Cuterebra

Cuterebra is a fly that can cause a myiasis (larva) infestation in domestic animals. Dogs and cats are abnormal hosts to this parasite, meaning that they are accidentally infected by it. 

Normal hosts are rodents, notibly rats, squirrels, mice, and rabbits. There is no breed, sexe, or age predisposition. Animals with sores, that are contaminated, debilitated, and weak are more at risk. 

This parasite can be found everywhere and infestations in our area ar more frequent during the summer or autumn when there are more humid temperatures. 

The female deposits groups of 5 to 10 eggs on blades of grass and in or around burrows. Depending on the species, the female can lay between 1200 and 4000 eggs. After approximately 12 days, the eggs are ready to hatch and so in a matter of 3 seconds when there is a rapid increase in ambient temperature and concentration of carbon gas. 

The larva leaves its shell and, due to the sticky substance with which it is coated, sticks to snu object, such as the skin of an animal present in the area. Generally, it penetrates the animal through its natural openings, but can also do so through lacerated skin. The larva chooses a specific site to develop in its regualr host, but to achieve this, it must undergo a somewhat long migration. 

Given that dogs and cats are not regular hosts, the larva's tissue migration is often erratic when compared to with regular hosts. Thus, it can find itself in the skull, the brain, nasal passages, the pharynx, and eyelids. Once inside the subcutaneous tissues where it feeds off the blood, it creates an opening in the skin (a pore) that allows it to breathe ambient air. Once its development has finished at the end of 19 to 73 days depending on the species, the larva expands the opening to create an exit. It then falls to the ground and buries itself under the surface where it transforms into a pupa and then a fly after a variable period of time.   

When the larva is present at the cutaneous level, inflammation, pain (variable), and open wounds can be observed upon physical examination. Purulent material can exude from the lesion. The final diagnostic is acquired when the larva is seen. A blood test as well as urine analysis are recommended in order to exclude any other possible or predisposed causes. A bacterial culture can be added when an infection is present.

Treatment consists of completely removing the larva. It is important not to crush or shatter it as they may result in an allergic reaction. The affected area should be carefully cleaned and disinfected. A debridement and antibiotic treatment might be necessary. Certain antiparasitic medications can provide help during treatment. Afterwards, the dog should be kept in an area where flies do not have access (at home with a screen) until the wounds have healed.