Fasciolosis is a parasitic worm infection caused by the common liver fluke Fasciola hepatica as well as by Fasciola gigantica. The disease is a plant-borne trematode zoonosis, and is classified as a neglected tropical disease (NTD). It affects humans, but its main host is ruminants such as cattle and sheep. The disease progresses through four distinct phases; an initial incubation phase of between a few days up to three months with little or no symptoms; an invasive or acute phase which may manifest with: fever, malaise, abdominal pain, gastrointestinal symptoms, urticaria, anemia, jaundice, and respiratory symptoms. The disease later progresses to a latent phase with fewer symptoms and ultimately into a chronic or obstructive phase months to years later. In the chronic state the disease causes inflammation of the bile ducts, gall bladder and may cause gall stones as well as fibrosis. While chronic inflammation is connected to increased cancer rates, it is unclear whether fasciolosis is associated with increased cancer risk.
Up to half of those infected display no symptoms, and diagnosis is difficult because the worm eggs are often missed in fecal examination. The methods of detection are through fecal examination, parasite-specific antibody detection, or radiological diagnosis, as well as laparotomy. In case of a suspected outbreak it may be useful to keep track of dietary history, which is also useful for the exclusion of differential diagnoses. Fecal examination is generally not helpful because the worm eggs can seldom be detected in the chronic phase of the infection. Eggs appear in the feces first between 9–11 weeks post-infection. The cause of this is unknown, and it is also difficult to distinguish between the different species of fasciola as well as distinguishing them from echinostomes and Fasciolopsis. Most immunodiagnostic tests detect infection with very high sensitivity, and as concentration drops after treatment, it is a very good diagnostic method. Clinically it is not possible to differentiate from other liver and bile diseases. Radiological methods can detect lesions in both acute and chronic infections, while laparotomy will detect lesions and also occasionally eggs and live worms.
Because of the size of the parasite, as adult F. hepatica: or adult F. gigantica: , fasciolosis is a big concern. The amount of symptoms depends on how many worms and what stage the infection is in. The death rate is significant in both cattle (67.55%) and goats (24.61%), but generally low among humans. Treatment with triclabendazole has been highly effective against the adult worms as well as various developing stages. Praziquantel is not effective, and older drugs such as bithionol are moderately effective but also cause more side effects. Secondary bacterial infection causing cholangitis has also been a concern and can be treated with antibiotics, and toxaemia may be treated with prednisolone.
Humans are infected by eating watergrown plants, primarily wild-grown watercress in Europe or morning glory in Asia. Infection may also occur by drinking contaminated water with floating young fasciola or when using utensils washed with contaminated water. Cultivated plants do not spread the disease in the same capacity. Human infection is rare, even if the infection rate is high among animals. Especially high rates of human infection have been found in Bolivia, Peru, and Egypt, and this may be due to consumption of certain foods. No vaccine is available to protect people against Fasciola infection. Preventative measures are primarily treating and immunization of the livestock, which are required to host the live cycle of the worms. Veterinary vaccines are in development, and their use is being considered by several countries on account of the risk to human health and economic losses resulting from livestock infection. Other methods include using molluscicides to decrease the number of snails that act as vectors, but it is not practical. Educational methods to decrease consumption of wild watercress and other water plants have been shown to work in areas with a high disease burden.
Fascioliasis occurs in Europe, Africa, the Americas as well as Oceania. Recently, worldwide losses in animal productivity due to fasciolosis were conservatively estimated at over US$3.2 billion per annum. Fasciolosis is now recognized as an emerging human disease: the World Health Organization (WHO) has estimated that 2.4 million people are infected with Fasciola, and a further 180 million are at risk of infection.Anonymus (1995). Control of Foodborne Trematode Infections. WHO Technical Series No. 849. WHO, Geneva, 157 pp.
