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Strongyloidiasis is the disease caused by the parasite Strongyloides stercoralis - an intestinal nematode with worldwide distribution, but is especially common in tropical and subtropical regions. The disease usually manifests as intestinal symptoms. Strongyloidiasis is a common infection of wild and domestic animals including mammals, birds, reptiles and amphibians.

The tiny worm is almost invisible to the naked eye. Most roundworms or their eggs are found in the soil and can be picked up on the hands and ingested or can enter through the skin. With the exception of the roundworm that causes trichinosis, mature roundworms eventually end up or live in human intestines and cause a variety of health problems.

This parasite has different types of life cycles. One is direct, similar to that of the hookworm. Once inside a human body they pass through the right side of the heart to the lungs. From the lungs, the adolescent parasites go up the windpipe into the mouth, are swallowed, and reach the upper part of the small intestine where they develop into mature worms. Strongyloides stercoralis is the only intestinal nematode found in North America with the capacity to proliferate within the human host without further infection from the outside environment.

Some of the most common parasitic roundworms in humans are:

Enterobius vermicularis, the pinworm that causes enterobiasis;

Ascaris lumbricoides, the large intestinal roundworm that causes ascariasis;

Necator and Ancylostoma, two types of hookworms that cause ancylostomiasis;

Trichuris trichiura, the whipworm that causes trichuriasis;

Strongyloides stercoralis that causes strongyloidiasis; and

Trichinella spiralis that causes trichinosis.

Disease

Strongyloides migration through the body may result in several conditions:

Dermatitis is produced by migration of the infective juveniles through the skin (cutaneous infection).

Mild to severe symptoms of pneumonia during migration to air-sacs of lungs. (Cases of reproduction in the air-sacs have been observed but they are relatively rare). Inflammation of the intestinal mucosa may also result. This phase of Strongyloides infection can present to the physician as an acute asthma attack.

The effects of Strongyloides infection can be exacerbated in patients with comorbid pulmonary or autoimmune diseases who are treated with systemic steroids. This may lead to hyperinfection and respiratory compromise. People exposed to endemic areas with a history of immunosuppression and respiratory complications should be considered for Strongyloidiasis.

One case example was of a woman who spontaneously developed hemorrhagic pulmonary secretions and an acute rash of the abdomen. On physical exam, the she appeared with a temperature of 102.2 and pulse of 104. The abdomen was soft, tender to palpation with positive tympany on percussion. Sputum specimens were sent for staining and culture to evaluate for possible Pneumocystis, Strongyloides, Cryptococcus, or Mycobacterium infections. Serological analysis for cryptococcal antigens and coccidioidal antibodies was performed along with a urinary screen for Legionella species antigen. The terminal diagnosis was"Strongyloides hyperinfection syndrome" leading to peritonitis, respiratory failure, and death.

It is not rare for Strongyloides to cause diarrhea accompanied by emaciation and exhaustion. In a minority of cases, the organism will become extra-intestinal and may lead to septic shock and meningitis. In massive infections, ("hyperinfection") death may result unless therapeutic measures are taken.

Strongyloidiasis is more often fatal in 2-month-old infants, who are possibly infected through breast-feeding (transmammary transmission). Infection produces the condition known locally as swollen belly disease or swollen belly syndrome, which causes grossly distended abdomens, invariably fatal in these infants.

Prevention

* Have a house with a cement floor rather than an earth floor.

* Use a privately owned bathroom rather than a public bathroom.

* On an individual level, wearing shoes in risk-areas is strongly advised and will significantly lower one's
likelihood of becoming infected.

*Examine and treat all infected dogs, cats, and monkeys that are in contact with people.

* Practice strict personal hygiene.

* Adequate public health services and sanitary facilities.

Diagnosis

Since symptomatic Strongyloidiasis is usually transient and non-specific, clinical diagnosis of this parasitosis can be very difficult. Eggs produced in the intestine immediately hatch into rhabditiform larvae, making it extremely difficult to detect ova in the stool. Similarly, as the parasitic worms live within the bowel tissue rather than in the intestinal cavity, it is harder to find worms in the stool.

In order to approach one hundred percent sensitivity in detecting intestinal infection, it is common for seven serial stool specimens have to be examined for Strongyloides larvae. Where available, the optimal diagnostic test for Strongyloides stercoralis infection is the ELISA (Enzyme Linked Immunoabsorbant Assay), in which parasite specific IgG is detected with sensitivity and specificity exceeding ninety percent.

Strongyloides Serology Microwell ELISA tests for Strongyloides antibodies is commercially available, easy to administer, and relatively affordable. It should be included in rountine blood tests for patients that may have come into contact with the parasite, even if they aren't showing symptoms yet.

Treatment

Like the infective larvae of all nematodes, the Strongyloides larva is resistant to most chemical agents. Unlike other intestinal nematode infections, treatment of Strongyloidiasis depends on the complete elimination of the organism, rather than a simple decrease in the worms in the host.

The treatment regimens for uncomplicated Strongyloidiasis usually require a two or three-day course, with follow-up stool examinations to ensure eradication of the larvae. For hyperinfection syndrome or disseminated infection, drug therapy must last at least one week, or until parasites are no longer detectable. When larvae are present in the sputum, as in pulmonary Strongyloidiasis, treatment guidelines are not well defined. In one case of hyperinfection involving a lung abscess in an asthmatic patient, Strongyloidiasis was successfully treated with a five-day course of thiabendazole.

Ivermectin (200 ¼g/kg po once/day for 1 or 2 days or single doses given at an interval of 2 wk) is effective for uncomplicated infection and is generally well tolerated.

Doses of 200 ¼g/kg once/wk for 4 wk have been used for hyperinfection.

Albendazole (400 mg bid for 2 days) is an alternative, but failures occur.

Albendazole and ivermectin can be used together in hyperinfections. Cure should be documented by repeated stool examinations.

Thiabendazole was the drug of choice for strongyloidiasis, but it is more toxic than ivermectin and is no longer commercially available in the US. When thiabendazole is used, uncomplicated infection is treated with 25 mg/kg po bid for 2 days (maximum 3 g/day) and results in 80 to 90% cure. Repeated courses may be required. Adverse effects of thiabendazole, which are frequent and occasionally disabling, are nausea, vomiting, abdominal pain, dizziness, headache, paresthesia, malaise, pruritus, and flushing

In hyperinfection syndrome, therapy should be continued for at least several days after parasites have disappeared from all samples.

Prevention of primary infections is the same as for hookworms. To prevent potentially fatal hyperinfection syndrome, patients with possible exposure to Strongyloides (even in the distant past), patients with unexplained eosinophilia, and patients with symptoms suggestive of Strongyloidiasis should undergo several stool examinations and serologic testing before receiving corticosteroids or other immunosuppressants.

The persistence of infection, increasing international travel, lack of familiarity by health care providers, and potential for hyperinfection all make Strongyloidiasis an emerging infection to reckon with.

AACC Media
ECMID 2015
July 27-31
April 25-28