Mammomonogamus is a genus of parasitic nematodes of the family Syngamidae that parasitise the respiratory tracts of cattle, sheep, goats, deer, cats, orangutans, and elephants. The nematodes can also infect humans and cause the disease called mammomonogamiasis. Several known species fall under the genus Mammomonogamus, but the most common species found to infest humans is M. laryngeus. Infection in humans is very rare, with only about 100 reported cases worldwide, and is assumed to be largely accidental. Cases have been reported from the Caribbean, China, Korea, Thailand, and Philippines.
The worm usually inhabits the upper-respiratory region in the trachea, bronchus, or larynx, and can elicit chronic coughing and asthma-like symptoms. One interesting case from Thailand reported finding worms in the patient's duodenum, suggesting M. laryngeus can also be a gastrointestinal parasite. More research is needed because the life cycle is not completely known. Diagnosis is made by recovering the worms on bronchoscopy or oesophagogastroduodenoscopy. Due to the scant amount of information available on this parasite in literature, increased awareness is necessary, especially in endemic areas near M. laryngeus’ reservoir hosts, for clinicians, the local population in the endemic area, and traveling tourists, to effectively recognize and prevent mammomonogamiasis.
Taxonomic classification
Mammomonogamus is classified in the family Syngamidae. The Syngamidae are in the superfamily Strongyloidae and order Strongylata, making them close relatives to hookworms and other nematodes.
The generic name Mammomonogamus is derived from the Latin term ('breast'), and the Greek terms ( 'single') and ( 'marriage'), which most likely is referring to the distinct characteristic of the male and female worm acting as a single unit through the male being joined in permanent copulation to the middle portion of the female's body.
Species within this genus are M. laryngeus, M. nasicola, M. gangguiensis, and M. auris. Only M. laryngeus is known to infect and cause disease in humans. Because of the close resemblance of M. laryngeus to the gapeworm from the genus Syngamus that commonly infect birds, M. laryngeus was originally called Syngamus laryngeus and Syngamus kingi. The classification was revised in 1948 when Ryzhikov reconstructed the phylogenetic relationship of the family Syngamidae and recategorized the parasite as M. laryngeus.
Infestation with M. laryngeus has been called mammomonogamiasis, mammomonogamosis, syngamosis', or 'syngamiasis.
History
The parasite in this genus of greatest significance to humans is M. laryngeus, due to the occasional, incidental cases reported in humans. While M. laryngeus commonly infects domestic ungulates and ruminants, the first reported case of a human infection was by Dr. King, who diagnosed the parasite in a woman from St. Lucia, Antilles. The next case originated in Brazil in the 1920s, where the connection with bovine species was confirmed.
Morphology
The most distinct feature of M. laryngeus is the “Y” shape formed when the male is joined to the female in copula. The smaller male uses its posterior bursa to attach to the female vulva located on the side near the middle of the female worm. The adult worms usually remain permanently joined in this “Y” formation as they settle on the mucosal epithelium of the larynx, trachea, or bronchi.
Adult M. laryngeus worms are red to reddish-brown in color due to their hemophagous nature. They possess spicules ranging from 23-30 μm in length and cup-shaped buccal capsules (mouths) that open at the anterior end. Located deep in the buccal cavity are eight to 10 teeth that are not thought to be used for attachment.
The adult male is about half the length of the female. Case reports have found male worms ranging from 3–6.3 mm in length and 360-380 μm in width. The larger females were reported to be 8.7-23.5 mm long and 550-570 μm wide. The female also has a pointed posterior end with a long or short tail. The female while in copula lays many ellipsoid-shaped eggs that are about 40 x 80 μm in size, not operculated, and usually possess thicker shells than hookworm eggs.
Life cycle
Although the complete lifecycle of M. laryngeus is not fully known due to the rareness of the parasite in humans, the parasite is thought to adopt a lifecycle similar to Syngamus trachea, the common gapeworm infection in birds that was initially thought to be mammomonogamiasis. Currently, two existing hypotheses may help aid medical diagnostics, especially in endemic areas such as the tropics, the Caribbean, and Brazil.