Experimental Ehrlichia canis infection in the dog does not cause immunosuppression

Conventional and Holter Electrocardiographic Assessment of Dogs Infected Naturally With Acute Canine Monocytic Ehrlichiosis

Canine Monocytic Ehrlichiosis (CME) is a disease of worldwide distribution caused by the bacteria Ehrlichia canis, appearing primarily in hot climates due to the massive prevalence of its vector, the tick Rhipicephalus sanguineus. Previous studies have shown that dogs afflicted by CME in the chronic phase can develop infectious myocarditis, arrhythmias, and alterations in heart rate variability (HRV), but there are few studies correlating cardiac diseases with the acute phase of CME. This study aims at assessing electric cardiac alterations and HRV in the time and frequency domains during the acute phase of CME. This study assessed 22 animals divided into 2 distinct groups: the control group, comprised by 10 healthy dogs, and the sick group, comprised of 12 dogs infected naturally with ehrlichiosis which presented clinical and hematological signs compatible with the acute phase of the disease. The animals underwent conventional and Holter electrocardiographic evaluations, systolic blood pressure measurement, complete blood count and biochemical assays (urea, creatinine, alanine aminotransferase (ALT), alkaline phosphatase (AP), and gamma glutamyl transferase (GGT)). The sick group presented higher activity in the sympathetic nervous system than in the parasympathetic nervous system, manifest as a significant increase in mean heart rate and a reduction in the HRV indexes for the time and frequency domains. The frequency-domain HRV indexes presented sympathetic prevalence during the sleep and vigilance states. Sinus tachycardia was the predominant heart rhythm in 58.33% of the animals. The mean systolic blood pressure diverged between the groups and no significant arrhythmias were observed during monitoring. The serum concentrations of urea, creatinine, AP, ALT, and GGT were within the established reference values for the species. We observed no indication that there was enough time during the acute phase for the disease to evolve in a way that resulted in arrhythmias, as is common in the chronic phase, but we observed that animals in the acute phase already present reduced HRV indexes.

ACVIM consensus statement on the diagnosis of immune-mediated hemolytic anemia in dogs and cats

Immune-mediated hemolytic anemia (IMHA) is an important cause of morbidity and mortality in dogs. IMHA also occurs in cats, although less commonly. IMHA is considered secondary when it can be attributed to an underlying disease, and as primary (idiopathic) if no cause is found. Eliminating diseases that cause IMHA may attenuate or stop immune-mediated erythrocyte destruction, and adverse consequences of long-term immunosuppressive treatment can be avoided. Infections, cancer, drugs, vaccines, and inflammatory processes may be underlying causes of IMHA. Evidence for these comorbidities has not been systematically evaluated, rendering evidence-based decisions difficult. We identified and extracted data from studies published in the veterinary literature and developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria for IMHA, comorbidities, and causality. Succinct evidence summary statements were written, along with screening recommendations. Statements were refined by conducting 3 iterations of Delphi review with panel and task force members. Commentary was solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted. The resulting document is intended to provide clinical guidelines for diagnosis of, and underlying disease screening for, IMHA in dogs and cats. These should be implemented with consideration of animal, owner, and geographical factors.

Canine amoebic meningoencephalitis due to Balamuthia mandrillaris

A 1-year-old Siberian Husky dog with acute-onset of seizures, recumbency, paddling, and muscular fasciculations was autopsied. A locally extensive hemorrhagic and malacic focus was noted in the right cerebral frontal cortex, and severe necrotizing and hemorrhagic, neutrophilic meningoencephalitis was diagnosed microscopically. Amoebic trophozoites and cysts were identified within the affected cerebral parenchyma and confirmed by indirect immunofluorescence assay and real-time PCR as Balamuthia mandrillaris. B. mandrillaris is found in soil and water and the infection has been reported in both immunocompromised and immunocompetent humans and rarely in the dog.

Quantitative and qualitative leukocyte abnormalities in dogs with experimental and naturally occurring acute canine monocytic ehrlichiosis

BACKGROUND

Canine monocytic ehrlichiosis (CME) is one of the most important tick-borne diseases worldwide. Cytopenias have been observed in both acute (nonmyelosuppressive) and chronic (myelosuppressive) CME; however, leukocyte abnormalities and indices have been incompletely described in dogs with acute CME.

OBJECTIVES

The aims of this study were to analyze temporal changes in differential leukocyte counts, leukocyte morphology, myeloperoxidase index (MPXI), and lobularity index (LI) in dogs with experimental and naturally occurring acute CME.

METHODS

Differential leukocyte counts and morphology were evaluated in archived blood smears from 13 Beagle dogs experimentally infected with Ehrlichia canis and evaluated weekly for 42 days postinfection (DPI); 20 dogs with naturally occurring acute CME also were evaluated. MPXI and LI were obtained from ADVIA reports. Wilcoxon tests were used to assess changes over time; leukogram results in natural cases were assessed in comparison with reference intervals.

