Myiasis is defined as the invasion of organs and tissues of humans beings or other vertebrates by fly larvae. Larvae feed on living or dead host tissues; and in the case of intestinal myiasis, on the host's food. They may infest different parts of the body as in cutaneous, urogenital, ophthalmic, nasopharyngeal and intestinal myiasis. The infestation of already existing wounds is referred to as traumatic myiasis ( Service 2000).
Fungating and necrotic wounds are common among cancer patients in India because many patients have advanced neglected tumours. Necrotic and decomposing tissue attracts flies, with India's tropical climate being especially conducive to their breeding. Poverty, poor sanitation, and lack of aseptic wound care exacerbate the problem (Bahr and Bell 1987).
This problem has been neglected at personal and professional levels. Many cases of maggot infestation are not detected or treated. This is a retrospective study from an inpatient palliative care unit.
Seventy one patients with maggot infestation were seen in the Cipla Palliative Care Centre, Pune, over a six year period. Their records were reviewed.
The age sex distribution of the patients is depicted in [Table - 1]. Eighty three percent of the patients had cancer of the head and neck and 10% had breast cancer. The majority of patients (77%) were from poor socioeconomic backgrounds. Ten were destitute.
Patients presented with the following symptoms: 92% experienced oozing, 38% reported malodour. Most patients experienced pain which was described variously as biting (65%), gnawing (15%), or throbbing (4.2%). 12% noted a wriggling sensation.
The extent of the infestation was judged by counting the number of maggots removed. Thirty one patients had fewer than 50 maggots. Twenty had more than a hundred maggots. In four cases numerous maggots were seen to leave the dead body soon after death possibly because of the reduction in body temperature (Service 2000).
Twenty minutes before removal, the patient was given oral diclofenac. The wound was washed with normal saline and hydrogen peroxide and anaesthetized with lidocaine spray. Acriflavin or turpentine were applied to induce the maggots to emerge from the wound. (Ether and chloroform are also effective, but more expensive.) Maggots were removed using forceps, and the wound was dressed with an antibiotic preparation.
The sight of maggots was often frightening for the patient and the care giver, and support and counselling were very important. The care giver was taught proper wound care and counselled to not to show revulsion.
Myiasis results from files laying eggs in tissues. The three main families of flies involved in myiasis are the Calliphordiae,( Timbu flies, screwworms, greenbottles and bluebottles) Sarcophagidae (flesh fly) and Oestridae (warble flies and botfly) (Service 2000, Hall 1995).
There are two forms of myiasis: obligate, where it is necessary for the maggots to feed on living tissues and facultative, where files opportunistically use necrotic wounds as a site in which to oviposit and incubate their larvae (Burgess 2003). The cases of wound infestation (traumatic myiasis) described here are all of the latter type.
Obligatory parasites found in India include screwworms such as chrysoma bezzania. These invade healthy tissues in the nose, mouth, eyes and vagina causing pain and disfigurement. Surgery may be required to remove deeply emebedded larvae (Service 2000).
Traumatic myiasis is caused by different species. In temperate climates the most common flies infesting wounds are the greenbottles (Lucilia sericata and Lucilia cuprina of the Calliphordiae family) (Service 2000). Larvae of the common housefly, Musca domestica have also been identified especially in neglected wounds (Magnarelli 1981, Service 2000, Burgess 2003). The common housefly is found worldwide. Its life cycle is similar to that of the Calliphorid flies
Life cycle of musca domestica
Each female fly can lay up to 500 eggs in several batches of about 75 to 150 eggs. Eggs hatch within 10-24 hours in warm weather. The legless maggots feed on decomposing tissues and go through three instars to reach full size in 5 days. The mature larva is 3 to 9 mm long, creamy white in colour, cylindrical, with a tapering head. The fully developed larva leaves the tissues and to find a cooler drier environment in which to pupate. The pupal stage generally lasts a further five days. The emerging fly escapes from the pupal case through the use of an alternately swelling and shrinking sac, called the ptilinum on the front of its head which it uses like a pneumatic hammer.
Maggots should be picked out as they emerge from the wound. Turpentine and acriflavin packs should be applied for three to four days after the last visible maggot has came out. This allows time for any eggs remaining within the wound to hatch and for larvae to emerge (Service 2000).
It is not surprising that more than eighty percent of the patients in this study had head and neck cancers. These cancers are common in India because of tobacco chewing and smoking. Patients present late and die slowly of advanced local disease. The face and neck are are often left uncovered. Even if disfiguring wounds are covered, a moist soiled dressing is not a protective barrier.
Poverty was a common characteristic of most affected patients. For many, preventive measures such, proper disposal of garbage, and putting screens on windows, are not feasible. Care givers should be taught to keep the wound covered and dry, and to burn or bury soiled dressings. Topical metronidazole can be used to help reduce wound odour.
Health care professionals should consider the role of pallaitive radiation for necrotic fungating wounds. Attention to environmental hygeine measures is also important. Flies and their larvae are resistant to many insecticides and larvicides. Fans mounted over doorways may help reduce the number of flies entering the building. Ultraviolet light traps can kills flies by electrocution (Service 2000).
Maggot infestation is distressing problem. The sight, smell and stigma can lead to patients being turned out of their homes. Palliative care workers in India need to be proactive in caring for and educating patients about wound care.
[Table - 1]