میزان شیوع و شدت آلودگی نشخوارکنندگان به دیکروسلیوم دندریتیکم در سه استان ساحلی دریای خزری

Introduction

Dicrocoelium dendriticum is one of the digenean trematodes that primarily live in bile ducts of a wide range of herbivorous as final hosts. However, humans, carnivores and rodents can be infected with the small liver trematode (Meshgi et al., 2012; Ohotori et al., 2014). The life cycle of Dicrocoelium has unique complexities, because it involves both snails and ants as first and second intermediate hosts. The main host will be affected by eating metacercaria-infected ants (Otranto and Traversa 2002).

Three known Dicrocoelium species include D. hospes, D. chinensis and D. dendriticum, the first species belongs to Africa, the latter is found in Asia (China) and the third is worldly distributed (Manga-Gonzalez et al., 2001; Otranto et al., 2007).

Although D. dendriticum is native in cattle of Iran, its different aspects have been neglected in the country. There have been very few epidemiological based studies in Iran. Most of the documents in Iran are abattoir-based reports on the prevalence of infection in sheep, goat and cattle. Different abattoir-based studies have been conducted in several provinces including Fars (Ansari-Lari, and Moazzeni, 2006), Guilan (Ahmadi et al., 2010), Northern Khorasan (Oryan et al., 2011) and Lorestan (Ezatpour et al., 2014). In a study, the prevalence of Dicrocoelium infection in dogs has been reported to be 14% in a region of Khorasan-Razavi province (Beiranvand et al., 2013).

Although serological methods have been developed for diagnosis of Dicrocoelium, the use of slaughterhouse examination (evaluation of adult worms in the liver) in this context seems to be more common at detecting dicrocoeliasis after stool examination compared with the other parasitological methods (Meshgi and Khodaveisi, 2014; Rehbin et al., 2002). It is worth noting that dicrocoeliasis is not only important in terms of health, but also in terms of economics. Confiscation of parasitized livers lead to direct losses and indirect losses due to hepatobiliary alterations which can affect on animal food digestion, growth, milk and meat production and then lead to heavy economic losses (Manga-Gonzalez et al., 2004;  Manga-Gonzalez et al., 2010).

Presence of a wide range of hosts, as well as a variety of land snails (100 species) and ants (21 species) as intermediate host have a great impact on the prevalence of Dicrocoelium infection in endemic areas (Manga-Gonzalez et al., 2001). Although Dicrocoelium infection has been present in Iran since ancient times, its prevalence has been increasing in recent years. However, there is not any report or other scientific documents about this fluke infection based on stool test (in live animals). Therefore, the present study was aimed to estimate the prevalence and intensity of Dicrocoelium infection in sheep and cattle in littoral states of the Caspian Sea.

Material and Methods

Sampling sites: The present study was conducted in Guilan, Mazandaran and Golestan provinces in the coastal strip of the Caspian Sea.

In total, 1344 faecal samples were collected directly from the rectum of 672 cattle and 672 sheep over a period of 3 months in the fall of 2016. For this purpose, 4 cities in every province, 4 villages in each city, and 4 districts in each village were chosen for sampling. Finally, a total of 48 geographic areas were sampled (Table 1).

Stool examination: Samples were collected directly from the rectum of all animals. Stool samples (4-6 gr) were labelled immediately (location name, collecting date, and kind of animal, etc.) and separately transferred to the parasitology laboratory.

 The samples (4-6 gr) were examined using flotation method by Zinc chloride and sodium chloride saturated solution (specific gravity: 1.58). The number of Dicrocoelium eggs per gram of feces (EPG) was obtained based on the type of livestock and sampling area.

Table 1: The number of collected samples based on geographic location and type of livestock

* Different Villages= A, B, C, D           

Results

The present study was aimed to determine the prevalence and intensity of sheep and cattle Dicrocoeliasis in the province of Guilan, Mazandaran and Golestan along the Caspian Sea. Moreover, the results are presented in two parts: the frequency and intensity of infection.

The prevalence of infection: Our finding indicated that sheep was infected 4 times more than cattle in all three provinces.

The average prevalence in Guilan Province was 36.21% in sheep and 9.37% in cattle. The highest infection rates in both hosts belonged to Langrood and Talesh (about 50% of sheep and 10% - 12.5% of cattle).

The average prevalence in Mazandaran province was about half that of infection in Guilan province. As matter of fact, it was calculated to be 21.35% and 4.16% in sheep and cattle, respectively. Furthermore, the highest infection rates were observed in Chalus and Noor, Mazandaran province (about 23%-33% in sheep and 6%-10% in cattle). In Golestan province, infection of sheep was only observed in Aliabad-Katul and Bandar-Gaz. The average infection of sheep and cattle was determined to be 6.87% and 1.87% in Golestan province (Table 2).

The intensity of infection: The average number of eggs per gram of feces in sheep was higher compared with cattle. The average number of Dicrocoelium eggs per gram of feces in sheep in three provinces of Guilan, Mazandaran and Golestan was 20.81, 6.76 and 2.44, while it was 6.86, 2.28 and 1.5 in cattle, respectively. Significant difference was observed between the EPG in different areas, but the highest rates were obtained in Langrood (about 32 in sheep and 9 in cattle) and Talesh (about 27 in sheep and 9 in cattle) from Guilan province (Table 2).

