Topics in Companion Animal Medicine RSS feed: Current Issue. Topics in Companion Animal Medicine is dedicated to providing the practitioner with the most recent advances in companion animal medicine. Each quarterly issue includes a comprehensive review of the latest developments and techniques regarding an important topic in veterinary medicine, guest edited by a leading expert in the field. Topics in Companion Animal Medicine also features peer-reviewed original research articles, case reports and review articles; as well as timely editorials addressing issues that affect the companion animal practitioner. New and Forthcoming Issues February Nutrition, Geriatrics and Behavior May Clinical Pathology and Hematology August Proteinuric Renal Disease November Heartworm Disease http://www.companimalmed.com/?rss=yesElsevier Inc.en © 2011 Published by Elsevier Inc. All rights reserved. Topics in Companion Animal Medicine1938-9736264November 2011 © 2011 Published by Elsevier Inc. All rights reserved. healthpermissions@elsevier.comhttp://www.companimalmed.com/article/PIIS1938973611000894/abstract?rss=yesEditorial Board10.1053/S1938-9736(11)00089-4Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3iihttp://www.companimalmed.com/article/PIIS1938973611000900/abstract?rss=yesContents10.1053/S1938-9736(11)00090-0Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3iiiiiihttp://www.companimalmed.com/article/PIIS1938973611000821/abstract?rss=yesThe articles brought together here deal with heartworm and have the goal of providing some background and future to the veterinary practitioner on aspects of this parasite, which remains a significant plague to dogs within the United States and many other parts of the world. Many people are aware of the current controversy over whether resistance has already reared its head in the world of heartworm, but, to a great extent, this publication has skirted the issue to some extent, although it has not been hidden from either. The purpose of this collection of different articles should provide the reader with some information that will underpin the basics for veterinary practice through some history of where things are today and some insights into where they might go in the near and not too distant future.Introduction: HeartwormDwight D. Bowman10.1053/j.tcam.2011.09.001Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews159159http://www.companimalmed.com/article/PIIS193897361100081X/abstract?rss=yesAlthough there has been extensive veterinary focus on both the effectiveness of macrocyclic lactones for heartworm prevention in dogs and their adulticidal effects, little attention has been directed to their effects on heartworm microfilariae. With routine use of macrocyclic lactones, in some cases knowingly, in dogs with existing heartworm infections, veterinarians should recognize the benefits, and possible complications, arising from this behavior. Macrocyclic lactones remain our only class of heartworm prevention available, and preserving their effectiveness is critical. Drugs in this class share common traits: there are currently no Food and Drug Administration—approved microfilaricides in the US marketplace, but because all macrocyclic lactones have microfilaricidal properties (to varying degrees), they are widely used by veterinarians for this purpose. Originally formulated to be used in dogs without patent heartworm infections, all have been demonstrated as safe to use at label doses, and higher, in microfilaremic dogs. All of the product labels indicate that dogs should be tested for heartworm infection before starting preventive therapy. Although microfilaricidal, microfilariae reduction may take many months to occur, and some dogs may never clear. The effects of macrocyclic lactones on the numbers of circulating microfilariae may be due to several different underlying causes (i.e., direct effect on the nervous system, affecting stages found in the uterus of the female worms), but the details of all mechanisms by which microfilariae are killed and/or cleared in dogs treated with macrocyclic lactones have not yet been fully elucidated. Some 10% to 20% of heartworm-infected dogs that begin monthly heartworm preventive treatment without adulticide therapy will have the continued and persistent presence of circulating microfilariae, and the concern is that this may be selecting for resistance to these molecules. The veterinary literature now includes evidence of increased genotypic homozygosity in specific dogs in one area of the country for a marker gene associated with macrocyclic lactone resistance in nematodes of ruminants. This article will review the biology of microfilariae, as well as the evolution of diagnostic testing for heartworm infection. The effects of macrocyclic lactones on microfilaria behavior and survival will be discussed, as well as the use and effects of macrocyclic lactones in microfilaremic dogs, with or without adulticide treatment. The effect of doxycycline on heartworm microfilariae, optimal testing methodologies, and verification of effective clearance of microfilariae after adulticide treatment and microfilaricidal therapy so that dogs do not remain a potential source of infection for other dogs are all covered.Macrocyclic Lactones and Dirofilaria immitis MicrofilariaeDwight D. Bowman, Claire Mannella10.1053/j.tcam.2011.07.001Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews160172http://www.companimalmed.com/article/PIIS1938973611000833/abstract?rss=yesWolbachia is an obligate intracellular endosymbiont and likely mutualist living within the heartworm Dirofilaria immitis and a number of other filarial nematodes in the family Onchocercidae. The bacterial infection is passed from worm to worm