The neurological and/or ocular forms of FIP can be confused with feline systemic toxoplasmosis, which is why so many cats with these forms of FIP are tested for toxoplasmosis and treated with clindamycin or other antibiotics. However, systemic toxoplasmosis is an exceedingly rare disease of cats, especially when compared to FIP.
FIP can be easily differentiated by origin (cattery, foster/rescue, shelter), signalment (age, gender, breed), and basic blood test results. Deep fungal infections (coccidioidomycosis, blastomycosis, histoplasmosis) can cause similar clinical signs to dry FIP but are still uncommon even in their endemic regions. Lymphoma may also be a differential diagnosis for dry FIP, but this disease is usually sporadic and in older cats.
The diagnosis of neurological and/or ocular disease is ultimately based on where a cat comes from, the clinical signs, age, common changes in complete blood count (anemia, lymphopenia), serum protein changes (high total protein, high globulin, low albumin, low A:G ratio). The diagnosis may be confirmed if there is still doubt, by characteristic changes in cerebrospinal fluid (CSF) and aqueous humor (high protein, high white blood cells, neutrophils, lymphocytes, macrophages), suggestive lesions on MRI, PCR or immunohistochemistry on CSF, or high serum coronavirus antibody titer by IFA (>1:3200). One must be careful, however, to follow the 70% rule, i.e., no single typical laboratory abnormality will occur 100% of the time.
The rapid response of FIP to GS-441524 is in itself a diagnostic indicator.
When Feline Infectious Peritonitis (FIP) affects a cat’s nervous system or eyes, it manifests in a couple of specific ways:
Neurological FIP - This form affects the cat’s brain and spinal cord
Below are some examples of anisocoria from FIP
Ocular FIP - This form impacts the eyes
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Cats with ocular FIP might have inflammation in the eyes, which can cause symptoms like eye redness, cloudiness, or swelling
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They might also have changes in their vision, which could make them bump into things or appear disoriented
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Symptoms can include anterior uveitis, keratic precipitates, hyphema, hypopyon, chorioretinitis, retinal hemorrhages, or retinal detachment
Below are exampoles of how OCULAR FIP can present
WHAT IS FIP?
Cats with abdominal effusions usually manifest with abdominal swelling, while cats with thoracic (chest) effusions often manifest in breathing problems (dyspnea). Many of these cats will be noticeably jaundiced due to high levels of bilirubin and/or have strongly yellow-tinged serum and urine. Neurological and ocular signs are seen in less than 1 in 10 cats with wet FIP.
Below are a few examples of cats with wet abdominal FIP
FIP is ultimately caused by a feline enteric coronavirus (FECV). In about 10% of cats, mainly kittens, the virus will undergo specific mutations that allow it to escape the cells lining the lower intestine and infect the most basic cell of the immune system, the macrophage. This mutant virus is known as feline infectious peritonitis virus (FIP) and is initially contained to local lymphatic tissues associated with the lower intestine. FIP-infected macrophages can then spread the infection to other sites within the abdominal and chest cavities and to distant organs such as the eyes and brain. When this occurs, we are dealing with either OCULAR or NEUROLOGICAL FIP. More detailed information on FECV infection and clinical manifestations of FIPV disease can be found at: ccah.vetmed.ucdavis.edu
This initial infection is naturally eliminated in all but 0.3-1.4% of cats, which for unknown reasons are unable to develop the required protective immunity.
The form of disease that is manifested is referred to simply as wet (effusive) or dry (non-effusive). The wet form occurs in about two-thirds of cats and the dry form in one-third.
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There can also be a combination of types of FIP (wet/neuro, wet/ocular, dry/neuro, dry ocular with neuro)
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The form of FIP can change from one to the other such as dry-to-wet (kitty has been sick for a while and now has effusion that has developed)
• Weight loss
• Fever unresponsive to antibiotics
• Jaundice
• Severe anemia/non-regenerative anemia
• Stunted growth/failure to thrive
• Not jumping or climbing
• Lethargy
• Sneezing, nasal discharge
• Loss of interest in food
• Not playing
• Not socializing
• Excessive sleeping
WET FIP
The most common form of the disease is referred to as “wet FIP.” Wet FIP tends to be more acute in onset and is accompanied by:
NEUROLOGICAL & OCULAR FIP
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FIP can also take a more chronic form referred to as “dry FIP”. Dry FIP, as the name implies, is not associated with fluid accumulations in the abdomen or chest, but rather with more localized masses in the kidneys, spleen, liver and terminal bowel, eyes, and the linings of the lungs and heart, and central nervous system.
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Uveitis (intraocular inflammation, also called OCULAR FIP) can affect the eyes, making them look cloudy and changing the colour of the iris. Inflammation can enter the brain and spinal cord and cause a spectrum of progressive neurologic abnormalities (also called NEUROLOGICAL FIP).
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FIP accounts for over one-half the cases of inflammatory intraocular and nervous system disease in cats under 3-5 years of age. Ocular and neurological involvement is associated with 60% of cats with Dry FIP.
DRY FIP
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Weakness of the limbs (usually affects hind legs but may affect any combination of limbs)
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Difficulty jumping or jumping in an atypical way
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Stumbling, tipping over, swaying
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Tilting head to one side
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Abnormal eye movements/nystagmus
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Seizures, tremors, legs shaking, muscle twitching
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Depression, changes in behavior
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Hyperesthesia syndrome
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Anisocoria
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Peripheral neuropathy (weakness, numbness, or pain, usually in the paws)
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Urinary or fecal incontinence
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Dementia