Signs and symptoms Humans The course of fasciolosis in humans has 4 main phases: Incubation phase: from the ingestion of metacercariae to the appearance of the first symptoms; period: few days to 3 months; depends on the number of ingested metacercariae and the immune status of the host Invasive or acute phase: fluke migration up to the bile ducts. This phase is due to the mechanical destruction of hepatic tissue and the peritoneum by migrating juvenile flukes, causing localized and or generalized toxic and allergic reactions.Facey, R.V., Marsden, P.D. (1960). "Fascioliasis in man: an outbreak in Hampshire". Br. Med. J. ii, 619–625. The major symptoms of this phase are: Fever: usually the first symptom of the disease; Abdominal pain Gastrointestinal disturbances: loss of appetite, flatulence, nausea, diarrhea Hives Respiratory symptoms (very rare): cough, shortness of breath, chest pain, coughing up blood Enlargement of the liver and spleen Fluid in the peritoneal abdominal cavity (ascites) Low level of red blood cells in the bloodstream Yellow discoloration of the skin or white parts of the eyes Latent phase: This phase can last for months or years. The proportion of asymptomatic subjects in this phase is unknown. They are often discovered during family screening after a patient is diagnosed. Chronic or obstructive phase: This phase may develop months or years after the initial infection. Adult flukes in the bile ducts cause inflammation and epithelial hyperplasia. The resulting cholangitis and cholecystitis, combined with the large body of the flukes, are sufficient to cause mechanical obstruction of the biliary duct. In this phase, biliary colic, epigastric pain, fatty food intolerance, nausea, jaundice, itching, right upper quadrant abdominal tenderness, etc., are clinical manifestations indistinguishable from cholangitis, cholecystitis and cholelithiasis of other origins. Hepatic enlargement may be associated with an enlarged spleen or ascites. In case of obstruction, the gall bladder is usually enlarged and edematous with thickening of the wall.Hepatobiliary Fascioliasis: Sonographic and CT Findings in 87 Patients During the InitialPhase and Long-Term Follow-Up. Adnan Kabaalioglu, Kagan Ceken, Emel Alimoglu, Rabin Saba, Metin Cubuk, Gokhan Arslan, Ali Apaydin. AJR 2007; 189:824–828). Fibrous adhesions of the gall bladder to adjacent organs are common. Lithiasis of the bile duct or gall bladder is frequent and the stones are usually small and multiple.
Other animals Veterinary clinical signs of fasciolosis are always closely associated with infectious dose (amount of ingested metacercariae). In sheep, as the most common definitive host, the clinical presentation is divided into 4 types: Acute type I fasciolosis: infectious dose is more than 5000 ingested metacercariae. Sheep suddenly die without any previous clinical signs. Ascites, abdominal haemorrhage, icterus, pallor of membranes, weakness may be observed in sheep. Acute type II fasciolosis: infectious dose is 1000–5,000 ingested metacercariae. As above, sheep die but briefly show pallor, loss of condition, and ascites. Subacute fasciolosis: infectious dose is 800–1000 ingested metacercariae. Sheep are lethargic, anemic, and may die. Weight loss is a dominant feature. Chronic fasciolosis: infectious dose is 200–800 ingested metacercariae. The asymptomatic or gradual development of bottle jaw (accumulation of fluid in the submandibular tissue) and ascites (ventral edema), emaciation, and weight loss.
In blood, anemia, hypoalbuminemia, and eosinophilia may be observed in all types of fasciolosis. Elevation of liver enzyme activities, such as glutamate dehydrogenase (GLDH), gamma-glutamyl transferase (GGT), and lactate dehydrogenase (LDH), is detected in subacute or chronic fasciolosis from 12 to 15 weeks after ingestion of metacercariae. Economical effect of fasciolosis in sheep consists in sudden deaths of animals as well as in the reduction of weight gain and wool production. In goats and cattle, the clinical manifestation is similar to sheep. However, acquired resistance to F. hepatica infection is well-known in adult cattle. Calves are susceptible to disease but more than 1000 metacercariae are usually required to cause clinical fasciolosis. In this case, the disease is similar to sheep and is characterized by weight loss, anemia, hypoalbuminemia, and (after infection with 10,000 metacercariae) death. The Importance of cattle fasciolosis consists in economic losses caused by condemnation of livers at slaughter and production losses especially due to reduced weight gain.
In sheep and sometimes cattle, the damaged liver tissue may become infected by the Clostridium bacteria C. novyi type B. The bacteria will release toxins into the bloodstream resulting in what is known as black disease. There is no cure and death follows quickly. As C. novyi is common in the environment, black disease is found wherever populations of liver flukes and sheep overlap.
Cause
Fasciolosis is caused by two digenetic trematodes F. hepatica and F. gigantica. Adult flukes of both species are localized in the bile ducts of the liver or gallbladder. F. hepatica measures 2 to 3 cm and has a cosmopolitan distribution. F. gigantica measures 4 to 10 cm in length and the distribution of the species is limited to the tropics and has been recorded in Africa, the Middle East, Eastern Europe, and South and Eastern Asia. In domestic livestock in Japan, diploid (2n = 20), triploid (3n = 30) and chimeric flukes (2n/3n) have been described, many of which reproduce parthenogenetically. As a result of this unclear classification, flukes in Japan are normally referred to as Fasciola spp. Recent reports based on mitochondrial genes analysis have shown that Japanese Fasciola spp. is more closely related to F. gigantica than to F. hepatica. In India, a species called F. jacksoni was described in elephants.
Transmission