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Keywords:

  • Adverse reaction;
  • Platelet recovery time;
  • Platelets;
  • Vaccine

Abstract

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Background

Vaccination is often cited as a potential cause of immune-mediated thrombocytopenia (ITP) in dogs. Although an association has been documented in humans, particularly in children, this relationship has not been definitively established in dogs.

Objectives

To identify the presence of an association between recent vaccination and ITP in dogs.

Animals

Forty-eight client-owned dogs with presumptive idiopathic ITP and 96 age-matched, client-owned dogs with non-immune-mediated disease.

Methods

Retrospective, case-control study. Dogs were identified through the Veterinary Medical Database (VMDB) and Hospital Information System at Purdue University.

Results

The median age at presentation for dogs with ITP was 7 years (range: 2–15 years). The majority of the ITP group was comprised of mixed breed dogs (38%); no pure breed was represented by more than 3 cases. The number of dogs that were vaccinated within 42 days of diagnosis of ITP did not differ significantly (P = .361) between cases of presumptive ITP (4/48, 8%) and the control group (13/96, 14%).

Conclusions and Clinical Importance

This study failed to confirm the presence of an association between presumptive idiopathic ITP in dogs and recent vaccination; however, the possibility of an association cannot be completely ruled out based on the small sample populations and requires further investigation.

Abbreviations
DIC

disseminated intravascular coagulation

IMHA

immune-mediated hemolytic anemia

ITP

immune-mediated thrombocytopenia

MMR

measles-mumps-rubella

pRBCs

packed red blood cells

PT

prothrombin time

PTT

partial thromboplastin time

PUVTH

Purdue University Veterinary Teaching Hospital

RBC

red blood cell

VMDB

Veterinary Medical Database

Immune-mediated thrombocytopenia (ITP) is a condition in which antibodies are directed against platelets leading to their phagocytosis and destruction by macrophages.[1] These antibodies are typically gamma G immunoglobulin[2, 3] and are most often directed against platelet surface antigens such as glycoprotein IIb and IIIa.[4]

Immune-mediated thrombocytopenia in dogs is a relatively uncommon hemostatic disorder, occurring in approximately 5% of thrombocytopenic dogs that present to veterinary institutions.[5, 6] The disease is considered idiopathic or primary when no underlying cause is identified and is considered secondary when an etiology is established.[7] A variety of causes of ITP have been documented in dogs such as rickettsial infections,[8, 9] drug administration,[10, 11] systemic lupus erythematosus,[12] and neoplasia.[13] To definitively establish the cause of thrombocytopenia as immune-mediated, antiplatelet antibody testing is required. However, antiplatelet antibody assays are not widely available and have variable sensitivity and specificity, therefore a clinical diagnosis of ITP is typically made on the basis of exclusion of other identifiable causes of thrombocytopenia and response to treatment.[14]

In addition to the above-mentioned causes of ITP, recent vaccination in humans is associated with ITP, particularly after immunization with the measles-mumps-rubella (MMR) vaccine in children.[15-17] This association in humans has raised concern in the veterinary community of a similar association in dogs, although a definitive relationship has not been established in dogs. Thrombocytopenia occurs in dogs after vaccination with distemper and hepatitis vaccines[18, 19]; however, the platelet count does not often decrease below 100,000 cells/μL, nor does this decrease typically result in clinical signs of hemorrhage.[19] In 1 case, a dog developed severe thrombocytopenia that resulted in clinical bleeding after recent vaccination.[19] Despite limited evidence, the concern that there is a relationship between clinically relevant ITP and recent vaccination drives some clinicians to withhold vaccination in dogs with previously diagnosed ITP.

