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. 2009 Aug;50(8):835–840.

Granulocytic anaplasmosis in three dogs from Saskatoon, Saskatchewan

Ken R Cockwill 1, Susan M Taylor 1,✉, Elisabeth CR Snead 1, Ryan Dickinson 1, Kevin Cosford 1, Sarah Malek 1, L Robbin Lindsay 1, Pedro Paulo Vissotto de Paiva Diniz 1
PMCID: PMC2711468  PMID: 19881921

Abstract

Three dogs from Saskatoon, Saskatchewan were diagnosed with acute granulocytic anaplasmosis. Fever, lethargy, inappetence, vomiting, diarrhea, and lameness were reported. Lymphopenia, thrombocytopenia, and splenomegaly were identified in all dogs. Inclusions were identified within the cytoplasm of blood neutrophils, and infection with Anaplasma phagocytophilum was confirmed by polymerase chain reaction.

Introduction

Anaplasma phagocytophilum is the causative agent of granulocytic anaplasmosis in dogs. This is a tick-transmitted disorder that was previously known as canine granulocytic ehrlichiosis (1). In 2001, molecular analysis prompted the reclassification of several Ehrlichia species to the genus Anaplasma. The species Ehrlichia equi, Ehrlichia phagocytophila, and the unnamed causative agent of human granulocytic ehrlichiosis (HGE) were merged into a single species and renamed, Anaplasma phagocytophilum (1,2). These are gram-negative, obligate intracellular bacteria that parasitize neutrophils in dogs, people, cats, and horses worldwide and in cattle, sheep, and goats in Europe (1,3,4). The geographic distribution of the disease in people and domestic animals closely follows the distribution of the Ixodes spp. ticks required for transmission (1). Anaplasma phagocytophilum is transmitted in North America by Ixodes pacificus on the west coast and Ixodes scapularis east of the Rocky Mountains (5,6). Saskatchewan has not been considered an endemic area for I. pacificus or I. scapularis ticks, but small numbers of adult I. scapularis have been detected in the province, presumably carried into the province as larvae or nymphs on migratory birds (7). This report describes A. phagocytophilum infection in 3 dogs native to Saskatchewan with no history of travel outside the province.

Materials and methods

Blood-EDTA samples from dogs 1 and 3 were submitted to the Vector Borne Diseases and Diagnostic Laboratory (VBDDL), North Carolina State University, Raleigh, North Carolina, USA, for A. phagocytophilum and Bartonella spp., DNA amplification. Blood-EDTA sample from dog 2 and ticks collected from dogs 1 and 3 were submitted to the Zoonotic Diseases and Special Pathogens section, National Microbiology Laboratory (NML), Public Health Agency of Canada, Winnipeg, Manitoba, for A. phagocytophilum and Borrelia burgdorferi DNA amplification.

DNA extraction, amplification and quality control at the VBDDL

DNA was manually extracted from 200 μL of canine ethylene-diaminetetraacetic acid (EDTA)-whole-blood samples using a commercial kit (Qiagen, Chatsworth, California, USA). DNA concentration was quantified by spectrophotometry (Nanodrop Technologies, Wilmington, Delaware, USA), and the absence of polymerase chain reaction (PCR) inhibitors was demonstrated by the amplification of a fragment of the GAPDH gene (8). Anaplasma phagocytophilum 16S rRNA gene and Bartonella spp. 16S-23S rRNA intergenic spacer (ITS) amplifications were performed using conventional 1-step PCR in an Eppendorf Mastercycler EP (Eppendorf, Hamburg, Germany) as described previously (9,10). The DNA from the blood of a healthy, specific pathogen-free dog was used as a PCR negative control. Anaplasma phagocytophilum DNA (GenBank accession number NC_007797) and Bartonella henselae DNA (BX897699) were used as positive controls. In order to prevent PCR amplicon contamination, sample preparation, reaction setup, PCR amplification, and amplicon detection were all performed in separate areas.

