Immune mediated neutropenia and thrombocytopenia in 3 giant schnauzers

Neutropenia, thrombocytopenia, and splenomegaly were recognized in 3 adult female giant schnauzers. Antineutrophil antibodies were demonstrated in 2 dogs. Following splenectomy, administration of prednisone and azathioprine resulted in normalization of neutrophil and platelet numbers in all dogs.

Evaluation of antineutrophil IgG antibodies in persistently neutropenic dogs

BACKGROUND

Immune-mediated neutropenia (IMN) is one of several causes of persistent neutropenia in dogs. A test to detect IMN in dogs is not available.

HYPOTHESIS

A flow cytometric immunofluorescence assay will provide a sensitive method for detection of antineutrophil antibodies in dogs.

ANIMALS

The study included 12 neutropenic dogs and 20 healthy dogs.

METHODS

An indirect immunofluorescence assay was used to detect immunoglobulin G (IgG) binding to dog neutrophils. Leukoagglutination was evaluated by light microscopy. Neutrophil distribution in scatter plots, neutrophil fluorescence intensity, and the percentage of neutrophils with increased fluorescence intensity was evaluated by use of flow cytometry.

RESULTS

Antineutrophil antibodies were detected in the serum of 5 of 6 dogs with a clinical diagnosis of IMN. Leukoagglutination was present in 3 dogs. Four dogs had altered neutrophil distribution in forward-angle versus side-angle light scatter plots. Five of 6 dogs had increased neutrophil fluorescence intensity and 4 of 6 dogs had an increased percentage of neutrophils with increased fluorescence intensity.

CONCLUSIONS AND CLINICAL IMPORTANCE

The flow cytometric test for antineutrophil antibodies detects dogs with a clinical diagnosis of IMN. Testing for antineutrophil antibodies should include observation for leukoagglutination, observation of scatter plots for altered distribution of the neutrophil population, observation of the shape of the fluorescence histogram, determination of neutrophil fluorescence intensity, and determination of the percentage of neutrophils with increased fluorescence intensity.

G-CSF treatment of canine cyclical neutropenia: A comprehensive mathematical model

OBJECTIVE

To study the effects of different G-CSF temporal treatment schemes using a comprehensive mathematical model of the mammalian hematopoietic system that couples the pharmacokinetics of granulocyte colony-stimulating factor (G-CSF) to the hematopoietic stem cell, neutrophil, platelet, and erythrocyte dynamics.

MATERIALS AND METHODS

Data from cyclical neutropenic (CN) grey collies are used to build an extended model that reproduces the dynamics of circulating blood cells found in laboratory data from the dogs with and without daily G-CSF therapy. The effects of varying the treatment initiation time, and whether injections are given daily, every other day, or every three days, are examined.

RESULTS

The mathematical model is able to reproduce the large variation in data that occurs from one dog to another. Different drug delivery times, with no other changes in the model parameters, can have significant long-term effects on neutrophil numbers. The frequency of drug delivery also has long-term effects on the oscillations.

CONCLUSION

Using a realistic representation of the effects of G-CSF on the tissue-level hematopoietic system, the model matches a wide range of laboratory data. This implies that it would be possible to generate individualized predictions for specific dogs if data were available in real time. The proposed interventions are practical and may reduce the amount of G-CSF required while potentially maintaining or even improving the treatment effects.

An indirect flow cytometric test for detection of anti-neutrophil antibodies in dogs

OBJECTIVE

To develop a clinically applicable assay for detection of serum anti-neutrophil antibodies in dogs.

SAMPLE POPULATION

Serum samples of 20 healthy dogs and 20 sick dogs.

PROCEDURES

An indirect immunofluorescence assay was developed in which canine serum was incubated with paraformaldehyde-fixed neutrophils and subsequently incubated with fluorescein-conjugated rabbit anti-dog IgG. Neutrophil median fluorescence intensity and the percentage of neutrophils with an increase in fluorescence intensity were determined by use of a flow cytometer.