RESULTS

In experimental dogs, significant decreases in neutrophil, monocyte, lymphocyte, and eosinophil counts, and a mild left shift occurred within 14 DPI. The MPXI decreased significantly between 14 and 21 DPI and remained low, while LI increased from 14 to 35 DPI. Lymphocyte counts rebounded at 21 DPI, normalizing total WBC counts. Neutrophil toxicity was seen rarely, but reactive lymphocytes were observed frequently. Dogs with natural infection had variable patterns of leukocyte changes.

CONCLUSIONS

Acute CME is associated with several discrete quantitative and qualitative leukogram changes indicative of concurrent inflammation, antigenic stimulation, and stress. Changes in MPXI and LI warrant further investigation in dogs with CME and other diseases.

Comparative Experimental Infection Study in Dogs with Ehrlichia canis, E. chaffeensis, Anaplasma platys and A. phagocytophilum

Dogs acquire infections with the Anaplasmataceae family pathogens, E. canis, E. chaffeensis, E. ewingii, A. platys and A. phagocytophilum mostly during summer months when ticks are actively feeding on animals. These pathogens are also identified as causing diseases in people. Despite the long history of tick-borne diseases in dogs, much remains to be defined pertaining to the clinical and pathological outcomes of infections with these pathogens. In the current study, we performed experimental infections in dogs with E. canis, E. chaffeensis, A. platys and A. phagocytophilum. Animals were monitored for 42 days to evaluate infection-specific clinical, hematological and pathological differences. All four pathogens caused systemic persistent infections detectible throughout the 6 weeks of infection assessment. Fever was frequently detected in animals infected with E. canis, E. chaffeensis, and A. platys, but not in dogs infected with A. phagocytophilum. Hematological differences were evident in all four infected groups, although significant overlap existed between the groups. A marked reduction in packed cell volume that correlated with reduced erythrocytes and hemoglobin was observed only in E. canis infected animals. A decline in platelet numbers was common with E. canis, A. platys and A. phagocytophilum infections. Histopathological lesions in lung, liver and spleen were observed in all four groups of infected dogs; infection with E. canis had the highest pathological scores, followed by E. chaffeensis, then A. platys and A. phagocytophilum. All four pathogens induced IgG responses starting on day 7 post infection, which was predominantly comprised of IgG2 subclass antibodies. This is the first detailed investigation comparing the infection progression and host responses in dogs after inoculation with four pathogens belonging to the Anaplasmataceae family. The study revealed a significant overlap in clinical, hematological and pathological changes resulting from the infections.

Butyrylcholinesterase as a marker of inflammation and liver injury in the acute and subclinical phases of canine ehrlichiosis

The aim of this study was to evaluate the role of butyrylcholinesterase (BChE) as a marker of inflammation and liver injury in the acute and subclinical phases of canine ehrlichiosis. Forty-two serum samples of dogs naturally infected with Ehrlichia canis were used, of which 24 were from animals with the acute phase of the disease and 18 with subclinical disease. In addition, sera from 17 healthy dogs were used as negative controls. The hematocrit, BChE activity, hepatic injury (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)), nitric oxide, and cytokines levels were evaluated. The BChE activity was significantly elevated (P<0.05) in dogs with the acute phase of the disease when compared to healthy animals. However, there was a reduction on BChE activity on dogs with subclinical disease compared to the other two groups. AST and ALT levels were significantly higher (P<0.05) in the acute phase, as well as the inflammatory mediators (NOx, TNF-α, INF-γ, IL-4, IL-6) when compared to the control group. On the other hand, IL-10 levels were lower in the acute phase. Based on these results, we are able to conclude that the acute infection caused by E. canis in dogs leads to an increase on seric BChE activity and some inflammatory mediators. Therefore, this enzyme might be used as a marker of acute inflammatory response in dogs naturally infected by this bacterium.

Effects of doxycycline on haematology, blood chemistry and peripheral blood lymphocyte subsets of healthy dogs and dogs naturally infected with Ehrlichia canis

Canine monocytic ehrlichiosis (CME), caused by Ehrlichia canis, is a vector-borne disease with a worldwide distribution. It has been proposed that the pathogenesis, clinical severity and outcome of disease caused by Ehrlichia spp. can be attributed to the immune response rather than to any direct rickettsial effect. Moreover, doxycycline, the antimicrobial of choice for the treatment of CME, has immunomodulatory and anti-inflammatory properties associated with blood leukocyte proliferation function, cytokine synthesis, and matrix metalloproteinase activity. In order to assess the potential effects of doxycycline, dependent and independent of its antimicrobial activity, the present study compared changes in haematology, blood chemistry and circulating lymphocyte subpopulations in 12 healthy dogs and 20 dogs with CME after doxycycline therapy. Some changes were recorded only in the CME affected dogs, probably due to the antimicrobial effect of doxycycline. However, increases in mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, platelet count and α2-globulins, and decreased plasma creatinine were observed in both healthy and CME affected dogs. The absolute count of B lymphocytes (CD21(+)) increased initially, but then decreased until the end of the study period in both groups. A potential effect of doxycycline unrelated to its antimicrobial activity against E. canis is suggested, taking into account the results observed both in healthy dogs and in dogs with CME.

