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Feline Heartworm Disease
Feline Heartworm Disease is caused by the parasite Dirofilaria immitis and has been reported worldwide in cats. It is diagnosed consistently in cats in endemic areas. New England is considered an endemic area for heartworm disease in cats and is second only to the Southeast in the incidence of this disease.
The life cycle of the parasite involves a definitive host (dog or coyote), mosquitoes, and a susceptible cat. Now in general, the cat is not considered a definitive host for the parasite. That is, in the cat, the larvae seem to be disoriented and more often than not migrate aberrantly through the tissue to end up in sites other than the heart where they cause inflammatory reactions. For a cat to become infected, a mosquito must bite an infected dog or coyote with microfilaria (heartworms don’t lay eggs but rather lay live young called microfilaria that circulate in the dog's blood). After the proper climactic conditions, the microfilaria inside the mosquito mature into infectious larvae and are inoculated by the mosquito into the cat. For small numbers of larvae the cat's natural resistance eliminates the infection. But where the mosquitoes carry many larvae, some of these larvae cause disease either by aberant migration or actually develop into an adult worm in the cat's heart. Clinical signs that your cat may present with are related to the larval migration (asthma, vomiting, lethargy, weakness, seizures). The presence of an adult worm in the heart is often asymptomatic until the cat experiences sudden death or an acute onset of difficult breathing or collapse.
On physical examination, your vet may hear a soft heart murmur or find harsh lung sounds. Some of the tests that should be done to make the diagnosis are: Serology to look for antibody to the worm's antigen or the antigen itself, an electrocardiogram, radiographs, a complete blood count and serum chemistry, a tracheal wash and an echocardiogram.
If your cat is positive for antibody but negative for the presence of the heartworm antigen, it means that your cat has been infected by molting larvae but at that time does not have an adult worm in the heart. If your cat is positive for the antigen as well, there is one or more female heartworms in the right side of the heart. Your veterinarian will want to rule out other diseases like lungworm, bronchial asthma and hyperthyroidism.
Treatment with the adulticide (Thiacetarsamide) that is used in the dog is unpredictable and many times can be life threatening. Conservative treatment is aimed at controlling the inflammation in the lungs as the worm may embolize there at the end of its life span.
In general, the worm in cats lives less than 2 years compared to the dog where it can live up to 5 years. Furthermore cats with adult heartworms have a lower worm burden, that is they have fewer than 4 worms, usually only one.
Prevention is the key and we are urging everyone, even house cats to use prevention seasonally in New England (between the months of May and November).
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Diabetes Mellitus
Your cat has been diagnosed with Diabetes Mellitus. Diabetes occurs in cats when there is decreased or no production of insulin by the pancreas. Predisposing causes of this disease include obesity, pancreatic injury or disease, and use of certain pharmaceuticals. Insulin is critical to the body to allow the cell to use sugar (glucose) for energy. Diabetic cats have excess glucose in the blood that cannot be used by the body causing the body to be starved for sugar. Because there is so much unusable sugar in the blood, some escapes through the kidneys which are not able to handle such high sugar levels. Some of the body’s water is also lost along with this sugar.
Clinical signs of diabetes may include: excessive thirst, excessive appetite, increased dilute urine output, weight loss and abnormal posture (“down in the hocks" stance). Because there is sugar in the urine of diabetic cats, bacteria love to live there. Many diabetic cats will also have a urinary tract infection. If diabetes goes untreated, an emergency situation can develop called ketoacidosis. This occurs when the body has starved too long and begins breaking fat into simple energy particles, which contribute to a metabolic acid/base imbalance. The cat will become too weak to eat or drink, and can develop a life-threatening dehydration. This condition can usually be avoided with careful treatment and regulation of diabetes.
The main treatment for diabetes is insulin injections. Many cats will need an injection twice daily but some can be regulated with a once daily injection. Many different types of insulin exist and not every cat can be regulated with the same type of insulin. Some cats can be regulated well with human insulin, called Humulin, which comes in different formulas to last different lengths of time. The longest acting human insulin is called Humulin U which lasts 6-12 hours with peak activity 3-6 hour after injection in cats. Some cats can be regulated on this type of insulin twice daily. Because this insulin was created for humans the structure of the insulin particle is slightly different than the cat insulin particle. Some cats will form antibodies to this insulin rendering it completely inactive. Most cats do best with a type of insulin called PZI which is very long acting. In most cats it lasts 12-24 hours with peak activity 6-12 hours after injection, so some cats will need it once daily and some twice daily.
