What Are Botflies in Dogs?
Botflies in dogs refer to the larvae of Cuterebra, a type of botfly that infests dogs by embedding themselves as parasites in the skin, eyes, upper respiratory tract, or central nervous system (brain/spinal cord). During their larval stage, they are also known as “warbles” or “wolf worms”.
These botflies are commonly found in the United States, Canada, and Mexico. In the northern regions of the U.S., the incidence of the disease is seasonal, peaking in late summer and early fall when adult flies are most active. While rabbits and rodents are the typical hosts for botflies, dogs can become infected if they encounter the larvae in grass, particularly while hunting these animals or being near their burrows.
Symptoms of Warbles in Dogs
Symptoms of botfly infestation, or warbles, in dogs vary depending on the location of the Cuterebra infestation:
Cutaneous Cuterebriasis Symptoms:
- Swelling around the affected skin area, typically around the face or neck
- Lethargy
- Loss of appetite
- Vomiting
In rare instances, severe systemic inflammation known as disseminated intravascular coagulopathy (DIC) may occur, leading to excessive bleeding or clot formation that obstructs blood flow to vital organs.
Upper Respiratory Tract Infestation Symptoms:
- Sneezing
- Swelling of the face or nose
- Nasal discharge
- Coughing
- Increased breathing rate
- Difficulty breathing
Ophthalmic (Eye) Infestation Symptoms:
- Conjunctivitis (pink eye)
- Discharge from the eye
- Swelling of the eyelids
- Inflammation of the inner eye
Central Nervous System (Brain and Spinal Cord) Infestation Symptoms:
- Circling behavior
- Wobbliness (ataxia)
- Head pressing
- Head tilt
- Seizures
- Fever
- Low body temperature
- Paralysis
- Abnormal behavior
- Blindness
Causes
Botflies in dogs, known as Cuterebra, result from an infestation of larvae belonging to the Cuterebra group of botflies. North America is home to 34 species of Cuterebra.
Botflies deposit their eggs on blades of grass or in nests, where they later hatch. Dogs contract a botfly larva when they come into contact with a blade of grass hosting a maggot. The maggot is stimulated to crawl onto the dog or another passing host by the dog’s movements against the grass.
These small maggots navigate until they find an opening such as the mouth, ear, nose, etc., where they can enter the host. From there, they migrate through various internal tissues, ultimately reaching the skin where they form a warble, a small lump.
Once mature, the maggots, which can grow up to an inch in length, drop out of the host and pupate in the soil. Eventually, an adult botfly emerges from the pupa, initiating the cycle anew.
Dog Breeds That Are Prone to Cuterebra
Any dog breed can be susceptible to Cuterebra infestation. Nonetheless, research indicates that 80% of afflicted dogs weigh less than 10 pounds, with 40% of these cases involving Yorkshire Terriers, likely influenced by the breed’s size and popularity.
Diagnosis
Veterinarians diagnose botflies in dogs by examining evidence of fly larvae, particularly in cases of skin or respiratory tract infestation. If a dog exhibits respiratory symptoms like sudden onset or issues localized to one side, such as nasal discharge and facial swelling, the vet will assess the possibility of botfly larvae presence in the throat, mouth, or nasal passages. This examination typically requires general anesthesia.
For cases involving the nervous system, veterinarians employ CT scans, spinal taps, or MRIs to detect signs of botfly larvae infestation in dogs.
Treatment
Treatment for botflies infestation in dogs involves manual extraction of the larvae from the skin, respiratory tract, or eyes, followed by thorough wound cleaning. Antibiotics may be prescribed to address any secondary infections that arise.
In cases where the infestation affects the dog’s brain and spinal cord, Ivermectin, found in dog heartworm medications, is utilized. While it can halt the progression of symptoms, it may not completely eliminate existing ones. Veterinarians may combine Ivermectin with diphenhydramine (Benadryl) to prevent allergic reactions.
Living and Management
Following the removal of botflies, it’s important to observe the affected area for any signs of discharge, swelling, or slow healing. Cases involving eye or brain infestations may require weeks to months for complete resolution.
While some dogs with Cuterebra eye infestations recover well after larva removal and anti-inflammatory treatment, others may experience complications such as blindness or glaucoma. Skin infestations of Cuterebra can occasionally lead to systemic inflammatory response syndrome (SIRS) or disseminated intravascular coagulopathy (DIC), although such occurrences are rare.
Botflies in Dogs FAQs
How can you tell if your dog has a botfly?
Symptoms in dogs vary depending on the location of the botfly in their body. Watch for the symptoms mentioned above, particularly if your dog has access to rodent or rabbit burrows.
Can a botfly kill a dog?
Dogs with skin and upper respiratory Cuterebra infestations generally have a favorable prognosis after complete removal of the larvae. However, cases of nervous-system cuterebriasis carry a 30% mortality rate for dogs, often due to euthanasia necessitated by the severity of symptoms.
How long can a botfly live in a dog?
Botfly larvae reside in their host for 3-6 weeks.
Can humans get botflies from dogs?
Once a botfly is inside a dog’s body, it cannot be transmitted to another animal or to a human.
How do dogs get botflies?
During summer, adult Cuterebra botflies deposit their eggs at the entrances of rodent or rabbit dens, their primary hosts. Dogs can inadvertently become infested with Cuterebra after sniffing around rabbit or rodent dens or directly contacting the eggs.
The host’s body heat prompts the botfly eggs to hatch, and the larvae adhere to the host’s skin. While larvae cannot directly penetrate the skin, they can enter through a dog’s mouth, nose, open wounds, or any other skin openings.
They migrate through the skin and develop further in the tissue layers beneath it. After 3-4 weeks of development, a noticeable nodule with an external breathing hole may appear on your dog’s skin.