RESULTS

Neutrophils incubated with serum from healthy and sick dogs had a normally distributed curve when displayed as a histogram. Alloantibodies or immune complexes that significantly affected test results were not detected. Hyperglobulinemia did not appear to affect test results. The neutrophil donor did not significantly affect test results. With 1 exception, results for the sick dogs did not differ appreciably from those for healthy dogs. Serum from a dog with steroid-responsive neutropenia had a greater neutrophil fluorescence value and percentage of neutrophils with an increase in fluorescence intensity, compared with either healthy or sick dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The indirect immunofluorescence test gave consistent results for healthy and sick dogs and detected anti-neutrophil antibodies in a dog with steroid-responsive neutropenia. Definitive evaluation of the test will be dependent on evaluation of persistently neutropenic dogs and correlation of test results with a response to immunosuppressive therapy.

Aftershocks of Cancer Chemotherapy: Managing Adverse Effects

Most cytotoxic chemotherapy protocols used in small animals are designed to have a low risk of adverse effects; however, adverse events can occasionally occur. Timely and appropriate management of adverse events greatly increases client satisfaction and the likelihood of a successful treatment outcome. This article presents guidelines for the management of chemotherapy-associated hematological and gastrointestinal disturbances, extravasation injury, and anaphylaxis.

Phase I evaluation of low-dose suramin as chemosensitizer of doxorubicin in dogs with naturally occurring cancers

BACKGROUND

Low and nontoxic concentrations (10-50 microM) of suramin, which is a nonspecific inhibitor of multiple growth factors, including fibroblast growth factors, enhances the activities of cytotoxic chemotherapeutic agents, such as doxorubicin and paclitaxel, both in vitro and in vivo. Suramin has not been evaluated as a chemosensitizing agent in dogs with cancer.

HYPOTHESIS

Nontoxic suramin can be used safely as a chemosensitizer in dogs.

ANIMALS

Sixteen dogs of various breeds with measurable tumors were treated; 1 dog that had undergone amputation for osteosarcoma received adjuvant therapy.

METHODS

The dogs received 53 courses of treatment with suramin in combination with doxorubicin. The suramin dosage was 6.75 mg/kg IV 3 h before standard doxorubicin administration every 2 weeks. The pharmacokinetics and clinical efficacy were determined.

RESULTS

The pharmacokinetics of low-dose suramin followed a 2-compartment model with half-lives of 2 h and 6 days. The distribution volume was a 0.34 +/- 0.12 L/kg, and clearance was 1.86 +/- 0.76 mL/kg/h. During the time interval that doxorubicin was present at therapeutically active concentrations (ie, from the start of infusion to 24 hours), the plasma concentrations were maintained within 20% of the target range (8-60 microM) in 72% of the treatments. The toxicity of the suramin/doxorubicin combination was mild and comparable to the toxicity expected for doxorubicin monotherapy. Objective partial responses were observed in 2 out of 16 evaluable dogs (13%). All 5 dogs that previously received doxorubicin showed improved responses to the suramin/doxorubicin combination.

CONCLUSIONS AND CLINICAL IMPORTANCE

A fixed, low-dose suramin regimen yields the desired target plasma concentrations in most dogs, and appears to enhance the activity of doxorubicin without enhancing toxicity.

Dexamethasone, melphalan, actinomycin D, cytosine arabinoside (DMAC) protocol for dogs with relapsed lymphoma

BACKGROUND

In general, treatment of relapsed lymphoma is associated with a lower probability of response and shorter duration of remission. The purpose of this study was to evaluate the efficacy of the combination chemotherapy protocol DMAC (dexamethasone, melphalan, actinomycin D, and cytosine arabinoside) for reinduction of remission in dogs with relapsed lymphoma.

HYPOTHESIS

That DMAC would be an effective reinduction protocol for dogs with relapsed lymphoma.

ANIMALS

Fifty-four dogs.

