Canine Heartworm Disease Canine Heartworm Disease is a serious and potentially fatal disease caused by the parasite Dirofilaria Im mitis. The disease can infect over 30 species, including humans, however dogs are the definitive host. The most common way this disease is transmitted from one animal to the next is through mosquitoes. A mosquito carrying infective heartworm larvae bites a dog and transmits the infection to them. The larvae grow, develop, and migrate in the body over a period of 6 to 7 months, in which time they become sexually mature male and female worms.
this is the pre patent period. The worms then reside in the heart, lungs, and associated blood vessels. The worms begin to mate and release micro filaria into the blood stream. When a mosquito bites an infected dog it takes in some of the micro filaria in the blood. After 10 to 30 days there is larvae in the mosquito’s salivary gland which can then be passed on to the next dog the mosquito bites. Canine Heartworm Disease can also be transmitted to puppies through the placenta of an infected mother.
However in this case the puppies will only be carriers, but this makes them at risk of severe reactions when starting canine heartworm prevention. Another way larvae can be passed is through blood transfusions. To prevent this all donors must be cleared of heartworm disease before donating. Dogs infected with Canine Heartworm Disease can have from 1 to 250 worms living in them for 5 to 7 years. The organs usually being affected the greatest are the heart and lungs and with each case the way it affects them is different.
Some dogs only have an acute case; this is when no abnormal clinical signs are observed. The next level of the disease would be just a mild one were a cough is present. Dogs with a cough, exercise intolerance, and abnormal lung sounds would have a moderate form. The last and most severe form is when the dog is experiencing the previously mentioned clinical signs and / or , dyspnea, (liver enlargement), syncope, ascites (fluid in abdomen), abnormal heart sounds and possibly death. Diagnosing the disease can be relatively simple, but this depends on accurate patient history and ones ability to recognize varied clinical signs and then perform diagnostic procedures. These diagnostic procedures may include antigen testing, x-rays, ultrasonography, angiography, a complete blood count, the Knott’s or Filter test, and in the worst case necropsy.
Of these, antigen testing is the preferred method for both heartworm diagnosis and screening. However the test can only detect circulating micro filaria so if the animal was infected in the last 6 to 7 months the results would be negative. On the other hand if the animal was treated for heartworm’s in the past 16 weeks the results of an antigen test would be positive. For these reasons the diagnosis of Canine Heartworm should not be left entirely to the results of one time antigen testing.
The treatment for Canine Heartworm Disease is usually successful, with the goal being to kill all adult worms and micro filaria. There are two FDA approved for killing adult worms. The first is Im miticide (dihydrochloride) and it is administered intra muscular. The best feature is its potential ability to minimize post- complications.
The second drug is called Caparsolate (sodium) and it is administered IV. This drug however causes more side effects and has more possible complications. After treatment has been completed you must wait 3 to 6 weeks before treatment is administered. This allows the worms to stop reproducing and die, so no additional micro filaria is released. The two most effective ‘s are Ivermectin and Milbemycin.
When administered it is recommended the dog be hospitalized for eight hours following the treatment in case of a possible adverse reaction. Three weeks following the treatment a concentration test for micro filaria is preformed at which time there will hopefully be a negative result and the dog is ready to start a prevention program. Prevention is accomplished through administration of either or one of the macro lide anthelmintics. Diethylcarbamazine is reliable, safe and effective, however it must be administered daily and the dog must be completely micro filaria free.
Due to this veterinarians usually recommend a macro lide anthelmintic because they are also safe and effective but they don’t need to be administered as often. The most common is a monthly chew called Heartguard or Heartguard Plus and it contains Ivermectin. Along the same lines is one called Interceptor and it contains Milbemycin. Revolution can also be used; it’s a topical containing Selamectin. Before beginning any preventative the dog should be tested for Canine Heartworm Disease to avoid complications and so the animal can be treated. This includes puppies, who should start preventatives at 6 to 8 weeks.
Regular testing should also be done to determine if the prevention has been effective. Keep mind preventing Canine Heartworm Disease is a much safer and cheaper route then subjecting a dog to and treatments.