thrombocytopenia is the most commonly occurring platelet disorder in dogs , with a prevalence rate among the admissions to one us hospital of approximately 5% .
thrombocytopenia may result from a variety of pathophysiological mechanisms including reduced platelet production , increased platelet sequestration , increased platelet utilisation or destruction .
immune - mediated thrombocytopenia ( imtp ) is a disease characterised by the premature destruction of antibody - coated platelets by macrophages .
this disease may occur as a primary disease , termed primary imtp or idiopathic thrombocytopenic purpura , or as a secondary disease associated with conditions such as neoplasia , inflammation or infection .
the pathogenesis of primary imtp is thought to involve the production of antibodies directed against normal host platelet - surface antigens , whereas in secondary imtp the pathogenesis remains largely undefined .
angiostrongylus vasorum is a metastrongyloid nematode that parasitises dogs and other canidae via an indirect lifecycle involving slugs , snails and frogs that act as intermediate or paratenic hosts .
the first report of angiostrongylus vasorum infection in ireland was in a greyhound . following this ,
the infection became well - recognised within greyhound kennels in ireland   and the first reported case in england was a greyhound that had been imported from ireland .
more recently , angiostrongylus vasorum infection has been reported in several pet dogs in ireland ; however , the overall prevalence of the nematode in this country is unknown .
commonly reported clinical signs include cardiopulmonary signs such as coughing , exercise intolerance and dyspnoea . in some cases progression of the signs to right - sided heart failure   or sudden death attributed to acute heart failure  
coagulopathies have also been widely reported in association with both naturally occurring and experimental angiostrongylus vasorum infections .
in addition , neurological and ocular signs have been documented   or more general signs such as weight loss , poor growth and weakness .
thrombocytopenia has been reported in association with angiostrongylus vasorum infection in a number of canine cases   with reported incidences in the two largest case series of four out of 20 cases   and two out of 35 cases . in one of the previous cases ,
the cause of the thrombocytopenia was demonstrated to be immune - mediated . in other cases the cause has been attributed to a consumptive coagulopathy resembling disseminated intravascular coagulation .
this case report describes the presentation , diagnosis and successful treatment of a jack russell terrier with severe immune - mediated thrombocytopenia associated with angiostrongylus vasorum infection . to the authors ' knowledge
, this is only the second report of imtp and angiostrongylus vasorum infection and is the first to be diagnosed antemortem .
a twenty - month - old male entire jack russell terrier was presented to the university veterinary hospital ( uvh ) , university college dublin with a four - day history of thrombocytopenia , small inguinal echymotic haemorrhages , coughing and reduced exercise tolerance .
the referring veterinarian had performed bronchoscopy on day one , which had revealed a stream of blood running ventrally along the trachea , appearing to source from the right main - stem bronchus .
the bronchoscopy had been terminated at this stage and further examination had revealed small echymotic haemorrhages in the inguinal region .
treatment with vitamin k1 ( konakion ; roche ) at a dose of 10 mg twice daily per os had been commenced and a blood sample submitted to the uvh clinical pathology laboratory for haematology and a coagulation screen .
the haematology results were received on day three and revealed severe thrombocytopenia ( 2.0  10/l ) , evidence of increased erythrocyte turnover but without anaemia ( packed cell volume ( pcv ) 0.38
l / l ) , a mature neutrophilia ( 16.8  10/l ) and a monocytosis ( 2.6  10/l ) .
there was no known access to rodenticides and the dog had not received drug therapy other than vitamin k1 .
the dog was bright , alert and in good body condition ( weight 7.3 kg ) . only very occasional
coughing had been observed since first presentation , although exercise intolerance was apparent . a clinical examination revealed pink mucous membranes with a normal capillary refill time .
the respiratory rate was approximately 36 breaths per minute with a slight increase in lung sounds noted bilaterally on auscultation .
there were several petechial haemorrhages evident on the gingivae , along with mild bilateral epistaxis and the inguinal echymoses .
