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Furuncular myiasis caused by Dermatobia hominis in a domestic cat – case report

Abstract Dermatobiosis is defined as a parasitosis caused by the larval stage of the human botfly Dermatobia hominis, often observed in large animals but considered unusual in pet animals. The aim of the report is to describe a naturally infested cat treated in a reference dermatology service with clinical presentation similar to neoplasia or abscess. A six-year-old spayed male Brazilian Shorthair cat with outdoor access, from the countryside of Rio de Janeiro state, was treated for two nodules, one located in the sacral region and one in the tail. The patient was restrained, and digital compression of the lesions resulted in expulsion of D. hominis larvae, accompanied by a purulent secretion. The removal of larvae and use of antiseptic at the site resolved the furuncular myiasis. It is possible to assume that the parasitism reported here resulted from the animal’s living arrangement, in a rural area with cattle parasitized by D. hominis. We conclude that parasitism by D. hominis should be present on the list of differential diagnoses of cats with nodules and that mechanical removal associated with the use of antiseptics is resolutive.


Introduction
Dermatobia hominis is a dipteran belonging to the Cuterebridae family. It is a neotropical species that inhabits areas of forests and woods surrounding river valleys and plains. Its distribution occurs from Argentina to southern Mexico, including all Brazilian territory (Taylor et al., 2017).
Dermatobiosis generates discomfort, pain and can lead to secondary infections in various domestic and wild animals, as well as humans. The bovine species is the most affected by this furuncular myiasis, but pets can occasionally be affected, mainly those living in forest areas and in the presence of parasitized cattle (Bowman et al., 2002;Campos et al., 2021).
The female blue-metallic botfly, after copulation, deposits eggs in mosquitos and zoophilic flies, which carry the eggs in their abdomens until they hatch, giving rise to first-stage larvae (Amarante, 2014). The increase in temperature from the host body determines the hatching of these larvae, which penetrate the skin and migrate to the subcutaneous tissue, causing furuncular myiasis (Taylor et al., 2017).
The primary lesion is equivalent to an inflammatory papule or boil, comprising a central orifice with the presence of exudate (Clyti et al., 2008). The diagnosis is exclusively clinical and is performed by inspection and palpation of skin lesions, from which serous, hemorrhagic-serous or even purulent exudate can emerge (Clyti et al., 2008;Guimarães et al., 1982).
The treatment is performed by mechanical removal through digital compression. However, more recent studies have considered pharmacological treatment with the use of antiparasitic formulations also to be effective. The use of fluralaner for the expulsion of larvae in domestic cats (Campos et al., 2021) and the use of sarolaner on dogs have been reported (Andriotti et al., 2021).
The aim of this report is to describe the occurrence of this parasitism in a domestic cat (Felis catus), since the existence of few cases described in the literature emphasizing the clinical presentation can hamper differential diagnosis.

