Diseases #16
Canine Heartworm is a serious disease in dogs east of the Mississippi River and other subtropical, tropical parts of the world. It is found wherever mosquitoes are populous. It is common in areas with major annual rainfall. It is caused by the filarial worm, Dirofilaria immitis.
Dirofilia immitis is transmitted to dogs via a mosquito bite. A mosquito bites an infected dog and draws up microfilaria (immature worms) into its body. Three stages of worm development (L1, L2, L3) occur in the mosquito. They move up to the mouthparts of the insect within 30 days and are infective to dogs. A susceptible dog is bitten and stages L3-L5 occur with final development in the heart; particularly the right ventricle within 6-8 months of being injected by the mosquito. Worms often migrate to the right atrium, lungs and often liver causing clinical disease. Heart disease causes the majority of clinical signs in the dog. There may be one or multiple quantities of worms in the dogs heart. Males and females mate producing microfiliaria that will than be picked up by a mosquito on blood feeding. Cats can get heartworm but it is not that common. If infected, they usually have only about one worm in their hearts. Many are asymptomatic and are many times diagnosed only on post mortem.
Many dogs that are diagnosed with heartworm do not show any signs. That is quite common. Dogs with active heartworm infections are presented with a typical heart cough caused by the mechanical presence of the parasite in lung tissue. Dogs are often debilitated, thin and have difficulty breathing due to the parasite clogging up the right ventricle. Sort of like a blockage in a kitchen sink. Blood backs up and the heart can not pump efficiently. Animals do not have the energy to exercise. Some animals at this point may die of heart failure and collapse.
The occult heartworm test is the most commonly used test to diagnose Canine Heartworm disease. Years ago, the only test was examining a blood smear and look for the small wiggly microfiliaria. A lot of cases were missed. Some adults do not produce microfilaria. There may be 2 males or 2 female worms that can not mate yet cause clinical disease. These are the occult forms. Even if there are males and females in abundance with subsequent microfilarial development the occult test is the preferred way to go. One of the most commonly used test is the Idexx® Snap Heartworm RT Test. This is highly sensitive. In areas with Ehrlichiosis (Florida), Lyme Disease, Anaplamosis plus Lyme disease there is an Idexx® 4Dx Plus Test. All these tests detect surface antigens (proteins) that are found on the parasite. There may be false positives. If there are few parasites in the heart, there may not be enough antigen available to be detected. Antigen detection is only detected by the test on female worms. There could be numerous males and a negative test would be produced.
Once a heartworm dog is diagnosed a CBC and Chemistry profile are performed to judge the overall health of the animal before treatment is instituted. Radiographs or ultrasounds are performed and will normally show a enlargement of the right ventricle and dilitation of the pulmonary artery.
Diagnosis of heartworm disease is confirmed by a positive occult heartworm test. A history and physical findings lead the doctor to a presumptive diagnosis. There may also be murmurs heard during chest auscultation. Many of these dogs are young to middle aged and it is relatively unusual to pick up murmurs suggestive of primary heart disease in middle aged dogs.
Treatment occurs in several steps. In the first step the animal is given 2 injections of Immiticide® about 2 months apart that will kill adult heartworms. Prior to this, most dogs will be put on 2 weeks of Doxycycline to treat the potential bacteria, Wolbachia, that lives on the surface of the heartworm parasite. This is serious and animals are always hospitalized for this procedure and kept quiet. As the parasite dissolves it is possible for the pieces of the worm to act as emboli and cause pulmonary and or heart failure. It is absolutely crucial that the animal not be exercised or walked or excited for weeks after Immiticide® treatment. One month later the dog is treated to rid the body of circulating microfilaria. This is done by oral administration of ivermectins.
Some dogs may not be treated because of severe organ failure. Instead of treating those animals, the organ illness is addressed. Dogs that are treated may have clinical heart and or lung disease. Those conditions need to be addressed.
Economically, the treatment regimen is expensive. In South Florida, complete treatment is about $1500. Another good reason to have pet insurance! Some people can not afford the cost of heartworm treatment. Doing nothing will just allow that animal to serve as a source of infection. In those cases ivermectin administration, once a month, will at least clear the microfilaria so the animal is not infective to mosquitoes.
The prognosis for heartworm dogs once treated is very good. Once the adults and microfilaria are cleared the animal feels so much better. It has a lot more vigor and energy. The appetite returns and the animal gains weight back. Most animals have a satisfying outcome. A more guarded prognosis is given to those animals that were treated but have permanent heart and or lung disease.
