Drug-induced thrombocytopenia

A variety of drugs may cause thrombocytopenia. Although it occurs more often than drug-induced anemia it is less well understood because techniques for studying drug-platelet-immune interactions have been unavailable until recently. The mechanisms by which drugs cause thrombocytopenia are varied. Bone marrow suppression or increased peripheral destruction of platelets could be involved. Nonimmunologic as well as immunologic mechanisms may also occur. These different mechanisms of drug-induced thrombocytopenia are reviewed. Diagnostic methods and treatment are also summarized.

Mechanism of thrombocytopenia in African swine fever

Pigs were inoculated with an African swine fever (ASF) isolate of moderate virulence, and the changes in the number of circulating blood platelets during infection were correlated with the appearance of antiviral antibody and fluctuations in total plasma hemolytic complement concentrations. Thrombocytopenia was detected by postinoculation days (PID) 7 and 8, and antiviral antibody was detected by PID 7, using an indirect immunofluorescence technique. The total hemolytic complement concentration was moderately and transiently decreased from PID 5 to 9, but was consistently low from PID 18 to 26. Pigs inoculated with an ASF virus isolate of greater virulence had a decrease in platelet counts on PID 6 and 7, and the total plasma hemolytic complement levels decreased in all pigs by PID 6 to 7. Antibody to ASF virus was not detected in pigs inoculated with the more virulent isolate. Pigs sensitized to ASF viral antigen with an inactivated-virus vaccine or by previous infection with ASF were challenge exposed. Sensitized pigs became clinically ill and thrombocytopenic by 24 to 72 hours earlier than did inoculated, nonsensitized pigs. Vaccinated pigs inoculated with homologous virus had lower blood virus concentrations than did nonvaccinated pigs. African swine fever virus-sensitized pigs inoculated with heterologous virus had a higher fatality rate than did nonsensitized pigs, and the pigs died peracutely, with only a few gross lesions in evidence. In vitro experiments demonstrated that ASF virus antigen induced platelet aggregation in platelet-rich plasma from recovered, nonviremic pigs. Viral antigen, antibody, or complement was not demonstrable on the surface of platelets from pigs inoculated with ASF virus isolate, by direct immunofluorescence testing.

Splenectomy as adjunctive therapy for immune-mediated thrombocytopenia and hemolytic anemia in the dog

Splenectomy was done in 9 dogs having immune-mediated hematologic disorders refractory to medical therapy. These disorders were immune-mediated thrombocytopenia (n = 3), immune hemolytic anemia (n = 3), and Evan's syndrome (n = 3). The diagnoses were based on clinical observations, laboratory test data, and differential of other conditions. In the 12 months after splenectomy was done, the dogs reflected clinical improvement and return of platelet and/or erythrocyte counts to clinically acceptable limits; medical treatment was stopped or reduced in 8 of 9 patients. The exceptional patient had shown clinical improvement without change in the platelet count. At the end of 1 year, survival rate was excellent, and postsplenectomy complications, such as hemobartonellosis, did not appear. It is believed that splenectomy may be useful for treating immune-mediated thrombocytopenia, anemia, and Evan's syndrome that seem refractory to medication.

Bone marrow necrosis in the dog

Bone marrow necrosis in 4 dogs was characterized by refractory anemia with or without leukopenia and thrombocytopenia. Romanovsky-stained bone marrow had a diffuse blue discoloration, and marrow particles were elongated. Degenerating cells, cellular debris, and vacuolated macrophages also were seen. Examination of bone marrow sections revealed extensive replacement of normal stroma by necrotic debris and hemorrhage. The cause of the necrosis was not determined. Concomitant disorders included chronic ehrlichiosis, estrogen toxicosis, malignancy, endometrial cystic hyperplasia, and glomerulonephritis.

