Chimera

A disease that strikes at young cats. A disease that has no definitive diagnostic tests. A disease that is nearly 100% fatal. A disease that has no effective treatment. A disease that is infectious but is not contagious. Cat owners know and fear the diagnosis. FIP is the feline practitioners chimera. A poorly understood untreatable and deadly disease that offers no warning that it might be on the horizon.  

From what we currently understand, FIP is an inflammatory reaction to infection with the feline enteric coronavirus. The feline enteric coronavirus is not involved in SARS which is caused by a different species of coronavirus. The majority of cats infected with coronavirus typically encountered the virus in infected feces (litter box) and this typically occurs in environments where multiple cats are housed together. They will exhibit flu like symptoms for a few weeks maybe a few months and depending on the number of cats in the house they may or may not clear the virus. Homes with 5 or fewer cats seem to spontaneously clear the virus eventually but houses with more than 5 cats will almost never clear the virus. Cats that are exposed to and infected with coronavirus and cleared it are still susceptible to reinfection. They can easily pick up the virus again and again.

As long as the virus sticks to your cats gastrointestinal system your cat will not develop FIP and will most likely clear the virus, unless you have a lot of cats. There are multiple theories about how FIP occurs and how it spreads in the body. Today, in 2016, I can give you the most recent understanding we have and the most recent ideas being proposed about FIP.

It is currently thought that FIP is the body reacting to a mutated version of the Corona virus. We can’t cause transmission of FIP by putting a cat with FIP into a densely packed cat environment. We can cause transmission by taking fluid from one cat and injecting it into another cat. This supports the disease being infectious (fulfills Koch’s Postulates) but not actively contagious.

Assuming that we are correct about the virus that causes FIP being a mutated strain we can then make some inferences about how it causes disease. When the body is dealing with a virus it utilizes a particular cell called a macrophage. Macrophage means “big eater” in Greek and that is exactly what these cells do. The engulf cellular debris, foreign material, bacteria and viruses and package it into little sacks called phagostomes. The macrophage then joins forces with a cell called a lysome to form a phagocyte. This phagolysome fills the sack containing the invader with digestive enzymes and peroxides. Once the macrophage has ingested a foreign invader it will display a piece of the invader’s surface on the outside of its cell. This encourages the body to create antibodies and allows for a sort of seek and destroy mission to commence within the body. This is where FIP becomes a problem.

In FIP the mutated virus is immune to the degradation activity of the macrophage. So the body still goes through the action of creating more and more antibodies and macrophages but they don’t do anything and the virus continues to replicate. Increased numbers of viral particles cause an increase in the production of macrophages. These useless macrophages start to coalesce in the internal organs into tumors called pyogranulomas. FIP is the infiltration of these pyogranulomas into internal organs.

Diagnosing FIP is difficult to say the least. It typically is a rule out diagnosis meaning that even if that is what we are suspecting from the beginning, we still need to rule out just about everything else before we can be comfortable telling you your cat had FIP. This means blood work, sampling fluid from the abdomen and if possible taking a surgical biopsy. There are few diseases that cause the spread of pyogranulomas through the body and if we already suspect FIP for other reasons that would make me comfortable with the diagnosis.

Once we have a diagnosis treatment is limited or non existent. Because the pyogranulomas and inflammation are caused by the body’s immune system the mainstay of therapy for a long time was suppressing the immune system. Immunosuppression will slow the progression of the disease but because FIP is also a viral infection immunosuppression is not going to be a cure. In cases where there is a lot of abdominal effusion or fluid removing the fluid may help to lessen the symptoms and may also slow the progression of the disease.

Right now research is looking into different anti-viral therapies to treat FIP, people are also working on breeding cats that are more resistant to FIP. Currently neither of these approaches have been successful yet. FIP continues to be a fatal disease for the affected cats.

Sorry to be so glum during the fun Summer months! Hope you are enjoying the weather.

Thanks for reading.

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Full tilt

Do a handstand and your body knows that it is upside down. When you fall your body instinctively knows how to try to right itself. Not that it always succeeds but it knows how to try. It does this using a pair of organs located in the middle ear. This is called your vestibular apparatus.

The vestibular apparatus is made up of three semicircular canals filled with a fluid. There are sensory hairs in this fluid that detect the movement of the fluid and inform the brain about rotational movement and the body’s position in space. Within the cochlea of the ear there is a saccule containing a gelatinous material. Within this material are little bony structures called otoliths. These move up and down in the gelatin and  trigger small hairs that are attached to sensory nerves. This informs your brain of up and down motion of the body.

If the vestibular apparatus is disrupted by injury or disease we see changes in the way our patients understand their position relative to the outside world. Of the things that can disrupt the vestibular system we can classify them into three broad categories. These are; infections of the middle ear, lesions on the brain and the third category is called idiopathic meaning we do not know the cause.

A dog or cat with vestibular disease will stumble and stagger when they try to walk. They may circle to one side and may get motion sickness. They may also have rapid uncontrolled eye movements and they almost always have a head tilt to one side.

Brain lesions are typically accompanied by other signs that indicate that the problem is affecting more than just the peripheral nerves. Sometimes it can be difficult to preform a complete neurological examination but there will be some subtle clues such as changes in other nerves associated with the head (cranial nerves) on the opposite side of the head tilt that indicate there is something going on in the brain. Many people take these central lesions to be “strokes” and while vascular accidents do occur in our patients they are not terribly common. Typically we recommend advanced imaging of the brain using MRI or contrast CT if MRI is not available to get a better understanding of the problem.

Infections of the middle ear are a bit more common than central brain lesions. Sometimes they will accompany an infection of the external ear or sometimes they come on their own. The best way to diagnose a middle ear infection in general practice is by taking x rays of the middle ear. It is impossible to see the middle ear with an otoscope although sometimes we can infer that there is an infection in the middle ear based on our examination of the external ear canal. Middle ear infections require antibiotics for around 6 -8 weeks and sometimes will not resolve with out surgery to open and clear the middle ear.

The most common cause of vestibular disease in cats and dogs is idiopathic or unknown. These typically show up suddenly and will show signs of improvement over the following three days. It usually takes around 1 to 2 weeks to see complete resolution and it is not uncommon for a slight head tilt to persist. If an infection is not detected and a brain lesion is not suspected it is a good idea to look at tick titers especially in dogs living in areas where tick borne illnesses are common. Fungal titers are also a good idea and ruling out hypothyroidism should also be on the diagnostic list. In fact ruling out hypothyroidism, getting base line blood and urine, taking chest radiographs and (if everything looks ok) waiting three days is our current standard approach to these cases.

After arriving at a diagnosis or ruling everything out and going with an idiopathic diagnosis the best treatment we currently have is to treat and prevent nausea and keep our patients relaxed and calm. This allows them to be comfortable while the condition runs its course.

Thanks for reading.