The purpose of this study was to investigate whether an association between recent vaccination and ITP exists in dogs. We hypothesize that the proportion of recently vaccinated dogs with presumptive idiopathic ITP would be significantly higher than the proportion of recently vaccinated dogs within the control group.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Patient Selection—Dogs with ITP

A search of the computerized Veterinary Medical Database (VMDB)1 and Hospital Information System at Purdue University was performed to identify all dogs that were presented to the Purdue University Veterinary Teaching Hospital (PUVTH) from January 1994 to December 2010 that had a final diagnosis that included the term “thrombocytopenia.” Three-hundred and ninety medical records were identified and reviewed.

Criteria for inclusion into the study included a diagnosis of presumptive idiopathic ITP and a complete vaccination history. Dogs were classified as having idiopathic ITP if they had a platelet count of less than 40,000 cells/μL at the time of presentation, clinical signs of bleeding, a prothrombin time (PT), and partial thromboplastin time (PTT) that were not prolonged beyond 25% of the upper end of the reference range, a negative antibody titer for Ehrlichia canis, and no other evidence for an underlying cause of thrombocytopenia. A cut-off of 40,000 cells/μL was chosen to minimize the likelihood of including cases of secondary ITP and to ensure that ITP cases had clinically relevant thrombocytopenia.[14, 20-22] Diagnostic tests required for case inclusion were a CBC and serum biochemistry analysis at the time of presentation, a PT and PTT within 1 day of presentation to the PUVTH, E. canis antibody titer, and diagnostic imaging (thoracic radiographs, abdominal radiographs, or complete abdominal ultrasound). All dogs that were included in the ITP group were considered to have a presumptive diagnosis of ITP, as antiplatelet antibody assays were not routinely performed at the PUVTH. A vaccination history was considered complete if the type of vaccine that was given before presentation to the PUVTH was reported, as well as, the exact date or month of vaccination administration. If the vaccine was given in the 2 months prior to presentation, the exact date was recorded.

Cases were excluded from the study if they had a concurrent illness known to be associated with thrombocytopenia such as malignant neoplasia, severe systemic infection, bone marrow disease, rickettsial infection, or immune-mediated disease. Dogs that had a history of exposure to drugs known to be associated with ITP, including cephalosporins or trimethoprim-sulfadimethoxazole, in the 42 days prior to diagnosis of ITP were also excluded.

Patient Selection—Control Dogs

The control population consisted of dogs that were presented to the PUVTH for any non-immune-mediated illness during the study period. For each ITP case included in the study, 2 age-matched controls were randomly selected. Control cases were age-matched to within 1 year of their respective ITP case and were required to have a normal platelet count on their CBC at the time of presentation, as well as a complete vaccination history that included the type of vaccine given and date or month of last vaccination. If the time of vaccination was within 2 months of the date of presentation, the exact date was recorded.

Data Collection

Variables that were recorded for both ITP and control cases included sex, age, breed, and CBC results. Additional data that were collected in dogs with presumptive idiopathic ITP included results of coagulation profiles, bone marrow aspirates, diagnostic imaging, and infectious disease titers.

In dogs with presumptive idiopathic ITP, platelet recovery times and survival times were determined. Two separate platelet recovery times were calculated. The first was defined as the time from diagnosis of ITP to a platelet count of greater than 40,000 cells/μL and the second was defined as the time from diagnosis of ITP to a platelet count within reference range. Short-term survival was defined as the time in days from presentation to the PUVTH to discharge or death. Death that occurred spontaneously or because of euthanasia before discharge was considered ITP related. Long-term survival time was recorded as the duration of time in days from discharge to either death or the last known contact date. The follow-up information was gathered by phone conversation with the referring veterinarian.

Laboratory Methods

Values for the white blood cell count, red blood cell (RBC) count, RBC indices, and platelet counts were determined by standard automated and manual methods.2 Platelets were manually counted if the platelet number as determined by the automated analyzer was “clumped” or if the automated count was 50,000 cells/μL or less. This approach is standard practice for all CBC samples submitted to the Purdue University School of Veterinary Medicine Clinical Pathology Laboratory. Serum biochemistry analytes were determined by standard automated methods.3 The PT and PTT were analyzed by standard automated methods.4 Infectious disease titers were submitted to various reference laboratories. Most were submitted to the Louisiana Veterinary Medical Diagnostic Laboratory.

