INTRODUCTION

Myiasis is parasitic infestation of animal and human tissues and organs caused by fly larvae. The infestation can be localized on the skin, necrotic tissues and in cavities such as the nostrils, gastrointestinal tract and genitourinary tract ¹.

Myiasis can be classified according to the affected tissues or anatomical region as cutaneous or systemic. As for the latter, although its initial location is the skin, it can migrate to the gastric, intestinal, rectal, urinary, auricular and ophthalmic tissues ², causing dermal, cutaneous or subdermal myiasis; Urogenital myiasis; Gastrointestinal or enteral myiasis; Ocular myiasis; Nasopharyngeal myiasis; Etc. ^3,4.

According to the degree of parasitism, myiasis can be classified as obligatory when larvae feed exclusively on living tissues, optional when larvae require necrotic and accidental tissues when they are caused by free diopters, but under certain circumstances can be ingested by the host and develop in it accidentally ^1,5-7.

The most common etiological agents are larvae from genus: Sarcophaga, Dermatobia, Oestrus, Gasterophilus, Cochliomya, Lucilia, Chrysomya and Musca⁸. Larvae are initially fed for a given time on living or dead tissues of the host, as well as on their organic fluids ^7,8.

The most frequently associated diseases and risk factors for myiasis are: exposed ulcers, hemorrhoids, cutaneous bacterial infections, heavily exuding wounds, lack of personal grooming, farm animal raising, alcohol-related behaviors such as insensitivity and sleeping outdoors, ingestion of contaminated food, abandoned individuals with diminished physical or mental functions ^9,10.

CLINICAL CASE STUDY

The first case corresponds to a 70-year-old patient living in Medellín, Antioquia, who entered the hospital due to digestive problems: fetid feces, diarrhea, no mucus or blood, subjective fever, headache, general malaise, severe cramps. The patient reported that she sometimes saw the presence of a small animal moving inside her feces, which was extracted for laboratory examination.

The sample was sent to the Colombian Institute of Tropical Medicine (ICMT-CES) and identified as dipterous larvae in the third stage of development of the species Ornidia obesa (Diptera: Syrphidae) following the description of Montoya et al ¹¹ (Figure 1).

Figure 1 a and b. Larva 3 of Ornidia obesa. Patient # 1. Intestinal myiasis 

The second case refers to an 11-year-old patient living in Medellin, who consulted several times for chest and abdominal pain, dyspnea, bloody stools and diarrhea and an initial diagnosis of infectious gastroenteritis. For more than five months, the parasites were removed through his mouth and nose, despite treatment with albendazole.

The collected larvae was sent to the laboratory of the Colombian Institute of Tropical Medicine - CES where they were identified as larvae of Ornidia sp. Following the description by Montoya et al. ¹¹, which does not allow to reach a species due to the L1 larval state (Figures 2-5).

Figure 2 Larval L1 of Ornidia sp. 

Figure 3 Larval L1 of Ornidia sp. 

Figure 4 Ornidia sp., Posterior extremity. 

Figure 5 Ornidia sp, anterior end 

The taxonomic identification of the larvae found in both patients was confirmed in the Laboratory of the Department of Preventive Veterinary Medicine and Animal Health of the Faculty of Veterinary Medicine and Animal Husbandry of the University of Sao Paulo (Dr. Marcelo Labruna).

DISCUSSION

According to the eating and behavioral habits of the dipterans that cause them, myiasis can be classified into specific, semi-specific and accidental. Specific are those due to larvae that feed on living tissues, such as C. hominivorax, D. hominis. Semi-specific or secondary myiasis are those caused by larvae that survive feeding on necrotic tissues, for example: C. macellaria, Sarcophaga sp; And accidental myiasis, as its name implies, is installed by accident and caused especially by M. domestica, F. canicularis, and species of the family Syrphidae as Eristalis tenax and O. obesa, as the case reported in this work ^2,10.

The most important human myiasis in our environment are caused by larvae of D. hominis and C. hominivorax^9-11. In other countries such as Chile and Brazil there are reports of the presence of accidental myiasis by E. tenax and O. obesa^10,12.

It is important to emphasize that the larvae of syrphids have different eating habits and adults have a main ecological function of pollination. The results of the studies in Colombia indicate a wide distribution of syrphids species which, as reported in this work and in literature, may produce accidental myiasis in humans ¹¹.

Regarding accidental myiasis caused by Diptera of the Syrphidae family, the clinical case of a 27-year-old Chilean female patient was reported for the first time, who in a menstrual period presented a sensation of foreign body moving in the vaginal region and then expelled Larvae that were identified as third instar larvae of Eristalis tenax (Diptera: Syrphidae) ¹⁰.

Similarly, intestinal myiasis by O. obesa larvae was reported in Brazil in an eight-year-old girl who was taken to the hospital with hyperthermia, abdominal pain and intestinal obstruction. In the physical examination two larvae and one pupa of this species were found. According to the medical report, the patient may have consumed food contaminated with eggs or larvae ¹³. For the case in Colombia, no records of this type of accidental myiasis by O. obesa were found, being this the first reported case.

In different reports of myiasis ^2,4, the patients present important immunocompromised conditions, among others, advanced age and malnutrition; as well as intrinsically attractive factors for the oviposition of flies, such as the presence of tissues with abundant protein rich exudates, that also serve as chemotactic agents for flies ^3,4.

For the case of the type of myiasis reported in the present study, these are not necessarily risk factors for accidental myiasis. Proper management of organic waste and food handling must be effective in the prevention of this type of cases.

Finally, it is pertinent to draw attention to the treatment of myiasis. Oral ivermectin administration is based on diverse scientific evidence ^9,12, in addition to assisting in the control of larvae in difficult-to-access cavitary myiasis. However, it is important to emphasize the importance of mechanically monitoring and extracting the larvae, as these could invade healthy tissue and cause significant damage, including intense pain and deformation ⁴. This possibility of invasion, in turn, depends on the dipterous species involved in the infestation ^3,4.