. Incidence of AE was estimated to be between 0.6 and 2.8 cases per 100,000. Overall for TAR, human AE prevalence appeared relatively low; however, the pilot mass screening in Dingqing in eastern TAR indicated that human AE disease is a potential public health problem, possibly similar to that already well described in Tibetan communities bordering TAR in north-west Sichuan and south-west Qinghai provinces.

Echinococcus spp. and echinococcosis

Echinococcus spp. are cestode parasites commonly known as small tapeworms of carnivorous animals. Their medical importance lies in the infection of humans by the larval stage of the parasites, predominantly including Echinococcus granulosus, which is the causative agent of cystic echinococcosis (CE) and Echinococcus multilocularis, which causes alveolar echinococcosis (AE). A few other species or genotypes are only very rarely or not at all found in humans. Due to the emerging situation in many parts of Europe, the present article will predominantly focus on E. multilocularis . The natural life cycle of E. multilocularis involves predominantly red and arctic foxes as definitive hosts, but domestic dogs can also become infected and represent an important infection source for humans in highly endemic areas. In the definitive host, egg production starts as early as 28 days after infection. After egg ingestion by a rodent or a human, larval maturation will occur practically exclusively within the liver tissue. The geographic distribution of E. multilocularis is restricted to the northern hemisphere. In Europe, relatively frequent reports of AE in humans occur in central and eastern France, Switzerland, Austria and Germany. Within the past ten years, the endemic area of Europe now includes many more countries such as Belgium, The Netherlands, Italy, and most former Eastern countries as far as up to Estonia. The Asian areas where E. multilocularis occurs include the whole zone from the White Sea eastward to the Bering Strait, covering large parts of Siberia, western and central parts of China and northern Japan. Worldwide there are scant data on the overall prevalence of human AE. Some well-documented studies demonstrate a generally low prevalence among affected human populations. The annual mean incidence of new cases in different areas including Switzerland, France, Germany and Japan has therefore been reported to vary between 0.1 and 1.2/ 100,000 inhabitants. The incidence of human cases correlates with the prevalence in foxes and the fox population density. Recently, a study documented that a fourfold increase of the fox population in Switzerland resulted in a statistically significant increase of the annual incidence of AE cases [1] (Schweiger et al., 2007). This dramatic increase in red fox populations has also been reported throughout Europe, especially in urban areas. The so-called city-fox phenomenon and, thereafter, the increased proximity of foxes with humans and an urban domestic dog – rodent cycle may, therefore, have significant public health implications [1-3]. In infected humans the E. multilocularis metacestode (larva) develops primarily in the liver. Occasionally, secondary lesions form metastases in the lungs, brain and other organs. The typical lesion appears macroscopically as a dispersed mass of fibrous tissue with a conglomerate of scattered vesiculated cavities with diameters ranging from a few millimeters to centimeters in size. In advanced chronic cases, a central necrotic cavity containing a viscous fluid may form, and rarely there is a bacterial superinfection. The lesion often contains focal zones of calcification, typically within the metacestode tissue. Histologically, the hepatic lesion is characterized by a conglomerate of small vesicles and cysts demarcated by a thin PAS-positive laminated layer with or without an inner germinative layer [4]. Parasite proliferation is usually accompanied by a granulomatous host reaction, including vigorous synthesis of fibrous and germinative tissue in the periphery of the metacestode, but also necrotic changes centrally. In contrast to lesions in susceptible rodent hosts, lesions from infected human patients rarely show protoscolex formation within Correspondence: bruno.gottstein@ipa.unibe.ch Faculty of Medicine, Institute of Parasitology, University of Bern, Bern, Switzerland Gottstein Acta Veterinaria Scandinavica 2010, 52(Suppl 1):S5 http://www.actavetscand.com/content/52/S1/S5

SOCIOECONOMIC AND BEHAVIOR RISK FACTORS OF HUMAN ALVEOLAR ECHINOCOCCOSIS IN TIBETAN COMMUNITIES IN SICHUAN, PEOPLE’S REPUBLIC OF CHINA

Data from two cross-sectional investigations on 7,138 subjects were used to explore risk factors of human alveolar echinococcosis (AE) in Tibetan communities. The overall human AE prevalence was 3.1% (223 of 7,138), females had a higher prevalence (3.6%, 132 of 3,713) than males (2.7%, 91 of 3,425; P = 0.011), and herdsmen had a higher prevalence (5.2%, 154 of 2,955) than farmers (1.8%, 12 of 661; P < 0.001) and urban populations (2.1%, 49 of 2,360; P < 0.001). Age in all populations, number of dogs kept, fox skin ownership in farmers, not preventing flies from landing on food in herdsmen, using open streams as drinking water sources, and playing with dogs in urban populations were statistically significant risk factors. The results suggest that AE is highly endemic in the eastern Tibetan plateau, in Sichuan Province, the role of the dog is important for human infection, and other factors associated with environmental contamination may vary according to structure and practices of communities.

Landscape Dynamics and Risk Modeling of Human Alveolar Echinococcosis

Human alveolar echinococcosis (AE) is a rare but fatal liver disease caused by a parasitic tapeworm. Between 1994 and 1997 a medical survey in a rural area in central China revealed the highest incidence rate of the disease recorded in the world to date, with 15.8 percent of the population infected in one village. Hypotheses on the nature of the transmission mechanisms from the natural to human environment focused on the effects of recent landscape change from forest to agricultural land. Archived Landsat MSS and TM data were used to examine relationships between landscape and human AE prevalence in 31 villages. The results showed a significant positive correlation between AE and the proximity of villages to forest, grassland, and shrubland vegetation, and a negative correlation with the area of cultivated land. A predictive model, based on spatial characteristics of the landscape, is now being developed with the aim of designing management tools for disease control.