Data Analysis

Recent vaccination was defined as vaccination performed in the 42 days before presentation based on similar criteria used in a study that identified a relationship between ITP and recent immunization with the MMR vaccine in children.[17] To determine whether ITP was related to recent vaccination in dogs, the number of ITP cases vaccinated in the 42 days before presentation to the PUVTH was compared with the number of control cases that were vaccinated in the same time period.

Statistical analysis was performed using a commercial software program.5 Chi-square analysis was used to determine significant associations between ITP and recent vaccination. The Fisher's exact test was used to determine significant associations between proportionate survival of the group that was vaccinated 42 days before presentation and the group that was not vaccinated within that time period. A value of P < .05 was considered significant.

Results

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Study Populations

One-hundred and forty-four dogs were included into the study—48 dogs with presumptive ITP and 96 control dogs.

Within the ITP group, 24 breeds were represented. Mixed breed dogs constituted the majority of cases (38%) and no single breed was represented by more than 3 cases. Of the 48 dogs, 25 (52%) were spayed females, 18 (38%) were castrated males, 3 (6%) were males of unknown neuter status, 1 (2%) was an intact female, and 1 (2%) was a female of unknown neuter status. The median age at the time of diagnosis was 7 years (range: 2–15 years). The median weight of dogs with presumptive idiopathic ITP was 25.8 kg (range: 4.2–58.0 kg). The most common clinical signs of dogs with ITP at the time of presentation were petechiae (35/48, 73%) and ecchymotic hemorrhages (27/48, 56%). Other reported signs included melena (20/48, 42%), oral bleeding (18/48, 38%), hematoma formation or excessive bleeding from wounds and venipuncture sites (17/48, 35%), pale mucous membranes (13/48, 27%), ocular bleeding (11/48, 23%), hematochezia (9/48, 19%), heart murmur (9/48, 19%), hematemesis (9/48, 19%), hematuria (8/48, 17%), vestibular signs (5/48, 10%), and hemoptysis (4/48, 8%). Of the 48 dogs with presumptive idiopathic ITP, 46 (96%) had negative Rickettsia rickettsii antibody titers. The 2 cases without testing for antibodies against R. rickettsii did not have clinical signs consistent with infection such as lymphadenopathy or fever.[23] Most cases were tested for Borrelia burgdorferi (44/48, 92%) and 3 were positive. Two of the 3 tests were positive because of a Lyme vaccine based on Western blot testing. Forty-one (85%) of 48 presumptive idiopathic ITP cases were tested for antibodies against Babesia canis and all were negative. Many cases were also tested for antibodies to Ehrlichia platys (33/48, 69%) and all were negative. Fourteen (29%) were tested for Anaplasma phagocytophilum antibodies, all of which were negative. Of the 48 presumptive ITP cases, 10 (21%) were tested for Ehrlichia risticii antibodies, all of which were negative. All 48 dogs with presumptive ITP had thoracic and abdominal radiographs performed, and those of 37 (77%) and 34 (71%) dogs, respectively, were considered within normal limits. None of the minor radiographic abnormalities in the other dogs were considered to be related to the cause of thrombocytopenia. Forty-four (92%) of 48 dogs with presumptive ITP had an abdominal ultrasound performed and no evidence of an underlying cause of thrombocytopenia was identified. Thirty-six (75%) of 48 presumptive idiopathic ITP dogs had a bone marrow aspirate, a bone marrow core biopsy, or both that revealed either a normal number of megakaryocytes or megakaryocytic hyperplasia. Three dogs had bone marrow aspirate samples that demonstrated megakaryocytic hypoplasia, 2 of which were confirmed with a bone marrow core biopsy or upon necropsy. The other 9 dogs either had nondiagnostic bone marrow aspirate samples or did not undergo bone marrow sampling.