DNA extraction, amplification and quality control at the NML

DNA was extracted from whole blood and ticks using a commercial kit (Qiagen) following the manufacturer’s instructions for extraction of DNA from tissue. To enhance liberation of DNA from blood-fed ticks, each tick was bisected longitudinally and half of each tick was further cut into smaller pieces prior to placement in lysis buffer. Amplification of DNA was accomplished using an Applied Biosystems Prism 7900 sequence detector (B. burgdorferi and A. phagocytophilum) or by using nested PCR techniques (A. phagocytophilum only) employing standard thermocyclers and visualizing amplicons on 2% agarose gels stained with ethidium bromide. Regardless of the pathogen, samples were considered positive when they produced cycle threshold values < 40 with 2 different primer and probe sets on real-time PCR, or appropriately sized bands in the nested PCR format. The primer and probe sets for detection of B. burgdorferi targeted 23S and ospA region of the genome as described by Ogden et al (11). For A. phagocytophilum, screening was performed using primers directed towards the msp2 gene (12) while ANK genes (13) were targeted in the confirmatory nested PCR. Appropriate positive (previously positive extracts from ticks) and negative (water) controls were incorporated into each set of PCR reactions. To ensure DNA extraction was successful in ticks, PCR was also performed on tick extracts using a primer and probe set that targets the 16S gene of all Ixodes species of ticks (11). To prevent potential cross-contamination, all critical phases in the PCR process were performed in separate rooms within the NM, similar to the process described at VBDDL.

Case series

Case 1

A 10-year-old, castrated male Nova Scotia duck tolling retriever was presented to the Western College of Veterinary Medicine Veterinary Teaching Hospital (WCVM VTH) in July 2007 with a 2-d history of lethargy and 2 episodes of vomiting. Vaccinations against distemper, hepatitis, parvovirus, parainfluenza, and rabies were current. The dog had never traveled outside the Saskatoon area and lived primarily indoors, with supervised off-leash walks outdoors.

Physical examination revealed a depressed and lethargic dog with a temperature of 40.9°C, tachycardia, and tachypnea. Abdominal palpation elicited a painful response. A complete blood (cell) count (CBC) documented a normal white blood cell (WBC) count and mature neutrophil count with a left shift (bands 0.455 × 109/L; reference range: 0.0 to 0.1 × 109/L) and slight toxic change indicating an acute inflammatory response. Lymphopenia (0.182 × 109/L; reference range: 1.2 to 5.0 × 109/L) was attributed to stress. Platelets were estimated to be normal.

A serum biochemical profile revealed increases in amylase (1680 U/L; reference range: 343 to 1375 U/L) and lipase (2030 U/L; reference range: 0 to 769 U/L), most consistent with acute pancreatitis. There were also mild increases in cholesterol (7.29 mmol/L; reference range: 2.70 to 5.94 mmol/L), alkaline phosphatase (ALP) (176 U/L; reference range: 9 to 90 U/L), and alanine aminotransferase (ALT) (62 U/L; reference range: 19 to 59 U/L). Serum globulins were slightly increased (39 g/L; reference range: 23 to 37 g/L), suggesting inflammation or antigenic stimulation. Potassium was slightly decreased (3.7 mmol/L; reference range: 3.8 to 5.6 mmol/L), most likely secondary to inappetance and vomiting. Urine was appropriately concentrated (urine specific gravity 1.035).

Thoracic and abdominal radiographs were normal. Abdominal ultrasound revealed pancreatic enlargement, and mild splenomegaly with numerous hypoechoic masses (0.6 to 1.8 cm diameter) within the splenic parenchyma. One mesenteric lymph node was enlarged.

Treatment for presumed pancreatitis was initiated with intravenous (IV) fluids (Normosol-R with 20 mEq KCL/L), 3.0 mL/kg, bodyweight (BW)/h, ampicillin (Novopharm, Toronto), 20 mg/kg BW, IV, q6h, selenium (Selenium-E; Vetoquinol Canada, Lavatrie, Quebec), 0.1 mg/kg BW, IM, q24h, and buprenorphine (Reckitt Benckiser Healthcare UK, Hull, England), 0.02 mg/kg BW, IV, q12h.