Suspected immune-mediated megakaryocytic hypoplasia or aplasia in a dog

Megakaryocytic hypoplasia or aplasia causing thrombocytopenia was diagnosed in a 3-year-old Miniature Poodle with scleral hemorrhage, melena, ecchymoses, and blood-loss anemia. Immunosuppressive, cytotoxic, and lithium carbonate therapy resulted in successful correction of the dog's disease. It is important to recognize megakaryocytic hypoplasia or aplasia as the cause of thrombocytopenia, since the response to therapy will be slower when there is stem cell injury.

Thrombocytopenia associated with vaccination of a dog with a modified-live paramyxovirus vaccine

Thrombocytopenia (10,000/mm3), with hematochezia and melena, appeared in a dog 8 days after it was given modified-live canine distemper, virus vaccine and persisted for approximately 5 days. Clinical investigation discounted other possible causes of thrombocytopenia; the condition was considered to be associated with vaccination. The problem spontaneously resolved. The appearance of thrombocytopenia after modified-live canine distemper virus vaccination is not unknown and may assume a severe form. This condition may be mistaken for idiopathic thrombocytopenia of immune origin, and in other instances, it may contribute significantly to surgical risk if concurrent coagulation disorders are present. Administration of levamisole HCl may alleviate the decrease in platelet count in affected animals.

Megakaryocytic infection and thrombocytopenia in African swine fever

Pigs infected with an African swine fever field isolate of modified virulence became acutely thrombocytopenic four to five days after the onset of fever and viremia. By eight days after inoculation, all pigs were thrombocytopenic. Immunofluorescence microscopy demonstrated that 2 to 10% of the megakaryocytes were infected. By 13 days after inoculation, platelet counts returned to within normal limits, and there was megakaryocytic hyperplasia despite a continued viremia. Secondary complications delayed the return of normal circulating platelet levels in some pigs. The clinical findings of African swine fever are discussed in light of the gross and histologic lesions.

An appraisal of bone marrow biopsy in assessment of sick dogs

Dogs were classified into a number of disease categories according to hematological, cytological and serochemical changes. Aspiration and core bone marrow biopsies were examined in 128 dogs in the various disease categories and compared to marrow samples in 36 dogs which appeared clinically normal. Differential cell counts on bone marrow smears were examined in relation to the blood variables in all animals. Blood and bone marrow data (group means) were compared among the normal and disease groups. Anemia, responsive and poorly responsive was the most frequent blood abnormality. Most dogs in the thrombocytopenia group had increased numbers of megakaryocytes in the marrow but two dogs had a marked decrease. The frequency of serious alteration of marrow production of the erythroid, myeloid and megakaryocytic series was less than anticipated. Marrow hemopoiesis was not significantly compromised in dogs with lymphoma or in dogs with other types of cancer. Bone marrow examination was necessary for the diagnosis of myelofibrosis and pancytopenia and was very helpful in the groups with insufficient change in the blood to permit a definitive diagnosis to be made. The myeloid-erythroid ratio was a useful indicator of marrow response while the erythroid maturation index and the myeloid maturation index were useful for identification of altered patterns of maturation (ineffective hemopoiesis). The reticulocyte response in absolute numbers is the most efficient and clinically relevant measure of erythroid response.

Reproduction of acute bracken poisoning in a calf with ptaquiloside, a bracken constituent

Acute bracken fern toxicity in a calf was reproduced with ptaquiloside, a norsesquiterpene glucoside, isolated from the boiling water extract of bracken fern. Ptaquiloside was dissolved in 500 ml of saline and administered by drench at increasing dosages for six days out of every seven for the following periods: 400 mg/day for 24 days, 800 mg/day for 14 days and 1600 mg/day for four days. Neutrophilic granulocytes began to decrease markedly around 50 days after the start of the experiment, and granulocytopenia continued for a further 35 days until the autopsy, despite the discontinuance of ptaquiloside administration. Thrombocytes showed a relatively slow depression and reached 1 X 10(5)/mm3 at the lowest level. The calf was autopsied 86 days after the start of administration of ptaquiloside. Sternal bone marrow was found to be mostly replaced with fat marrow and only small foci of erythropoietic cells and a small number of megakaryocytes remained.

