Ultrasonographic Liver Findings in a Sheep Flock Involved in Chronic Fasciolosis

Fasciola hepatica is one of the common causes of the disease in ruminants. Infection of cattle and sheep occurs by ingestion of the parasite infection stage in wet rangelands and areas below sea level. Symptoms of fasciolosis include anemia, weight loss and submandibular edema, and sometimes diarrhea. Diagnosis of liver contamination with this parasite is possible via observing yellow-brown eggs of the parasite in feces. One of the consequences of this parasite is the destruction of the liver tissue due to the migration of parasite larvae and the reduction of oxygen in these areas. This parasite causes a variety of clinical symptoms in sheep, which may affect the hematopoietic system, the liver, the lungs and the intestines. Fasciola hepatica is one of the trematodes which mainly affect the liver of sheep, and these livestock are accidentally infected by eating plants or drinking contaminated water with the metacercariae of this parasite (Mezo et al., 2004). The penetration of the worm into the intestinal wall leads to local bleeding and inflammation, then this parasite brings itself to the liver parenchyma through the peritoneum within 4-6 weeks, causing severe parenchymal degeneration and inflammation. Sometimes worms die and form cavities filled with necrotic holes, which subsequently replace scar tissue in that area (Keiser et al., 2010). Parasites often infect the liver parenchyma and never get bile ducts, However, in some cases, these parasites are also carried to the bile ducts and gallbladder and cause inflammatory reactions and dilatation of these ducts (Kaya et al., 2011). In some rare cases, immature worms migrating from the intestine to the liver may divert their pathways and cause Ectopic Fasciolosis and affect other parts of the body including abdominal wall, pancreas, lungs, pleural space (Moazeni and Ahmadi 2016).

There are several methods for diagnosis of fasciolosis, including direct parasitological methods, indirect immunological tests, or other non-invasive methods. It is not helpful to find egg parasites in the feces at the beginning of the disease because it takes at least 4 months for the  worm to mature and lay its first eggs. On the other hand, due to the frequency of laying eggs, repetition of these tests is necessary. In ectopic infections, fecal testing cannot be worthwhile. Immunological methods are mainly based on antibody measurements, and few of these tests detect antigens in the bloodstream or the antigen-antibody complexes (Keiser et al., 2012). Since clinical and laboratory findings of the fasciola may be mistaken for many other diseases, sometimes it is necessary to use other methods such as diagnostic imaging to confirm the diagnosis and evaluate the response to treatment (Scott et al, 2005). From diagnostic imaging methods, ultrasound is a non-invasive, accessible and inexpensive method for detecting injuries due to the presence of this worm in the bile ducts and may exhibit a worm-shaped structure that does not have acoustic shadowing (Martínez-Valladares et al., 2010). In ultrasonography local and stained echogenicity, liver abscess, hypoechoic or hyperechoic nodules that have spread to the thickened capsule of the liver, ecogenic mass in the gallbladder, ecogenic damages under the capsule of the liver and dilatation of the internal and external biliary ducts of the liver may be seen (Gonzalo-Orden et al., 2003). In some studies, ultrasonography has been used to evaluate the treatment process of sheep’s fasciolosis (Winkelhagen et al., 2012).

To our knowledge, some studies have exhibited findings as diagnostic imaging and sonography in some animal diseases, but  this is the first study of ultrasonographic analysis of sheep flock with naturally infected fascioliasis and we intend to introduce the possibility of ultrasonography technique in non-invasive and close to accurate diagnosis of fascioliasis.

Materials and Methods

In this cross-sectional study, 256 sheep of the Makoei breed, including 130 male (50.8%) and 126 female (49.2%) with diagnosis of chronic fasciolosis were confirmed by appearance of fluke eggs in feces and, using enzyme-linked immunosorbent assay (ELISA) were referred to the Department of Radiology and Ultrasonography, Faculty of Veterinary Medicine, Islamic Azad University Urmia. Average age of sheep was 2.1 years (minimum age 7 months and maximum age 6 years). After obtaining basic information including age and sex, Doppler ultrasound was performed on the liver of each sheep with dorsal and left lateral recumbency and for each ultrasonography, at least 5 and maximum 15 min, time were considered.  EUB-8500 XP ultrasound device  (Hitachi Medical Corporation, Tokyo, Japan) and a convex probe with a frequency of 3.5 MHz were used for ultrasonography. Data after collecting were analyzed by SPSS software (version 11.5) and the statistical test was chi-square test. P value less than 0.05 was considered significant.