RESULTS

Seventy-two percent of the dogs achieved remission (44% complete remission [CR] and 28% partial remission [PR]), 11% had stable disease (SD), and 17% had progressive disease (PD). The median remission duration was 61 days (range, 2-467+ days). The median remission durations for dogs with CR, PR, and SD were 112, 44, and 27 days, respectively. Factors that affected the response rate were previous treatment with doxorubicin and an inability to achieve remission with the previous protocol. Thrombocytopenia occurred in 56% of the dogs (grade 1 in 3 dogs, grade 2 in 6 dogs, grade 3 in 7 dogs, and grade 4 in 7 dogs) and neutropenia in 17% of the dogs (grade 2 in 1 dog, grade 3 in 2 dogs, and grade 4 in 4 dogs). Gastrointestinal toxicosis occurred in 22% of the dogs (grades 1 in 5 dogs, grade 2 in 3 dogs, and grade 3 in 1 dog).

CONCLUSIONS AND CLINICAL IMPORTANCE

The DMAC protocol is an effective rescue protocol for dogs with relapsed multicentric lymphoma. Although thrombocytopenia is a common manifestation of toxicity, in general, the protocol is well tolerated.

Granulocyte and granulocyte macrophage colony-stimulating factors as therapy in human and veterinary medicine

Granulocyte colony-stimulating factors (G-CSFs) and granulocyte macrophage colony-stimulating factors (GM-CSFs) are endogenous cytokines that regulate granulocyte colonies and play a major role in the stimulation of granulopoiesis (neutrophils, basophils and eosinophils) and in the regulation of microbicidal functions. There are numerous pathological conditions in which neutrophils are decreased, the most common being neutropenia associated with cancer chemotherapy, which increases the risk of serious microbial infections developing with the potential for high morbidity and mortality. New methods in molecular biology have led to the identification and cloning of CSF genes and biopharmaceutical production. Since then, CSFs have been widely used for the prevention and treatment of neutropenia associated with cancer chemotherapy, for mobilising haematopoietic cell precursors, and for other neutropenia-related pathologies. This review focuses on the use of CSFs within both human and veterinary medicine. Clinical applications, pharmacology, tolerability and the potential role of these factors in veterinary medicine are considered.

An adult dog with cyclic neutropenia treated by lentivirus- mediated delivery of granulocyte colony-stimulating factor

Cyclic neutropenia occurs in humans and gray collie dogs, is characterized by recurrent neutropenia, and is treated by daily injections of recombinant granulocyte colony-stimulating factor (G-CSF). After showing that canine recombinant G-CSF increased neutrophil counts in an affected dog, we administered intramuscularly 2 x 10(9) infectious units (IU) of a lentiviral vector encoding canine G-CSF cDNA. Elevated, therapeutic neutrophil production was obtained for nearly 18 months. Lentiviral vector treatment provided a mean neutrophil count of 29,230 +/- 12,930 cells/microl, which was significantly increased over both the pretreatment value (5,240 +/- 4,800 cells/microl; p < 0.0001) and the neutrophil count during G-CSF administration (17,820 +/- 11,100 cells/microl; p < 0.0001). By systemic infusion of recombinant G-CSF to normal dogs we estimated that 2 x 10(9) IU of lentivirus delivered 3.5 microg of G-CSF per kilogram per day. After lentiviral vector treatment the gray collie gained weight, showed no clinical signs of infection and fever, and no longer needed housing in a pathogen-free environment. Genomic DNA harvested from muscle at the injection sites was positive for provirus, whereas gonad, lung, spleen, heart, liver, kidney, and noninjected muscle samples were negative. These studies show that an adult animal is responsive long-term to lentivirus-mediated G-CSF delivery, suggesting this approach may be applied for treatment of adult patients with cyclic and other neutropenias.

Evaluation of clinicopathologic features, response to treatment, and risk factors associated with idiopathic neutropenia in dogs: 11 cases (1990–2002)

OBJECTIVE

To evaluate the clinicopathologic features, response to treatment, and risk factors associated with idiopathic neutropenia in dogs.

DESIGN

Retrospective case series.

ANIMALS

11 dogs.

PROCEDURES

Medical records of dogs with idiopathic neutropenia were reviewed. Signalment, history, clinical signs, and response to treatment were recorded and compared with that in dogs with neutropenia attributable to known causes and to dogs without neutropenia (controls).