transovarially; the organisms are in ovarian cells, the developing microfilariae, and multiply and persist in all later developmental stages through the mosquito and into the next host. Besides being present in the ovaries of the adult worms, they also are present in large numbers within the hypodermal tissues of the nematode. It is now know that these bacteria that were first observed in heartworms more than 30 years ago are actually related to similar Wolbachia bacteria that are found in arthropods. Wolbachia is an alpha-proteobacteria, and this group includes a number of important arthropod-transmitted bacterial agents of dogs and cats: Rickettsia rickettsii, R. felis, Anaplasma platys, Ehrlichia canis, E. chaffeensis, and E. ewingii. Alpha-proteobacteria are also important as obligate intracellular mutualists in plants in which they are responsible for nitrogen fixation. Recent work on the treatment of heartworms in dogs with doxycycline stems from related work with the human filarial nematode Onchocerca volvulus that causes river blindness in people.Introduction to the Alpha-proteobacteria: Wolbachia and Bartonella, Rickettsia, Brucella, Ehrlichia, and AnaplasmaDwight D. Bowman10.1053/j.tcam.2011.09.002Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews173177http://www.companimalmed.com/article/PIIS1938973611000869/abstract?rss=yesDog heartworm (Dirofilaria immitis) is dependent on mosquito vectors for its maintenance and transmission among vertebrate hosts. Consequently, D. immitis abundance and distribution are closely linked with mosquito vector biology and ecology. Information on the important dog heartworm vectors in the United States is limited and no comprehensive surveillance of dog heartworm in US mosquitoes has been undertaken to date. Here, we review information gleaned from a number of field surveys documenting heartworm presence in wild mosquito populations as well as laboratory assessments of mosquito vector capacity. Various biological and ecological factors likely contribute to the relative importance of different vector species. We describe some of these factors, rank the leading criteria for efficient vectors, and present the most likely vector species found across the United States. Considering the recent emergence of drug resistance among D. immitis strains, practical knowledge of heartworm vector biology and control should be incorporated into heartworm disease management programs. We conclude by proposing that heartworm control would benefit by targeting mosquito vectors, and we suggest ways in which veterinarians can incorporate the recognition of vector importance into heartworm prevention recommendations imparted to clients.Mosquito Vectors of Dog Heartworm in the United States: Vector Status and Factors Influencing Transmission EfficiencyNicholas Ledesma, Laura Harrington10.1053/j.tcam.2011.09.005Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews178185http://www.companimalmed.com/article/PIIS1938973611000857/abstract?rss=yesReports of loss-of-efficacy (LOE) events in dogs infected with Dirofilaria immitis despite adherence to accepted prophylaxis regimens with a macrocyclic lactone anthelmintic are attracting considerable attention. It is crucially important to distinguish among several possible causes for these LOE reports, one of which is the evolution of resistance to these drugs in heartworms. We review here recent evidence at the molecular level that supports the hypothesis that parasites derived from LOE cases have experienced a strong selection event and that these populations are characterized by very high frequencies of single-nucleotide polymorphisms in a D. immitis gene encoding a P-glycoprotein transporter, comprised of homozygous guanosine residues at 2 locations (“GG-GG” genotype). Furthermore, an infected dog adopted to Canada from the southern United States harbored a microfilarial population that was insensitive to very high doses of macrocyclic lactones and was characterized by a high frequency of the GG-GG genotype associated with LOE cases. We propose that this case be defined as a drug-resistant heartworm infection and suggest that a simple assay for the existence of resistant parasites is a 7-day microfilariae suppression test, which can be performed in a veterinary clinic as part of an effort to document the geographic distribution of this phenotype.Evidence for Macrocyclic Lactone Anthelmintic Resistance in Dirofilaria immitisTimothy G. Geary, Catherine Bourguinat, Roger K. Prichard10.1053/j.tcam.2011.09.004Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews186192http://www.companimalmed.com/article/PIIS1938973611000845/abstract?rss=yesVector-borne diseases, including canine heartworm disease (CHWD), are of major socioeconomic and canine health importance worldwide. Although many studies have provided insights into CHWD, to date there has been limited study of fundamental molecular aspects of Dirofilaria immitis itself, its relationship with the canine host, its vectors, as well as the potential of drug resistance to emerge, using advanced -omic technologies. This article takes a prospective view of the benefits that advanced -omics technologies will have toward understanding D. immitis and CHWD. Tackling key biological questions using these technologies will provide a “systems biology” context and could lead to radically new intervention and management strategies against heartworm.Heartworm Genomics: Unprecedented Opportunities for Fundamental Molecular Insights and New Intervention StrategiesRobin B. Gasser, Cinzia Cantacessi10.1053/j.tcam.2011.09.003Topics in Companion Animal Medicine 26, 4 (2011)2011-11-01Topics in Companion Animal Medicine2011-11-01264S1938-9736(11)X0005-3Topical Reviews193199