Fascioliasis: causative agent, symptoms, diagnosis, treatment, prognosis

What is fascioliasis?

Fascioliasis Is a rare infectious disease caused by parasites. These parasites are liver worms (trematodes) that live in animals that feed on plants. Hepatic flukes can be found in some parts of the world on aquatic plants. When the parasite enters the liver, the biliary tract can be blocked.

Causes

Fascioliasis is caused by two types of parasitic flatworms or trematodes that mainly affect liver. It belongs to the group of foodborne trematode infections and is a zoonosis, i.e. an animal infection that can be transmitted to humans.

Two types of trematodes that cause fascioliasis (Fasciola hepatica and Fasciola gigantica) are leaf worms large enough to be seen with the naked eye (adult pathogen F. hepatica size 20-30 mm x 13 mm; adult pathogen F. gigantica size 25–75 mm x 12 mm). The disease they cause is similar.

Until recently, human cases occurred sporadically, but the disease is now increasingly reported in Europe, America and Oceania (where only F. hepatica), as well as in Africa and Asia (where both species are present). WHO estimates that at least 2.4 million people are infected in more than 70 countries around the world, with several million people at risk. There is not a single contingent where there is no fascioliasis, and it is likely that where animal cases are reported, there are also human cases.

Life cycle

The life cycle of fascioliasis is complex. It includes the final host (where the adult worm lives), the intermediate host (where the larval stages of the worm develop), and the host (which entails suitable aquatic plants).

The process begins when infected animals (cattle, sheep, buffaloes, donkeys and pigs, and also horses, goats, camels, llamas and other herbivores) defecate in freshwater sources. Since the worm lives in the bile ducts of such animals, its eggs are evacuated in feces and hatched into larvae, which settle in a special type of aquatic snail (intermediate host).

Once inside the snail, the larvae multiply and eventually release more larvae into the water. These larvae swim to nearby aquatic or semi-aquatic plants, where they attach to leaves and stems and form small cysts (metacercariae). When plants with small cysts enter the body, they act as carriers of infection. Watercress and watermint are good plants for transmitting fascioliasis, but inlaid larvae can also be found on many other salad vegetables. Ingestion of free metacercariae floating in water (possibly separated from host plants) may also be a possible mode of transmission.

Symptoms and Signs

After the larvae are ingested with contaminated food or water, an asymptomatic incubation period begins, which lasts from several days to several months. This is followed by an acute and chronic clinical phase.

• Acute phase. The acute phase, lasting 2-4 months, begins when immature worms penetrate the intestinal wall and peritoneum, the protective membrane surrounding the internal organs. From here, they pierce the surface of the liver and feed through its tissues until they reach the bile ducts. This invasion kills liver cells and causes intense internal bleeding. Typical symptoms include fever, nausea, swollen liver, skin rash, and severe abdominal pain.
• Chronic phase. The chronic phase begins when the worms reach the bile ducts, where they mature and begin to produce eggs. These eggs pass into the bile and from there into the intestines, where they are excreted in the feces, thereby completing the transmission cycle. Symptoms include intermittent pain, jaundice and anemia. Pancreatitis, stones in gallbladder and bacterial super infections can also occur. Patients with chronic infections experience scarring of liver tissue (liver fibrosis) as a result of prolonged inflammation.

Epidemiology of fascioliasis

Both animals and humans are infected with fascioliasis infection in the same way.

Environmental transmission is usually carried on by animals. Humans do not usually contribute to the parasite's life cycle; they become infected only occasionally after basic hygiene measures are not followed (eating raw vegetables contaminated with larvae or drinking water contaminated with larvae). In addition, worms Fasciola poorly adapted to humans and, in some cases, unable to develop into mature adult worms and produce eggs.

In some areas, transmission of the pathogen to humans is constant and intense, and a geographic population of cases may occur. This picture may be explained by the cycle of transmission from person to snail from plant to person, without the participation of any animal. Indigenous communities in the South American Highlands are well-known hotspots for fascioliasis: a widespread infection is reported here that can be explained in this way transmission.

Where it occurs sporadically, fascioliasis affects people of all age groups, and there is no particular risk group. Where infection is highly endemic, the prevalence and intensity of infection tends to peak in school-aged children. People living in rural areas are usually more susceptible to infection; however, cases can occur anywhere and can follow the trade routes of host plants that are part of the normal diet in many countries.

