1. Background
Cystic Echinococcosis (CE) is one of the transmissible major diseases between animals and humans (1). The disease is common in most parts of the world, especially in countries with flourished animal husbandry. This disease causes much health and economic losses, annually (1-4). The disease causative agent is Echinococcus granulosus parasite, regarded as the second important parasitic worm disease in the world with global emission (5). Cystic Echinococcosis larval infection is caused by the growth of metacestode cysts in the intermediate host. The grown metacestodes in the organs of intermediate host typically generate a lot of protoscolices, and each of them has the potential to become adult worms in the body of the final host, since the infected organs are eaten (6-9). Studies have reported an average prevalence of 24.41%, 8.51%, 18.89%, and 35.76% in sheep, goat, bison, and buffalo, respectively (10). The infection of dog, as the definitive host of the disease, has been reported from 5% to 49% in various parts of Iran, and also 27.8% in sheep dogs (1). The disease has been reported from most provinces of Iran. In Iran, average surgical cases is estimated 1.2 per 100000 people (8). The overall direct and indirect annual costs of diagnosis, treatment, and control of CE are estimated as US$ 232.25 million in Iran, which indicates the importance of the issue (11). On the other hand, 60% of the infected rural population remains asymptomatic (10, 11).
Due to the spread of infection in various parts of the body and lack of a certain diagnosis method, serologic methods are quite useful in the diagnosis of the disease (2). The most appropriate immunoglobulin for detection of the history of CE or exposure to parasite is IgG, because the level remains high for a long time in blood (9, 12-16).
Enzyme Linked Immunosorbent Assay (ELISA), one of the serological methods for detection of hydatidosis with advantages, such as high sensitivity and specificity and implementation for many samples at the same time, is an appropriate method for seroepidemiological studies. Many researchers have reported on the prevalence of human hydatidosis by ELISA from several provinces of Iran (17-20).
2. Objectives
Considering the close contact of nomadic people with sheep dog, the present study was conducted to investigate the seroepidemiology of CE among in-migration and out-migration nomads in Lorestan province.
3. Methods
3.1. Study Area
Lorestan province is located in Western Iran, with an area of 28294 km2 and population of 1754000. Lorestan province is the thirteenth province in Iran in terms of population, and is considered as one of the most populous provinces of Iran. The city of Khorramabad is the capital of the province. Lorestan province is a mountainous land and apart from a few deserts, it is totally covered by the Zagros Mountains. Lorestan province is also the third province in terms of water with 12% of the water in Iran. This province, because of vast mountains, meadows, and proper precipitation, is the habitat for people, whose main occupation is animal husbandry and agriculture.
3.2. Sample Collection
In this cross-sectional study, among 5920 people living in the in-migration and out-migration nomadic areas in Aligudarz and Sepiddasht in Lorestan province, a total of 315 people from August to November in 2016 were randomly selected and demographic data, such as age, gender, occupation, education, drinking water, washing method of vegetables, and history of contact with dogs were completed using the questionnaire. Then, in order to investigate the presence of IgG antibodies, 5 mL of blood sample was provided and located inside the cold box, and sent as soon as possible under cold chain conditions to the nearest health center laboratory for centrifugation and serum production. The serum samples were stored at -20 °C until use.
3.3. Enzyme Linked Immunosorbent Assay Test
The collected sera were examined in terms of IgG antibodies against CE, using the Echinococcus ELISA Kit (Pishtazteb), in accordance with the manufacturer’s protocol. All the samples at the same time and same condition were evaluated by ELISA. The absorbance was measured by an ELISA reader at 450 nm and reference wave of 630 nm. The samples with optical density 10% higher than the specified cut-off were considered positive in terms of specific IgG against CE. The data were statistically analyzed using SPSS version 20 and STATA 12. T-test and chi-square were also used.
4. Results
Among 315 subjects, 161 (51.1%) were male and 154 (48.9%) were female. The most frequent age group was 10 to 20 years old, which constituted almost 25% of the participants. The seroprevalence of CE among the nomads was 5.7%. Table 1 shows the description of characteristics of the participants in this study. Among 18 (5.7%) subjects, who were serologically positive, 13 (72.22%) were male and five (27.77%) were female. Although the chance of infection with CE in males was 2.61 times more than females, yet the difference was not statistically significant (P < 0.065). In this study, 82.22% of infections were found in the age group under 30 years, and the highest prevalence percentage (7.79%) was in the age group of 20 to 30, yet no significant difference was seen between the age groups (P < 0.719).
