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Parasitology Expertise From the NCVP: American Association of Veterinary Parasitologists, Highlights from the 60th Annual Meeting

Parasitology Expertise From the NCVP: American Association of Veterinary Parasitologists, Highlights from the 60th Annual Meeting
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Brian H. Herrin, DVM, and Susan E. Little, DVM, PhD, Diplomate ACVM (Parasitology)
Oklahoma State University

The Parasitology Expertise from the NCVP column is brought to you in partnership between the National Center for Veterinary Parasitology (ncvetp.org) and Today’s Veterinary Practice. The mission of the NCVP is to further the discipline of parasitology by bringing together partners from academia and industry to address emerging issues, serve the veterinary profession by developing future leaders in veterinary parasitology, and provide diagnostic and consulting services worldwide. Its goals include:

  • Training graduate veterinarians and other scientists in clinical, applied veterinary parasitology
  • Promoting outstanding, clinically relevant veterinary parasitology research
  • Providing diagnostic veterinary services in clinical parasitology to practicing veterinarians
  • Offering balanced, science-based consulting expertise on parasite treatment and prevention strategies.

The American Association of Veterinary Parasitologists (AAVP) 2015 Annual Meeting took place July 11 to 14 in Boston during the American Veterinary Medical Association Convention. Organized as a joint meeting with both the Annual Livestock Insect Workers Conference (LIWC) and Biennial International Symposium on Ectoparasites of Pets (ISEP), the scientific sessions at this tripartite event described exciting advances in our understanding of companion animal parasitology.

As part of the NCVP’s ongoing commitment to advancing the understanding of parasitology in the veterinary profession, this article summarizes a few of the many clinically useful presentations shared at the meeting, including:

  • Unusual parasites in unexpected places
  • Increasing risk of parasites and vector-borne infections
  • Previously unrecognized diversity of ticks in North America
  • New and improved parasite diagnostic testing strategies.

To review the full program of presentations, visit the AAVP website at www.aavp.org.

UNUSUAL PARASITES IN UNEXPECTED PLACES

While the common happens, well, commonly, there are always those unusual cases that present to the clinic. Many of these patients’ diagnoses involve parasites imported from other areas due to translocation of pets, underscoring the importance of collecting a full travel history when providing patient care.

The novel parasites section of the AAVP meeting highlighted cases in which clinicians involved their veterinary parasitology colleagues to help make a difficult diagnosis of a rare or unexpected parasite.

First Report of Cylicospirura felineus in a Feral Domestic Shorthair Cat in North America

Michael Kent, MS, PhD, Oregon State University

  • Cylicospirura felineus is a rare parasite seen primarily in the stomach of bobcats in North America; however, this case of C felineus infection in a cat from Louisiana marked the first case reported in a domestic cat in North America.1
  • The main finding was several nodules located within the submucosal layer around the fundus of the stomach, each with red, slender nematodes protruding and, while an incidental finding, this parasite represents a differential diagnosis for multiple masses in the stomach of cats.
  • Infection with this parasite can mimic feline gastrointestinal eosinophilic sclerosing fibroplasia.

Eucoleus (Capillaria) boehmi in the Dog: Six Case Studies

Thomas J. Nolan, MS, PhD, University of Pennsylvania

  • Eucoleus boehmi is a nematode that inhabits the nasal mucosa of dogs (Figure 1); this presentation reviewed 6 reported cases in the mid-Atlantic region.
  • Diagnosis of this parasite is accomplished either by identifying:
    • Eggs on fecal examination, correctly identifying them to species
    • Adult worms in the nasal cavity via rhinoscopy (with or without biopsy).
  • The eggs of this parasite must be differentiated from those of the canine whipworm, Trichuris vulpis.
  • In this limited sample, both milbemycin oxime (single dose of 2 mg/kg PO) and topical moxidectin at the label-approved dose appear to be successful at treating the infection, but veterinarians should follow up over time with fecal flotation or rhinoscopy as nasal polyps may return.2,3
Figure 1. Eucoleus boehmi: Canine fecal flotation with centrifugation demonstrating the asymmetrical egg of E boehmi. These eggs are approximately 54 to 60 mcm by 30 to 35 mcm and must be differentiated from Trichuris vulpis, E aerophilus, and other capillarids in a canine fecal examination. Courtesy National Center for Veterinary Parasitology