Fascioliasis is a global disease, with human cases reported in more than 75 countries around the world. The recognized high transmission areas are the highlands of South America, the Nile Valley, the Caspian Sea Basin, and East Asia and Southeast Asia. No country can be considered free from the risk of fascioliasis.

The epidemiological picture of fascioliasis is quite diverse: the infection is usually hypoendemic with low and stable prevalence levels in a specific population group. Sporadic outbreaks can occur among such populations, usually associated with sudden changes in climatic conditions that increase the life cycle of either the parasite, the snail, or both. Scientists have also found that the epidemiology of fascioliasis is strongly related to the geographic and ecological characteristics of the area where transmission occurs, and different patterns can be distinguished: this suggests that fascioliasis can adapt to different ecological niches.

In Africa and Asia, where both are present F. hepatica, and so F. gigantica, mixed infections are possible. In Asia, hybridization has been described between two species found in coinfected humans or animals. The offspring resulting from such hybridization is characterized by intermediate morphological characteristics between the two species, as well as different ploidies (diploid, triploid and mixoploid); such worms are often sterile.

Diagnostics

The diagnosis of fascioliasis can be suspected on the basis of the clinical picture, anamnestic recall of the use of raw vegetables, detection of eosinophilia (the number of eosinophils in the blood> 500-1000 per μl of blood) and typical results with ultrasound or computer tomography. Confirmation relies on various types of diagnostic methods.

• Parasitological methods detection of Fasciola eggs in stool samples; their cost and sensitivity may vary depending on the type used; they can only be used in the chronic phase; some of them allow to quantify the intensity of the infection (therefore, to estimate the severity of the infection);
• Immunological methods detecting worm-specific antibodies in serum samples or worm-specific antigens in serum or stool samples; they are usually more sensitive than commonly used parasitological methods; detection of antibodies does not distinguish between current, recent and past infections; their ability to quantify the intensity of infection is a matter of controversy; stool tests are easier to perform and reportedly better accepted by people in endemic areas;
• Molecular methods, such as polymerase chain reactionare still in the experimental stage.

Note. Since fascioliasis is predominantly prevalent in developing countries, the quality of diagnostic methods is just as important as their availability and applicability in the field.

Fascioliasis treatment

Triclabendazole, the only drug recommended by the WHO against fascioliasis, is active against both immature and adult parasites, and therefore can be used in the acute and chronic phases. Treatment rates are high, while post-treatment adverse reactions are usually temporary and moderate. The recommended dosage regimen is 10 mg / kg body weight, administered as a single dose both in clinical practice and in prophylactic chemotherapeutic interventions. In clinical practice, when treatment fails, the dosage can be increased to 20 mg / kg body weight in two divided doses 12-24 hours apart.

Disease control with triclabendazole

From a public health perspective, the fight against human fascioliasis mainly depends on timely treatment triclabendazole, a drug that cures infected people and prevents the development of advanced morbidity.

In areas where fasciolysis occurs sporadically, clinical management of patients attending a local hospital is sufficient to control the disease. Diagnostic protocols adapted to the socio-economic environment of the endemic should be adopted. districts, and provide triclabendazole to peripheral health centers to increase access to treatment.

In communities where cases are clustered, consideration should be given to implementing large-scale the spread of the anthelmintic (preventive chemotherapy) in subareas, villages or communities where there is a cluster. Preventive chemotherapy in such lesions can be carried out as a targeted treatment for schoolchildren (5-14 years old), usually in a population with the highest prevalence and intensity of infection, or as a universal treatment (mass administration of drugs) for all those living in them population. In such areas, individual diagnosis is not required; Rather, treatment decisions are based on an assessment of the public health significance of the disease.

Several countries are fighting fascioliasis with triclabendazole. The examples below show some of the approaches implemented:

• management of an individual case using a simplified diagnostic protocol (in Vietnam);
• mass examinations in suspicious areas with subsequent treatment of positive cases (in Egypt);
• targeted treatment of high-risk populations, especially children living in endemic areas (in Bolivia (Plurinational State of));
• the massive introduction of drugs for entire communities identified as highly endemic (in Peru).

Forecast

The prognosis is excellent with adequate therapy. However, due to the large number of people infected worldwide, fascioliasis causes significant morbidity. In children, fascioliasis is often associated with severe anemia, although it is rarely fatal.