Table 1.Seropositivity of Cystic Echinococcosis According Toepidemiological Factors in Nomads of Lorestan Province, Iran
| Variable | No. of Samples | Frequency of Contamination (%) | P Value |
|---|---|---|---|
| Gender | |||
| Male | 161 | 13 (8.07%) | 0.09 |
| Female | 154 | 5 (3.26%) | |
| Level of education | |||
| Illiterate | 194 | 9 (4.64%) | 0.55 |
| Low literate | 106 | 8 (7.55%) | |
| Diploma | 15 | 1 (6.67%) | |
| Age group (years) | |||
| < 10 | 75 | 5 (6.67%) | 0.72 |
| 10 - 19 | 81 | 5 (6.17%) | |
| 20 - 29 | 77 | 6 (7.79%) | |
| 30 - 39 | 47 | 1 (2.13%) | |
| 40 - 49 | 16 | 0 (0%) | |
| ≥ 50 | 19 | 1 (5.26%) |
In terms of education, more seropositive cases were seen amongst subjects with low education, yet no significant difference was observed between educational level and seropositivity of CE (P < 0.546). All the subjects with a positive serum had direct contact with dogs, failure to properly wash fruits and vegetables, had no knowledge of the disease and also all of them used spring water for drinking and washing vegetables. In terms of occupation, all cases were working in agriculture and animal husbandry (Table 1).
5. Discussion
The hydatid cyst is one of the major zoonotic diseases frequently seen in most tropical and semi-tropical areas in the world, especially in areas where a close relationship was seen between humans and dogs. Annually, many people are at risk of serious complications and even death caused by the disease (5, 6, 21-23). In order to assess the prevalence of the disease in Iran, several studies have been based on hospital information or seroepidemiology data (10, 24). Rafie et al. showed the prevalence of human hydatid cysts in Khuzestan province was 13.8% by ELISA (7). Sarkari et al. reported that the prevalence of human hydatidosis in Yasujas was 7.2% by ELISA (25). In the serological study of human CE in Kerman, the prevalence was 8.8% (12). Mirnejade-Asl and Fasihi Harandi, in a seroepidemiological study of CE using ELISA in Mugan plain, Iran, reported the prevalence of hydatidosis infection as 9.2% (26). The prevalence of CE in dogs as the certain host was 2% to 26%, and in intermediate host (sheep, goats, calves, and camels), it was also reported as 1.5% to 70% (8, 17, 27, 28).
This seroepidemiological study was also conducted to complete the available information about CE for the first time in the nomads of Lorestan province with limited access to medical facilities. According to the results, the percentage of positive CE serum cases was estimated 6.77%. Serum positivity in males (55.56%) was higher than females (44.44%), yet no significant difference was seen between positive sero-epidemiology and gender (P < 0.065).
Zibaie et al. (2011) reported the seroprevalence of 15.4% in Khorramabad city, Lorestan province; the results are not in agreement with the current study. One of the reasons might be that people in Khorramabad city use vegetables from farms around the city, where the stray dogs are often found, while the nomadic people usually use mountain vegetables, and the access of stray dogs to these vegetables is lower (27). However, on the other hand, Zibaie et al. showed that most positive cases were aged 20 to 29 years old, which is consistent with the present study (27).
Due to difficult access to nomadic people that sometimes might require long walking distance with ice supply limitation to keep the cold chain of the samples, and restriction of vehicles to travel to these areas, this study is the first study in Lorestan province and might be one of the few studies in Iran that examined CE seroprevalence in the nomadic population. Determining the prevalence of CE and publishing these results could be effective to sensitize relevant authorities in various areas of medical and veterinary sciences to provide the required facilities and equipment for disease control and prevention. Thus, it seems that complementary studies in livestock and humans are required. In general, according to the results, in order to prevent and control the zoonotic disease, increased awareness of nomads in understanding the transmission ways of the disease is suggested through health education programs corresponding the educational level of the target population, the majority of whom are illiterate. Active surveillance is also recommended in these areas.