Table 2. Prevalence and intensity of Dicrocoelium infection in 3 provinces, Coastal regions of the Caspian Sea in the present study. Table 2: Prevalence and intensity of Dicrocoelium infection in 3 provinces, Coastal regions of the Caspian Sea in the present study

Discussion

This study is a comprehensive survey of D. dendriticum infection in 3 provinces of the Caspian Sea, northern part of Iran. A total of 1344 fecal samples of sheep and cattle were collected and then tested from different climatic zones in Guilan (n=640), Mazandaran (n=384) and Golestan (n=320).

The status of Dicrocoelium infection in three provinces has shown a significant difference. The average prevalence of infection in sheep and cattle from Guilan was 36.21% and 9.37%, while it was 21.35% and 4.16% in sheep and cattle of Mazandaran province, respectively. Furthermore, infection in Golestan province was at a lower level than the other two provinces (in sheep 6.87% and cattle 1.87%).

It should be taken into consideration that D. dendriticum is important for two reasons. First, the zoonotic potential of D. dendriticum. Transmission pattern of infection in definitive hosts, including humans and animals, is by eating ants infected with metacercaria. In this regard, human is known as an accidental host, when infected ant is eaten accidentally by human via food (such as bread or vegetables). However, human infections are generally rare but about other hosts, especially ruminants, presence of ants in pastures and meadows greatly increase the possibility of livestock infection such as cattle and sheep (Fakour and Meshgi, 2011; Kose et al., 2015).

The second importance of Dicrocoelium infection in large and small ruminants is due to severe economic losses. On the one hand, confiscation of parasitized livers in the slaughterhouse inspection leads to direct losses, weight loss, reduced milk, anemia, reduced product quality, digestive disorders, liver failure, and other factors can cause indirect economic losses (Mauelli et al., 2007). It should be noted that although indirect loss is less measurable, but due to its gradual, progressive and non-visible nature, it can have very important consequences.

Previous studies in Iran are based on the slaughterhouse reports and just according to the confiscation of parasitized livers. This method has great weaknesses for estimating the true prevalence. For example, the native nature of infection is not evaluated in this method, or cases of slaughtered animals may not be recorded such as illegal slaughter (Fakour and Meshgi, 2011; Meshgi and Khodaveisi, 2014).

In Iran, Dicrocoelium has been  previously  reported based on slaughterhouse inspection at  prevalence  rates  ranging  from 1.79% to 0.34% in sheep, 1.47% to 0.69% in cattle and 2.1% to 0.1% in goat in  the  province  of Fars (Ansari-Lari and Moazzeni, 2006). The parasite has been found infecting sheep and cattle in north Khorasan at a prevalence rate of 4.54% and 11.03%, respectively (Oryan et al., 2011). In Guilan province, Dicrocoelium is present at higher prevalence rates in sheep (85%), cattle (66%) and goat (23.25%) (Ahmadi et al., 2010). In the present study, the highest frequency was observed in sheep (36.21%) and cattle (9.37%) from the Guilan province and then found in sheep (21.35%) and cattle (4.16%) from Mazandaran province. In addition, the infection intensity based on the number of Dicrocoelium eggs per gram of feces was higher in sheep samples compared with the cattle. The average of EPG of feces was determined to be 20.81 and 6.86 in sheep and cattle from Guilan province, respectively. Furthermore, the average number of EPG was 6.76 and 2.28 in sheep and cattle from Mazandaran province, respectively. In the Golestan Province, frequency and intensity of infection was found at very low level.

Although these three province areas were close to each other in the littoral states of the Caspian Sea, they have different climates and weather. Rainfall, vegetation, soil type, relative humidity and altitude from the sea are different in the three provinces. Dicrocoelium intermediate host snail has been described to be a land snail which is placed on the ground or on the stem of forage. Nature of interest for the first intermediate host of Dicrocoelium is dry and calcareous or alkaline soils (Manga-Gonzalez et al., 2001). In all three provinces, infection in sheep has always been more than cattle. It is believed that sheep, particularly in Guilan and Mazandaran provinces are responsible for the distribution of infection of Dicrocoelium because of their higher population and free  roaming  in  the  environment. The high level  of  environmental  contamination  with  parasite  eggs  should  be  expected daily  providence if about 20 Dicrocoelium eggs per gram of faeces is released by sheep (Otranto and Traversa, 2002).

On the other hand, intermediate host snails and ants have a high population in pastures. A Dicrocoelium eggs have created up to 600 cercariae in the snails, which ultimately leads to infection of a lot of ants with metacercaria. Subsequently, an ant can develop up to 300 metacercaria and then eating an infected ant can create a lot of adult worms in the final host, as a result, it should be interpreted that the widespread infection of Dicrocoelium will be  achieved (Manga-Gonzalez et al., 2010;  Otranto and Traversa, 2002).

In conclusion, the results of the current comprehensive survey showed that Dicrocoelium has been increasing in the three provinces in the littoral states of the Caspian Sea. Guilan and Mazandaran have a high incidence, which emphasizes the need for a comprehensive study, and development of control program in endemic regions of Iran.

Acknowledgments

The authors would like to thank from all people who collaborated in this survey. Project support (No. 31383), was provided by the Center for Research of Endemic Parasites of Iran (CREPI). The authors thank gratefully the CREPI support.