Cuterebra Ophthalmomyiasis

Ophthalmomyiasis interna anterior in a dog: keratotomy and extraction of a Cuterebra sp. larva

A 1-year-old female spayed mixed-breed dog was presented for evaluation of acute onset of lethargy and blepharospasm OD. Slit-lamp biomicroscopy revealed a segmented larva embedded in the inferonasal iris. Moderate anterior uveitis was present. After pharmacologic dilation, mild vitreal hemorrhage and chorioretinal migration tracks were identified. The dog was treated empirically for uveitis for 5 days, after which a keratotomy and larval foreign body extraction was performed. The dog recovered uneventfully from intraocular surgery and remained visual and comfortable. Parasite evaluation confirmed the larva to be a Cuterebra sp. To the authors' knowledge, this is the first report of canine ophthalmomyiasis interna anterior, and the first report of successful surgical removal from the anterior segment in a dog with preservation of vision.

Ophthalmomyiasis externa in a puppy due to Cuterebra infestation

An 8 wk old Scottish terrier was evaluated for a 2×2 cm mass located directly adjacent to the lateral canthus of the right eye. Examination revealed a well-developed Cuterebra larva at the lateral aspect of the orbital cavity, anchored at the lateral canthus. The larva was manually removed under general anesthesia, and the eyelid margin was repaired. Systemic and topical antibiotics along with systemic anti-inflammatory treatment were instituted. The lesion healed completely, revealing a normal functional right eye 10 days after removal of the Cuterebra larva. Careful manual removal of the larva is recommended along with correction of any resultant conformational defects. The remaining cavity can be left to heal; however, antibiotic therapy is recommended.

Cuterebra cutaneous myiasis: case report and world literature review

BACKGROUND

Most cases of myiasis in North America are caused by fly larvae from South America or Africa, as these cases represent travelers returning from endemic regions. The etiology of creeping eruptions and furuncular lesions in North American patients who have no history of recent travel can therefore be a diagnostic problem. Among cases acquired in North America, Cuterebra species are the usual cause. Dermatologists and dermatopathologists should be aware that this unusual infestation may occur without a travel history.

METHOD

Here we report a case of Cuterebra cutaneous myiasis acquired in New Jersey. A world literature review of articles on Cuterebra myiasis in humans, without age or year restriction, was performed. The pertinent references of those articles were also searched.

RESULTS

Most cases occur in the skin, as a furuncle. Sometimes a cutaneous creeping eruption is present. Children account for at least half of the reported cases. The infestations tend to occur in the late summer, and most frequently in the north-eastern and southern states of the United States. An overview of the clinical and histopathologic diagnostic features are presented.

CONCLUSIONS

Though rare, myiasis can occur in North America without a travel history. Awareness of this entity, its epidemiologic patterns and diagnostic characteristics, can prevent lengthy delays in diagnosis and unnecessary treatments.

Insect/mammal associations: effects of Cuterebrid bot fly parasites on their hosts

The effect of parasites on their hosts has implications for basic and applied ecology (e.g., species' population dynamics and distributions, biological control, and threats to at-risk species) and coevolution. Cuterebrid bot flies comprise one of the most-studied groups of insect parasites of mammals. Interest in their impact dates from at least 1857, when Cuterebra emasculator was so named because of the erroneous belief that its larvae castrate their hosts. This review addresses the effects of cuterebrid larvae on host biochemistry, physiology, behavior, and ecology. Despite high prevalence (peak values commonly range from 30% to 70%), at average intensities (one to three larvae per host) these parasites generally have little effect on the fitness or population dynamics of their typical hosts. This outcome likely reflects parasite/host coevolution favoring parasites that minimize harmful effects on hosts required for their survival and hosts that best tolerate perennial parasites they cannot avoid. In contrast, aggravated effects occur at higher intensities and with atypical hosts. Additional field studies involving experimental manipulation of infestation and spanning more than a few seasons are required to confirm these conclusions.