In the 96 control dogs, 42 breeds were represented. Seventeen dogs (18%) were of mixed breeding. There were 6 (6%) Labrador Retrievers, 6 (6%) Golden Retrievers, 5 (5%) Miniature Schnauzers, 5 (5%) Rottweilers, 5 (5%) Yorkshire Terriers, 4 (4%) Beagles, and 3 (3%) Jack Russell Terriers, with other breeds represented by no more than 2 cases. Of the 96 dogs, 44 (46%) were spayed females, 37 (39%) were castrated males, 6 (6%) were males of unknown neuter status, 5 (5%) were females of unknown neuter status, and 4 (4%) were intact male dogs. The control dogs were presented to the PUVTH for a variety of reasons including neoplasia (n = 27), neurologic disease (n = 13), urinary disease (n = 12), gastrointestinal disease (n = 10), orthopedic disease, including trauma (n = 9), respiratory disease (n = 8), endocrine disease (n = 5), ophthalmologic disease (n = 5), dermatologic disease (n = 3), behavioral aggression (n = 3), and pacemaker implantation (n = 1).

Comparison of Recent Vaccination between Groups

Four (8%) of the 48 dogs with presumptive ITP were vaccinated in the 42 days before presentation to the PUVTH compared with 13 (14%) of the control dogs. There was no statistical difference between the 2 groups (P = .361). The mean and median time from vaccination to presentation to the PUVTH for the presumptive ITP group were 281 and 198 days (range: 19–1,386 days), respectively, and 231 and 204 days (range: 6–1,397 days) for the control group.

ITP Population—Clinicopathologic Findings and Platelet Recovery Time

The median platelet count of all dogs with presumptive idiopathic ITP at the time of presentation was 1,000 cells/μL (range: 0–39,500 cells/μL). Twenty-five (52%) of the 48 dogs were anemic at presentation. The anemia was most commonly characterized as a normocytic (21/25, 84%), normochromic (23/25, 92%), highly regenerative anemia (13/18, 72%). The median hematocrit at the time of presentation was 27.1% (range: 7–59.9%). Sixteen (33%) of the 48 dogs with idiopathic ITP had a left shift present on the CBC.

Information regarding platelet recovery time to 40,000 cells/μL was available for 38 (79%) of 48 presumptive idiopathic ITP dogs—9 did not survive to discharge and 1 did not have a complete medical record. The median time to a platelet count of greater than 40,000 cells/μL for these dogs with information regarding platelet recovery time was 4 days (range: 1–15 days). Information regarding platelet recovery time to a platelet count within reference range was available for 36 (75%) of the ITP dogs. The median time to a platelet count within reference range for these dogs was 11 days (range: 2–42 days). Platelet counts for 2 of the 48 ITP dogs never completely normalized based on the last CBC recorded in the medical record.

ITP Population—Treatment

Forty-five (94%) of 48 dogs in the ITP group were treated with corticosteroids in the form of prednisone (dose range: 1–4 mg/kg/day PO)—most (35/45, 78%) received between 2 and 4 mg/kg/day. Twenty-one (44%) of the 48 ITP dogs received dexamethasone (dose range: 0.04–0.5 mg/kg/day IV). Eighteen of these dogs received the dexamethasone before initiating oral prednisone treatment, whereas the other 3 were never transitioned to oral prednisone because they did not survive to discharge.

Ten (21%) of the 48 presumptive ITP dogs were treated with azathioprine (2 mg/kg/day PO) before discharge, in addition to the above detailed doses of corticosteroids. The platelet recovery time to 40,000 cells/μL was available for 7 of these 10 cases and ranged from 4 to 12 days with a median of 6 days. The platelet recovery time to a platelet count within reference range for these 7 dogs ranged from 12 to 21 days with a median of 15 days. Seven (70%) of 10 dogs that received azathioprine survived to discharge.

