Background

The condition myiasis was first described in 1840 by Hope FW. The term myiasis is derived from the Greek word myia meaning fly and asis meaning disease. Myiasis is caused by dipterous larvae that feed on the host living and/or, dead tissues, liquid food substances and ingested food (Sharma et al., 2008). Maggots inhabit any organ and tissues which are accessible to fly oviposition (Ribeiro et al., 2012). The larvae penetrate the tissues and cause problems depending on the body site (Caissie et al., 2008). Apart from the skin, the nose, ears, eyes and sinuses are the common sites of invasion whereas the mouth, uro-genital tract, throat and gastrointestinal tract are less commonly affected sites (Caissie et al., 2008). Clinically, myiasis is classified as primary and secondary. Primary myiasis is caused by biophagus larvae which feed on living tissue while secondary myiasis is caused by necro-biophagus flies which feed on dead tissues. Secondary myiasis is more common and is seen in patients with necrotic lesions (Shinohara et al., 2004; Koteswara and Prasad, 2010; Sheikh et al., 2011). Another classification of myiasis categorizes it into the following types:

A) Accidental myiasis in which the larvae get ingested along with the food;

B) Semi-specific myiasis when the larvae lay on neurotic tissue of the wound;

C) Obligatory myiasis which requires living tissues for larvae development; and

D) Facultative myiasis which requires neurotic tissues for flies to lay eggs and incubate them (Caissie et al., 2008).

Based on anatomic sites involved, myiasis is classified as:

A) Cutaneous myiasis;

B) Myiasis of external orifices; and

C) Myiasis of internal organs (Sheikh et al., 2011).

Oral myiasis was first described by Laurence in 1909 (Koteswara and Prasad, 2010). The conditions leading to persistent mouth opening and poor oral hygiene, severe halitosis, facial trauma and supportive lesions may predispose the patient to oral myiasis. Oral myiasis has been reported amongst epilepsy patients with lacerated lip wounds following a seizure, secondary to medical and/or, anatomic conditions like cancrum oris (noma), cerebral palsy, fractures, secondarily infected, open fractures with necrotic sloughs, incompetent lips and thumb sucking habits, advanced periodontal disease, at tooth extractions sites, fungating carcinoma of buccal mucosa and patients with tetanus with surgical opening of mouth maintained to ensure a patent airway (Sharma et al., 2008; Koteswara and Prasad, 2010). The life cycle of the organisms starts when adult fertile flies infect the wounds and feed on exudates and lay eggs in the injured and neurotic tissues. The first instar larvae hatch after 12-24 hrs and enter the living tissues with feed for 5-7 days and moult twice. The third instar larvae (last stage) stop getting nourishment from the host tissues and leave the host and pupate on the ground. Adult flies emerge after 1-2 weeks (Maheshwari and Naidu, 2010). Incidence of oral myiasis is comparatively lesser than that of cutaneous myiasis as oral tissues are not exposed for prolonged periods to the external environment (Kumar, 2012).

1 Case Report

A 75 year old female patient with abandoned life and of low socio-economic status presented to with a chief complaint of swelling in the upper lip and bleeding from gums in the upper front tooth region due to worms since 4 days. Extra-oral examination revealed a diffuse swelling in the same region. On intra-oral examination, the patient had only 18 teeth with advanced periodontal disease. Physical examination revealed larvae in the upper anterior teeth, both vestibular areas, subjacent to the upper lip and on the hard palate. (Figure 1) An erythematous, ulcerative and eroded lesion was seen on upper gingiva burrowed by worms, irregular in shape. Detached attached gingiva was present both on the labial as well as the palatal aspects. (Figure 2) Incisive canal and foramen ovale were appreciated on clinical examination. Based on the above noted clinical findings, a provisional diagnosis of oral myiasis was made and the patient was submitted to the removal of visible larvae. A total of more than 100 larvae were removed with the help of tissue holding forceps and the area was cleaned with betadine and saline and the removed larvae were taken for entomological examination. Laboratory investigations were requested and an occlusal radiograph was taken to rule-out the involvement of bone and fortunately, the infestation involved only soft tissue. (Figure 3) HIV I and II were non-reactive and HBS antigen was found to be negative. On second visit after three days, cotton bud impregnated with turpentine oil was applied at the site and no larvae were observed.