haematology at the time of referral ( day four ) demonstrated severe thrombocytopenia ( 1.0  10/l machine count , confirmed as accurate on examination of a smear ) accompanied by a mild , regenerative anaemia ( pcv 0.27
g / l ) and mild elevation of serum alkaline phosphatase ( 103 u / l ) .
thoracic radiography ( figure 1 ) revealed a widespread mixed alveolar - interstitial lung pattern .
this was apparent throughout the lungfield , but was particularly marked within the left lung lobes , which contained subtle air bronchograms .
pleural fissure lines were visible between both the right middle and right caudal lobes and the accessory and left caudal lung lobes , however a significant pleural effusion was not discernable .
right lateral ( a ) and dorsoventral ( b ) thoracic radiographs taken on the day of referral ( day four ) , showing a widespread mixed alveolar - interstitial lung pattern .
this is visible throughout the lungfield , but is particularly marked within the left lung lobes .
pleural fissure lines are visible between both the right middle and right caudal lobes and the accessory and left caudal lung lobes , however a significant pleural effusion is not discernable .
a presumptive diagnosis of immune - mediated thrombocytopenia was made and treatment was commenced on day four with vincristine ( vincristine ; faulding pharmaceuticals ltd . ) at a single dose of 0.02 mg / kg i / v and prednisolone ( prednicare ; animalcare ) at a dose of 2.7 mg / kg split twice daily per os ( 10 mg twice daily ) . the dog was confined to strict cage rest with minimal handling to minimise the risk of spontaneous haemorrhage . over the next three days of hospitalization coughing or changes in respiratory rate were not observed .
several small echymotic haemorrhages developed on the ventral abdomen on day two of hospitalisation ( day six ) but other signs were not observed , although his appetite was poor .
significant change in the platelet count was not observed over the first three days of treatment . on the fourth day of hospitalisation ( day seven ) , the pcv had dropped to 0.19 l / l despite the absence of evidence of further bleeding on clinical examination .
spherocytes were not noted on the blood smear and a coombs ' test was negative . at this stage ,
gastrointestinal blood loss was a concern and treatment was commenced with ranitidine ( zantac ; glaxowellcome ) at a dose of 2 mg / kg every eight hours and sucralfate ( antepsin ; chugai ) at a dose of 400 mg every eight hours .
, major and minor cross matches were performed against two blood donors in case of a requirement for a blood transfusion should the dog deteriorate further .
severe thrombocytopenia ( 6.0  10/l ) was still apparent following an automated platelet count , however manual counts revealed approximately five platelets per high power field , suggesting higher numbers were present and some platelet clumping was occurring .
faeces passed at the end of day seven , showed evidence of both melaena and haematochezia .
angiostrongylus vasorum l1 larvae were identified in the faecal sample confirming a patent infection with the parasite .
treatment was commenced with fenbendazole ( panacur ; hoechst ) at a dose of 50 mg / kg daily for seven days in addition to the prednisolone , ranitidine and sucralfate . the dog continued to be bright over the next four days and showed no clinical evidence of haemorrhage or melaena . on day eleven of hospitalisation ( day 14 of the history ) , the platelet count had risen to 24.0  10/l , although examination of the smear again identified platelet clumping suggesting the true count was considerably higher . a buccal mucosal bleeding time was performed to confirm adequate primary haemostasis ; a normal result was obtained and the dog was discharged .
the prednisolone was continued at a dose of 1.4 mg / kg ( 10 mg ) per os daily and the seven - day course of fenbendazole completed .
after two weeks the prednisolone was reduced to 0.7 mg / kg ( 5 mg ) per os daily .
the dog was re - examined at the uvh three weeks after the initial referral . at this stage
residual clinical signs were not apparent and the platelet count was within the reference range .
the prednisolone dose was reduced to 0.7 mg / kg ( 5 mg ) per os every 48 hours for one week and then 0.35 mg / kg ( 2.5 mg ) every 48 hours for a further week before being completely withdrawn .
thrombocytopenia may result from reduced platelet production , increased platelet sequestration , increased platelet utilisation or destruction .