Ten (21%) of the 48 presumptive ITP dogs received a single injection of vincristine (0.02 mg/kg IV) during hospitalization, in addition to the above-detailed doses of corticosteroids. Information regarding platelet recovery time was available for 8 of the 10 dogs that received vincristine. These 8 cases had a platelet recovery time to 40,000 cells/μL between 2 and 10 days with a median of 4 days. The time for the platelet count to reach reference range for these 8 cases was between 3 and 42 days with a median of 10 days. Nine (90%) of 10 dogs that received vincristine survived to discharge.

Six (13%) of the 48 presumptive ITP dogs received a single dose of human immunoglobulin (dose range: 0.35–0.81 g/kg IV), in addition to the above-detailed doses of corticosteroids. Platelet recovery times were available for 5 of the 6 dogs that received human immunoglobulin. The median platelet recovery time to 40,000 cells/μL was 5 days (range: 2–10 days). The median time for the platelet count to normalize was 12 days (range: 2–13 days). Five (83%) of 6 dogs that received human immunoglobulin survived to discharge.

Forty-six (96%) of the 48 presumptive ITP cases were treated with doxycycline (dose range: 5.8–17 mg/kg/day PO) and most were treated with a full 4-week course. Most dogs also received famotidine either IV or PO (35/48, 73%) and many received a sucralfate slurry PO (20/48, 42%). Other adjunctive treatments, after diagnosis of ITP, included ampicillin (8/48, 17%), ampicillin/sublactam (2/48, 4%), amoxicillin/clavulanic acid (1/48, 2%), cefazolin (1/48, 2%), enrofloxacin (4/48, 8%), prednisolone acetate 1% (7/48, 15%), timolol (2/48, 4%), artificial tears (2/48, 4%), neomycin-polymixin B-bacitracin ophthalmic ointment (2/48, 4%), diphenhydramine (4/48, 8%), butorphanol (3/48, 6%), hydromorphone (3/48, 6%), buprenorphine (2/48, 4%), tramadol (2/48, 4%), acepromazine (2/48, 4%), potassium gluconate (2/48, 4%), cimetidine (2/48, 4%), pentoxyfylline (1/48, 2%), vitamin K (2/48, 4%), meclizine (1/48, 2%), misoprostol (1/48, 2%), filgrastim (1/48, 2%), and fenbendazole (1/48, 2%).

Nineteen (40%) of the 48 presumptive ITP dogs required between 1 and 7 blood transfusions per dog in the form of whole blood or packed red blood cells (pRBCs). Most of the dogs received whole blood IV (15/19, 79%) at a dose between 7.4 and 44 mL/kg/transfusion with a median of 20 mL/kg/transfusion. Nine (47%) of the 19 ITP dogs that received a RBC transfusion received pRBCs, in addition to whole blood or alone at a dose of 4.5–27.5 mL/kg/transfusion with a median of 10.4 mL/kg/transfusion. Five (10%) of 48 presumptive ITP dogs received between 1 and 3 platelet transfusions per dog at a dose of 1.8–13.5 mL/kg/transfusion with a median of 8.7 mL/kg/transfusion.

ITP Population—Survival Data

Thirty-nine (81%) of the 48 presumptive idiopathic ITP dogs survived to discharge with a median hospitalization time of 6 days (range: 0–19 days). Follow-up information beyond discharge was not available for 1 of the 48 ITP dogs. Most (36/47, 77%) dogs with ITP survived to at least 1 month after discharge. Twenty (43%) of the 47 presumptive idiopathic ITP dogs that survived to discharge, survived beyond 1 year of discharge. Fourteen (70%) of those 20 dogs survived to beyond 2 years of discharge.

