BACKGROUND

Mammomonogamus laryngeus (Syngamus laryngeus) is a nematode found in tropical mammals1 and very rarely in humans.2 About 8% of travellers to the developing world require medical assistance during or after travel and in approximately 8% of cases a respiratory disorder is diagnosed.3 Chronic cough is a common complaint, but we have found no published data on its prevalence in travellers. This case underlines the importance of a correct travel history as a part of the medical examination and describes a very unusual cause of chronic cough.

CASE PRESENTATION

The patient was on a cruise in the Caribbean (departing from Martinique where the tourist group bought food and beverages) from 14 to 21 July 2007. She reported eating fresh salads while on the cruise.

Upon return to Italy on 25 July 2007 she began to complain of a worsening cough, which was initially treated with anti-histaminic drugs and then (1 month later) with amoxicillin, to no avail. Two chest x rays (September and October) were normal. Gastro-oesophageal reflux disease was then suspected and treated. At the end of September the patient experienced two episodes of haemoptysis. A thoracic CT scan was performed without abnormal findings.

A fibre optic bronchoscopy showed and removed a Y-shaped red object around the division of the subsegmentary bronchi of the right inferior bronchial hemi-system. Two worms were identified and diagnosed as male and female M laryngeus in copula (see fig 1).

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Figure 1

Male and female Mammomonogamus laryngeus in copula. The female cephalic part with typical cup-shaped appearance is shown in the circle.

On 26 November 2007 the patient was re-evaluated. The crawling sensation in her lungs had completely disappeared, but she still complained of chronic cough with rare episodes of haemoptysis. A course of an anti-helmintic drug combination was then started (see below).

INVESTIGATIONS

Except for bronchoscopy (see above), all investigations were normal. In particular, neither eosinophilia nor increased IgE were noted, even before parasite removal. Stool exam was negative. The patient did not produce any sputum for examination.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis in a case with chronic cough is wide and many diseases must be considered including asthma, chronic bronchitis, bronchiectasis, left cardiac failure, lung cancer, sarcoidosis, fungal diseases, Wegener granulomatosis, tuberculosis, pertussis, allergy and drug reactions (ACE inhibitors). Whenever the travel history is suggestive, a number of other hypotheses should be considered such as schistosomiasis, paragonimiasis, other distomatoses, and larval migration of nematode worms. In our case the repeated haemoptysis raised the suspicion of tuberculosis or lung cancer.

TREATMENT

Worm removal can be sufficient to cure the disease,4 although respiratory symptoms may last for months. Our patient was also treated with a course of anti-helmintic drugs according to the literature,4^–7 with ivermectin (one dose of 200 μg/kg) followed by a 2-day course of thiabendazole (1250 mg bid) and then a final 2-day course of albendazole (400 mg bid).

OUTCOME AND FOLLOW-UP

The cough improved after treatment and had completely disappeared 3 months later. A second fibre optic bronchoscopy was negative.

DISCUSSION

The name Mammomonogamus is from the Latin “mamma” (breast), the Greek “monos” (single) and the Greek “gamos” (marriage).

This parasite was discovered by King8 in the sputum of a patient in Santa Lucia, Antilles, and first described by Travasson in 1921 in a patient from Salvador, Bahia (Brazil).

The female is about 10 mm long, the vulva is in the anterior part of the body, the uterus contains many eggs, the cephalic part is cup-shaped without chitinous plaque or outside teeth (or with 8–10 small teeth at its base and no leaf crowns), and the posterior end is sharp and pointed. The male is about 3 mm long, the cup-shaped buccal capsule is smaller, and the copulative bag is in the posterior end. The male is joined permanently to the female with the typical Y-shaped appearance (fig 1). The eggs are ellipsoid, non-operculated and measure about 45×80 μm. M laryngeus is haematophagous and thus blood red coloured.

The life cycle is not completely known. There are two main hypotheses, based on case reports and the similar bird parasite Syngamus trachea:

1. The infection is acquired by direct ingestion of adult worms present in water or contaminated food; this method of transmission is suggested by the short incubation period (6–11 days),5^,7 which is incompatible with the time required for adult worms to develop from eggs. In our case the incubation period was 12 days at most, according to the patient’s history.

2. Embryonated eggs or infective larvae or paratenic hosts containing infective larvae are ingested and through a pulmonary cycle reach the trachea or bronchi, the preferred sites of infection. The adult pair produce eggs which are ingested and passed in faeces or sputum. This hypothesis is suggested by the life cycle of S trachea and the description of transient lung opacities in patients infested with M laryngeus.9

The previously reported cases of syngamosis (about 100 since the discovery of the worm) occurred in tropical countries where the parasite is endemic (mostly the Caribbean and Brazil, although Korea, Thailand and the Philippines have also recently reported cases).10

Eosinophilia may be present in human syngamosis and seems not to be related to the number of worms.4 Most reported cases had only one pair of worms. The clinical manifestations are characterised by chronic non-productive cough, transient pneumonia, haemoptysis, a crawling sensation in the airways and asthma.4^,9

Diagnosis is based on instrumental procedures, such as fibre optic bronchoscopy. Occasionally, the parasite may be ejected during an excess of cough.7 Eggs may be found in sputum or faeces. There are no controlled studies on treatment. The removal of parasites usually results in resolution of clinical signs; nonetheless, patients have often also been treated with anti-helmintic drugs.5^,6

In our case the diagnosis was delayed due to the rarity of the disease (although the travel history had been considered) and the absence of eggs in stools and/or eosinophilia.

The travel history is crucial. Our patient had visited Martinique as had approximately half of all reported cases.4 The short incubation period (in contrast to most causes of chronic cough) is another clue to diagnosis.