Review on Epidemiology, Control and Public Health Importance of Bovine Fasciolosis

    

    

    Figure 3: Lifecycle of Fasciola species.
    

Ecology of intermediate host: Breeding of Lymnea Snails and developments of intra Mollusca stages of the flukes often reach optimum threshold during the wet month of the year. During Dry period, breeding of the snails and developments of larval flukes slow down or stop completely and snails undergo states of aestivation [20]. The risk factors include climate and environmental factors, such as presence of streams, wetland and pastures, and higher rainfall and temperature are identified [21].

Fasciola spp. is a parasite threating domestic ruminants and public health. Transmission of this trematode infection is depending on the presence of intermediate “lymnaea snail” host and final host. This snail host commonly presents in high density during rainfall period annually and/or in highly moist pastures soil [22]. Fasciolosis is commonly distributed in countries where cattle and sheep are raised and there is a niche for Lymnae snail.

The life cycle takes place in Intermediate (IH) and Definitive Hosts (DH). Definitive hosts include cattle, sheep, many other ruminants, equidae, swine and rabbits Spread of fasciolosis is largely dependent on the ecology of the snails which act as IH and serve as means of transmission to animals. Lymnaea natalensis aquatic snails is important for F. gigantic in Africa, where as Lymnaea natalensis truncatula is an amphibian, wide distribution worldwide, and the most common IH for F. hepatica [12].

Factors influencing the agent

The variation in pathological changes of the liver may probably be due to different factors such as exposure of the animal in the infested area with the intermediate host and period of infection, and climateecological conditions caused by rainfall, altitude temperatures, ph. and suitability of the environment for the survival of the snails [23]. The risk factors include climate and environmental factors, such as presence of streams, wetland and pastures, and higher rainfall and temperature are identified [21].

Temperature: Temperature is an important factor affecting the development rate of snails and the stages of parasites outside the host. The mean day and night temperature of 100C or above is necessary for the snail host to breed and for the Fasciola to develop within the snail [24]. Metacercariae will not survive for more than six weeks at 25 degrees, but can survive for eight weeks at temperatures of -2 degrees [25].

All activities cease at temperature below 50C. This is also minimum range for the development and hatching of Fasciola eggs. However, when temperature rises to 150C and is maintained above this level that a significant multiplication of snails and flukes larvae stages ensures unfavorable condition [9].

Moisture: The ideal moisture condition for snail breeding and the development of Fasciola species within snails are provided when rainfall exceeds transpiration and field saturation is attained. Such conditions are also essential for the development of fluke eggs for miracidia searching snails and for the dispersal of cercariae being shed from the snail [9].

PH: Fields with clumps of rushes are common sites having a slight ph. Eggs incubated at 270C will develop and hatch within a pH range of 4.2 to 9.0, but development is prolonged when pH exceeds 8.0 [26].

Pathogenesis of fasciola

Many systemic changes will be induced by liver fluke infections that ultimately cause reduced productivity in livestock. Both anorexia (inappetance) and the quality of the diet of infected sheep contribute to hypoalbuminemia during the infection [27]. Infection with trematode parasites can lead to severe losses to farmers, hence affecting sustainability of food production. Acute hepatic fasciolosis mainly a condition on cattle and sheep, which may lead to death [20].

The development of infection in definitive host is divided into two phases, the parenchymal or migratory phase and biliary [28]. Acute hepatic fasciolosis is caused by the passage of young Fasciola hepatica through the liver parenchyma. Acute hepatic insufficiency and hemorrhage result. The migration of larvae also been thought to stimulate the development of occasional case of bacillary hemoglobinuria in cattle.

Chronic hepatic fasciolosis develops only after the adult flukes establish in the bile duct. The severity reaction in cattle, calcification of the bile ducts appears to hinder the establishment and feeding of challenge infection. There by reinforcing immune response goes in there mode of resistance [29]. Pathogenesis of fasciolosis varies according to the parasitic development phases; parenchymal and biliary phases. The parenchymal phase occurs during migration of flukes through the liver Parenchyma and is associated with liver damage and hemorrhage. The biliary phase coincides with parasite residence in the bile ducts. The results from the haematophagic activity of the adult flukes which damage the bile duct mucosa by their circular spines [9].

Life cycle and host range

Life cycle: The life cycle of Fasciola spp. is a typical of digenetic treamatodes. Eggs laid by the adult parasite in the bile ducts of their hosts pass into the duodenum with the bile [30]. Therefore, immature eggs are discharged in the biliary ducts and passed in the stool. Eggs become embreyonated in freshwater over ~2 weeks; embreyonated eggs release miracidia, which invade a suitable snail intermediate host. In the snail, the parasites undergo several developmental stages (sporocysts, rediae, and cercariae) [31].

The hatchling is called a miracidium, a free-swimming, ciliated larva. Miracidia will then grow and develop within the intermediate host into a sac-like structure known as a sporocyst or into rediae, either of which may give rise to free-swimming, motile cercariae larvae. Adult metacercariae depending on the individual trematode’s life cycle, then infect the vertebrate host or be rejected and excreted through feaces [32].