Immune-mediated disorders of cats

Immune-mediated disorders in cats share many clinical and pathologic similarities with their counterparts in other species. Cats, however, are unique among domestic animals owing to the involvement of feline leukemia virus. In addition, a number of other infectious organisms can produce immune-mediated sequelae--that is, FIP virus, FeSFV, and H. felis. Therefore, the diagnostic and therapeutic aims in the management of feline immune-mediated disorders must take into account the probability of a primary or underlying disease process.

Propylthiouracil-associated hemolytic anemia, thrombocytopenia, and antinuclear antibodies in cats with hyperthyroidism

Nine of 105 cats with hyperthyroidism treated with propylthiouracil developed a serious immune-mediated drug reaction during treatment. Adverse clinical signs, which developed after 19 to 37 days (mean, 24.8 days) of propylthiouracil administration, included lethargy, weakness, anorexia, and bleeding diathesis. Physical examination revealed pale mucous membranes, and petechial hemorrhages of the skin and oral cavity. Results of hematologic testing revealed severe anemia and thrombocytopenia. The direct antiglobulin (Coombs') test was positive in all 7 cats evaluated, whereas the serum antinuclear antibody titer was greater than or equal to 1:10 in 5 of the 8 cats tested. In 4 of the cats, treatment included appropriate supportive therapy and cessation of propylthiouracil; in these cats, anemia and thrombocytopenia resolved and Coombs' and antinuclear antibody tests became negative within 2 weeks.

Lymphosarcoma and associated immune-mediated hemolytic anemia and thrombocytopenia in horses

Three horses with equine lymphosarcoma were examined because of clinical signs including chronic weight loss, respiratory distress, peripheral edema, and chronic colic. Clinicopathologic findings included evidence of an immune-mediated hemolytic anemia. Immune-mediated thrombocytopenia also was diagnosed in 1 of the horses and suspected in another. One horse died in spite of treatment, 1 died 5 hours after surgical removal of a tumor encircling the jejunum, and 1 was euthanatized because of deteriorating condition. Necropsy of each horse revealed extensive neoplastic infiltration of peripheral lymph nodes and abdominal or thoracic viscera with neoplastic lymphocytes.

Treatment and thrombocyte levels in experimentally induced canine ehrlichiosis and canine babesiosis

Three dogs which were carriers of Babesia canis were infected with Ehrlichia canis. These animals developed clinical signs and haematological evidence of ehrlichiosis and made an uneventful recovery, despite the fact that they were subsequently treated with doxycycline only. Three control dogs which were also carriers of B. canis were clinically normal, despite the fact that they showed a distinct drop in the thrombocyte levels associated with increases in the numbers of parasitized red cells.

Serologic diagnosis of infectious cyclic thrombocytopenia in dogs using an indirect fluorescent antibody test

An indirect fluorescent antibody test was used for detection of serum antibodies to the platelet-specific rickettsial organism that is the causative agent of infectious cyclic thrombocytopenia (ICT) in dogs. The test converted from negative to positive in 7 of 7 experimentally inoculated dogs. One of 2 attempts to recover the rickettsial agent of ICT from naturally occurring seropositive dogs, by blood inoculation of experimental dogs, was successful. Seemingly, the test did not detect antibodies to Ehrlichia canis, nor did a similar test, using E canis antigen slides, detect antibodies to the rickettsial agent of ICT. The rickettsial agent of ICT has been classified tentatively as E platys. When applied to sera from a group of healthy random-source dogs, the test revealed a relatively low (5%) occurrence of positive reactions. A higher occurrence of positive reactions (35%) was noticed in sera from a group of thrombocytopenic dogs from the University of Florida. A majority of these positive sera were also positive for antibodies to E canis. The highest occurrence of positive reactions was found (greater than 50%) in E canis-positive sera from dogs at the University of Florida, as well as from dogs from 9 other states.