The best bet is prevention. Not only will it save your dogs life but it is a heck of a lot cheaper to use preventative. Dogs six months of age and under but over 6-8 weeks of age can go straight on preventative as it is impossible to have heartworm disease at that age. Dogs over 6 months of age will require an occult heartworm test. If negative for screening, they are placed on year round monthly preventative. Years ago, there was just one preparation on the market. Heartgard® was the first to hit the market. Now a days there are countless brands available plus those combined with other products to kill fleas, ticks and other parasities. Your veterinarian can guide you through the process to select a preventative suitable for your family and pet.
Hepatic encephalopathy is a metabolic disorder caused by a secondary liver (hepatic) disease. The buildup of ammonia in the blood and associated central nervous clinical signs are hallmarks of the disease.
The liver is the largest gland in the body. It is a true manufacturing facility. It manufactures bile and albumin plus breaks down drugs and toxic substances into non-toxic metabolites. An exception to this is the problem with cats. They lack an enyzme, gluconyl transferase, that does not metabolize toxic products making cats extremely ill. A prime example of that is Tylenol® poisoning. In this case there is a congenital defect called a portosystemic shunt. Normally blood flows from the intestine via the portal vein to the liver where all the work is done breaking down harmful substances before entering the general circulation. A portosystemic shunt bypasses the liver allowing toxic substances such as ammonia to accumulate in the general circulation. Excess ammonia causes central nervous clinical signs. The most common cause is congenital but other diseases such as acute liver disease can lead to this problem.
Clinical signs commonly seen are: disorientation, bumping into objects, circling, wandering, personality changes, vomiting, orange colored urine amongst others. Animals may also howl and drink more water.
A CBC and Chemistry profile will usually detect elevation in the liver enzymes such as ALT and Alkaline Phosphatase. A urinalysis may show elevated bile pigments present (bilirubinuria). Radiographs or an ultrasound may show an abnormal shape to the liver which than dictates a liver biopsy. This will confirm the diagnosis.
A diagnosis of hepatic encephalopathy is suspected in dogs presented with central nervous signs and associated liver disease. A history and complete physical exam are crucial. Results of a liver biopsy confirm the diagnosis.
Treatment is geared towards regaining liver health as well as reducing the toxic ammonia absorbed from the intestinal tract. Many dogs are extremely ill when presented or even comatose. Liver treatment involves supportive care. Intravenous fluids are always given. Intravenous antibiotics and vitamins are administered. An esophageal feeding tube is inserted. Dietary requirements need to be met with a high quality protein diet. Hill's® Prescription Canine l/d fits the bill. Other supportive care such as electrolytes will be monitored. Lactulose is an oral drug that is used to decrease serum ammonia levels. Lactulose is composed of galactose and fructose that are not digested. They pass to the colon where bacteria convert them into formic and acetic acid. This acidity forces water into the lower intestinal tract (hence its other function is a cathartic/laxative) and forces ammonia into the colon where the acidity converts straight NH3 into NH4 which is passed in the feces. Surgical repair may be attempted by a board certified surgeon.
The prognosis for hepatic encephalopathy is guarded and depends upon the initial presentation of the disease. If caught early and treated appropriately dogs do stand a chance. Relapses are possible and surgery is not always 100% effective. Animals presented comatose have a poor overall prognosis.
The liver is one of the most important organs in the body responsible for the buildup and breakdown of many chemicals needed for mammalian survival. Anything that interferes with the livers functioning can lead to general liver disease (hepatopathy). Liver diseases can be caused by: toxins, bacterial abscesses, viruses (Canine Adenovirus), ammonia buildup, gall bladder disease, immune-mediated diseases, Cushing's Disease, Diabetes Mellitus, nodular hyperplasia amongst many more.
The hepatocyte is the basic cell in the liver. Interfering with its cellular function can degrade it causing individual cell death. Regardless of the causative agent, this cellular degradation can lead to focal or generalized liver disease with associated clinical signs.
Clinical signs result from primary or secondary liver disease. Primary liver disease is one where the primary cause is liver disease. Secondary disease is where the liver is injured secondary to a disease somewhere else in the body; such as Cushing's Syndrome. Associated signs may involve: increased fluid consumption and urination, abdominal pain, distended abdomen, jaundice, anorexia, depression, lethargy, anemia, seizure activity amongst others.
A CBC and Chemistry profile are performed and will show an elevation of liver enzymes plus other abnormalities depending on the actual cause of liver disease. Radiographs and ultrasound procedures may show abnormalities in liver size or shape. Additional tests may be needed depending upon the causitive agent.
Diagnosis of a hepatopathy is based on historical and clinical evidence. Lab Work will confirm an initial diagnosis of liver disease. The difficulty is in finding the exact cause of that disease.