Figure 1. Eucoleus boehmi: Canine fecal flotation with centrifugation demonstrating the asymmetrical egg of E boehmi. These eggs are approximately 54 to 60 mcm by 30 to 35 mcm and must be differentiated from Trichuris vulpis, E aerophilus, and other capillarids in a canine fecal examination. Courtesy National Center for Veterinary Parasitology

Canine Ocular Onchocerciasis in Western Canada: Adoption-Mediated Introduction of a Zoonotic Parasite

Guilherme Verocai, DVM, MSc, PhD, Diplomate ACVM, University of Calgary & University of South Florida

  • The causative agent of canine onchocerciasis is Onchocerca lupi, an ocular nematode of dogs and wild canids.4 While this case was diagnosed in Canada, the canine patient was from Arizona, an area where the infection is more common, albeit still considered relatively rare.
  • Canine onchocerciasis commonly presents with conjunctivitis, lateral scleral thickening, and conjunctival masses.
  • Treatment requires surgery, which may include removal of nodules or enucleation, and ophthalmology consults are often involved. Post surgery, a combination of high dose ivermectin and doxycycline has been used to target any microfilaria circulating in the skin.
  • This case highlights the importance of considering full travel history when diagnosing novel parasites and infections.

Parasites on the Move: Canine Peritoneal Larval Cestodiasis in a Colorado Dog

Lora Ballweber, DVM, MS, Diplomate ACVM, Colorado State University

  • Asexual multiplication of larval Mesocestoides species causes severe, life-threatening disease in dogs and, occasionally, cats. Aggressive treatment is necessary, and prognosis is grave.5
  • This clinical case presentation described a dog that moved from Oregon to Colorado; developed abdominal distention, ascites, and diarrhea; and was diagnosed with diffuse granulomatous peritonitis.
  • Microscopic and molecular examination of tissue recovered during exploratory surgery confirmed canine peritoneal larval cestodiasis caused by Mesocestoides, a parasite that is more commonly reported from the West Coast.

INCREASING RISK OF PARASITES & VECTOR-BORNE INFECTIONS

Research continues to document the importance of parasites in ever-expanding geographic locales. This apparent spread of parasites is likely due to a number of different factors, including fluctuating climate patterns, changing habitat, movement of animals (and their parasites) to new areas, increased contact between animals, and even recognition of parasites where they likely have existed for some time.

A number of presentations focused on newly recognized geographic distributions of parasites and vector-borne disease agents.

Geographic Distribution of Angiostrongylus cantonensis in Florida

Heather Stockdale-Walden, MS, PhD, University of Florida

  • The rat lungworm, Angiostrongylus cantonensis, can cause severe neurologic disease in a variety of aberrant hosts, including humans, dogs, horses, nonhuman primates, and other animals.
  • New distribution locales for this parasite have recently been reported, suggesting it is likely much more widespread in the southern United States than previously recognized.6
  • This presentation shared current data on the widespread distribution of Angiostrongylus cantonensis in northern, central, and southern Florida as determined by sampling and testing rats, rat feces, and mollusk intermediate hosts throughout the state.

Canine Infection with Borrelia burgdorferi, Dirofilaria immitis, Ehrlichia Species, and Anaplasma Species in Canada, 2013–2014

Brian Herrin, DVM, Oklahoma State University

  • Canada is considered newly endemic for Lyme borreliosis7 and canine serology provides an excellent sentinel system to document the geographic spread of the maintenance cycle for this disease agent.
  • This presentation shared current data on the geographic distribution of the agent of Lyme disease and other vector-borne infections in Canada using recent data provided by veterinarians testing dogs in practice.
  • Nationwide, 2.5% of dogs tested were positive for specific antibodies to B burgdorferi, the causative agent of Lyme disease, with endemic foci of higher canine seroprevalence recognized in Nova Scotia, eastern Ontario, New Brunswick, and Quebec.