The next day, three 10-mL blood samples were collected aseptically at 30 min intervals from alternating jugular veins and the left saphenous vein, and submitted for standard aerobic and anaerobic bacterial culture. Urine collected by cystocentesis was also submitted for culture. Culture results were negative.

Collection of fine-needle aspirates from the spleen for cytological evaluation was recommended based on the ultrasonographic abnormalities. Results of a coagulation profile revealed a normal prothrombin time (PT) (8.6 s; reference range: 7.5 to 9.9 s), slight prolongation of the partial thromboplastin time (PTT) (15.9 s; reference range: 9.6 to 13.8 s), and increased fibrin degradation products (FDPs) (> 20 μg/mL; reference range: < 5 μg/mL), suggesting accelerated fibrinolysis. One unit (250 mL) of fresh frozen plasma was transfused over 2 h.

On day 3 of hospitalization, fine-needle aspirates were obtained from the hypoechoic splenic masses using ultrasound guidance. Cytological evaluation of the aspirates revealed aggregates of large and small lymphocytes, splenic parenchymal cells, hemosiderin-laden macrophages and occasional neutrophils. Basophilic, round, granular cytoplasmic inclusions up to 2 μm in diameter were identified within approximately 3.5% of the mature neutrophils on the smears, felt to most likely represent morulae of the granulocytic rickettsial organism A. phagocytophilum. A peripheral blood smear, repeated after the splenic aspirate results were reported, revealed severe thrombocytopenia (estimated < 20 × 109/L; reference range: 200 to 900 × 109/L) and rickettsial cytoplasmic inclusions within approximately 5% of mature neutrophils (Figure 1). Review of the blood smear from the day of presentation revealed that morulae had been present within approximately 11% of the mature neutrophils.

Figure 1.

Figure 1

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Inclusions (arrows) within 2 neutrophils on a blood smear from a dog with A. phagocytophilum infection. Modified Wright’s stain. Bar = 20.0 μm.

A tentative diagnosis of A. phagocytophilum infection was made. Treatment was initiated with doxycycline (Apodoxy-tabs; Apotex, Toronto, Ontario), 10 mg/kg BW, PO, q12h. Thorough examination of the dog revealed a partially engorged female Ixodes scapularis tick attached to the dorsal portion of the tail. The tick was removed, and submitted to the NML for analysis. The species of the tick was confirmed as Ixodes scapularis and PCR testing was positive for A. phagocytophilum and negative for Borrelia burgdorferi.

Pre-treatment whole blood from the dog collected in EDTA was submitted to the VBDDL. The blood sample was positive for A. phagocytophilum by PCR analysis. The dog clinically improved within 24 h of initiating doxycycline administration, and was discharged from the hospital. Re-evaluation 2 wk later showed that the dog was bright and alert and had a good appetite. There were no abnormalities on physical examination and CBC revealed a normal platelet count. No morulae were identified in blood neutrophils.

Case 2

An 8-year-old, castrated male, Siberian husky was presented to the WCVM VTH in July 2007 with a 2-day history of lethargy, rear limb stiffness, inappetence, and excessive panting. Two days before presentation, the owner had removed and discarded several attached ticks from the dog after it had spent the previous day running loose on a farm. The dog had been generally healthy, but had a history of periodic mild rear limb stiffness that improved with administration of meloxicam (Metacam; Boehringer-Ingelheim, Burlington, Ontario) 0.1 mg/kg BW, PO, q24h. The rear limb stiffness during the 2 d before presentation had been more severe than previously noticed. Vaccinations against infection with distemper, hepatitis, parainfluenza, parvovirus, and rabies were current. There was no history of travel outside the province.

Physical examination revealed a quiet but responsive, febrile (40.5°C) dog in good body condition. The only abnormality was a stiff, short-strided gait in all limbs. No specific region of pain or swelling could be identified.

