Fascioliasis is caused by the flatworm; belonging to class trematoda, named as Fasciola (F.) hepatica and F. gigantica. These worms are commonly known as liver flukes.
Fascioliasis mainly occurs in temperate regions due to easy availability of intermediate host, i.e., aquatic snails (Lymnaeidae). F. hepatica causes significant economic losses by affecting sheep, cattle and other livestock species through mortality and morbidity.
Fascioliasis also has zoonotic importance with more than 90 million people infected all over the world. This disease is more prevalent in tropical countries like Pakistan, Bangladesh, India, Turkey and Iraq. The annual losses due to fascioliasis have been reported to be US$ 3.6 billion.
Fasciolosis has different prevalence throughout the world depending upon associated risk factors including climate, gander, species, breed of animals and seasons of sampling.
However, different prevalence reported around the globe included Kenya 8%, Nepal 70.59%, Egypt 71.4%, Bangladesh 31.14% and India 30-70%. The prevalence of fasciolosis has been recorded to be 14.71% in different regions of Pakistan, however, it varies in different areas due to different climatic conditions and animals grazing habits.
Highest prevalence of fascioliasis was reported in Khyber Pakhtunkhwa (KPK) with 55% in Peshawar, Pakistan. Comparatively low prevalence was recorded to be 23.97% and 17.68% in Multan and Bahawalpur Districts of lower Punjab.
The lowest prevalence was documented in the central Punjab with 10.48 % in Lahore. In Pakistan, several studies have been made to evaluate the occurrence of fascioliasis in different regions of Pakistan through different techniques.
As it was recorded 6.5% from bile sample via microscopy, whereas, 3.5% in fecal samples by microscopic examination in sheep of different districts of Punjab, Pakistan. While, the same samples were examined through molecular techniques (PCR) given different results.
The prevalence was recorded as 8.5% in bile samples and 3.5% in fecal samples through PCR. Similarly, sample was collected from five Districts included Sargodha, Jhang, Muzafargarh, Lodhra and Lyyah were evaluated through microscopical method, while, 25.46% samples were positive.
The prevalence also varies under different managemental conditions, whereas, the prevalence was 25.59%, 26.16%, 13.7% and 10.5%, respectively in slaughtered buffaloes, buffaloes at livestock farms, veterinary hospitals and in household buffaloes.
Overall highest (24.0%) seasonal prevalence in all types of buffaloes was recorded during autumn, followed by spring (20.0%), winter (13.0%). While the lowest (9.0%) was recorded during summer.
Metacercariae is the infective stage for the mammalian host, which is transmitted by ingestion of infected aquatic snail i.e. Galba truncatula (Most common snail specie in Europe, Africa, Asia and South America) and contaminated fodder with metacercaria.
Infection mainly occurs in two phases;
i) parenchymal phase or acute phase which involves the subsequent migration of juvenile through the liver parenchyma resulting in extensive liver damage, necrosis (liver rot), urticaria, eosinophilia, hemorrhages, anemia and eventually death,
ii) biliary phase or chronic phase which involves the obstruction of bile duct due to mature flukes resulting in biliary obstruction, cholangitis, jaundice, hyperplasia of biliary epithelium and hardened liver due to massive fibrosis.
However, the mortality rate is higher in acute form of fascioliasis. Most common clinical signs in sheep and goat include bottle jaw, anemia, emaciation and ascites, which leads to high economic losses in the form of decreased milk production, wool production, low weight gain and increased mortality.
Diagnosis of this parasite is mostly done by conventional method, in which the eggs of parasite are identification from feces based on their morphology under the microscope.
Nevertheless, this technique may help in species identification. But this method fails in early diagnosis as major pathogenic effect occurs before the egg shedding by liver flukes and this method also required a skilled person.
However, for the early diagnosis, serological technique is much beneficial, as the antibodies produced in response to the antigens present in the tegument of juvenile can be detected by this method which makes this technique more sensitive.
Many sero-diagnostic methods have been developed for fascioliasis, which include indirect hemagglutination, ELISA, immunoprecipitation and indirect fluorescence antibody test.
Among these techniques, ELISA is more specific and sensitive technique for early diagnosis of fascioliasis. Moreover, ELISA kits are commercially available and are suitable for diagnosis at farm level.
These kits were used in Denmark at Danish dairy farm for detection of fasciliasis from bulk of milk and the blood samples were collected from slaughtered animals.
So, there is need of early detection of fascioliasis infection by provision of ELISA kits at farm level, to decrease the economic losses due to late detection by conventional methods.
Authors: Arsalan Zafar, Muhammad Kasib Khan, Zaheer Abbas, Hammad Ur Rehman Bajwa
Department of Parasitology, University of Agriculture, Faisalabad.