Prevalence of Canine Gastrointestinal Helminths in Southeast Municipal Dog Parks

Molly Savadelis, Researcher, University of Georgia

  • As long suspected by veterinarians and parasitologists, parasitic infections are common in dog parks, and a significant number of fecal samples in dog parks contain nematode eggs.
  • Fecal samples were collected from dog parks in 3 different southeastern states; after diagnostic evaluation, the data demonstrated that 27% of collected fecal samples harbored nematode eggs. Hookworms were most common, followed by whipworms and ascarids.
  • Dog park use has been previously implicated as a risk for infection with Giardia and Cryptosporidium in dogs,8 and off-leash activity at dog parks was identified as a specific risk factor for infection.9

PREVIOUSLY UNRECOGNIZED DIVERSITY OF TICKS IN NORTH AMERICA

The major tick species present in North America have been known for some time, but recent research has revisited the identity of some of these ticks using molecular as well as morphologic tools. Two presentations on this research were shared.

Diversity of the Brown Dog Tick, Rhipicephalus sanguineus, in North America

Livvy Jones, Veterinary Student (Class of 2017), Oklahoma State University

  • One of the most common ticks found on dogs in the U.S. may actually be comprised of a complex of morphologically similar, but genetically distinct, populations of ticks.10
  • Not all subpopulations within this species complex are able to breed with other cohorts, supporting the concept that the group contains different, morphologically identical species.
  • According to the initial data presented, at least 2 lineages of brown dog ticks appear to be infesting dogs in North America.
  • The diversity seen in the ticks referred to as brown dog ticks may also affect the ticks’ ability to transmit certain infections, including Ehrlichia canis, to dogs.11

Genetic Diversity of Amblyomma Species in the Southern United States

Amanda Blom, DVM, Oklahoma State University

  • In recent years, the Gulf Coast tick, Amblyomma maculatum (Figure 2), has expanded its range across the southern U.S.
  • At the same time, entomologists determined that some ticks, which morphologically appear to be A maculatum, are actually A triste, a species more commonly found in Central and South America.12
  • This presentation described the genetic analysis and genetic diversity of Amblyomma species, specifically A maculatum, collected from several southern states.
  • Higher than expected sequence diversity was present in wild ticks, while colony ticks demonstrated homogeneity; it was not possible to distinguish between A triste and A maculatum with the sequences used.
FIGURE 2. Amblyomma maculatum: A maculatum is known as the Gulf coast tick; this figure shows a male and female of the species. Originally restricted to regions along the Gulf of Mexico, this tick is now found as far north as Kansas. A triste has similar variegated markings on its scutum, making morphologic differentiation of the 2 species difficult. Courtesy National Center for Veterinary Parasitology

FIGURE 2. Amblyomma maculatum: A maculatum is known as the Gulf Coast tick; this figure shows a male and female of the species. Originally restricted to regions along the Gulf of Mexico, this tick is now found as far north as Kansas. A triste has similar variegated markings on its scutum, making morphologic differentiation of the 2 species difficult. Courtesy National Center for Veterinary Parasitology

 Slow Kill Protocol Approach A description, the efficacy, and the problems associated with a slow kill protocol approach to heartworm treatment is addressed in Principles of Treatment: Canine Heartworm Disease (March/April 2015 issue), available at tvpjournal.com.

NEW & IMPROVED PARASITE DIAGNOSTIC TESTING STRATEGIES

Diagnosing parasites accurately is a key component of clinical parasitology. Several presentations focused on the creation and validation of novel assays to enhance identification of parasitic infections in practice.

False Negative Antigen Tests in Dogs Infected with Heartworm (Dirofilaria immitis): An Update & Case Series

Jeff Gruntmeir, Researcher, Oklahoma State University

  • Heat treatment of serum prior to testing for heartworms has been shown to disrupt immune complexes, improving detection of heartworm antigen.
  • As many as 5% to 10% of dogs in animal shelters and more than 50% of dogs on slow kill protocols that initially test negative convert to positive after immune complexes are removed by heat treatment.13,14
  • This presentation shared data from a study in which 34 dogs suspected of being infected with heartworm initially tested negative for antigen. However, after heat treatment to disrupt immune complexes, antigen was detected in 22/34 (64.7%) of the samples; microfilariae were also present in whole blood from some, but not all, of the dogs with blocked antigen.
  • The importance of clinical judgment in making an accurate diagnosis was highlighted because, in these patients, veterinarians suspected heartworm infection, despite the negative antigen test, due to:
    • Presence of microfilaria in whole blood (Figure 3)
    • History of poor or no preventive use
    • Clinical signs consistent with heartworm infection (eg, coughing, murmur)
    • Radiographic evidence of disease.
FIGURE 3. Dirofilaria immitis: Microfilaria of D immitis from a modified Knott’s preparation on whole blood. The microfilariae are approximately 295 to 325 mcm in length, and have a tapered head and straight tail. It is recommended that a modified Knott’s test be performed along with every heartworm antigen test. Courtesy National Center for Veterinary Parasitology