A CBC revealed mild leukopenia (4.6 × 109/L; reference range: 4.80 to 13.9 × 109/L), lymphopenia (0.092 × 109/L; reference range: 1.2 to 5.0 × 109/L) and monocytopenia (0.046 × 109/L; reference range: 0.08 to 1.0 × 109/L). There was also moderate thrombocytopenia (93 × 109/L; reference range: 200 to 900 × 109/L). Round, basophilic, granular cytoplasmic inclusions were identified within approximately 27% of the mature neutrophils on the blood smear, most consistent with morulae of A. phagocytophilum. A serum biochemistry profile revealed moderate hypoalbuminemia (22 g/L; reference range: 28 to 38 g/L), and mild increases in cholesterol (7.52 mmol/L; reference range: 2.70 to 5.94 mmol/L) and ALP (99 U/L; reference range: 9 to 90 U/L). Cytologic examination of synovial fluid collected from both carpal, tarsal, and stifle joints revealed increased neutrophils in 3 joints, but all of these samples had blood contamination, making interpretation difficult. Blood collected in EDTA and submitted to the NML was positive for A. phagocytophilum using PCR.

Treatment was initiated with doxycycline (5 mg/kg BW, PO, q12h). The fever resolved within 12 h, and the dog was discharged from the hospital 2 d later with instructions to continue doxycycline administration for 21 d.

Three weeks later, the dog was presented to the WCVM VTH for re-evaluation. The dog was clinically normal and had a normal gait. No physical abnormalities were present. A CBC revealed a mild monocytosis (1.265 × 109/L; reference range: 0.08 to 1.0 × 109/L). The platelet count was estimated to be normal on the blood smear and no morulae were identified in the neutrophils. One year following treatment, a CBC and a blood smear were re-evaluated and found to be normal.

Case 3

A 6-year-old, spayed female Shih tzu cross was presented to the WCVM VTH in September, 2007 for evaluation after 5 d of lethargy, inappetance, and large bowel diarrhea characterized by increased frequency (4–5 times per day), mucus, and urgency. The owner had fed a boiled chicken and rice diet for 2 d, with no improvement in the appetite or diarrhea. The dog had vomited bile-stained fluid several times in the 48 h prior to presentation. The dog also had a 3-day history of a “shifting” rear leg lameness. Vaccinations against distemper, hepatitis, parvovirus, parainfluenza, and rabies were current. The dog had never traveled outside of Saskatchewan and lived primarily indoors but spent time each day within a fenced backyard and was walked off-leash in a local dog park.

Physical examination revealed a quiet, alert, febrile (40.1°C) dog that was approximately 7% dehydrated. An engorged tick was found on the right side of the neck, removed, and submitted for analysis. The right submandibular and right prescapular lymph nodes were enlarged. Thoracic auscultation and abdominal palpation were unremarkable. Rectal examination yielded soft, orange-yellow feces.

The CBC documented a normal WBC count and mature neutrophil count with a mild left shift (bands 0.142 × 109/L; reference range: 0.0 to 0.1 × 109/L) and slight toxic change. There was a mild lymphopenia (0.639 × 109/L; reference range: 1.2 to 5.0 × 109/L), and a marked thrombocytopenia (30 × 109/L; reference range: 200 to 900 × 109/L). Examination of the blood smears revealed round, basophilic, granular cytoplasmic inclusions within approximately 4% of the mature neutrophils, most consistent with morulae of A. phagocytophilum.

A serum biochemistry profile revealed mild hypokalemia (3.5 mmol/L; reference range: 3.8 to 5.6 mmol/L) attributed to anorexia. There were elevations in cholesterol (6.75 mmol/L; reference range: 2.70 to 5.94 mmol/L), bilirubin (5 μmol/L; reference range: 1.0 to 4.0 μmol/L) and alkaline phosphatase (ALP) (149 U/L; reference range: 9 to 90 U/L) suggesting cholestasis. Amylase and lipase were normal. Urine was appropriately concentrated (urine specific gravity 1.057). A direct fecal wet mount was negative for parasites and cytologic evaluation of a stained (Diff-Quik) fecal smear did not reveal excessive numbers of Clostridial spp. or Campylobacter spp.