Case report
A six-year-old spayed male Brazilian Shorthair cat weighing 4.7 kg was brought on July 14, 2022 to the Veterinary Dermatology Service of the Veterinary Hospital of Federal Rural University of Rio de Janeiro (HVPA-UFRRJ). The owners reported as main complaint the presence of nodules at the base of the tail and on the tail, with evolution of approximately 20 days. The initial aspect described was an increase in volume at the site of the lesions. The owners further reported that the animal did not present generalized itching, instead only scratching in the places where there were nodules.
The feline in question had not been treated with any medication, including antiparasitics, and had normal appetite and water intake. Its diet was based on dry feed; moist food sachets were rarely provided. Regarding hygiene, the owners stated they did not have the practice of bathing the animal.
The animal lives in a house in a rural area with a backyard with access to the street. The presence of three more cats and one dog was reported, in addition to the nearby presence of livestock such as cattle and horses. Moreover, it was reported that one of the other cats suffered from the same type of lesion, which healed without requiring any type of treatment.
The owners reported that the animal is active, receptive and docile. When asked about the presence of ectoparasites, they reported observing ticks in the area and the presence of fleas on the animal. Moxidectin plus imidacloprid had been applied six months previously, with no follow-up.
On physical examination, areas of focal hypotrichosis were observed in the region of the left thoracic limb and left flank. At the base of the tail, in the lumbar region, a nodular lesion approximately 0.5 cm in diameter was observed, containing a central orifice ( Figure 1A). On the tail, the same type of lesion was observed, but it was approximately 1 cm in diameter.
The animal was restrained with the aid of a towel, respecting cat-friendly management, and sedation was not necessary. Digital compression was performed, which first expelled a dead larva of D. hominis from the tail, and a second larva, still alive, from the base of the tail ( Figure 1B).
In the latter case, after expulsion, a purulent content was drained. The wounds were sanitized with 0.2% aqueous chlorhexidine solution. The use of topical isoxazolin was recommended, along with sanitizing lesions with 1% chlorhexidine until total healing ( Figure 1C and 1D). The animal returned for review after seven days, presenting total healing of the wounds.
The feline species is rarely described as a host of D. hominis, because of its self-grooming behavior (Pezzi et al., 2019). However, when that behavior is not happening properly because of physical problems, cats can be affected by the dermatobiosis (Pezzi et al., 2019;Verocai et al., 2010). In this case, de patient had no other clinical changes other than the skin lesions, and the owners reported it was at its normal behavior, so it is possible that the dermatobiosis happened because of higher exposition due to living close to cattle parasitized by D. hominis.
When reported in this host, the furuncular myiasis happened in different sites, including interdigital (Silva Junior et al., 1998), in the ventral cervical region (Verocai et al., 2010), dorsal cervical, pelvic and thoracic limbs (Teixeira et al., 2016), tail and base of the tail (Campos et al., 2021). In the cat described here, the parasitosis was found in the region of the tail and its base, as described previously by Campos et al. (2021). But due to the scarcity of reports in felines, it would be premature to indicate any developmental predilection for a particular body region.
The nodule caused by the presence of D. hominis can generate pain, inflammation, restlessness, irritation and itching, in addition to tissue destruction, necrosis (Marcial et al., 2003) and drainage of a hemorrhagic-serous exudate (Mendes de Almeida et al., 2007). In agreement with descriptions in the literature, the cat reported here presented swollen abscesses that drained a secretion causing discomfort, shown by local pruritus. It is important to highlight that the initial condition mimicked other skin diseases, such as folliculitis, mycobacteriosis, sporotrichosis and neoplastic diseases, which can induce veterinarians to misdiagnose the cause, as reported by Deak et al. (2020).
The diagnosis of furuncular myiasis is based on the presence of fistulas and larvae (Wall & Shearer, 2001). However, the diagnosis can be difficult in the first days of the myiasis due to the small size of the larvae, so they can only be observed when reaching three to four millimeters, with traumatic action (Marcial et al., 2003). In the case described here, due to the considerable larval size, the diagnosis was easy through inspection and palpation of the nodules. We stress that the diagnosis in this late case, after evolution of approximately 20 days, may have been associated with the behavior of the animal, which sometimes spends long periods outside the owners' home.
The residual wound present after larval removal continues to drain a secretion, which may predispose development of bacterial infections and secondary myiasis by Cochliomyia hominivorax (Mendes de Almeida et al., 2007). In the reported animal, after the procedure, asepsis was performed and the use of antiseptic was prescribed to avoid aggravation of the condition due to infections and/or parasitosis secondary to the primary disease. The adoption of this management should prevent the occurrence of secondary myiasis. Treatment in canines is described as mechanical removal of the larva, i.e., by digital pressure or surgical removal (Orfanou et al., 2011). The literature contains a report of treatment of two felines with sedation and removal of larvae by compression (Teixeira et al., 2016), while a second report indicates efficacy of treatment based on topical fluralaner, which can promote spontaneous expulsion of the larva (Campos et al., 2021). In this case, the animal tolerated the expulsion of larvae by digital compression, with no need for sedation or prior association of drugs with larvicidal effect.

Conclusions
We conclude that although the parasitism by D. hominis in felines is uncommon, it should be among the differential diagnoses in animals from rural areas, especially with livestock breeding such as cattle, which are often parasitized. The mechanical removal of larvae with topical wound management via application of antiseptics was an effective treatment in this report. acknowledgements To Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for funding this study. This study was financed in part by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES).
To Thomaz Ricco Lamaz

ethics statement
All procediments were consented by the animal owner Financial support LXC, JIF, RTBS, DP, YMM and BSMLM -None.