The immunopathology of canine vector-borne diseases

The canine vector-borne infectious diseases (CVBDs) are an emerging problem in veterinary medicine and the zoonotic potential of many of these agents is a significant consideration for human health. The successful diagnosis, treatment and prevention of these infections is dependent upon firm understanding of the underlying immunopathology of the diseases in which there are unique tripartite interactions between the microorganism, the vector and the host immune system. Although significant advances have been made in the areas of molecular speciation and the epidemiology of these infections and their vectors, basic knowledge of the pathology and immunology of the diseases has lagged behind. This review summarizes recent studies of the pathology and host immune response in the major CVBDs (leishmaniosis, babesiosis, ehrlichiosis, hepatozoonosis, anaplasmosis, bartonellosis and borreliosis). The ultimate application of such immunological investigation is the development of effective vaccines. The current commercially available vaccines for canine leishmaniosis, babesiosis and borreliosis are reviewed.

Experimental infection and co-infection of dogs with Anaplasma platys and Ehrlichia canis: hematologic, serologic and molecular findings

BACKGROUND

Rhipicephalus sanguineus is a ubiquitous tick responsible for transmitting Ehrlichia canis and most likely Anaplasma platys to dogs, as either single or co-infections. The objective of this study was to assess the effects of either simultaneous or sequential experimental infections with E. canis and A. platys on hematological and serological parameters, duration of infection, and efficacy of doxycycline therapy in dogs infected with one or both organisms. Six dogs per group were either uninfected, A. platys infected, E. canis infected, A. platys and E. canis co-infected, A. platys infected and E. canis challenged or E. canis infected and A. platys challenged at day 112 post-infection (PI). Doxycycline treatment was initiated at 211 days PI, followed by dexamethasone immunosuppression beginning 410 days PI.

RESULTS

Initially, transient decreases in hematocrit occurred in all groups infected with E. canis, but the mean hematocrit was significantly lower in the A. platys and E. canis co-infected group. All dogs except the controls developed marked thrombocytopenia after initial infection followed by gradually increased platelet counts by 112 days PI in groups with the single infections, while platelet counts remained significantly lower in the A. platys and E. canis co-infected group. Both sequential and simultaneous infections of A. platys and E. canis produced an enhanced humoral immune response to A. platys when compared to infection with A. platys alone. Likewise, co-infection with E. canis and A. platys resulted in a more persistent A. platys infection compared to dogs infected with A. platys only, but nearly all A. platys infected dogs became A. platys PCR negative prior to doxycycline treatment. E. canis infected dogs, whether single or co-infected, remained thrombocytopenic and E. canis PCR positive in blood for 420 days. When treated with doxycycline, all E. canis infected dogs became E. canis PCR negative and the thrombocytopenia resolved. Despite immunosuppression, neither A. platys nor E. canis DNA was PCR amplified from doxycycline-treated dogs.

CONCLUSIONS

The results of this study demonstrate that simultaneous or sequential infection with A. platys and E. canis can alter various pathophysiological parameters in experimentally infected dogs, and because natural exposure to multiple tick-borne pathogens occurs frequently in dogs, awareness of co-infection is important in clinical practice.

Immunophenotype of dogs with subclinical ehrlichiosis

The purpose of this study was the characterization of the different subsets of lymphocyte cells in dogs with subclinical ehrlichiosis in order to contribute to the knowledge of the immune response developed in the course of this disease. Thirty-eight dogs with subclinical ehrlichiosis and 15 unaffected dogs from two shelters in the area of Valencia (eastern Spain) were included in the study. The study of lymphocyte populations was made by flow cytometry. Monoclonal antibodies against CD3, CD4, CD8, and CD21 were used. Based on our results, the most common findings of the subclinical phase of canine ehrlichiosis were lymphocytosis, relative neutropenia, and a decrease in the neutrophil/lymphocyte ratio. Lymphocytosis in these dogs was from an increase of T lymphocyte counts. Tc cell counts in dogs with subclinical ehrlichiosis were higher than in healthy dogs. This rise in the number of Tc lymphocytes resulted in a reduced percentage of Th lymphocytes and in a decrease in the CD4/CD8 ratio.

Defining the immune response to Ehrlichia species using murine models

Pathogenic bacteria belonging to the family Anaplasmataceae include species of the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis, first known as the causative agent of human monocytic ehrlichiosis, also infects several vertebrate hosts including white-tailed deer, dogs, coyotes and goats. E. chaffeensis is transmitted from the bite of an infected hard tick, such as Amblyomma americanum. E. chaffeensis and other tick-transmitted pathogens have adapted to both the tick and vertebrate host cell environments. Although E. chaffeensis persists in both vertebrate and tick hosts for long periods of time, little is known about that process. Immunological studies will be valuable in assessing how the pathogen persists in nature in both vertebrate and invertebrate hosts. Understanding the host immune response to the pathogen originating from dual host backgrounds is also important to develop effective methods of diagnosis, control and treatment. In this paper, we provide our perspective of the current understanding of the immune response against E. chaffeensis in relation to other related Anaplasmataceae pathogens.