Cytologic evaluation of fine-needle aspirates from the right submandibular and prescapular lymph nodes revealed mild reactive hyperplasia and an increase in plasma cells. Synovial fluid was collected from the carpal, tarsal, and stifle joints bilaterally and examined cytologically; moderate neutrophilic inflammation was identified within the left stifle and the right tarsus. No inclusions were observed within joint neutrophils. Thoracic radiographs were normal. Abdominal radiographs revealed splenomegaly. Abdominal ultrasound confirmed that the spleen was diffusely enlarged with normal echogenicity and smooth contours. Iliac and mesenteric lymph nodes were mildly enlarged and a small nodule was identified on the caudal pole of the left adrenal gland. Treatment was initiated with IV fluids (Normosol-R solution with 20 mEq KCL/L, 3 mL/kg BW/h) and doxycycline (5 mg/kg BW, PO, q12h). Famotidine (Omega, Montreal, Quebec), 0.5 mg/kg BW, SQ, q12h was administered while the dog was hospitalized. Within 24 h, the dog’s diarrhea resolved, appetite returned to normal, and she was discharged from the hospital. Doxycycline was continued for 21 d, and re-evaluation 7 d and 21 d later revealed resolution of all clinical signs, a normal platelet count, and no visible morulae on the blood smear.

Serum from the day of presentation was negative for antibodies against A. phagocytophilum, E. canis, and B. burgdorferi (Snap 4Dx; Idexx Laboratories, Westbrook, Maine, USA). Whole blood from the dog submitted to the VBDDL was positive for A. phagocytophilum and negative for Bartonella spp. by PCR. The tick that had been removed was identified by the NML as a partially engorged adult female Ixodes scapularis and blood collected from the tick was positive for A. phagocytophilum and negative for Borrelia burgdorferi by PCR.

Discussion

Infection with A. phagocytophilum has been recognized in a variety of mammalian hosts. Many canine infections are subclinical and self-limiting, but acute infection has been associated with a febrile illness and a wide range of clinical signs (1). Fever, lethargy, and anorexia, as exhibited by all 3 dogs in this report, are the most common clinical signs. (2,14–21). Lameness, a stiff gait, reluctance to move, and musculoskeletal pain are also commonly reported, but polyarthritis is rarely documented (2,14–18,21–23). Severe polyarthritis seems to be a more consistent feature of infection with other tick-borne agents such as Ehrlichia ewingii and B. burgdorferi (1,4,16,17).

Gastrointestinal signs of vomiting, diarrhea, and abdominal discomfort, as manifested by dog 1 and dog 3 have been previously reported in a few dogs with acute A. phagocytophilum infection (1,2,16,19). The findings of vomiting, fever, abdominal pain, increased band neutrophils, elevated amylase and lipase, and pancreatic enlargement in dog 1 resulted in a presumptive diagnosis of pancreatitis. Increases in serum amylase have, however, been reported in 50% of dogs with acute anaplasmosis (14). Vomiting and diarrhea were the primary reason for presentation in 2 dogs in this report, and the rapid resolution of clinical signs after initiating doxycycline therapy in both dogs suggests a link between the gastrointestinal clinical signs and A. phagocytophilum infection.

Other less common clinical signs in dogs with acute granulocytic anaplasmosis include polyuria and polydipsia, cough, dyspnea, spontaneous hemorrhages, uveitis, and nervous system dysfunction (1,2,4,14,15,17,22,23). Seizures, ataxia, proprioceptive deficits, vestibular deficits, and spinal pain and meningitis have also been reported (14,17,21,23). Lymphadenopathy occurs in 10% to 20% of cases; aspiration cytology typically reveals reactive hyperplasia and occasionally an increase in plasma cells as seen in dog 3 (14,21–23). Splenomegally, as detected in 2 dogs in this report, was present in 13% of naturally infected dogs in 1 report, and in 100% (7/7) of experimentally infected dogs (14,21). Microscopically, spleens from experimentally infected dogs had reactive hyperplasia with enlarged activated lymph nodules, increased numbers of macrophages and plasma cells in the red pulp, and many inclusions within splenic neutrophils (14,21). In dog 1, inclusions within neutrophils were more apparent on cytologic examination of fine-needle aspirates of the spleen than on a blood smear.