In some cats an anti-diabetic drug called Glipizide can help control diabetes. It is very rare that this drug can be used as the only treatment but in some cases it can aid in regulation in addition to insulin.
Diet, exercise and body fat are considered important to the control of diabetes. There are two theories on what the perfect diabetic food should consist of. One theory states that a high fiber diet will aid in diabetic control by allowing a slow steady release of glucose from the intestines to the blood. The other states that a diet high in protein will decrease the dependence on dietary carbohydrates, and that protein will be relied upon for energy. Both types of diets have helped in control of diabetes in both humans and cats.
Obese cats with diabetes will be easier regulated and may have a less severe form of diabetes if they get down to a healthy weight. Since it is important for diabetics to eat in order to utilize their insulin, a good way to help an obese diabetic cat loose weight is through a moderate increase in exercise instead of strict diet. Exercise will also help glucose get into cells.
ALWAYS HAVE FRESH WATER AVAILABLE.
The goal for the treatment of a diabetic cat is not to have perfectly normal blood glucose at all times but to have an acceptable blood glucose level at almost all times. It is important for a cat to have enough insulin in their body for most of the day to be able to use food for energy and maintain a healthy weight and most importantly; avoid ketoacidosis.
In a 24-hour period it is considered very good if a cat can maintain a blood glucose level between 100 and 300. This is often not possible. Some cats will have a higher blood glucose level at the time they are due for their next injection. High blood glucose for a short period of time is not dangerous, however blood glucose that is too low can be very dangerous. It is very important not to give too much insulin.
In order to determine the correct insulin dose for a cat and keep them well regulated, frequent testing of the blood glucose level is required. This testing can be done in the hospital initially with a blood glucose curve. This consists of blood glucose checks throughout the day after administration of insulin. It allows the veterinarian to monitor your cat’s response to insulin and determine how many hours after insulin administration, the lowest blood glucose will occur (also called the nadir). Once this is known, the effect of insulin doses can be monitored by “spot checks”, or one blood glucose measurement at the cat’s nadir.
Sometimes another test is performed to determine the cat’s average blood glucose over several weeks which helps asses overall regulation.
As a cat is being regulated it is not uncommon to need insulin dose changes, or even a change in the type of insulin. Many cats will need more or less insulin as their weight changes, or the severity of their diabetes changes. In rare instances a few cats will eventually not need insulin anymore. Illness of any type can interfere with diabetic regulation as well.
Because regulation of a diabetic cat can involve many trips to the hospital, some owners of diabetic cats will learn how to test blood glucose levels at home. This involves the purchase of a glucometer and test strips from a drugstore. This is an inexpensive device, which requires only a small drop of blood for measurement. A small needle is used to prick a vein on the cat’s ear to get the drop of blood. Most cats are well behaved for this procedure. If you have an interest in learning how to do this at home we would be happy to teach you. It is important that you keep a journal of insulin doses and blood glucose levels and carefully record the time of day.
For the first few weeks of regulation at home it is a good idea to speak with a doctor or technician daily to answer your questions about regulation, and help you adjust the dose of insulin.
Insulin must be stored in a refrigerator. It is normal for some particles to settle to the bottom of the bottle. It is important to have the insulin well mixed before drawing it up into the syringe. Insulin particles are very delicate so it is important not to shake the bottle but to gently roll it instead. You will need a prescription for insulin syringes. They come in a box of 100. You may use a new syringe each time, but it is considered ok to use each syringe a few times before disposing of it. You will be instructed on how to give insulin properly.
If you get into a struggle giving the insulin and you are not sure if the cat got it all, do not try to give more. You may risk a low blood glucose crisis. Wait until the next scheduled insulin dose. If the cat is not eating for any reason hold the insulin and call your veterinarian. If you know that the cat will not be able to eat because of travel or surgery or any other reason hold the insulin dose. If you miss a scheduled dose by more than an hour do not try to give it, just skip it and wait for the next scheduled dose.
It is important to be able to recognize a low blood glucose crisis. Signs include lethargy, listlessness, grogginess or a drunken appearance. Do not give insulin if this occurs. Offer food right away. If your cat will not eat, have some Karo syrup handy to smear in his/her mouth. A very low glucose level can lead to seizures. Contact your veterinarian right away. He/she will need to determine what the cause of the low glucose was.