FIGURE 3. Dirofilaria immitis: Microfilaria of D immitis from a modified Knott’s preparation on whole blood. The microfilariae are approximately 295 to 325 mcm in length, and have a tapered head and straight tail. It is recommended that a modified Knott’s test be performed along with every heartworm antigen test. Courtesy National Center for Veterinary Parasitology

Diagnosis of Feline Whipworm Infection in Southern Florida

Jinming Geng, DVM, MS, PhD, IDEXX Laboratories, Inc

  • Feline whipworms, Trichuris campanula and Trichuris serrata, are considered common in much of the world but are rarely identified in North America, except in Florida and the Caribbean Islands.
  • Data were presented from a study that identified Trichuris species in a high proportion of feral cats from Florida.
  • Centrifugal fecal flotation documented eggs of Trichuris species in 26% of feral cat samples, while enzyme-linked immunosorbent assay (ELISA) detected Trichuris species antigen in 39% of fecal samples.
  • These data underscore both the importance of this parasite in cats in this Florida region and the utility of fecal ELISA for identifying whipworm infections.15

Evaluating Schistosoma mansoni Point-of-Care Immunodiagnostic Tests for Detection of Heterobilharzia americana Antigen in Dogs

Jessica Rodriguez, DVM, Texas A&M University

  • Heterobilharzia americana is a schistosome (trematode) of raccoons that occasionally infects dogs and horses (Figure 4).16 Diagnosis is generally made by identification of eggs in fecal saline sedimentation or by fecal polymerase chain reaction, but intermittent egg shedding may make these tests insensitive.
  • This presentation provided information from a study that evaluated the ability of point-of-care immunodiagnostic tests designed for the human parasite, Schistosoma mansoni, to detect H americana.
  • While the assay was successful at detecting infection in some samples, diagnosis was most likely determined when this approach was combined with the aforementioned microscopic and molecular techniques.
FIGURE 4. Heterobilharzia americana: Fecal sedimentation with saline demonstrating H americana eggs from a dog; these eggs are approximately 74 to 113 mcm by 60 to 80 mcm and contain fully formed miracidia. Intermittent egg shedding makes fecal sedimentation an insensitive test for diagnosing this parasite. Courtesy National Center for Veterinary Parasitology

FIGURE 4. Heterobilharzia americana: Fecal sedimentation with saline demonstrating H americana eggs from a dog; these eggs are approximately 74 to 113 mcm by 60 to 80 mcm and contain fully formed miracidia. Intermittent egg shedding makes fecal sedimentation an insensitive test for diagnosing this parasite. Courtesy National Center for Veterinary Parasitology

Modified Knott’s Technique A stepwise approach to the modified Knott’s technique is described in Heartworm Diagnostics: What Do the Latest American Heartworm Society Canine Guidelines Tell Us? (November/December 2014 issue), available at tvpjournal.com.

IN SUMMARY

As shown in this brief review, the presentations at the AAVP Annual Meeting were focused on the future, highlighting novel parasites, geographic distributions, and diagnostic techniques. The AAVP continues to strive to provide evidence-based recommendations that clinicians can put into practice.