The diagnosis of acute granulocytic anaplasmosis is most often suspected when inclusions are identified within circulating granulocytes (1,24). Anaplasma phagocytophilum is an obligate intracellular parasite that inhabits membrane-lined vacuoles, forming inclusions (morulae) in the cytoplasm of blood neutrophils and occasionally eosinophils (15). Experimentally, morulae first become apparent 4 to 14 d post-infection, and are detectable for only 4 to 8 d (21). The percentage of neutrophils containing inclusions is variable, ranging from 1% to 42%, with the greatest parasitemia noted during severe clinical illness (2,14,15,18,21). Use of a concentration technique such as a buffy coat examination may increase the likelihood of finding morulae in a sample (4). Morulae of A. phagocytophilum cannot be distinguished from those of E. ewingii, so in regions where these infectious agents and their vectors overlap, molecular techniques are required to distinguish the two (1).

Thrombocytopenia has been documented in 100% of experimentally infected dogs with acute granulocytic anaplasmosis and in more than 80% of naturally infected dogs (2,14–17,20–22,24). The decrease in platelet numbers ranges from mild to severe, but spontaneous hemorrhages rarely occur. Mechanisms for the thrombocytopenia may include hypersplenism, consumption, and immune-mediated destruction (1,16,22). Thrombocytopenia is most pronounced during peak parasitemia, as manifested by identification of morulae, and even without treatment, platelet numbers typically return to normal within 7 d (20,21).

Lymphopenia is common in dogs with acute granulocytic anaplasmosis, and was evident in the 3 dogs in this report (1,14,15,17,21). Mild to moderate neutropenia has also been described (2,14,21,22). A mild nonregenerative anemia is common (2,14,21), and rarely severe immune-mediated hemolysis occurs (22). Common serum biochemical abnormalities include increases in serum ALP and hypoalbuminemia (1,14,15,17).

Acute A. phagocytophilum infection should be suspected in a dog showing characteristic clinical signs and having morulae identified within neutrophils on a blood smear. Serologic tests can be used to confirm the diagnosis, but these have some limitations. Positive serology may represent current infection, resolved infection, or merely exposure. It is recommended that a 4-fold increase in antibody titer between paired acute and convalescent (21 d apart) samples be demonstrated to confirm active infection (1,15,22). The incubation period between exposure to an infected tick and development of acute granulocytic anaplasmosis is approximately 7 d, and up to 40% of dogs tested during the acute, symptomatic phase of their illness will be negative on serology (4,14,15,24). The commercially available ELISA screening test (Snap 4Dx) detects antibodies against A. phagocytophilium, so will be negative in many dogs with acute granulocytic anaplasmosis, as seen in dog 3. Experimentally, dogs seroconvert 7 to 21 d after exposure to an infected tick, with serum titers peaking 3 to 4 wk after exposure and returning to normal in 7 to 8 mo (1,14,15,17,21).

While positive serologic testing confirms exposure, positive PCR for A. phagocytophilum confirms infection (1,2,4). In experimental infections, PCR was positive 6 to 8 d before morulae were visible in the blood and remained positive throughout infection (21). Polymerase chain reaction detection of A. phagocytophilum DNA is sensitive and specific, making PCR the diagnostic test of choice for confirming acute granulocytic anaplasmosis (17). Testing for the 16S rRNA gene of A. phagocytophilum should be performed on EDTA anticoagulated blood collected prior to antibiotic administration (1,4). Gene sequencing should also be performed, when available, since there is evidence that genetic variants may involve different reservoir hosts and cause different clinical manifestations (15).

Tetracycline-related antibiotics are the recommended treatment for granulocytic anaplasmosis in dogs. Doxycycline administration (10 mg/kg BW, PO, q24h for 10 to 21 d) results in rapid clinical improvement, and most dogs are clinically normal with 24 to 48 h of initiating therapy (4,15). Relapses are uncommon, but recovered dogs are susceptible to re-infection (1,15). Most canine patients make an uneventful recovery even without specific therapy.