Results

According to the results, 55.6% of sheep had ascites in the liver parenchyma along with subcapsular localized, small, confluent, multiple hypoechoic nodules with poorly defined borders (Fig/ 1) and in 5.7% and 11.3%, bile ducts and gallbladder were affected, respectively, and in 4.8%, both the liver and the bile ducts were involved (Figs. 2-3). In Table 1, the abundance of patients is shown by age and sex, and in Table 2, the types of ultrasonographic findings are given. In cases where bile ducts were involved, 11 sheep (61.1%) had duct dilatation without presence of Fasciola and 7 sheep (38.9%) had duct dilatation with parasites. There was no statistically significant relationship between sex and region of liver that was involved (Table 3). Also, there was no statistically significant relationship between age and region of liver that was involved (Table 4). The most common site of injury was in the posterior part of the right lobe liver (Chart 1).

Table 1. The abundance of patients based on age and sex

Table 2. Distribution of ultrasound findings in patients with Fasciolysis

Table 3. Distribution of affected area based on the gender of patients

Table 4. Distribution of age patients based on the affected area

Discussion

Sheep fasciolosis is a parasitic infection of the liver which, according to clinical symptoms is considered to havedifferential diagnosis with some other liver diseases and its diagnosis, especially of parenchymal tumors of the liver, gallbladder and biliary tract is important. In ultrasonography, small hypoechoic nodules, which are often environments and after treatment  their size is reduced, suggests a liver fasciolosis (Martínez-Valladares et al., 2010). The extent of hypoechoic lesions is often unclear and occasionally echogenic granuloma, fluid accumulation in the subcapsule, abscess and the discontinuous echogenic lines are seen that should differentiate them from secondary contamination of the liver with metastatic and primary malignant and benign tumors of the liver. The involvement of bile ducts in different forms was present in our study. In some cases there was only a common bile duct dilatation without parasites inside it and in others, there was a dilation of the common bile duct with parasite inside it that was seen as echogenic focal and it did not have an acoustic shadowing. The acoustic shadowing distinguishes the parasites from the stone.  It is necessary to point out that sometimes the cholesterol polyps and adenomatous polyps are seen as echogenic focal that have no acoustic shadowing, where the mobility of the parasite is a good distinction, but in these cases, it is also necessary to help with other clinical and laboratory findings. In this study, there was no racial susceptibility to infections caused by trematode and there was no increase in the prevalence of other variables such as sex and age. Trematode infections occur in all age groups, although intestinal trematode infections and schistosomiasis are more common in livestock with a lower age, but their prevalence is not higher (McManus and Dalton 2006). In our study, in relation to the area involved in liver and biliary tract, there was no difference between age groups and the sex of livestock, In other words, the age and sex do not seem to be an effective factor in the type of infection. In this study, in 7 out of 18 patients with common biliary duct dilatation, fasciola was not seen (38.8%) and 11 sheep (61.2%) had this dilation along with fasciola.

Conclusion: It is suggested that in order to prevent high diagnostic costs and prevent further damage to the sheep in endemic areas of this disease, serological tests should be used before any parasite examination begins. According to our study, the most common site of fasciolosis infection was in the posterior right lobe of the liver and it should be noted that ultrasound should not be the first step in examining this parasitic infection, but since it is easy to use, cost effective and non-invasive, and there is no risk of ionizing radiation, it can play an important role in the diagnosis and follow up of sheep’s chronic fasciolosis treatment. We recommend that similar studies be performed in endemic areas of the disease in order to obtain more complete information on the different aspects of ultrasonography of this parasitic infection.

Acknowledgments

This study was supported by Faculty of Veterinary Medicine, Urmia Branch, Islamic Azad University, Urmia, Iran.

Conflicts of interest

The author declared no conflict of interest.