combined with other treatments, can be used to manage these conditions (Atkins, 2012). The second class of dogs who may benefit from steroid therapy is dogs who are deemed at high risk of adverse reactions to Complications of treatment Staging, through the use of radiographs and bloodwork performed prior to heartworm treatment, may help predict the likelihood of complications. This allows clients to be appropriately educated and also may make it more likely for owners to take precautions to minimize complications. Evidence of severe pulmonary arterial obstruction is significantly correlated with the development of thromboembolic disease (American Heartworm Society, 2014). Although live heartworms lead to endarteritis and arterial muscle hypertrophy, dying and dead heartworms can also cause significant pathology. Decomposing worms release fragments that can lodge in the distal pulmonary arterioles and capillary beds of the caudal lung lobes. These worm fragments block blood flow, leading to inflammation and platelet aggregation, contributing to the development of thromboembolisms (American Heartworm Society, 2014). Pulmonary thromboembolism is an inevitable consequence of adulticidal therapy. Clinical signs of thromboembolism may include cough, hemoptysis, low grade fever, or exacerbation of right heart failure. These signs are typically seen within the first 7-10 days of adulticidal therapy, but can develop as late as 4 weeks after starting the treatment (American Heartworm Society, 2014). The single most important thing that owners can do to decrease the likelihood of complications is to limit activity. Controlling exercise, excitement and heat stress is essential in reducing the risk of complications during heartworm treatment (American Heartworm Society, 2014). All dogs should receive routine heartworm prevention the prevent heartworm infection. As discussed earlier, heartworms are found throughout the world. Transmission occurs in all of the United States except for Alaska, underscoring the need for heartworm prevention. Although the risk of heartworm disease is primarily seasonal in some parts of the country, it is recommended that all dogs receive year-round heartworm prevention. This increases owner compliance, while also decreasing the chances of exposure due to yearly weather variation. Additionally, heartworm preventives often have a “reach-back” property that makes year-round dosing more effective than seasonal dosing. As a prescription drug, heartworm prevention must be prescribed within the context of a valid veterinarian-client- patient relationship. Heartworm prevention should be started in all dogs by 8 weeks of age. If heartworm prevention is started in puppies older than 8 weeks of age, a heartworm test should be performed six months later, to ensure that puppies were not infected prior to starting heartworm prevention. In the case of adult dogs, an antigen and microfilaria test should always be performed prior to starting heartworm prevention, as well as six months after starting prevention (American Heartworm Society, 2014). There are numerous available options for heartworm prevention. A number of monthly heartworm preventatives are available, which can be administered orally or topically. Additionally, an injectable heartworm prevention is available, which can be administered by the veterinary staff at 6-month intervals. Encouraging heartworm prevention use in every patient plays a role not just in protecting those pets receiving prevention, but also in protecting other pets in the community. The routine use of year-round heartworm prevention will decrease the risk of heartworm disease to dogs that are not receiving heartworm prevention by lowering the number of dogs available as a source of microfilariae (American Heartworm Society, 2014).
microfilaricidal and adulticidal treatments (for example, dogs with a history of vaccine reactions). The routine usage of prednisone during microfilaricidal and adulticidal therapy is not currently recommended (Atkins, 2012). Caval syndrome Caval syndrome is treated with surgical removal of heartworms from the right atrium and the orifice of the triscuspid valve. This is performed using alligator forceps or an intravascular retrieval snare, introduced through the right jugular vein under local anesthesia. Some dogs may also require light sedation, depending on temperament and severity of clinical signs. Fluoroscopic guidance should be used if available, removing as many worms as possible. The murmur should soften or disappear immediately after heartworm removal and hemoglobinuria should resolve over the next 12-24 hours. Patients should be stabilized as needed with intravenous fluid therapy. Once stabilized (within a few weeks), adulticide therapy should be performed to eliminate any remaining worms (American Heartworm Society, 2014). Assessing the efficacy of heartworm treatment If adulticide treatment effectively killed all of the adult female worms, a heartworm antigen test should be negative by six months post-treatment. Unfortunately, this test does not confirm complete clearance of heartworms because immature or male heartworms may still be present. However, this test remains the best available method for assessing treatment efficacy (American Heartworm Society, 2014). If an antigen test is positive prior to six months post-treatment, the test should be repeated after the 6-month timeframe. Macrocyclic lactones The macrocyclic lactones include ivermectin, milbemycin oxime, moxidectin, and selamectin. Macrocyclic lactones exert an effect on microfilariae (L1 larvae), L3 larvae, L4 larvae, and (in some cases, with continuous use) L5/adult heartworms. These products are administered monthly, for guaranteed efficacy against L1, L3, and L4 larvae. Beyond 30 days, the efficacy against late-stage L4 larvae declines, though there are still benefits against L3 larvae. Therefore, administering a dose late is typically not a significant concern. The efficacy against L3 larvae is not predictable enough, however, to justify dosing prevention less frequent than once monthly (American Heartworm Society, 2014). Clients and breeders often express concerns about the use of macrocyclic lactones in Collies and other herding breeds. At the doses used in heartworm prevention, macrocyclic lactones are safe even in dogs with the MDR1 gene mutation. Problems are only encountered when these drugs are used at extra-label doses (such as when inaccurately dosing large-animal ivermectin) or when these drugs are combined with other P-glycoprotein drugs (American Heartworm Society, 2014). Macrocyclic lactone resistance In recent years, there has been increasing concern over the possibility of heartworm strains that are becoming resistant to macrocyclic lactones. These cases of resistance are most frequently observed in the lower Mississippi Delta region. In many cases, these claims of resistance are thought to be caused by poor client compliance (Atkins, 2014). In 2014, however, a study was performed to assess the possibility of macrocyclic lactone resistance. Two dogs with suspected resistant strains of D. immitis had blood samples collected and microfilariae were isolated from these blood samples. These microfilariae were used to infect mosquitoes in the laboratory. After 14 days, infective L3 larvae were harvested from the mosquitoes and injected into dogs. Even dogs who were on an appropriate dose of heartworm prevention developed
PREVENTION
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