RESULTS

Compared with dogs with neutropenia attributable to known causes, dogs with idiopathic neutropenia had lower neutrophil counts and were younger. When compared with control dogs, age < 4 years was identified as a risk factor for developing idiopathic neutropenia. In all dogs with idiopathic neutropenia, remission of neutropenia occurred within 18 days after administration of prednisone (2 to 4 mg/kg [0.9 to 1.8 mg/lb], PO, daily) and no serious complications or infections developed.

CONCLUSIONS AND CLINICAL RELEVANCE

An immune-mediated pathogenesis should be considered for dogs with idiopathic neutropenia in which the cause is not known. Severe neutropenia and young age were significantly associated with idiopathic neutropenia in dogs. Prognosis appeared to be excellent with prednisone treatment.

Pathogenesis of a Texas feline immunodeficiency virus isolate: An emerging subtype of clade B

We have recently provided evidence that Texas feline immunodeficiency virus (FIV-TX) isolates are an emerging subtype sharing a common ancestry with clade B isolates. Specific, pathogen-free cats were infected, intravenously, with 500, 2000 or 8000TCID(50) of the FIV-TX53 virus to study the acute stage of infection. Infection of cats resulted in lymphadenopathy at 10 days post-infection (p.i.). By 7 weeks p.i., gag specific antibody could be detected from sera of all infected cats. Virus could be detected by culturing PBMC and by nested capsid PCR. A reduction in the absolute numbers of lymphocytes and neutrophils was observed in infected cats although there was no trend identified between this reduction and the viral dose administered. By 11 weeks p.i., the CD4(+)/CD8(+) T cell ratios from all infected cats had dropped from approximately 2 to below 1. While decrease in the ratio was dependent on the viral dose, the T cell ratios of cats receiving the highest dose had significantly dropped below 1 by 4-7 weeks p.i. This decrease in the ratio was accompanied by a sharp and temporal decline in the absolute CD4(+) T cells and a slight increase in the absolute CD8(+) T cell numbers with a dramatic expansion of cells with CD8beta(low) chain expression.

Effects of noncytopathic type 2 bovine viral diarrhea virus on the proliferation of bone marrow progenitor cells

The purpose of this study was to investigate the effects of isolates of noncytopathic type 2 Bovine viral diarrhea virus (ncpBVDV-2) of high and low virulence on the proliferation of bone marrow progenitor cells. Holstein calves 6 to 7 mo old and BVDV-naïve were inoculated intranasally with a BVDV isolate of high virulence (HV24515), a BVDV isolate of low virulence (LV11Q), or uninfected cell culture medium. Serial bone marrow and peripheral blood samples were collected before and after inoculation. Bone marrow mononuclear cells (BMMCs) were isolated and cultured for 5 d, and the mean number of colony-forming unit-granulocyte-macrophage (CFU-GM) colonies was determined. Tritiated (3H)-thymidine uptake by BMMCs was determined to indicate overall proliferative capacity. Virus isolation was done on concurrent samples of BMMCs and peripheral blood. Virus was isolated from BMMCs and peripheral blood buffy-coat cells as early as day 2 or 3 after inoculation. Neutropenia developed in both groups inoculated with a BVDV isolate. However, in the calves given LV11Q, neutrophil counts rebounded earlier in response to increased proliferation of BMMCs, whereas the response was delayed in calves given HV24515. Thymidine uptake was significantly increased (P = 0.0047) in BMMCs after inoculation compared with before inoculation in the calves given LV11Q but not in those given HV24515 or in the control calves. The median number of CFU-GM colonies was significantly decreased (P = 0.0164) after inoculation compared with before inoculation in the calves given HV24515, whereas there was no significant difference in the calves given LV11Q or in the control calves. The data support the hypothesis that the prolonged neutropenia observed in calves given HV24515 results at least in part from decreased proliferative capacity of bone marrow progenitor cells.