Disseminated intravascular coagulation in six horses

Disseminated intravascular coagulation (DIC) was diagnosed as a secondary disease in 6 horses. Four horses had localized and/or systemic sepsis, one horse had disseminated neoplasia, and one had idiopathic ulcerative enteropathy. The diagnosis of DIC was based on the finding of at least 3 of 4 abnormalities: thrombocytopenia, prolonged prothrombin time, prolonged activated partial thromboplastin time, and a high concentration of fibrinolytic degradation products. The most common clinical signs other than those attributable to the primary disease process were abnormal hemorrhage (4 hours) and venous thrombosis (4 horses). All horses eventually died or were euthanatized because of the severity of the primary disease.

Pathology of the mononuclear cell leukemia of Fischer rats. II. Hematology

Complete hemograms were evaluated for 57 rats with mononuclear cell leukemia and compared to hemograms obtained from 52 age- and sex-matched nonleukemic rats. All leukemic rats had marked hemolytic anemia and associated spherocytosis, reticulocytosis, anisocytosis, and polychromasia. The anemia varied with the stage of illness and was more severe in rts with advanced leukemia. Death appeared to be related to anemia. There was a marked neutrophilia with left shift, mild lymphopenia, and moderate to severe thrombocytopenia. Atypical mononuclear cells were detected in circulation in all but three rats. Total white blood cell counts ranged from 5.0-370 x 10(3) cells/ml. There was an increase in erythrocyte osmotic fragility with separation into two distinct populations of erythrocytes. Eight of nine rats were Coombs' positive indicating an immune-mediated pathogenesis for the anemia. Hemostasis tests revealed a markedly prolonged prothrombin time, hypofibrinogenemia, slightly increased to normal partial thromboplastin time, and undetected fibrin degradation products. These findings suggest significant liver disease associated with the leukemia.

Vincristine in the treatment of thrombocytopenia in five dogs

Five dogs with idiopathic thrombocytopenic purpura were successfully treated with vincristine alone or in combination with a glucocorticoid. Glucocorticoid therapy alone appeared ineffective in increasing the platelet count. Four dogs were effectively treated after a single dose of vincristine, but the remaining dog required an additional dose. Vincristine, although effective, is not recommended as the primary therapy of idiopathic thrombocytopenia in the dog. High cost and potential side effects should make its use restricted to cases in which glucocorticoid therapy is either ineffective or contraindicated.

Autoimmune thrombocytopenia in dogs and cats

Autoimmune thrombocytopenia has been recognized as a distinct entity in the dog and cat. It is characterized by: (1) clinical signs of thrombocytopenia, such as hemorrhages into the skin and tissues and from body orifices, (2) coagulation defects related to thrombocytopenia, such as prolonged bleeding time and poor clot retraction, (3) hematologic changes such as severe to moderate thrombocytopenia, often blood loss anemia, and signs of increased erythropoiesis, and (4) an absence or decreased number of megakaryocytes in the bone marrow during early phase and increased number during compensatory phase. Megakaryocytes may also show morphologic abnormalities. Serologic diagnosis of AITP in the dog and cat currently involves demonstration of antiplatelet antibody in serum by PF-3 test and/or associated with marrow megakaryocytes by a technique of direct immunofluorescence. Circumstances leading to formation of antiplatelet antibody remain unknown. Immune-mediated platelet destruction is believed to occur in the reticuloendothelial system, primarily in the spleen. Treatment consists primarily of corticosteroids and other immunosuppressive drugs. Dogs with primary AITP generally respond favorably to such therapy.

[A case of thrombocytopenia in a Collie dog (author's transl)]

A case of thrombocytopenia in a Collie dogIdiopathic thrombocytopenia, the most common cause of the hemorrhagic syndrome in the dog, was diagnosed in an adult male Collie. The bleeding tendency was manifested by anemia, ecchymotic hemorrhages, melena and bilateral epistaxis. Hook-worms increased the anemia. The clinical diagnosis was confirmed by a reduced platelet count. Prednisone was the specific treatment.

