Anisakidosis is a parasitic infectious disease associated with ingestion of roundworm larvae. The main symptoms are disorders of the gastrointestinal tract and allergic reactions of varying severity. Diagnosis of the disease is usually instrumental with visualization of larvae in the mucous membrane; microscopy of vomiting and faeces almost never reveals the pathogen. Treatment includes etiotropic anthelmintic drugs, pathogenetic and symptomatic therapies, as well as a variety of surgical manipulations.
Anisakidosis is a nematodosis in which a person is accidentally involved in the life cycle of a parasite. The first mention of the symptoms of helminthiasis dates back to 1955. Anisakidosis is most often found in the countries of Southeast Asia, the USA, Canada, European countries (France, Belgium, Norway, Great Britain). The growing popularity of dishes from raw, dried and lightly salted fish, active tourism make anisakidosis a significant problem of clinical infectology and parasitology. Seasonality is not traced, adult men are more often ill.
Causes of anisakidosis
The causative agent of the disease is a roundworm larva of the Anisakidae family. The source and final host of anisakidosis are marine life – seals, dolphins, whales, rays, waterfowl. Intermediate reservoirs can be fish, shellfish, crustaceans. The transmission path is alimentary, associated with the use of seafood in raw or poorly heat-treated form. The prevalence of squid in the world ocean reaches 28%, populations of herring, flounder, terpug, cod – up to 100%. Anisakid larvae are found in the digestive tract of fish and only after their death migrate into the muscle tissue.
The main risk factors are considered to be living in coastal marine territories; work in the fishing industry related to the cutting and processing of carcasses; professions related to the preparation of dishes from poorly processed or raw fish and seafood (cooks and kitchen workers). It is believed that the risk of infection with anisakidosis increases when cod, squid and mackerel are used for culinary purposes. Persons with sensitization to pathogen antigens belong to the risk group for the occurrence of anaphylaxis symptoms, according to various data, their number ranges from 0.4 to 22% of residents of endemic zones.
Mature individuals of anisacids lay eggs that fall into the water and are swallowed by intermediate reservoirs – marine fish or mollusks, where helminths live in the digestive system, less often in the musculature. When eaten by the final hosts, larvae reach puberty in the intestines of the latter and excrete eggs on environmental objects with feces. Anisakid larvae inside the human body never turn into adults, usually they are in the body for no more than 3 months. Helminths can affect the entire digestive system from the pharynx to the large intestine.
The predominant localization of the parasite is the stomach and small intestine, the larvae are able to migrate to the gallbladder, hepatic and pancreatic ducts, mesenteric lymph nodes, and parotid tissue. Penetrating deep into the mucosa, the pathogen causes symptoms of local inflammation with ulcerative-necrotic, hemorrhagic changes, the formation of granulomas. Granulomas are an accumulation of leukocytes, mainly eosinophils, which causes toxic-allergic local and general symptoms, dysfunction of visceral nerve endings.
Clinical manifestations of anisakidosis are diverse, but this helminthiasis can be systematized according to the degree of invasion deep into the body and the localization of the parasite. Most often, the disease occurs in a mild form, moderate and severe course require immediate treatment due to the threat or presence of complications. There is also an acute, subacute, chronic form of infection. The classification includes:
- Gastric helminthiasis. It is more common in people with normal non-atrophic gastrointestinal mucosa, the parasite is localized mainly in the large curvature of the organ. This form accounts for up to 95% of cases of anisakidosis.
- Intestinal helminthiasis. Manifestations are nonspecific, 50.7% of patients develop intestinal obstruction, 8% of patients have perforation or peritonitis, 2% have intestinal bleeding. Laparotomy is performed in 7% of cases of the disease.
- Toxic-allergic helminthiasis. Symptoms of sensitization of the body come to the fore, occurring in 3.5% of people with symptoms of parasitosis, clinically manifesting from skin rashes to Quincke’s edema, urticaria, anaphylactic shock.
The incubation period varies from 12 hours to 7-14 days. With gastric localization, the disease begins acutely with sharp pains in the epigastric region, nausea, vomiting. Fever is uncharacteristic, on the contrary, there are indications of a decrease in body temperature. With concomitant gastric ulcer, streaks of blood are often detected in the vomit. Skin manifestations – rashes on the body by the type of urticaria, blisters with itching. Intestinal symptoms rarely occur earlier than the 5th day after eating infected foods, manifest with diffuse widespread abdominal pain.
Uncomfortable sensations are usually limited to the umbilical, right iliac regions, bloating, flatulence, nausea, vomiting are noted. A short–term breakdown of the stool is possible, in which mucus, blood is detected, then persistent constipation associated with partial paralysis of the intestine. Intoxication is determined in the form of weakness, dizziness, decreased performance, fever of more than 37.5 ° C. Life-threatening disorders of consciousness, a sharp increase in abdominal pain, a rapid drop in blood pressure, rapid (for 1-2 hours) are considered life-threatening temperature rise.
The most common complications of anisakidosis are perforation, intussusception, perforation of the intestine with the development of symptoms of peritonitis, bleeding. Due to excessive swelling of the mucous membrane of the digestive tract, intestinal obstruction may occur; when the parasite is localized in the biliary and pancreatic ducts, mechanical jaundice, cholecystitis, cholangitis, pancreatitis and pancreonecrosis, respectively, are possible. Potentially fatal consequences of pathogens staying in the body without proper treatment are angioedema, anaphylactic shock.