2 Discussion

Oral myiasis is caused by the flies of dipteral which normally develop in decaying tissues (Sheikh et al., 2011). Factors favoring primary oral infection include poor oral hygiene, halitosis and non-closure of mouth for prolonged periods due to varying reasons. Few cases of oral myiasis have, also, been reported in healthy individuals with acceptable oral hygiene (Yazar et al., 2005). The present patient was, also, ill and had abounded life and abscess in the upper anterior region which was open all the time exposed to the flies to harbor and lay eggs. The female fly deposits its eggs in the presence of favorable conditions. After hatching, the larvae develop in the moist, warm environment, burrow into the oral tissues and obtain nutrition and grow (Yazar et al., 2005). Primary oral myiasis is usually located in the anterior part of the oral cavity affecting the anterior segments of both the jaws and palate suggesting a direct invasion of tissues. Rarely, posterior regions of the oral cavity are involved due to ingestion of infected material like meat (Sattur et al., 2012). The life cycle of these flies starts with the egg stage followed by the larvae, pupa and finally, the adult fly (Sharma et al., 2008). Open wounds, ulcers and open sores provide a favorable condition for growth of these. After the fly lays eggs in the dead and decaying tissues, the larvae hatch in about 8-10 hours and immediately burrow into the surrounding tissues. In this stage, there will be tissue inflammation leading to pain and other signs of discomfort. This burrowing may cause separation of the muco-periosteum from the bone. The heads of the larvae are positioned downwards so that the posterior spiracles become exposed to the open air to make respiration possible (Pereira et al., 2010). After the young larvae penetrate the skin to host, they take 8 to 12 days to develop into the pre-pupal stage and then, leave the host to pupate. This stage of larvae lasts for 6 to 8 days during which they are parasitic to the host. They hide deep into the tissues as they are photophobic which, also, helps them to secure a suitable niche to develop into the next stage, pupa. The surrounding bacteria release proteolytic enzymes which decompose the tissues and the larvae feed on this rotten tissue. The infected tissues frequently release a foul smelling discharge (Pereira et al., 2010). In the present case, also, larvae were present deep into the tissues in the anterior palatal region. There are two forms depending upon the condition of the tissues which are involved:

A) Obligatory where the infecting maggots require living tissues for the larvae development; and

B) Facultative where flies use necrotic wounds to lay eggs and incubate their larvae (Koteswara and Prasad, 2010).

An early diagnosis of myiasis can prevent involvement of deeper tissues. Management should be aimed towards the elimination of larvae (Yazar et al., 2005). The traditional management of myiasis is the mechanical removal of maggots (Rossi-Schneider et al., 2007). In case of multiple larvae and in advanced stages of development and tissue destruction, local application of various agents including oil of turpentine, larvicidal drugs like Negasunt, mineral oil, ether, chloroform, ethyl chloride, mercury chloride, phenol, saline, creosote, calomel, olive oil and idoform can be used to ensure complete removal of all larvae (Shinohara et al., 2004; Reddy et al., 2012). Turpentine, a toxic chemical, induces tissue necrosis. When applied topically, it produces reversible damages like epithelial hyperplasia, hyperkeratosis and ulcerations (Ramli and Rahman, 2002). This is followed by surgical debridement of the wound to remove the necrotic tissues. After the wound is debrided and the slough removed, the wound is irrigated with hydrogen peroxide and antiseptic betadine solution. When the wound is secondarily infected, broad spectrum antibiotics can be prescribed (Reddy et al., 2012). Recently, a systemic treatment with Ivermectin, derived from avermectin, obtained from actinomycetes, has been found to be effective when given orally in a single dose of 150 to 200 mg/kg of body weight and repeated, if required, after 24 hours (Shinohara et al., 2004; Rossi-Schneider et al., 2007; Jain et al., 2010; Melo Nunes et al., 2010). It acts by blocking the nerve endings through the release of gamma amino butyric acid (GABA) leading to palsy and death of the parasite (Shinohara et al., 2004). Bacon fat when applied on lesions prompts the larva to migrate into the fat. It may take 24 hours, however, for the larva to come-out and it may be necessary to remove the larvae with tweezers while coming out (Caissie et al., 2008).

Need of case reporting and species identification: It is of prime importance that the causative fly larva be either reared to adult or, preserved in 75% alcohol to identify the genus or, species. If many larvae are present, some should be preserved and others kept live for adult rearing. Preserved larvae allow identification of family, genus, and sometimes, the species of the infecting organism but adult specimens are much better known and therefore, more reliable for species diagnosis, hence, it is always useful to rear the larvae to adult whenever possible. Larval or, adult specimens should be sent to entomology or, parasitology center for authoritative identification. The documentation of myiasis cases based on proper identification of the parasite accompanied by detailed information on the patient’s history provides data on the epidemiology, distribution and behavior of these parasites and thus, facilitates the diagnosis, treatment and prevention of new cases (Caissie et al., 2008).

3 Prevention

According to Rossi-Schneider T, control of the fly population is a sanitary measure that should be adopted to reduce the occurrence of myiasis in human beings (Rossi-Schneider et al., 2007). Factors predisposing to attacks by myiasis-producing flies include: 1) summer season; 2) contact with infested hosts or, visit of an area of infested hosts; 3) poor hygiene and poor treatment of wounds; 4) sleeping outdoors; and 5) travel to an endemic area (Caissie et al., 2008). The disease can be prevented by controlling the fly population and by maintaining good personal hygiene. In this, patients with special needs including patients with mental and/or, physical disability should be well taken care-of (Ramli and Rahman, 2002; Sheikh et al., 2011; Bhagawati et al., 2013).

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