A mathematical model of hematopoiesis: II. Cyclical neutropenia

Cyclical neutropenia is a dynamical disease of the hematopoietic system marked by an oscillation in circulating leukocyte (e.g. neutrophil) numbers to near zero levels and then back to normal. This oscillation is also mirrored in the platelets and reticulocytes which oscillate with the same period. Cyclical neutropenia has an animal counterpart in the grey collie. Using the mathematical model of the hematopoietic system of Colijn and Mackey [A mathematical model of hematopoiesis: I. Periodic chronic myelogenous leukemia. Companion paper to the present paper.] we have determined what parameters are necessary to mimic laboratory and clinical data on untreated grey collies and humans, and also what changes in these parameters are necessary to fit data during treatment with granulocyte colony stimulating factor (G-CSF). Compared to the normal steady-state values, we found that the major parameter changes that mimic untreated cyclical neutropenia correspond to a decreased amplification (increased apoptosis) within the proliferating neutrophil precursor compartment, and a decrease in the maximal rate of re-entry into the proliferative phase of the stem cell compartment. For the data obtained during G-CSF treatment, good fits were obtained only when parameters were altered that would imply that G-CSF led to higher amplification (lower rate of apoptosis) in the proliferating neutrophil precursors, and a elevated rate of differentiation into the neutrophil line.

Risk factors associated with development of poxvirus lesions in hospitalized California sea lions

OBJECTIVE

To identify risk factors that may predispose California sea lions (Zalophus californianus) to development of cutaneous poxvirus nodules during hospitalization in a rehabilitation center.

DESIGN

Retrospective case-control study.

ANIMALS

90 California sea lions admitted to a rehabilitation center.

PROCEDURE

Hospital records of 275 stranded California sea lions admitted to the rehabilitation center between January 1 and December 31, 2002, were reviewed. All California sea lions (n = 18) that developed > or = 1 cutaneous poxvirus nodule during hospitalization were classified as cases. Seventy-two California sea lions that did not develop poxvirus lesions during hospitalization were randomly selected (control group). The frequencies of various exposure factors prior to admission, at admission, and during hospitalization for cases and control sea lions were compared by use of logistic regression.

RESULTS

California sea lions that had previously been admitted to the rehabilitation center were 43 times as likely to develop poxvirus lesions as sea lions admitted for the first time; those with high band neutrophil counts (> 0.69 X 10(3) bands/microL) at admission were 20 times less likely to develop poxvirus lesions than sea lions with counts within reference limits.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that sea lions with a history of prior hospitalization or band neutrophil counts within reference limits at admission were more likely to develop poxvirus lesions during hospitalization. Sea lions with histories of hospitalization should be kept in quarantine and infection control measures implemented to help prevent disease transmission to attending personnel and other hospitalized animals.

Ulcerative dermatitis, thrombocytopenia, and neutropenia in neonatal foals

This report describes transient ulcerative dermatitis, severe thrombocytopenia, and mild neutropenia in 6 foals from 4 mares from geographically diverse regions of the United States. The foals presented at <4 days of age with oral and lingual ulcers, and crusting and erythema around the eyes, muzzle, and perineal, inguinal, axillary, trunk, and neck regions. There was a severe thrombocytopenia (0-30,000 platelets/microL), leukopenia (1900-3200 white blood cells/microL), and mild neutropenia (500-1800 neutrophils/microL). Four of the 6 foals had petechiae and ecchymotic hemorrhages and 3 had bleeding tendencies. Results of examination of a bone marrow biopsy from 1 foal were normal and results of a platelet surface immunoglobulin test in another were negative. Histopathology of the skin in all foals showed subepidermal clefting with subjacent vascular dilation, dermal hemorrhage, and superficial papillary necrosis. The foals were treated supportively with broad-spectrum antibiotics (5/6), corticosteroids (3/6), gastric ulcer prophylaxis (6/6), whole-blood transfusion (4/6), and platelet-rich plasma (1/6). The skin lesions and thrombocytopenia (>50,000 platelets/microL) improved in 2 weeks (4/6). Two foals had a decline in their platelet counts when the steroids were decreased and needed protracted treatment. All foals survived and were healthy as yearlings. Two mares that had 2 affected foals each, upon subsequent pregnancies to different stallions, had healthy foals when an alternate source of colostrum was given. The findings in the cases in this report suggest a possible relationship between colostral antibodies or some other factor in the colostrum and the thrombocytopenia and skin lesions, although further investigation is warranted to confirm or refute this hypothesis.