Myiasis as a risk factor for prion diseases in humans

Prion diseases are transmissible spongiform encephalopathies of humans and animals. The oral route is clearly associated with some prion diseases, according to the dissemination of bovine spongiform encephalopathy (BSE or mad cow disease) in cattle and kuru in humans. However, other prion diseases such as scrapie (in sheep) and chronic wasting disease (CWD) (in cervids) cannot be explained in this way and are probably more associated with a pattern of horizontal transmission in both domestic and wild animals. The skin and mucous membranes are a potential target for prion infections because keratinocytes and lymphocytes are susceptible to the abnormal infective isoform of the prion protein. Iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) was also recognized after corneal transplants in humans and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes could also be important in prion infections. Some ectoparasites have been proven to harbour prion rods in laboratory experiments. Prion rods were identified in both fly larvae and pupae; adult flies are also able to express prion proteins. The most common causes of myiasis in cattle and sheep, closely related animals with previous prion infections, are Hypoderma bovis and Oestrus ovis, respectively. Both species of flies present a life cycle very different from human myiasis, as they have a long contact with neurological structures, such as spinal canal and epidural fat, which are potentially rich in prion rods. Ophthalmomyiases in humans is commonly caused by both species of fly larvae worldwide, providing almost direct contact with the central nervous system (CNS). The high expression of the prion protein on the skin and mucosa and the severity of the inflammatory response to the larvae could readily increase the efficiency of transmission of prions in both animals and humans.

Pars plana vitrectomy for the treatment of ophthalmomyiasis interna posterior in a dog

Unilateral chorioretinitis caused by ophthalmomyiasis interna posterior in a 5-month-old, female spayed Dachshund is reported. Larva removal by pars plana vitrectomy was performed after an unsuccessful photocoagulation of the organism. The larva was intact after surgical removal and was identified as a first stage instar Cuterebra spp. larva. The eye remains visual and comfortable with no signs of residual or recurrent inflammation postoperatively. This report describes, for the first time, the successful surgical retrieval of an intravitreal fly larva in a dog using vitrectomy techniques without sacrificing either the globe or vision, and taxonomic identification of the parasite.

Ophthalmomyiasis interna anterior in a cat: surgical resolution

A 4-year-old Domestic short-haired cat was presented for severe anterior uveitis in the right eye associated with a Cuterebra spp. larva in the anterior chamber. This report describes successful surgical removal of the parasite with preservation of vision.

Ophthalmomyiasis (interna posterior) of the posterior segment and central nervous system myiasis: Cuterebra spp. in a cat

A unilateral ophthalmomyiasis posterior in a 5-year-old female spayed Domestic Long-haired cat of a third or fourth stage instar Cuterebra spp. larvae is reported. The cat was presented for depression and anorexia. The organism was found on physical examination at presentation. The cat was euthanized because of the worsening systemic condition. The larva was demonstrated by histopathology with coagulation necrosis and hemorrhage of the optic nerve, retina and choroid, and anterior uveitis. No significant cerebrum and anterior brain stem lesions were found.

Ophthalmomyiasis caused by the sheep bot fly Oestrus ovis in northern Iraq

Myiasis is the feeding of fly larvae on vertebrates. The sheep bot fly larva of Oestrus ovis is a mammalian parasite of the skin, nose, ears, and eyes. When the larvae infest and feed on the structures of the eye, the condition is termed ophthalmomyiasis. Most often this infestation is limited to the external structures of the eye and is referred to as ophthalmomyiasis externa. The features of this condition are severe local inflammation, positive foreign body sensation, erythema, and lacrimation. Vision may or may not be reduced, depending on involvement of the cornea. A 20-year-old white male soldier sought treatment for an inflamed eye and an irritated cornea OS. His eyelids were swollen with marked periorbital edema and conjunctival erythema OS. On slitlamp examination, small whitish organisms were viewed on the conjunctiva OS. The organisms were removed, preserved, and sent to Nova Southeastern University where they were identified as O. ovis first-stage larvae. The patient was treated with antibiotic ointment, and the inflammation resolved within 1 week. O. ovis has a worldwide distribution, and although sheep are the preferred host, humans may also serve as an intermediate host in the organism's life cycle. This case represents one of several reports of ophthalmomyiasis in the Middle East caused by O. ovis. U.S. troops stationed in Iraq and surrounding areas are vulnerable to eye infestation by fly larvae, and health care providers need to include this condition in their differential diagnosis of anterior segment inflammatory disorders.