AAVP = American Association of Veterinary Parasitologists; ELISA = enzyme-linked immunosorbent assay; ISEP = International Symposium on Ectoparasites of Pets; LIWC = Livestock Insect Workers Conference

References

  1. Crossland NA, Hanks CR, Ferguson JA, et al. First report of Cylicospirura felineus in a feral domestic shorthair cat in North America. J Fel Med Surg 2015; Open Reports 1-4.
  2. Conboy G, Stewart T, O’Brien S. Treatment of E boehmi infection in a mixed-breed dog using milbemycin oxime. JAHAA 2013; 49(3):204-209.
  3. Veronesi F, Morganti G, Di Cesare A, et al. A pilot trial evaluating the efficacy of a 10% imidacloprid/2.5% moxidectin spot-on formulation in the treatment of natural nasal capillariasis in dogs. Vet Parasitol 2014; 200:133-138.
  4. Otranto D, Giannelli A, Latrofa MS, et al. Canine infections with Onchocerca lupi nematodes, United States, 2011-2014. Emerg Infect Dis 2015; 21(5):868-871.
  5. Boyce W, Shender L, Schultz L, et al. Survival analysis of dogs diagnosed with canine peritoneal larval cestodiasis (Mesocestoides spp.). Vet Parasitol 2011; 180(3-4):256-261.
  6. Stockdale-Walden HD, Slapcinsky J, Qvarnstrom Y, et al. Angiostrongylus cantonensis in introduced gastropods in southern Florida. J Parasitol 2015; 101(2):156-159.
  7. Bouchard C, Leonard E, Koffi JK, et al. The increasing risk of Lyme disease in Canada. Can Vet J 2015; 56(7):693-699.
  8. Wang A, Ruch-Gallie R, Scorza V, et al. Prevalence of Giardia and Cryptosporidium species in dog park attending dogs compared to non-dog park attending dogs in one region of Colorado. Vet Parasitol 2012; 184(2-4):335-340.
  9. Smith AF, Semeniuk CA, Kutz SJ, Massolo A. Dog-walking behaviours affect gastrointestinal parasitism in park-attending dogs. Parasit Vectors 2014; 7:429.
  10. Dantas-Torres F, Latrofa MS, Annoscia G, et al. Morphological and genetic diversity of Rhipicephalus sanguineus sensu lato from the New and Old Worlds. Parasit Vectors 2013; 6:213.
  11. Cicuttin GL, Tarragona EL, De Salvo MN, et al. Infection with Ehrlichia canis and Anaplasma platys (Rickettsiales: Anaplasmataceae) in two lineages of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) from Argentina. Ticks Tick Borne Dis 2015; in press (doi:10.1016/j.ttbdis.2015.06.006).
  12. Mertins JW, Moorhouse AS, Alfred JT, Hutcheson HJ. Amblyomma triste (Acari: Ixodidae): New North American collection records, including the first from the United States. J Med Entomol 2010; 47(4):536-542.
  13. Velasquez L, Blagburn BL, Duncan-Decoq R, et al. Increased prevalence of Dirofilaria immitis antigen in canine samples after heat treatment. Vet Parasitol 2014; 206(1-2):67-70.
  14. Drake J, Gruntmeir J, Merritt H, et al. False negative antigen tests in dogs infected with heartworm and placed on macrocyclic lactone preventives. Parasit Vectors 2015; 8:68.
  15. Elsemore DA, Geng J, Flynn L, et al. Enzyme-linked immunosorbent assay for coproantigen detection of Trichuris vulpis in dogs. J Vet Diagn Invest 2014; 26(3):404-411.
  16. Johnson EM. Canine schistosomiasis in North America: An underdiagnosed disease with an expanding distribution. Compend Contin Edu Pract Vet 2010; 32(3):E1-E4.

Version 2 Brian H. Herrin, DVM, is a PhD candidate and affiliate resident with the National Center for Veterinary Parasitology at Oklahoma State University. His research focuses on tick-borne diseases, speci-fically the spread of Lyme disease throughout North America. His work also focuses on using canine positive tests for antibody to B burgdorferi to describe areas that represent a high risk for human infection. Dr. Herrin received his DVM from Oklahoma State University through a dual DVM/PhD program.

 

Author_SE LittleSusan E. Little, DVM, PhD, Diplomate ACVM (Parasitology), is a veterinarian, parasitologist, and co-director of the National Center for Veterinary Parasitology at Oklahoma State University, where she serves as Regents Professor and the Krull-Ewing Chair in Veterinary Parasitology. Her research focuses on zoonotic parasites and tick-borne diseases. She has received the Pfizer (Norden) Distinguished Teaching Award, the National Student AVMA Excellence in Teaching Award, and the Pfizer Award for Research Excellence. She received her DVM from Virginia–Maryland College of Veterinary Medicine (Virginia Institute of Technology) and PhD from University of Georgia.

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