Human and canine infections with A. phagocytophilum have been reported in the Pacific northwest, the upper midwest, and the northeastern and mid-Atlantic United States, as well as in Europe and Asia (1,15,25). Human granulocytic anaplasmosis has been a nationally notifiable disease in the United States since 1998, facilitating tracking of the expanding geographic range of this infection. The only reported case in Canada was a dog from Vancouver Island (17). A study in 2006, examining the seroprevalence of tick transmitted infectious diseases in dogs from southern Ontario and Quebec, did not find any evidence of A. phagocytophilum infection and concluded that veterinarians in those provinces should only pursue diagnosis of tick-borne pathogens in dogs with a travel history (26). Results of a 2007 seroprevalence study, using in-house testing of samples from veterinary clinics across Canada, identified serum antibodies against A. phagocytophilum in a few dogs from Manitoba, Ontario, and Quebec, but the incidence was extremely low (1.78%, 0.09%, and 0.06%, respectively) and no travel history was obtained for the dogs that tested positive (27). None of the dogs tested in Saskatchewan were positive, but < 200 animals were tested, presumably because of the perception among veterinarians that vector-borne pathogens are not endemic to Saskatchewan.

The geographic distribution of confirmed granulocytic anaplasmosis in people and domestic animals closely follows the distribution of the Ixodes spp. ticks required for transmission (1). Anaplasma phagocytophilum is transmitted by the blacklegged tick, Ixodes scapularis east of the Rocky mountains (5,6). Saskatchewan has not been considered an endemic area for this tick, but small numbers of mature I. scapularis ticks have been identified that are thought to have been carried into the province by migratory birds (7,28). Migratory birds regularly disperse I. scapularis ticks to areas where they are not endemic (11,29) and occasionally establish new endemic populations in regions that were previously believed to be too cold to support self-sustaining populations (30). A recent study estimates that migratory birds disperse 50–175 million I. scapularis ticks across Canada each spring (11). White-tailed deer, white-footed mice, eastern chipmunks, dusky-footed wood rats, southern red-backed voles, mule deer, and black-tailed deer serve as hosts for Ixodes spp. ticks and natural reservoirs for A. phagocytophilum in North America (15). Transport of ticks by migratory birds, increases in deer population, wildlife migration, and environmental warming all have the potential to increase the geographical distribution of arthropod vectors like Ixodes scapularis (7,11,26,28–31).

Ixodes scapularis is a vector for both Lyme borreliosis and granulocytic anaplasmosis in dogs and people. Expansion of the range of this tick into regions previously considered nonendemic should raise concern in the veterinary and human medical communities about the increasing health risk. Tick-borne diseases should be considered as differential diagnoses in dogs and people with a variety of clinical symptoms during the spring, summer, and fall when the host ticks are most active (25). Preventing exposure of people and pets to tick vectors is recommended to lessen the risk of infection (4). Anaplasma phagocytophilum is transmitted through the salivary excretions of an attached Ixodes tick (4). Transmission occurs within 24 to 48 h in most cases, so attached ticks should be removed at least daily and tick preventative medications should be recommended in endemic areas (32,33).

This report illustrates the importance of being aware of infectious diseases that can infect our canine patients, even in regions presumed to be nonendemic. Granulocytic anaplasmosis should be considered as a differential diagnosis in all dogs with an acute nonspecific febrile illness, thrombocytopenia, lameness, and other abnormalities consistent with this diagnosis. Inclusions will be evident within neutrophils on blood smears from most symptomatic acutely infected dogs. The diagnosis can be confirmed using PCR or by serology on acute and convalescent blood samples.

Acknowledgment

The authors thank Brent Wagner, Department of Veterinary Microbiology, WCVM for his help with tick identification. CVJ

Footnotes

Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ( hbroughton@cvma-acmv.org) for additional copies or permission to use this material elsewhere.

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