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Cuterebra infestations in dogs and cats | VETgirl Veterinary Continuing Education Podcasts

In today’s VETgirl online veterinary continuing education podcast, we review Cuterebra infections and the occurrence of systemic manifestations of this disease. Many of you have probably seen a case, or at least seen some pretty wild online videos, in which a large, alien-like Cuterebra organism is dramatically pulled out of some poor patient. If not, I recommend that you watch this video immediately!

Removal of Cuterebra from a Dog | VETgirl Veterinary CE Blog

Cuterebra spp are large, bee-like flies whose larvae cause disease by entering the host via wounds or via the mouth, nose, or eyes (Delshad). Unfortunately, the little bugger can migrate around until it finds a nice home for itself, often in a subcutaneous space, where it creates a warble. Basically this is a furuncle (like a boil) with an air pore present, and owners or clinicians may even see the small larva occasional peeking out of the air pore. As you may expect given that the larva can migrate within the body, they can sometimes go to anatomic locations that are quite serious, such as the brain, eyes, or thorax. Systemic signs of illness unrelated to local effects of the parasite are typically considered rare.

So, Rutland et al out of Michigan State University’s Veterinary Teaching Hospital wanted to evaluate Cuterebra infections and systemic manifestations of disease in dogs and cats. The authors investigated clinical signs, patient outcome, and whether smaller breed dogs (particularly Yorkshire Terriers) developed more severe illness. In this retrospective study, medical records were reviewed for patients that met the investigators’ inclusion criteria between 2000 and 2014. Additionally, patients from another emergency and referral hospital were included, but only from 2013 to 2014. The inclusion criteria were dogs and cats with a confirmed diagnosis of a Cuterebra infection, meaning that the larva had to have been visualized by a veterinarian. Any anatomic location for the larva was considered acceptable. The investigators recorded the patient signalment, pertinent history, dates of presentation, date of discharge or death, physical examination findings, treatment, available diagnostic results, and location of the larva. Patients were also classified as having systemic inflammatory response syndrome (SIRS) or disseminated intravascular coagulopathy (DIC). The authors classified the patients as systemically ill if either SIRS or DIC were documented during hospitalization or if there was subjective evidence of systemic illness based on physical examinations and diagnostic results. The authors also investigated if Yorkshire Terriers were overrepresented in this study, which was performed based on the institutional observation that small breed dogs, particularly Yorkshire Terriers, were more severely affected by Cuterebra infections.

A total of 20 dogs were included in the study, with a mean body weight of 4.1 kg (range 1.4 to 20.9 kg) and a mean age of 4.6 years (range 8 months to 9.2 years). Of the 20 dogs, 8 were Yorkshire Terriers! Twenty-two cats were included in the study, with a mean body weight of 2.7 kg (range 0.4 to 6.6 kg) and a mean age of 1.48 years (range 1 month to 8.1 years). Interestingly, two of the cats were reported to be indoor only. All patients were examined during the summer, and the average number of hospital visits per patient was 1.5 (dogs) and 1.2 (cats), ranging from 1 to 4 for both. So why were these patients actually presenting? Well when considering all of the patient visits together, 14% were presenting for the complaint of Cuterebra, with another 14% presenting for epistaxis and 33% presenting for respiratory signs. The majority of Cuterebra were located in the subcutaneous tissues of the flank, neck, or abdomen. One dog had a Cuterebra flushed from the nasal cavity, and 2 others sneezed out a larva. Interestingly, none of the animals included in this study had neurologic changes.

In terms of laboratory findings, only one patient, a cat, had an eosinophilia. However 11 patients had a neutrophilia, and 11 patients had thrombocytopenia. All of the patients that had a urinalysis performed (13 in total) had proteinuria, and of these, all were hypoalbuminemic, showing evidence of a protein-losing nephropathy (PLN). Additionally, 3 dogs were azotemic at presentation, and 2 of these later developed anuric renal failure and were euthanized. One cat had an elevated ALT and bilirubin, and 4 dogs had an elevated ALP. There were 6 cats that were FeLV/FIV tested, and all were negative. Quite a variety of additional diagnostics were performed depending on the case, including airway endoscopy on 2 dogs and a cat. Warbles or larvae were identified in the trachea of the dogs and the nasal cavity of the cat. How exciting for the endoscopist! Though perhaps less exciting for the poor patient.

As mentioned, one of the primary points of interest for the authors was evaluating systemic disease resulting from Cuterebra infections, such as SIRS and DIC. In this population, systemic manifestations included everything from SIRS, DIC, multiple organ dysfunction, PLNs, anuric kidney failure, and liver disease! Of the 22 cats, 3 of them (14%) met the criteria for SIRS, but happily all 3 of these cats survived! However 10 dogs (50%) had SIRS at presentation, and half of these dogs died or were euthanized. There were other dogs that did not meet the criteria for SIRS at admission, but later fulfilled the criteria. Interestingly, all dogs that developed SIRS had body weights below 9.1 kg, and of the 9 dogs that developed DIC, all weighed less than 4.5 kg. Sadly there were 7 dogs that met the criteria for both DIC and SIRS, and only 2 of these dogs survived. Of the entire patient population, the mortality rate was 17%. The cats did quite well, however. Of the 22 cats, 21 survived! The one remaining cat was euthanized after the Cuterebra migrated through the abdominal cavity, resulting in suspected septic peritonitis. This means that 6 dogs did not survive, and it is noteworthy that all were < 4.5 kg and had DIC and/or SIRS. Though no statistically significant difference was reported between cats and dogs in terms of the development of systemic disease, it was noted that Yorkshire Terriers were significantly more likely to be infected with Cuterebra than other dog breeds.

While treatments were quite variable, they generally included some combination of larval extraction, fluid administration, antimicrobials, corticosteroids, supportive care, pain medications, and various other patient-specific therapies targeted for the individuals. There were no reports of the larvae being broken or damaged during extraction in the available records. This is important to note, as damage to the larvae during extraction has the potential to cause a dangerous anaphylactic reaction. Aside from the inconsistent treatment strategies, several other limitations were discussed by the authors, including the retrospective nature of the study, times of inadequate medical records, lack of a definitive identification of Cuterebra by a parasitologist, lack of neurologic cases, lack of diagnostics, the use of 2 institutions and large number of clinicians involved in case management, and the small number of patients overall.

So what can we take away from this VETgirl podcast? Well this article provides a fun and interesting look at Cuterebra infections in dogs and cats! The authors’ retrospective evaluation indicates that Cuterebra infections can lead to fairly severe systemic disease in certain patients, particularly in small-breed dogs. In this study, the mortality rate was 17%, which was actually slightly higher than this VetGirl would have anticipated, especially when considering the lack of neurologic cases. So while we typically think of those little Cuterebra stinkers as causing strictly a local problem for our patients, it is important to remember that they can cause significant systemic disease and even death, particularly in our small-breed dog patients.

References:
1. Rutland B, Byl K, Hydeskov H, et al. Systemic manifestations of Cuterebra infection in dogs and cats: 42 cases (2000-2014). J Am Vet Med Assoc 2017;251(12): 1432-1438.
2. Delshad E, Rubin AI, Almeida L, et al. Cuterebra cutaneous myiasis: case report and world literature review. Int J Dermatol 2008;47:363–366.

Abbreviations:
DIC: Disseminated intravascular coagulation
PLN: Protein-losing nephropathy
SIRS: Systemic inflammatory response syndrome

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