The median survival time beyond discharge was 439 days (range: 4–12,775 days). Only 1 of the 4 (25%) presumptive ITP dogs that was vaccinated within 42 days did not survive to discharge—this dog was euthanized because of a poor prognosis. The other 3 dogs survived beyond discharge—1 was euthanized 12 days later after discharge because of development of disseminated intravascular coagulation (DIC), which was diagnosed at necropsy, 1 had a last known contact time of 1,719 days after discharge, and 1 had a last known contact time of 3,154 days after discharge. Eight of the 44 (15%) presumptive ITP dogs that were not vaccinated within 42 days did not survive to discharge from the hospital. Those surviving ITP dogs that were not vaccinated within the 42 day time period had last known contact dates ranging from 4 days to 1,923 days and had a median survival time beyond discharge of 303 days. There was no statistically significant difference between the proportion of nonsurviving ITP dogs that were vaccinated in the 42 days before presentation and nonsurviving ITP dogs that were not vaccinated within this time period (P = .514).

Discussion

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

In our study, a diagnosis of presumptive idiopathic ITP was not found to be associated with recent vaccination. This result is consistent with findings by Putsche and Kohn where none of their 30 dogs with primary ITP had been vaccinated within 4 weeks before the onset of clinical signs.[24] However, the types of vaccines that were given to their population were not reported. We did attempt to evaluate whether the type of vaccine administered was related to the incidence of ITP diagnosed within 42 days after immunization; however, there were too few cases of ITP diagnosed within this time period to allow meaningful conclusions.

Although this study failed to find an association between recent vaccination and idiopathic ITP in dogs, the possibility of a causal relationship remains. In children, ITP has been associated with administration of vaccines for hepatitis B, tick-borne encephalitis, influenza, diphtheria-pertussis-tetanus, chicken-pox, human papillomavirus, and MMR vaccines.[15, 25-29] Of these, recent vaccination with the MMR vaccine in children has been most commonly associated with the development of ITP.[15, 25, 30, 31] Thrombocytopenia in these patients can result in clinical bleeding and purpura, but the thrombocytopenia typically resolves spontaneously within 1 month.[25] The platelet count nadir generally occurs 21 days after the vaccination and can be as low as 1,000 cells/μL; however, within 1 month the platelet counts are usually greater than 100,000 cells/μL.[31] The incidence of ITP after MMR vaccination is quite rare, occurring in only 1 in 21,000 to 40,000 inoculations.[32] It is possible that vaccine-associated ITP in dogs is similarly rare and would not have been detected by this study.

The relationship between vaccination and another immune-mediated hematologic disease, immune-mediated hemolytic anemia (IMHA), has been evaluated in dogs in 2 studies and results are conflicting. In 1 study, an association was noted between recent vaccination, defined as vaccination within 4 weeks of presentation, and the development of IMHA.[33] In that study, an increased number of IMHA cases (26%) were vaccinated within the 4 weeks before the onset of illness compared with a control population. A 2nd study, however, failed to identify a similar relationship.[34] Neither study documented the nature or number of all previous vaccinations, factors that may have predisposed dogs to an adverse immune-mediated event. The association between vaccination and other autoimmune disease in dogs, such as polyarthropathy or masticatory myositis, has not been investigated.