Host range: Fasciolosis is a disease of sheep, goats, and cattle and occasionally affects humans and It is caused by genus Fasciola commonly called liver fluke, but all age groups are affected at different manner of acquisition of the infection depending on the host. Calves are susceptible to fasciolosis but in excess of 1000 metacercariae are usually required to cause clinical fasciolosis [27].

Clinical signs

Fluke infection may predispose to other conditions due to impaired liver function and can reduce milk yield, fertility production and productivity and also death of the host [33].

All age groups of cattle are potentially at risk of fluke infection. During the movement of the immature stages of Fasciola hepatica, which may continue for months, symptoms may include abdominal pain, an enlarged liver, fever, and diarrhea. Cattle develop a greater fibrotic reaction in the liver compared to sheep, therefore parasite survival is reduced [9].

On a herd basis, clinical signs of fluke infection are usually vague (i.e., reduced productivity) and can be difficult to differentiate from the effects of less-than-optimal management or other chronic disease conditions. From a clinical standpoint, bovine fascioliasis generally can be considered a subclinical disease. Animals suffering from acute fasciolosis especially sheep and goat, may display no clinical signs prior to death; while some may display abdominal pain and discomfort and may develop jaundice [9,34].

In some cases the liver capsule may rupture and fluid may lick into the peritoneal cavity causing death due to peritonitis. More commonly on ingestion of fewer Metacercaria fever and eosinophilia is seen [34]. Death usually results from blood loss due to hemorrhage and tissue destruction caused by the migratory juvenile flukes in the liver resulting in traumatic hepatitis. This is more commonly seen in sheep than in other hosts. Sub-acute fasciolosis is caused by ingestion of a moderate number of metacercaria and is characterized by anemia, jaundice and ill thrift. The migrating fluke causes extensive tissue damage, hemorrhage and in particular liver damage which result severe anemia, liver failure and death in 8- 10 weeks [9].

The clinical signs of chronic fasciolosis are variable and depend upon the number of metacercaria ingested, but often include: Weight loss, Anemia, Bottle jaw, diarrhea, Constipation [35]. In chronic cases, mineralization (calcification) and fibrosis around bile ducts also causes the elimination of liver flukes and Calcification tends to be minimal or absent in sheep [36].

Diagnosis

Diagnosis of fasciolosis may be established based on the epidemiology of the disease, observations of clinical signs, and information on grazing history. However, confirmatory diagnosis is based on horoscopic examination in the laboratory and post-mortem examination of infected animals by the detection of flukes in the liver [37].

Post mortem examination: Fasciolosis is associated with liver damage and hemorrhage due to migration of flukes through the liver parenchyma. Adult flukes found in the bile duct and can be identified by incising the liver and it shed eggs into the bile then enter into the intestine to pass outside with feces [9]. Adult flukes can survive for many years in the livers of infected hosts and lay between 20,000 and 50,000 eggs/day. Caprological analysis is still commonly employed to diagnose bovine fasciolosis, despite the fact that eggs cannot be detected until the latent period of infections, when much of liver damage has already occurred [22].

Fecal examination: Diagnosis of fasciola is confirmed by finding the eggs in the feces. These eggs must be distinguished from the eggs of especially the large eggs of paramphistomes. The Fasciola eggs are oval, yellow brown and measures (130 to 150μm by 60 to 90 μm). Each egg will possess a distinct operculum [13].

The rate of egg production is responsible for the degree of pasture contamination and thus greatly influences the epidemiology of the disease. The eggs of fasciola are maintained in conditions of high humidity and cool temperatures, they may survive for up to a year [30].

Serological detection: Early diagnosis of the fasciolosis disease is essential to control and treat the infection. To overcome the deficiencies of diagnosis, various Enzyme-Linked Immunosorbent Assays (ELISAs) have been developed, which aim at detecting antifasciola antibodies in serum or milk, and antigens in serum or faeces. The Excretory-Secretory (ES) antigens of Fasciola or their partially purified components, are the most common source of antigens used in ELISA. Antibodies to these antigens can be detected as early as 2 weeks, and their concentrations can be determined between 8 and10 weeks post-infection [38].

The sensitivity and specificity of a copro antigen-based ELISA has been investigated by experimental infection [39] or by testing it on two distinct populations a positive population selected from an enzootic area and a negative population from a fluke-free area [40]. In vivo diagnosis of mild and pre patent infection is possible serologically. Example, detection of antibodies by ELISA in serum or milk is available and useful for diagnosis of infection in cattle in an individual or herd basis [24].