Phenylbutazone-induced blood dyscrasias suspected in three dogs

Blood dyscrasias developed after drug therapy in three dogs. Two died, one with pancytopenic marrow failure and the other with non-regenerative anaemia and thrombocytopenia. The third dog developed pancytopenia but recovered. An adverse reaction to phenylbutazone was suspected as the cause in each case, although two of the dogs had also received other drugs which sometimes cause blood dyscrasias in humans.

Serum complement and blood platelet adhesiveness in acute canine ehrlichiosis

Three dogs inoculated with Ehrlichia canis served as infected controls (group I), 3 dogs treated with cobra venom factor (CVF) after inoculation with E canis were the principals (group II), 3 noninfected dogs were the noninfected controls (group III), and 1 noninfected dog given CVF was the noninfected, decomplemented control (group IV). Thrombocytopenia occurred in all E. canis-inoculated dogs (groups I and II) within 3 weeks after they were inoculated. However, the severity of the thrombocytopenia was moderated in the group II dogs (decomplemented E canis-inoculated). Hypocomplementemia occurred in the CVF-treated dogs (groups II and IV) immediately and persisted for up to 5 days after administration of CVF. Hypocomplementamia also occurred in all E canis-infected dogs (groups I and II) during the period of maximal thrombocytopenia. The mean platelet retention was significantly decreased in all E canis-inoculated dogs and in the CVF-control dog (groups I, II, and IV). There was no correlation between platelet retention and the number of platelets in group III (nontreated, noninoculated) controls. The correlation between the decrease in platelet retention and the number of platelets was significant in the complement-intact infected dogs, yet was not significant in the decomplemented infected dogs. Data indicated that complement consumption occurred in acute canine ehrlichiosis and coincided, to a degree, with the development of thrombocytopenia. Decomplementation of inoculated dogs moderated the severity of the thrombocytopenia. Platelet function is also altered in acute stages of the disease.

Levamisole reduces the thrombocytopenia associated with myxovirus vaccination

Mature dogs were vaccinated with a myxovirus vaccine. At this time, half of the dogs were also given a subcutaneous injection of levamisole hydrochloride (2.2 mg/kg). Blood platelets were counted daily. The dogs that had received only the vaccine showed, after 48 hours, a 48% decrease in platelets. Levamisole reduced the thrombocytopenia associated with myxovirus vaccination. Levamisole could have a protective effect on platelets by preventing their aggregation induced by viral neuraminidase.

Secondary thrombocytopenia following phenobarbital treatments in a rhesus monkey (Macaca mulatta)

A rare adverse reaction due to phenobarbital (10 mg/kg/day for 11 days) developed in a rhesus monkey (Macaca mulatta). Clinical signs and measured hematological parameters correlated closely with descriptions of thrombocytopenia. Following cessation of phenobarbital, the monkey recovered within 11 days. Five months after initial thrombocytopenia, the monkey was challenged again with phenobarbital (10 mg/kg/day for 11 days). Appearance and progression of clinical signs were identical to the initial crisis.

Effect of orally administered ribavirin on experimental feline calicivirus infection in cats

Ribavirin administered orally at 75 mg/kg/day in 3 divided doses for 10 days, beginning either 1 or 4 days, after aerosol exposure of cats to calicivirus strain 255, failed to have any beneficial effect on the clinical course of the disease or to reduce viral excretion. Indeed, there was enhanced severity of the clinicopathologic findings in the treated exposed group, due largely to hemorrhage resulting from profound thrombocytopenia. Other toxic effects included depression of red and white blood cells, increased alanine aminotransferase activity, icterus, and body weight loss. Toxic effects were largely reversed within 1 week of cessation of treatment.

Cyclic thrombocytopenia induced by a Rickettsia-like agent in dogs

Hematologic manifestations and the ultrastructure of a platelet-specific microorganism isolated from a dog in Florida were studied. The agent was readily transmitted experimentally to adult dogs by intravenous inoculation with infected blood. Parasitemias and concomitant thrombocytopenias were cyclic in that both recurred within relatively constant periods of one to two weeks following experimental infections. Hemorrhage was not a manifestation of the disease even though thrombocytopenias were severe. Microorganisms were visualized by light and electron microscopy. They were observed only in platelets and were composed of single or multiple subunits (morula forms). The microorganisms were ultrastructurally very similar to those reported in Ehrlichia canis infections of dogs and Anaplasma marginale infections of cattle. Microorganisms were surrounded by single membranes which more or less conformed to the external surfaces of subunits that were surrounded by double membranes. From electron microscopic studies, it is suggested that these organisms be classified in the order Rickettsiales.