consumptive coagulopathies represent the most common cause of increased platelet utilisation , whereas immune - mediated thrombocytopenia , either primary or secondary , is the most common cause of increased platelet destruction .
imtp may occur in association with other immunological diseases such as systemic lupus erythematosus   or secondary to other conditions such as neoplasia , inflammation and infection   or following drug administration . in dogs ,
the infectious processes that have been reported in association with thrombocytopenia include ; bacterial infections , rickettsial infections and parasitic infections   including both dirofilariasis   and angiostrongylosis .
these infectious agents have the potential to induce autoimmunity via a variety of immunological mechanisms , for example molecular mimicry or the induction or alteration of host antigens . however ,
the potential role that these or other immunological processes might play in canine secondary , infection - related impt cases remains largely undefined .
a variety of criteria have been used to confirm a diagnosis of canine primary imtp , including ; the severity of thrombocytopenia , the presence of microthrombocytosis or platelet fragmentation , detection of anti - platelet autoantibodies , increased platelet counts following the administration of immunosuppressive doses of corticosteroids , normal to increased numbers of megakaryocytes in bone marrow and the exclusion of other aetiologies of thrombocytopenia .
firstly , whilst a positive test result for either platelet - bound or serum platelet - bindable igg in a dog with thrombocytopenia implies an immune pathogenesis , it does not aid differentiation between primary and secondary imtp . secondly ,
whilst direct assays for surface - bound antibodies in imtp offer high sensitivity compared to that achieved by indirect assays detecting serum antibodies , these direct assays can be difficult to perform in cases with very severe thrombocytopenia due to insufficient platelet numbers . performing a megakaryocyte direct immunofluorescence assay
may alleviate the latter problem , however the reported sensitivity with this test is highly variable ( 30% to 80% ) .
hence , this test has the potential to generate significant numbers of false negative results and has the additional disadvantage of requiring a bone marrow aspirate .
more recently platelet - bound antibodies have been evaluated by flow cytometric assay alleviating the problems associated with low platelet numbers , however this technique still does not allow the differentiation between primary and secondary imtp . in view of the limitations of the immunological testing outlined above and the limited availability of anti - platelet antibody tests , a presumptive diagnosis of imtp
this diagnosis was based on the initial severity of the thrombocytopenia , the response to immunosuppressive corticosteroid therapy and the exclusion of a consumptive coagulopathy .
the initial severity of the thrombocytopenia has been suggested to be a reliable feature of impt cases .
a response to corticosteroid therapy provides evidence of an immune - mediated pathogenesis ; typically imtp cases will have platelet counts of greater than 50 to 100  10/l within seven days of initiating treatment .
there is no definitive laboratory test to confirm a diagnosis of disseminated intravascular coagulation ( dic ) ; however , low platelet counts , erythrocyte fragmentation on peripheral blood smears , prolonged clotting times , low levels of antithrombin , and high levels of fibrin degradation products are accepted to be helpful indicators . in this dog
in addition , the thrombocytopenia was more marked than would typically be associated with dic ; thrombocytopenia at this level being much more typical of imtp . ideally , measurement of fibrin degradation products or d
- dimers would have provided further evaluation for dic . however the fdp assay was not performed due to a lack of reagents when a sample was submitted ( day four ) to an external laboratory , and unfortunately the sample was not retained .
a d - dimer assay was not available at the time . despite this , in view of the lack of other suggestive signs and the response to treatment , the diagnosis of dic was considered highly unlikely .
the majority of reported cases of angiostrongylosis have occurred in young dogs , as in this case .
a wide variety of clinical signs have been associated with infection , with respiratory signs , such as coughing , widely accepted as one of the most common clinical signs , as was observed in this current case .
clinical signs relating to a haemorrhagic diathesis are also common , reported to occur in approximately one third of the cases .
subcutaneous , mucosal and internal bleeding have all been reported , including haemorrhage within the central nervous system .
the mechanism underlying this bleeding tendency remains poorly characterized ; various mechanisms have been proposed including chronic disseminated intravascular coagulation , acquired von willebrand 's disease   and immune - mediated thrombocytopenia .