Clinical, biochemical, and hematological characteristics, disease prevalence, and prognosis of dogs presenting with neutrophil cytoplasmic toxicity

Neutrophil cytoplasmic toxicity is manifested as an abnormality in cell size or the cytoplasmic content upon examination of Romanowsky-stained blood smears, and is traditionally associated with infection and inflammation. The purpose of this retrospective study was to investigate the association of such changes with clinical and clinicopathologic characteristics, diseases, and prognoses in dogs. Dogs with neutrophil toxicity (n = 248) were compared with negative controls (n = 248). Statistical analyses included chi-square tests, independent t-tests, nonparametric Mann-Whitney tests, the chi-square trend test, and survival analysis. Dogs with neutrophil toxicity had a significantly higher prevalence of pale mucous membranes, tachycardia, fever, abdominal organomegaly, icterus, melena, and hematuria. Most mean hematologic variables were significantly different between groups. Dogs with neutrophil toxicity had a significantly (P < .05) higher prevalence of leukocytosis, leukopenia, neutrophilia, neutropenia, anemia, hyponatremia, hypokalemia, hypoproteinemia, hypoalbuminemia, and hypocalcemia. The prevalence of pyometra, parvovirus infection, acute renal failure, peritonitis, immune-mediated hemolytic anemia, disseminated intravascular coagulation, pancreatitis, septicemia, and neoplastic disorders was significantly higher among these dogs. Case fatality, hospitalization length, and treatment cost were significantly (P < .001) higher in dogs with neutrophil toxicity. Neutrophil toxicity severity was significantly (P < .0035) and positively associated with neutropenia, and negatively associated with leukocytosis and neutrophilia. A significant trend (P = .05) toward increasing case fatality with an increase of neutrophil toxicity was observed. In the neutrophil toxicity group, dogs with leukopenia (<5.0 X 10(3)/mm3) had a significantly (P < .0001) higher case fatality compared to dogs with normal or high leukocyte counts. We conclude that evaluation of blood smears for neutrophil cytoplasmic toxicity provides useful clinical information and can serve as a good prognostic predictor.

Relationship between red blood cell thiopurine methyltransferase activity and myelotoxicity in dogs receiving azathioprine

Thiopurine methyltransferase (TPMT) produces inactive metabolites of azathioprine and, in humans, has a variable amount of activity. Humans with low TPMT activity commonly develop myelotoxicity when receiving azathioprine. Our study sought to characterize the distribution of TPMT activity in a population of dogs and to determine whether the pretreatment knowledge of red blood cell (RBC) TPMT activity could predict myelotoxicity in dogs receiving azathioprine. RBC TPMT activity was measured in 299 healthy dogs, and 9 dogs that represented a wide range of enzyme activity received azathioprine at a standard therapeutic dose for 30 days. TPMT activity in healthy dogs was log normally distributed and varied over an approximately 7-fold range. Geometric mean, minimum, and maximum RBC TPMT activities were 37.1, 16.3, and 115 nmol per gram of hemoglobin (gHb) per hour, respectively. TPMT deficiency was not identified. Two populations of TPMT activity in dogs were detected by statistical modeling (commingling analysis). Dogs with intermediate TPMT activity (14-38 nmol/gHb/h) receiving azathioprine had significantly lower neutrophil counts during week 4 than during weeks 0-3, whereas those with high activity (>39 nmol/gHb/h) did not have a significant change in neutrophil count. An analysis of TPMT activity in 6 dogs with a history of azathioprine-associated myelotoxicity in a clinical setting revealed either intermediate or high TPMT enzyme activity in all dogs, suggesting that TPMT activity, as measured in RBCs, is not the sole cause of severe azathioprine-associated myelosuppression in dogs.