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Renal Failure
Your cat has been diagnosed with either acute or chronic renal (kidney) failure.
Acute renal failure occurs when an insult immediately damages the kidneys, such as a toxin or an infection. Chronic renal failure is insidious since the cat may have kidneys that have been affected by a disease process for quite a long time before clinical signs become apparent. Often renal compromise can be detected on routine blood chemistry performed while the cat is still healthy. The kidneys are what we call a redundant organ. Any animal can live normally with only one kidney so long as it remains healthy. One begins to see clinical signs characteristic of renal failure when 75% of the working tissue of both kidneys has been damaged.
Clinical signs of renal failure can include: lethargy, weight loss, increased water consumption, increased dilute urine output, dehydration, vomiting, gastric and oral ulcers, hypertension, anemia, uremic breath and coma.
1. Filter the blood to remove nitrogen waste products (by product of protein metabolism).
2. Conserve body fluids by reabsorbing water and electrolytes from the filtered blood and to excrete certain minerals.
3. Regulate the acid/base balance of the body (the kidney has its own buffering system).
4. Prevent anemia by releasing a hormone called erythropoietin that in turn directs the bone marrow to produce red blood cells.
5. Maintain normal blood pressure by releasing a hormone called rennin.
The kidneys can compensate for decreased function (loss if kidney tissue) due to disease or aging by opening more capillary beds within the remaining kidney tissue thus allowing more blood to flow through. This phenomenon is called "intrinsic autoregulation". After a certain point, however, the remaining kidney tissue is working maximally. This is when clinical signs start.
Our goal in treating chronic renal failure is to delay the progression of changes by "protecting" the kidneys, to assist the cat's hydration, and to correct electrolyte and mineral imbalances.
Certain tests are run to evaluate your cat's renal function. The complete blood count (CBC) screens the blood for anemia and infection. The serum chemistry screens the renal function by measuring the nitrogen waste products accumulating in the blood (BUN - blood urea nitrogen- and Creatinine). Also, the electrolytes are measures to detect abnormalities, particularly of Potassium. Other minerals are measured, specifically Phosphorus and Calcium.
His/her blood pressure will be checked because often cats with chronic renal failure are hypertensive and require medication to lower the blood pressure.
TREATMENT
Diuresis. It is impractical to dialyze in practice since these machines require total blood filtration and are prohibitively expensive. We can, however diurese. This means hospitalizing the cat for 3 - 5 days during which time intravenous balanced salt solution is administered around the clock. This helps to dilute the nitrogen waste and allow the kidneys to excrete a higher fraction of the waste. During this period, any electrolyte or acid/base imbalances are corrected. After the 3 or 5 day period, serum chemistries are repeated to evaluate response to diuresis. If a favorable response is seen, then the cat may be discharged for home diuresis. If the disease is not so severe, you may skip the hospitalization and go straight to home diuresis. This simple procedure takes no longer than 10 minutes every day or every other day and consists of administering the solution, usually lactated ringers solution subcutaneously (under the loose skin over the back).
Restricted protein diet. These diets are formulated with less protein and lower phosphates to ease the workload on the kidney. A new diet also has a "nitrogen trap" system that allows protein to be excreted by the gut rather than the kidneys.
Potassium supplementation to replace renal potassium loss. Low potassium caused weakness and further damages the kidney.
Phosphorus binders like amphojel are administered to promote excretion of calcium. Increased phosphorus also depresses appetite. Calcium and phosphorus must remain in a 2:1 ratio. Calcitriol is a drug that may be used to increase serum calcium, which in turn will lower serum phosphorus.
Pepcid is given daily to decrease the amount of acid produced by the stomach that have been increased by the circulating renal toxins.
A drug for high blood pressure. If the blood pressure is not normalized as the BUN and Creatinine come down, then the cat may need some medication to control blood pressure.
Winstrol. Winstrol is an anabolic steroid that can stimulate appetite and help prevent weight loss. Other appetite stimulants may be used.
Erythropoietin. This is the hormone that stimulates the bone marrow to produce red blood cells. The cat will need injections of this hormone if he/she is anemic.
Omega Fatty Acids. These supplements are antioxidant and have been shown to decrease the progression of kidney disease as well as assist in controlling hypertension.
The prognosis is highly variable, depending on your cat's response to treatment and your ability to continue therapy at home.
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