Dr. Luis Felipe Asteguieta Arana
MULTIMEDICA VISTA HERMOSA
Abdominal Angiostrongylosis is an atropozoonosis caused by a nematode of the superfamily Metastrongyloidea denominated Angiostrongylus costaricensis. From its original description by Morera and Céspedes in 1967, its epidemiology, life cycle, clinical manifestations and treatment have been gradually comprehended.
In Costa Rica it is a public health problem, while in Guatemala its epidemiology is practically unknown. It is known, through the works of Kramer MH, Creer GJ, Quiñónez JF that an epidemic crisis was presented in 1995, when 22 cases were reported in just seven and a half months. This contrasts with Costa Rica where 600 cases are reported each year. However, cases have been described from the south of the United States to the north of Argentina, being considered an endemic problem in Central America, the Caribbean and South America, that is, in tropical countries.
The human is infected by accidentally ingesting water, vegetables or fruit contaminated with mucous secretions of its intermediary host, the terrestrial mollusks of the Veronicellidae family, commonly known as earth slugs and snails. Specifically, in Guatemala the transmission during the epidemic was associated to the raw consumption of spearmint and shrimp in ceviche (raw fish marinated in lemon juice); as in 4 other varieties of ceviche where spearmint was part of the ingredients. In epidemiological studies in Brazil, the second most affected country, no preference for sex or age has been observed, clarifying that infestation is not specific to children as it was originally described. In Guatemala in 18 cases studied in 1995, the average age was 37 years and 61% were men.
In the life cycle of A. costaricensis there are 2 natural protagonists and humans are just an accident. It starts and ends with wild rodents (definite host), particularly the rats Sigmodon hispidus, the cotton rat, and Rattus, and even the dog has been implicated. Adult larvae (larvae in stage L5) inhabit the small mesenteric arteries of the rodents near the cecum, and lay their eggs in the intestinal wall where they germinate. Larvae in their first stage are eliminated with the feces and are ingested by slugs or snails, the intermediary hosts, these mature to a 2nd (L2) or 3rd (L3) infectious stage in the digestive system of the mollusks which in turn, eliminate larvae L3 with their mucoid secretions. Rats and other rodents devour such mollusks or food contaminated by them. It is in this stage where the human can be infested. In the definitive host (rodents or accidentally the human), the infectious larva enters the intestinal wall and migrates through the blood and lymph vessels to the heart, lungs, back to the heart and systemic arterial circulation to reach the mesenteric arteries, liver and other organs. There, the juvenile larvae reach maturity, both males and females.
Then they lay their eggs in the blood vessels, which migrate to the intestinal wall. The 1st larva stage takes place in the eggs and after incubation they are mobilized to the wall of the intestinal lumen. In a brilliant re-description of the migratory routes of A. costaricensis by Mota and Lenzi in a natural model (cotton rat), important findings were observed with implications to the comprehension of the disease in humans. The study revealed that L3 travels alternatively by 2 routes: 1. Lymph, venous and arterial vessels from the mesenteric system centrifugally, and 2. Venous ways of the porta system. Being the first one the most important one used by the majority of the larvae. While the larvae and adults that reached the liver via the porta system developed in the intrahepatic venous system migrating against the current until they reached the mesenteric veins where they lay their eggs and later embolize the portal hepatic vessels with the consequently damage at that level. This proved that the migration of A. costaricensis has its own migratory route and not as it was originally thought of, in a migratory pattern type migrans larva described by Morera in 1982.
In humans the time interval between infestation and the appearance of symptoms is estimated between 14 days and 3 years. Most cases are considered asymptomatic or oligosymptomatic and few present the classic picture of acute abdomen and fever with peripheric eosinophilia. Since A. costaricensis inhabits the mesenteric arteries of the ileocecal region, the clinical picture can present itself as appendicitis, including fever, abdominal pain, particularly in the lower right quadrant, anorexia, vomiting, gastrointestinal hemorrhage or palpable mass. The course and severity of the disease is variable, but it is estimated that the frequency of peritonitis and sepsis is between 1.3% and 7.4%. Studies in Brazil suggest that the disease is manifested with episodes of acute abdominal pain of short duration 2 to 3 days and sometimes recurring in various episodes for a period of 6 to 8 months.
Given that the inflammatory process per se, in humans, could prevent the parasite from reaching the intestinal lumen, the larvae or eggs are not detected in feces. So, the diagnostic rests on the clinical picture, peripheric eosinophilia and immunologic tests, these last ones with various margins of specificity and sensibility. Geiger mentions that in a parasite-specific IgG ELISA, a 76.2% and a 91.1% were observed, respectively. Finding that the titration of antibodies anti-A. costaricensis is a good diagnostic method in the acute phase of abdominal angiostrongylosis. Not in the chronic phase where there is an important decrease of the antibodies due to the rapid death of the parasite. However, all these studies recognize the lack of test standardization, requiring more investigation where probably new techniques like the PCR (Polimerase chain reaction) will have better results. This way the diagnostic remains in clinical and pathological territory. Graeff-Teixeira proposed the following histopathological criteria: (a) Microscopically 2 types, 1. Thickening of the intestinal wall (pseudoneoplastic pattern), and 2. Necrotic congestive lesion; (b) Microscopically, 1. Massive infiltration of eosinophils in the intestinal walls, 2. Granulomatous reaction, and 3. Eosinophilic vasculitits, affecting arteries, veins, lymph nodes and capillaries.
The differential diagnostic is limited, if the entity is kept in mind, and particularly if the clinical picture is taken into account; so, this must be done with: appendicitis, malign tumor, lymphoma or be confused with a Meckel diverticulum. If the histological findings are taken as a base, theoretically the differential diagnostic includes: Non-parasitic causes of gastrointestinal eosinophilia, like food and drug allergies, inflammatory disease of the intestine, polyarteritis nodosa, Chung-Strauss syndrome and post-radiation changes. At the parasite level it should be differentiated from Strongyloides stercolaris, Tocara canis (visceral larva migrans), filaria and S. mansoni.
In terms of treatment, it is oriented to solving the problem of the patient’s acute abdomen, which is unquestionably surgical. In the appropriate clinical context or combined with surgery, some drugs have been used. However, it should be taken into account that the disease is auto-limited and that in some cases it has been suggested that the drugs could cause parasite migration and worsen the clinical picture, although experimentally in rats the mebendazol did not show any migration. Drugs like tiabendazol, diethylcarbamazine, mebendazol and some medication candidate for studies in humans like flubendazole, pyrantel and drug PF1022A have been used. Ivermectine is used as an antihelminthic, for Strongyloidiasis and Ococercosis, as for treatment for ectoparasites like lice and scabies, and although data indicating that it has been specifically proven in this entity have not been shown, because of its wide spectrum of action, Bitar M could be an alternative. A proved case of abdominal Angiostongylosis after the surgery used high doses of mebendazol, 400mg/tid for 10 days with a good response.
Given that the disease is devastating and fatal in some cases more investigation is required for the pharmacological treatment.
Little is known about the prophylaxis of the disease and of disinfection methods, but it is evident that rodent pest control, specially rats, slugs, appropriate washing and disinfection of fruits and vegetables, particularly those that are eaten raw, will be reasonable actions. In Guatemala, spearmint and other herbs, frequently consumed, are of high risk to the population. So, Spearmint + Angiostongilus costaricensis + eosinophilia and fever suggest abdominal Angiostrongylosis, a cause of tropical acute abdomen little known in Guatemala.