Tracheopulmonary myiasis caused by a mature third-instar Cuterebra larva: case report and review

Myiasis is the infestation of vertebrate tissues with fly larvae (Diptera). Most human cases in North America are subcutaneous forms due to Dermatobia hominis imported from Central and South America. Human cases of myiasis acquired in North America are rare and are primarily subdermal or ophthalmologic forms of infestation caused by early stages of Cuterebra larvae. We report an unusual case of tracheopulmonary myiasis, resulting from the in situ development of a mature cuterebrine larva associated with high eosinophilia. Only two other cases of tracheopulmonary cuterebrid myiasis have been reported in humans, and they are reviewed herein. Cuterebra myiasis (cuterebrosis) remains a rare and aberrant cause of tracheopulmonary disease and is a newly described cause of eosinophilia in humans.

Furuncular myiasis caused by Dermatobia hominis, the human botfly

Myiasis is a common travel-associated dermatosis. Travelers to many parts of Central and South America are susceptible to infestation by Dermatobia hominis. Despite the common name of human botfly, D hominis infests a broad range of mammals and is a severe pest to economically important farm animals in endemic regions. The adult female does not lay the eggs on the host. Instead, the adult female infests hosts indirectly by using blood-feeding arthropods to serve as phoretic vectors to transport the eggs. We present a patient who acquired Dermatobia when bitten by a day-active mosquito during a visit to Guatemala. He had a locally painful, firm furuncular lesion with a central pore that drained serosanguineous exudates. The patient applied an occlusive ointment and recovered the larva after it emerged. In this report we discuss the life cycle of D hominis, the differential diagnosis, and therapeutic approaches.

Ophthalmomyiasis interna anterior associated with Cuterebra spp in a cat

An 8-year-old domestic shorthair cat was examined for severe anterior uveitis of the right eye that was unresponsive to aggressive treatment with anti-inflammatory drugs and for a possible intraocular parasite or foreign body trapped within a large fibrin clot in the anterior chamber. Surgical exploration of a presumed entry site on the caudal aspect of the third eyelid led to keratotomy and removal of a larval parasite later identified as a first instar Cuterebra spp. Aggressive treatment with anti-inflammatory drugs was continued after surgery, and intraocular pressure was monitored closely to ensure that the cat did not develop glaucoma. Two weeks after surgery, the cat had vision in the affected eye, with resolving uveitis and a normal fundus. Six weeks after surgery, the uveitis continued to resolve; however, the cat did not have vision in the affected eye, and examination of the fundus revealed retinal atrophy. In contrast to the condition in humans, a Cuterebra spp larval infection within the eye of cats may cause not only an intense, acute inflammatory reaction, but also retinal degeneration and blindness despite prompt surgical removal.

Cerebrospinal cuterebriasis in cats and its association with feline ischemic encephalopathy

Over the past 10 years, 10 cats with primary central nervous system infection by larvae of Cuterebra flies have been documented at Cornell University. Clinical abnormalities noted in all cats were progressive and most commonly consisted of depression (6/10), blindness (6/10), and behavior changes (2/10). Affected cats presented most commonly in July (2/10) and August (7/10); one cat was presented in September. The diverse histopathologic changes are unique to this aberrant migration and consist of a combination of five characteristic features: 1) parasitic track lesion (7/10), 2) superficial laminar cerebrocortical necrosis (10/10), 3) cerebral infarction (8/10), 4) subependymal rarefaction and astrogliosis with or without ependymal cell loss (7/10), and 5) subpial astrogliosis (7/10). Changes 2-5 occurred throughout the parenchyma unassociated with the track lesion or the parasite in the affected tissue. The larvae have been recovered most commonly in the region of the olfactory bulbs and peduncles, optic nerves, and cribriform plate, suggesting entry from the nasal cavity. Many of the changes noted are suggestive of a toxic factor elaborated by the parasite and borne within the cerebrospinal fluid, as well as vascular compromise as a component in those cats with brain infarction. Because of the prevalence of infarction associated with this syndrome and the lack of reported cases of such lesions in regions of the world devoid of the fly, we propose that aberrant cuterebral larval migration in the brain is the cause of feline ischemic encephalopathy.