Feline Ischemic Encephalopathy in Cats
Feline ischemic encephalopathy (FIE) is caused by the presence of a parasite, the Cuterebra larva, in a cat’s brain. Entering through the nose, the larva moves to the brain and may cause neurological damage to the middle cerebral artery (MCA) in the brain and degeneration of other cerebral areas. This can result in seizures, circling movement, unusual aggression, and blindness.
The disease occurs only in areas where the Cuterebra larvae of the adult botfly live, primarily in the northeast US and southeast Canada. FIE is a seasonal disease that occurs solely in the summer months, mainly in July, August, and September. Outdoor cats and cats with access to the outdoors are at risk, while indoor cats do not develop FEI.
Symptoms and Types
Symptoms of FEI include neurological signs, most commonly seizures, circling movements, altered behavior such as unexplained aggression, and blindness. Breathing issues (respiratory) may be apparent one to three weeks prior to any neurological signs, as the parasite migrates to the brain through the nasal passage.
FIE is caused by the Cuterebra larvae of the adult botfly. The adult botfly lays its eggs near the entrance of a rabbit, mouse, or other rodent’s den. When the eggs hatch, the larvae attach to the hair and skin of a host”rodent. A cat may become the host if it is outdoors, especially when hunting near rodent burrows.
The larva may attach itself to a cat’s hair, and make its way to the cat’s skin, throat, nasal passage, or eyes. FEI occurs when the larva enters through the cat’s nose and moves to the brain. Physical damage, such as breakdown (degeneration) of tissue and bleeding (hemorrhage) can occur due to spines on the parasite’s body. The parasite also secretes a chemical that may damage the middle cerebral artery (MCA) and cause it to spasm.
Urine tests, spinal fluid tests, and other lab tests may be conducted to diagnose FEI, but the best and most common diagnostic tool is an MRI scan. This may be able to detect a track lesion in the brain from the larva’s migration and other key neurological abnormalities. If the MRI is done more than two to three weeks after symptoms begin, it may also show a loss of brain matter in the area supplied by the MCA—another sign the Cuterebra larva is present.
The MRI scan is important in determining whether it is the Cuterebra larvae causing neurological symptoms. Other problems that may be to blame include external trauma, tumors, kidney disease, and infectious diseases.
Surgical removal of a parasite from a cat’s brain has never been reported. However, there are medications to relieve symptoms caused by the parasite. Anti-epileptic drugs help prevent seizures, while intravenous (IV) fluids ensure the cat maintains good nutritional status.
A drug treatment designed to kill the parasite is also available, but only used if the symptoms have been occurring for less than one week. After a longer period, it is likely the parasite has died.
Living and Management
After initial treatment, periodic neurological evaluations are recommended. Many cats return to their normal state, but in some cases complications may continue. These depend on the amount of damage done by the parasite, and can include uncontrolled seizures, compulsive circling, and other behavioral changes.
The primary method of prevention is to limit cats to the indoors, especially during summer months.