Detecting liver enzymes: Two enzymes are usually measured, Glutamate Dehydrogenase (GLDH), is released when parenchymal cells are damaged and levels become elevated within the first few weeks of infection. The other Gamma-Glutamyl Transferees (GGT) indicates damage of epithelial cells lining the bile ducts and raised levels are maintained for longer periods [12]. Elevation of liver enzyme activities, such a Glutamate Dehydrogenase (GLDH), Gamma-Glutamyl Transferees’ (GGT) and Lactate Dehydrogenase (LDH) is detected in sub-acute or chronic fasciolosis from 12-15 week after ingestion of metacercariae [41].

Significance of bovine fasciolosis

Economic significance of fasciola: Ethiopia has the largest livestock population in Africa, with a total cattle population of 57.83 million. Among the animal diseases that hinder the animal health are parasitic infections that have great economic impact [42]. Among many parasitic problems of farm animals, fasciolosis is a major disease which imposes economic impact on livestock production particularly of cattle and sheep [43]. Fasciolosis is an important cause of both production and economic losses in the dairy and meat industries. Over the years, the prevalence has increased and it is likely to continue increasing in the future [44].

Fasciolosis caused by Fasciola hepatica and Fasciola gigantica is responsible for heavy economic losses to farmers due to reduced weight gain, poor carcass quality, reduced milk yield, cost of treatment and control, mortality and condemnation of affected livers at abattoirs, increased susceptibility to secondary infections and the expense of control measures in Nigeria [45]. The annual loss due to these parasites in Ethiopia is estimated at 700 million Ethiopian birr/ annum [46].

The economic loss associated with an infected liver condemnation due to fasciolosis in different area of Ethiopia is ranging from 86, 83.2 ETB to 1,751,432 ETB or $2459.52- $50040.91 [47]. Fasciolosis is an economically important parasitic disease, which is caused by trematodes of the genus Fasciola that migrate in the hepatic parenchyma and establish in the bile ducts [48].

Public health significance of fasciolosis: Slaughterhouses provide an excellent meat inspection place where many zoonotic diseases observed but meat poor handling in or out the abattoir can leading to both economic losses and a lot of public health hazardous. Fasciolosis occasionally affects humans, thus Considered as a zoonotic infection but it is a disease of sheep, goat, and cattle mainly [10]. A person must ingest the metacercaria to become infected. Human acquire infection through ingestion of metacercaria that are attached to certain aquatic plant and vegetable. Experimental studies suggested that human consuming raw liver dish from liver infected with juvenile flukes could become infected [12].

A global analysis show that the expected correlation between animal and human fasciolosis only apparent a basic level. High prevalence in human infections is not found in areas where fasciolosis is a great veterinary problem. For instance, in South America, hyper endemics and mesoendemics are found in Bolivia and Peru where the veterinary problem is less important, while in countries such as Uruguay, Argentina and Chile, human fasciolosis only sporadic or hypo endemic [7].

F. hepatica may be acquired by man, but not directly from cattle. The person must ingest the metacercaria in order to become infected. The most common transmission route is ingestion of watercress although; depending up on the geographic location and a variety of edible aquatic plants can be vehicles of transmission [49].

The degree of pathogenicity of Fasciola hepatica to man depends on many factors, particularly the number of worms present and the organ infected, mechanical and the damage are characteristics. Global estimate prevalence is between 1.7 and 2.4 Million human infection worldwide and a further 180 Million at risk of infection [49].

Current status of prevalence and Estimation of economic losses by condemned organs dueto fasciolosis in different regions of Ethiopia (Table 1).

  

    

    
Annual economic loss in (ETB)
    
Reference
  
  

    
Asella
    
6,987,006
    
Shiferaw et    al.
  
  

    
Hawzie
    
885,5ooo
    
Germany et    al.
  
  

    
Wolkite
    
1825,82.4
    
Tesfaye and Tigisti [58]
  
  

    
Wolanchiti
    
4,522,550,ooo
    
Asefa and Tegang [52]
  
  

    
Nekemte
    
630.72
    
Alula et    al.
  
  

    
Sheno municipal abattoir, Oromia
    
1,751,432 annually
    
Mekonnen et    al. [47]
  
  

    
Addis Ababa abattoir enter price, A,A
    
157,684 annually
    
Bayou et    al. [59]
  
  

    
Areka municipal abattoir, southern Ethiopia
    
47,124.5/month
    
Moje et    al.
  
  

    
Awasa municipal abattoir southern Ethiopia
    
106,400/annum
    
Ababe et al.
  
  

    
Hosanna municipal abattoir southern Ethiopia
    
88,806.85/annum
    
Chakiso et    al.
  
  

    
Dessie municipal abattoir south wolo zone
    
2,495,346.13/annum
    
Belay et    al.
  
  

    
Nekemte municipal abattoir
    
63072/annum
    
Petrous et    al.
  
  

    
Kombolcha Industrial Abattoir
    
49491/annum
    
Ibrahim et    al.
  
  

    
Bedele, Ethiopia
    
228,360.6/annum
    
Yitagezu et    al. [60]
  

Table 1: Current prevalence of fasciolosis in Ethiopia by many outers.