Confirmation of the diagnosis is carried out by an infectious disease specialist, a parasitologist, sometimes doctors of other specialties are involved. It is important to carefully collect an epidemiological history with clarification of the nature of the food taken, stay in endemic territories. The main diagnostic laboratory and instrumental signs of parasitic infection are:
- Physical data. During an objective examination, there are no pathological changes in the case of an asymptomatic course. There may be urticary rashes, urticaria, traces of combing on the skin. Palpation of the abdomen reveals pain in the epigastrium, characteristic of gastric localization, rumbling, diffuse sensitivity with signs of intestinal form. Sometimes the symptoms of an acute abdomen are determined. Visual assessment of vomit and faeces is mandatory.
- Laboratory tests. In a general clinical blood test, leukocytosis and eosinophilia are detected in 30% of patients (more often with symptoms of stomach damage). There is an increase in the level of total Ig E, a transient increase in ALT and AST activity. With inflammation of the gallbladder, the level of alkaline phosphatase, total and direct bilirubin increases, with pancreatitis, high numbers of amylase, the level of urine diastase are noted. In the coprogram – creatorrhea, steatorrhea, leukocytes, erythrocytes.
- Identification of infectious agents. Microscopy of bowel movements, vomiting to confirm anisakidosis is not informative enough. The diagnostic level of SiGe in plasma reaches only by 4-6 weeks of infection. The basophil transformation test with A. simplex extract is highly specific; skin prick tests are used. A PCR study is carried out with histological materials, the possibility of using immune blotting is being studied.
- Instrumental methods. Chest X-ray is necessary for differential diagnosis of allergic symptoms; when examined with barium, filamentous filling defects, swelling of the gastric mucosa, narrowing of the intestinal lumen are revealed. On CT – segmental edema of the intestinal wall with proximal dilation without complete intraluminal occlusion, ascites; according to EGD – point erosion, ulceration, infiltration, swelling of the mucosa, larva anisakid.
Differential diagnosis is carried out with other worm infestations, especially nematodes, but since their symptoms are similar, the main role is assigned to laboratory and instrumental examination. Salmonellosis always proceeds with fever, characteristic abundant stool in the form of swamp mud. Food toxicoinfection has a violent beginning with repeated vomiting, loose stools, temperature reaction of the body, rapid dehydration. With cholera, first there is a breakdown of the stool, then there are symptoms of stomach dysfunction, bowel movements resemble rice broth.
Patients can receive outpatient treatment only with mild or asymptomatic course. A general regime is prescribed, a diet with mechanical sparing – coarse fiber, alcohol, fried, fatty foods, seasonings, marinades are excluded. It is recommended to increase the amount of liquid consumed, preferably boiled water. Patients with intense abdominal pain may be hospitalized for differential diagnosis with surgical pathology; such patients are prohibited from taking water and food during the examination period.
There is no specific algorithm for treating patients with symptoms of anisakidosis. Since larvae do not live long in the human body, the main importance is attached to the prevention of complications of parasitic invasion. There are data on the effectiveness of some essential oils (chamomile, thyme, peppermint), wood creosote on animal models. To date, the treatment of anisakidosis is carried out by the following methods:
- Etiotropic therapy. In fact, it has not been developed, the most effective drugs were albendazole, mebendazole, tiabendazole, used in short courses. Modern studies have shown that the effectiveness of albendazole and analogues depends on the pH of gastric juice, the more acidic the medium, the worse the drug dissolves and the less larvocidal effect it has. Extraction of larvae is possible during CT examination using gastrographin.
- Pathogenetic treatment. The use of detoxification, desensitizing therapy with infusion of antihistamines, corticosteroids is justified. In some cases, oral administration of desloratadine with prednisone led to a complete cure without the use of anthelmintic drugs.
- Symptomatic therapy. The appointment of enzyme, antiemetic drugs, sorbents, proton pump blockers, antispasmodics, antacids, sedatives and other pharmacological agents greatly facilitates the condition of patients. Skin symptoms are relieved by local hormone-containing ointments.
Laparotomy is performed when complications occur. The volume of surgical intervention is determined by the size of the lesion, the removed tissues can be used for pathohistological confirmation of the diagnosis. Modern equipment for minimally invasive surgery makes it possible to remove larvae and cauterize bleeding vessels of the mucosa already during diagnostic endoscopy. Early extraction is carried out with forceps, it is necessary to ensure that the helminth is completely extracted, inspect all parts of the stomach, especially carefully – a large curvature.
Abamectin, farnesol and nerolidol are considered as new effective drugs for the elimination of larval forms of anisakids. The absence of mechanisms to protect the helminth from oxidative stress induced by abamectin and farnesol confirms the susceptibility of parasites and the usefulness of these compounds in the treatment of anisakidosis; the process of lipid peroxidation starts after half an hour from taking medications. Modern studies of the problem of anisakidosis often pursue therapeutic and preventive purposes.
Recently described by scientists, the effect of essential oils of oregano, cumin and Spanish lavender on the muscular larvae of fish indicates that parasites do not cause any damage to the digestive apparatus of animals. The anthelmintic activity of essential oils is related to their chemical composition, which is dominated by mono-, sesquiterpenes; the mechanism of action has not yet been fully studied, probably includes membrane structure disorders that increase the permeability of cytoplasmic membranes and mitochondrial membranes in eukaryotic organisms.
Prognosis and prevention
Timely detection and treatment of anisakidosis symptoms suggests a favorable prognosis of the disease. No fatal cases have been recorded. Specific preventive measures (vaccines) have not been developed. Regular helminthological examination of marine life used for food purposes is necessary, compliance with the correct fish processing technology – rapid gutting, keeping inside freezers at -20 ° C for at least 60 hours, sufficient culinary processing, abstinence from eating raw seafood.