Carmustine, Vincristine, and Prednisone in the Treatment of Canine Lymphosarcoma

A chemotherapeutic protocol using carmustine in combination with vincristine and prednisone was tested in dogs with multicentric malignant lymphosarcoma. Of seven dogs treated, six (85.7%) achieved complete remission. A partial response occurred in one dog. Median survival time was 224 days (mean 386 days), and median duration of remission was 183 days (mean 323 days). Marked neutropenia was observed following carmustine administration. There were no significant alterations in platelets and red blood cell counts during treatment, and no abnormalities attributable to the chemotherapy were found in serum biochemical profiles. Results of this study showed that carmustine is an effective alternative option in the treatment of canine lymphosarcoma.

Experimental Babesia gibsoni infection in coyotes (Canis latrans)

Four 5 mo old captive raised coyotes (Canis latrans) were experimentally inoculated with approximately 1 x 10(6) Babesia gibsoni organisms. Parasites were detected 1 wk post-inoculation in all coyotes with maximum parasitemia of 8-11% occurring at 34 wk. Parasitemias remained at or above 1% for at least 12 wk and were still detectable 20 wk post-inoculation. All experimentally infected coyotes developed pale mucous membranes, splenomegaly, and a positive heme reaction in urine while one coyote exhibited mild depression and inappetence. Infected coyotes also developed a regenerative anemia, thrombocytopenia, and neutropenia. The mild clinical signs coupled with the high level and long duration of parasitemia indicate that coyotes could serve as reservoirs for B. gibsoni. Entrance of this foreign parasite into the United States suggests the need for strict quarantines and thorough health and blood film examinations for imported animals.

Efficacy and toxicity of paclitaxel (Taxol) for the treatment of canine malignant tumors

Paclitaxel (Taxol) was administered to 25 dogs with histologically confirmed malignant tumors at a dosage of 165 mg/m2 i.v. over 3-6 hours every 3 weeks. Dogs received premedication with antihistimines and corticosteroids to reduce hypersensitivity reactions. However, 64% of the dogs still experienced allergic reactions. Six dogs (24%) had grade 3 or 4 neutropenia, 6 dogs (24%) required hospitalization and 3 dogs (12%) died of sepsis. Five dogs (20%) had a partial response (osteosarcoma [2 dogs] mammary carcinoma [2 dogs] and malignant histiocytosis [1 dog]) for a median duration of 53 days. The overall toxicity was unacceptable at the 165 mg/m2 dose. Therefore, subsequent evaluations of paclitaxel in tumor-bearing dogs should a starting dose of 132 mg/m2 i.v. every 3 weeks.

Immune-mediated neutropenia suspected in five dogs

Five cases of suspected immune-mediated neutropenia in dogs are described. Clinical signs varied depending on whether the animals had a systemic infection or concurrent immune-mediated disease. Patients were diagnosed by excluding other causes of neutropenia, supportive bone marrow aspirate findings, an initial favourable response to corticosteroid administration in four of the cases, and concurrent immune-mediated disease. Four of the dogs were receiving medications at the time of diagnosis, and immune-mediated neutropenia secondary to drug therapy cannot be excluded. This study shows that appropriate immunosuppressive treatment can lead to a favourable outcome, however, care is required to avoid adverse effects associated with corticosteroid use. It is also imperative that medications are not withdrawn abruptly as a second remission may not always be achievable.

Oscillations in cyclical neutropenia: new evidence based on mathematical modeling

We present a dynamical model of the production and regulation of circulating blood neutrophil number. This model is derived from physiologically relevant features of the hematopoietic system, and is analysed using both analytic and numerical methods. Supercritical Hopf bifurcations and saddle-node bifurcations of limit cycles are shown to exist. We make the estimation of kinetic parameters for dogs and then apply the model to cyclical neutropenia (CN) in the grey collie, a rare disorder in which oscillations in all blood cell counts are found. We conclude that the major cause of the oscillations in CN is an increased rate of apoptosis of neutrophil precursors which leads to a destabilization of the hematopoietic stem cell compartment.