Given the retrospective nature of this study, we were limited by the information that was available for analysis. Information regarding the number of vaccinations during a dog's lifetime was not consistently available and could be an important factor in risk of development of ITP. It is possible that chronic immune stimulation by sequential vaccine administration is required to trigger an event in a susceptible dog. Another limitation of this study is the difficulty inherent in confirming a diagnosis of idiopathic ITP in dogs. None of the dogs with presumptive ITP were tested for antiplatelet antibodies and some of the dogs may have had thrombocytopenia of non-immune-mediated origin. However, this possibility is considered low given that all dogs had thorough diagnostic testing to exclude most underlying causes of thrombocytopenia, the majority dogs survived to discharge, and the majority of dogs had a good response to immunosuppressive treatment. Some ITP cases could have had thrombocytopenia secondary to a tick-borne disease that was not identified via antibody testing. However, all cases were negative for E. canis, one of the more common tick-borne causes of thrombocytopenia in our geographic region, and only 2 ITP cases did not have testing for antibodies against R. rickettsii. Those 2 cases did not have any other clinical signs typically associated with R. rickettsia infection such as fever, vasculitis, edema, or lymphadenomegaly making Rocky Mountain Spotted Fever very unlikely to be the cause of thrombocytopenia.[23] Although 4 cases of presumptive idiopathic ITP (8%) did not have testing for B. burgdorferi and 1 (2%) had a 1 : 60 antibody titer, a negative antibody titer for B. burgdorferi was not required for inclusion into the study because, to our knowledge, Lyme disease has not been definitively associated with thrombocytopenia. A negative antibody titer for B. canis was not required for inclusion despite its well-documented effect on platelet counts as it is uncommonly seen in this geographic area. In addition, the 7 cases that lacked titer submission did not have any laboratory findings consistent with B. canis infection such as evidence of hemolysis or autoagglutination.[35]Anaplasma phagocytophilum is a tick-borne disease frequently associated with thrombocytopenia and unfortunately, very few cases in the ITP group were tested for this infection. Most presumptive idiopathic ITP cases did not have convalescent antibody titers either, therefore, some may have in fact, been cases of secondary ITP. Antinuclear antibody testing was not performed in these dogs because they did not fit the diagnostic criteria for systemic lupus erythematosus.[36] Complete laboratory testing for DIC was not available as tests, such as antithrombin activity, fibrinogen concentrations, fibrin degradation product concentrations, and d-dimer concentrations, were not routinely performed.[37] It is possible that thrombocytopenia in some dogs in the ITP group could have been attributed to the presence of occult DIC. This possibility was considered unlikely given that most cases of DIC have an identifiable underlying disease process known to lead to activation of coagulation and no such disease process was identified in the presumptive ITP population, nor did the dogs have clinical signs associated with severe disease other than bleeding. The small sample size was also a limiting factor in our study and further studies examining the vaccination status of larger populations of idiopathic ITP are warranted.

Our findings raise the question of whether clinicians should be avoiding or advocating routine vaccination of dogs with a history of ITP. Unfortunately, this study was not designed to answer this specific question. In humans, the majority of children with previously diagnosed ITP did not develop recurrence of thrombocytopenia following further immunization.[17, 25, 30, 38, 39] However, sporadic reports of ITP relapses after revaccination do exist.[40] Further case-control studies with a larger sample population should be performed to determine whether further vaccination of dogs with a history of ITP is recommended.

This study failed to find a clinically significant relationship between recent vaccination and ITP in dogs; however, the possibility of an infrequent association cannot be ruled out. Although the relationship exists in humans, the incidence of ITP following vaccination is rare,[32] which might also be the situation in the canine population. The results of this study suggest that the incidence of ITP within 42 days of vaccination could be considered too small to be clinically relevant. Thus, we conclude that the benefits of routine vaccination in dogs likely outweigh the risk of vaccine-associated ITP. Although vaccination should continue to be advocated, the decision to vaccinate should be determined on an individual basis. In addition, this study did not rule out the possibility of a transient, nonclinical ITP postvaccination. Whether previously diagnosed cases of idiopathic ITP should be revaccinated requires further investigation.

Acknowledgment

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

The study was not supported by any grants.

Footnotes
  1. 1

    Veterinary Medical Database, School of Veterinary Medicine, Purdue University, West Lafayette, IN (http://www.vmdb.org); VMDB does not make any implicit or implied opinion on the subject of the article or study

  2. 2

    Cell-Dyn 3700, Abbott Laboratories, Abbot Park, IL

  3. 3

    Vitros 5.1 Chemistry System, Ortho-Clinical Diagnostics, Rochester, NY

  4. 4

    STA Compact, Diagnostica Stago, Parsipanny, NJ

  5. 5

    STATA SE 11.1 StataCorp, College Station, TX

References

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References