thrombocytopenia has been reported in association with angiostrongylus vasorum infection in a number of canine cases . in general the thrombocytopenia
reported in these cases has been mild to moderate ; none of the cases in the chapman series presented with severe thrombocytopenia . in a series of experimentally infected dogs  
the mean platelet count in infected dogs was significantly lower than in the control dogs for approximately six months post infection , with the lowest mean thrombocyte count being about 100  10/l post infection .
in one previous case , the thrombocytopenia was demonstrated to be immune - mediated . on post mortem examination , this dog was additionally confirmed to have myocarditis , thrombosing arteritis , pneumonia and chronic membranoproliferative glomerulonephritis .
dogs with angiostrongylosis and resultant bleeding diatheses were evaluated as part of two recent case series , yielding very variable causes for the haemorrhage .
collectively these studies examined ten such dogs ; one dog was mildly thrombocytopenic , two had mild thrombocytopenia and prolonged coagulation times , six had prolonged coagulation times alone and one had no demonstrable abnormality in haemostatic function .
hence , further investigations are required in order to fully characterize the mechanisms involved in the bleeding tendency infected dogs often show .
in general , although disorders of both primary and secondary haemostasis have been reported to occur with angiostrongylus infection , thrombocytopenia as the primary cause is uncommon .
the current case is the first reported case in which immune - mediated thrombocytopenia was observed in association with angiostrongylus vasorum infection and successfully treated .
it has been reported that approximately 40% of primary imtp cases show a recurrence of clinical signs .
it would be expected that if this current case showed imtp secondary to angiostrongylus vasorum infection , there would be no recurrence of the signs following treatment of the lungworm infection .
this dog was weaned off corticosteroids within five weeks and has since shown no recurrence of signs in seventeen months .
hence , there is some circumstantial evidence that the angiostrongylus vasorum infection may be linked to the imtp ; however , it can not be confirmed .
this is the first case report to describe the successful treatment of immune - mediated thrombocytopenia associated with angiostrongylus vasorum infection .
imtp in association with a. vasorum infection has been described previously ; however , the previous case was diagnosed post mortem .
both cases highlight the requirement to evaluate imtp cases for an underlying cause and the potential for a. vasorum infection to trigger immune - mediated platelet destruction .
the mechanism by which this destruction is triggered in the disease , whether it represents immune - complex deposition on platelets or the direct generation of anti - platelet antibodies , requires further evaluation .
the authors would like to colin rohu , the referring veterinarian , for referring this case to the university veterinary hospital and providing follow - up information .
in addition , the help of the nursing and laboratory staff along with the final year students on rotation is gratefully acknowledged .
 a twenty - month - old jack russell terrier was presented with a four - day history of thrombocytopenia , echymotic inguinal haemorrhages , coughing and reduced exercise tolerance . 
 clinical examination revealed several petechial haemorrhages on the gingivae and small echymotic haemorrhages in the inguinal region , along with mild bilateral epistaxis . 
 haematology confirmed a platelet count of 1.0  10/l . 
 thoracic radiographs revealed a wide - spread mixed alveolar - interstitial lung pattern , apparent throughout the entire lungfield , but particularly marked within the left lung lobes . 
 a presumptive diagnosis of immune - mediated thrombocytopenia was made and the dog was treated with vincristine and immunosuppressive doses of prednisolone . initially anaemia developed following gastrointestinal haemorrhage ; however , after symptomatic treatment the dog showed a marked clinical improvement . 
 evaluation for an underlying cause of the disease revealed angiostrongylus vasorum l1 larvae on faecal analysis and treatment with fenbendazole was commenced . 
 the dog made a full clinical recovery with all treatment was withdrawn within five weeks of diagnosis . 
 this is the second report of immune - mediated thrombocytopenia associated with angiostrongylus vasorum infection and it is the first to be successfully managed . 
 the report highlights that angiostrongylus vasorum should be considered in young dogs presented with thrombocytopenia . 
Introduction
Case History
Discussion
Conclusions
Acknowledgements