Unless an actual cause of liver disease is found, treatment of liver disorders involves supportive care. Many animals are presented extremely ill such as those suffering from Auto-Immune Hemolytic Anemia (AIHA). They need to be hospitalized and receive intravenous fluids and nutritional support. That involves correcting electrolytes and bleeding disorders plus providing fluid support to maintain renal and cardiac perfusion until an animal is able to drink and eat on its own. An esophageal feeding tube may be inserted. Other treatment may be required and dictated by the cause of liver disease. Once animals are able to keep food down, a high quality source of protein and vitamins are required. Hill's® Prescription Canine l/d is recommended as well as Nutrical® gel. Once they are able to eat and drink on their own, dog and cats gain weight rapidly.
The prognosis for hepatopathy cases depends upon the severity of the condition (that is, clinical presentation) and the cause of the liver disease. All animals discharged will require periodic lab work follow ups as well as physical exams.
Hemorrhagic Gastroenteritis is a very common disease process in mainly dogs but also seen in cats. Broken down, this fancy word means a gastrointestinal infection with internal intestinal bleeding. Anything that causes irritation or cellular damage to the intestinal tract can cause this disease. Common causes are: viral infections (Parvo Virus) & sharp foreign bodies (needles, tacks). The majority of causes are unknown and may involve pancreatitis, immune-mediated disease amongst others.
In idiopathic (unknown) causes, the intestinal tract become leaky and permeable allowing blood and fluids to enter into the gastrointestinal tract. The mechanism is not exactly known but leads to the associated laboratory findings and clinical signs.
Affected dogs will pass a bright red, jelly like diarrhea as well as vomiting bile and mucous. Some animals may be presented in hypovolemic shock. The majority of these cases are seen in small tiny dogs such as Poodles, Yorkshire Terriers and Miniature Schnauzers. They may also have a fever.
A CBC and Chemistry profile are always done. This will be useful to detect electrolyte disturbances as well as other organ involvement. The usual lab presentation is a dog with an extremely high hematocrit of about 65%. The normal is around 37%-55%. Total serum proteins are also lowered due to the "leaky" nature of the intestinal tract.
Diagnosis of straight HGE is made by performing a lot of rule outs such as foreign bodies and Parvo Virus. A history, physical exam and classical laboratory findings can suggest a diagnosis of HGE. The only way to confirm it is via an intestinal biopsy.
Treatment is supportive for most HGE animals. Intravenous fluids with 5% Dextrose are always administered while the animal is hospitalized. Vomiting is controlled with Cerenia® and or famotidine and the diarrhea is controlled with aminopentamide and carafate. Animals are administered intravenous antibiotics plus vitamins to maintain health. Electrolytes are corrected. The goal is to get the animal to eat and drink on its own. Once that occurs, the dog is sent home on chicken and rice (or facsimile), antibiotics, Nutrical® gel and other supportive measures.
If aggressive treatment is thrown at the dog early, the prognosis is quite good even though a few of them may relapse some time in the future. Future exams and blood work may be needed as the animal convalesces.
A hermaphrodite is an individual that has a combination of both male and female organs or genitalia. It is relatively uncommon in dogs and cat. In my 33 year career, I only diagnosed one case of true hermaphroditism in a female Cocker Spaniel. It is presented in animals with an XX or XY combo chromosome pattern or just an XX.
Female animals have two chromosomes, XX. Males have 2 chromosomes, XY. A female develops in the absence of testosterone. It is the "default setting". In the presence of testosterone (produced in the testes and adrenal cortex) a male will develop with an XY. In hermaphrodites this gets all jumbled up and can produce a myriad of combinations. Pseudohermaphrodites exist that have normal chromosomes but the external genital organs are different.
All sorts of combinations are possible. Females may develop an os penis in place of a clitoris yet have two ovaries or one ovary on one side and a testes on the other. Males may have testicles that have not descended into the scrotal sac. They may also have a vestigial uterus and or other internal female organs. None of these animals are capable of reproducing.
There are no specific lab tests to diagnose the disorder. Basic blood work such as a CBC and Chemistry profile may be performed since most animals are going to need to be neutered.
Diagnosis is suspected by the presence of abnormal external genitalia. Many times it may take years to figure out that an animal is a hermaphrodite. A key is the inability to reproduce or come into heat, if a female. A breeding male may not even have a sperm count due to the lack of testes or those retained in the inguinal canal or abdomen (cryptorchidism).
It is recommended that all hermaphrodites be neutered. You never know what you are going to see. In this Cocker Spaniel case I had in the early 1990's, I told the owner I would "try" to spay the dog. The uterine horns were immature and wrapped around the bladder. In place of an ovary at each end of the uterine horn, was a testicle. This was confirmed by a histopathological diagnosis.
Prognosis is good and depends upon effective neutering of the animal in question.