An epidemiological and ecological study of human alveolar echinococcosis transmission in south Gansu, China

Human alveolar echinococcosis (AE) is usually a rare, highly pathogenic zoonotic disease, transmitted across the northern hemisphere between fox and rodent hosts. In China the first cases were described in 1965; however very few epidemiological studies have been undertaken since. Following identification in 1991 of a serious focus of human AE in south Gansu province, detailed village-based community and ecological studies were carried out between 1994 and 1997. Hepatic ultrasound mass screening with serological testing (five tests) identified 84/2482 new AE cases (3%). An overall prevalence of 4.1% (135/3331) was recorded for the area when previous cases were also included. Based on a seropositive result only, without an ultrasound scan indication, no additional AE cases were identified. Of the evolutive AE cases, 96% were seropositive in at least one test, while up 15–20% of individuals who exhibited hepatic calcified lesions and 12–15% exhibiting hepatic nodular lesions were seropositive for specific Em2 or Em18 antibodies. Village ( n=31) human AE prevalence rates varied from 0 to 15.8%. Questionnaire analysis indicated that total number of dogs owned over a period was a risk factor ( P<0.006), but not a history of red fox hunting ( P>0.6). Rodent ecology studies revealed an association between density indices of voles ( Microtus limnophilus) and village AE prevalence rates, on the one hand, and village landscape characterised by a ratio of scrub/grassland to total area above 50% ( P<0.005). Long-term transmission of Echinococcus multilocularis and risk of zoonotic infection of south Gansu farmers may be related ultimately to a process of deforestation driven by agriculture. This in turn probably results in creation of optimal peri-domestic habitats for rodents that serve as intermediate host species (such as M. limnophilus) and subsequent development of a peri-domestic cycle involving dogs.

Recent Epidemiologic Trends in Alveolar Echinococcosis Prevalence in Humans and Animals in Hokkaido

We investigated chronological and geographical changes of alveolar echinococcosis (AE) prevalence in 14 administrative districts of Hokkaido based on the data of our epizootiologic and seroepidemiologic surveys. The results suggest that the chronological transitions of the enzootic state of AE in Hokkaido markedly reflect those of human AE prevalence, and that new prevalence of human AE has been emerging from central and western Hokkaido.

Human alveolar echinococcosis seroprevalence assessed by western blotting in Hokkaido.

To investigate the recent prevalence of human alveolar echinococcosis in Hokkaido, we took advantage of Western blotting analysis capable of classifying persons infected with Echinococcus multilocularis into two groups: the complete and incomplete types. From the geographic distribution, the residents with the complete type appeared for the first time in 1992 in the Oshima district (western Hokkaido). The age distribution indicated that persons with the complete type increased, since 1990, in the age groups younger than 30 years old.

A large focus of alveolar echinococcosis in central China

Human alveolar echinococcosis (AE) is a rare and highly pathogenic helminthic zoonosis due to infection with the intermediate stage of the small fox tapeworm, Echinococcus multilocularis. Parasite transmission is restricted to northern latitudes, including central and north China, from where few clinical and no detailed community studies have been reported. In August, 1991, 65 (5%) of 1312 people residing in three rural communes of Zhang County, Gansu Province, China were diagnosed as having hepatic AE after mass ultrasound scanning with serological back-up. This represents one of the highest prevalence rates of AE ever recorded. It is also the first time that mass ultrasound scanning and serology have been used together in an AE endemic region. The region was selected one year earlier, when a preliminary serosurvey on 606 unselected people in the same locality resulted in an 8·8% serum antibody positive rate with a 76% rate of confirmation of hepatic AE in 37 individuals who could be followed up in 1991. Seropositivity rates varied for villages between 0 and 20·5%. Overall, females (7·8%) had a significantly greater risk of infection than males (2·5%), especially in the 31-50 age group, a difference which may be related to contact with dogs and dog faeces over many years. Age-specific prevalence of AE increased from 0% in the under-5-year group to 8·2% in those aged 31-50. The youngest case was 11 years and the mean age of diagnosis was 40 years. Adult tapeworms of E multilocularis were identified from the small intestines of 10% of domestic dogs. Sylvatic animal hosts of the parasite have not yet been identified. The high prevalence of human AE in this region of central China is most probably due to semi-domestic transmission of E multilocularis between wild rodents and dogs, together with the poverty and poor hygiene in these rural communities.

PREVALENCE OF HUMAN ALVEOLAR ECHINOCOCCOSIS IN HOKKAIDO AS EVALUATED BY WESTERN BLOTTING

The Western blotting (WB) method was used to evaluate the prevalence of human alveolar echinococcosis in Hokkaido, Japan. One hundred and sixteen WB-positive serum specimens were found in 1987 and 1988, and were grouped into two serologically different types from their WB-immunostaining patterns: "complete type", that showed multiple bands with various molecular weights ranging from 29 to 205 kilodaltons (kDa), and "incomplete type", that revealed a few bands with low molecular weights of 30-35 kDa and/or with molecular weights higher than 90 kDa. Therefore, we found that the WB method is applicable for the sero-epidemiological studies of human alveolar echinococcosis in Hokkaido.