Acute canine ehrlichiosis: platelet survival and factor 3 assay

Ten dogs experimentally inoculated with Ehrlichia canis were thrombocytopenic 14 days after inoculation. Circulating platelet concentrations had declined rapidly by postinoculation day 10, but remained at or slightly below the 14-day concentration during the remainder of the 42-day experimental period. The percentage of circulating megathrombocytes also increased to 8.7 times preinoculation concentrations indicating the existence of accelerated thrombocytopoiesis. The release of platelet factor 3 (PF-3) from normal canine platelets was delayed after incubation of the platelets in globulin fractions from infected dogs. Inhibition of PF-3 release was attributed to the effect of an unidentified substance present only in the dialyzed globulin fraction of infected canine serums. The presence of antiplatelet antibody in these dogs was not evident. Survival of 51Cr-labeled platelets was decreased in infected dogs, but was most abbreviated in infected dogs that were thrombocytopenic when injected with labeled platelets. Thus, accelerated nonantibody-mediated destruction of platelets contributes markedly to the development of thrombocytopenia in dogs with acute ehrlichiosis.

Idiopathic monoclonal (IgA) gammopathy in a dog

Idiopathic monoclonal (IgA) gammopathy in a dog was differentiated from multiple myeloma, based on the lack of Bence Jones proteinuria, no osteolysis, and no plasma cell infiltration into bone marrow, as well as on the stability of the gammopathy for over 18 months. The dog was not treated but remained clinically normal for 18 months.

Studies on the pathogenesis of Rickettsia rickettsii in the dog: clinical and clinicopathologic changes of experimental infection

Beagle dogs inoculated with the agent of Rocky Mountain spotted fever, Rickettsia rickettsii, developed a clinical syndrome that extended from febrile exanthema to death and appeared to be dose related. Infected dogs were anorectic and lethargic and developed cutaneous lesions characteristic of Rocky Mountain spotted fever, including petechia, ecchymosis, edema, and necrosis. Hematologic changes after inoculation included anemia, leukopenia proceeding to leukocytosis, and thrombocytopenia. Changes in blood chemistry values included increases in serum alkaline phosphatase and cholesterol, and hyponatremia and hypochloremia. The prominent histopathologic change was necrotizing vasculitis. The canine disease is comparable with human Rocky Mountain spotted fever on a clinical, hematologic, biochemical, and pathologic basis, and may provide a model system for this disease in man. The results suggest the dog may be involved in the epidemiology of R rickettsii infections.

Haemorrhagic syndrome of cattle of suspected mycotoxic origin

An outbreak of disease characterised by haemorrhages, anaemia, leucopenia, thrombocytopenia, skin lesions, degenerative and inflammatory tissue changes and death was investigated in herd of dairy cows. A tentative diagnosis based on circumstantial evidence was of mycotoxicosis arising from the feeding of mouldy barley.

Clinical investigation of doxorubicin, daunomycin, and 6-thioguanine in normal cats

Cats frequently develop a variety of spontaneous hemolymphatic noeplasias. Long-term remissions in the nonlymphatic leukemic cat are difficult to obtain; therefore, more successful chemotherapeutic agents are sought for disease control. The purpose in the present study is to describe the clinical investigation of 3 antineoplastic drugs given to 23 normal cats. The cats tolerated doxorubican given at the dose level of 30 mg/m2 of body surface area once every 3 weeks; daunomycin, 15 to 30 mg/m2 once every 3 weeks; and 6-thioguanine, 25 mg/m2 for 5 days every 20 to 30 days.

Post-transfusion purpura in a pig

A pig which was being immunised with thrombocytes from another pig developed thrombocytopenia and purpura. This appears to be analogous to the post-transfusion purpura syndrome which has been reported in humans and it is suggested that similar systems in pigs could be useful models for experimental studies on the human condition.

Experimental immunologic thrombocytopenia in dogs: a study of thrombocytopenia and megakaryocytopoiesis

Immunologic thrombocytopenia was induced in dogs by intravenous or intraperitoneal injection of rabbit anti-canine platelet serum (APS) or by intraperitoneal injection of the IgG fraction of the APS. In contrast, dogs injected with normal rabbit serum (NRS) or the IgM fraction of the APS did not develop thrombocytopenia. Marrow samples obtained at 24-96 h after inoculation of the IgG fraction contained megakaryocytes giving a positive reaction with flurescein isothiocyanate or horseradish peroxidase-conjugated anti-rabbit globulin. In contrast, negative results were obtained with megakaryocytes in marrow samples collected before injection of the IgG fraction or after injection of the IgM fraction or NRS. The attachment of anti-platelet antibody to the surface of megakaryocytes was associated with appearance of morphologic abnormalities, particularly in mature megakaryocytes. Simultaneously, the number of immature megakaryocytes and acetylcholine esterase (AChE)-positive small cells (presumably megakaryocyte precursors) increased considerably. These changes coincided with the development of thrombocytopenia, and subsided as recovery ensued.

Detection of antiplatelet antibody in serum and on megakaryocytes of dogs with autoimmune thrombocytopenia

Blood and bone marrow samples from 13 thrombocytopenic dogs were examined to determine whether immunologic thrombocytopenia existed. Antiplatelet antibody was detected in serum of 8 of the dogs by platelet factor 3 test or its modification. Moderate to strong immunofluorescence of megakaryocytes was noticed in bone marrow smears stained with rabbit anticanine globulin conjugated with fluorescin isothiocyanate. Negative results were obtained with serum and bone marrow samples collected from 6 of the dogs during therapy for autoimmune thrombocytopenia. Clinical and laboratory findings varied in individual patients with circulating antiplatelet antibodies. Thrombocytopenia was present in all the dogs, with platelet counts ranging from less than 3,000 to 20,000/mu1 of blood. Signs of bleeding in tissues and body cavities were present in all dogs, but anemia was evidenced in only 3 dogs. Differential leukocyte counts were variable. Morphologic abnormalities such as vacuolation and reduced or absence of granulation of the cytoplasm and nuclear fragmentation were seen in some megakaryocytes.

The experimental production of haemolytic disease of the newborn in calves

Haemolytic disease in varying degrees of severity was produced experimentally in 15 newborn calves. Blood group antibodies, incompatible with some of the blood group factors of the calves, were produced in the dams of these calves by inoculation with non-parasitised red blood cells from the sire in most cases. These antibodies were absorbed by the calves from the colostrum. The resultant sensitisation of the calves' red cells produced acute intravascular haemolysis causing haemoglobinuria and anaemia. The principal factor governing the severity of the condition appeared to be the amount of sensitising antibody absorbed by the calf. The finding of leucopenia, thrombocytopenia, hypofibrinogenaemia, a reduction in plasma coagulation factors and the detection of fibrinogen degradation products indicated that disseminated intravascular coagulation occurs in this condition and is the cause of death in the acute cases where a haemorrhagic diathesis, fibrin deposition and oedema of the lungs are the main clinical and post mortem observations.

Recurring hemolytic anemia, babesiasis, and influenza A viruses in a yak at low altitude in Nepal

Episodes of hemolysis and leukocytosis which were associated with Babesia bigemina followed each of 3 challenge exposures to influenza A viruses. It is possible that viral infection altered the immunologic host-parasite equilibrium. Acute thrombocytopenia and rouleaux formation were also observed. Death, attributed to liver flukes, occurred 168 days after the yak was transferred from high to low altitude. A 2nd yak died of foot-and-mouth disease, thus supporting the Nepali belief that yaks will not survive at the lower altitudes of Kathmandu.