Effects of the dose of Ehrlichia phagocytophila on the severity of experimental infections in lambs

Evaluation of an Indirect Immunofluorescence Assay for the Detection of Anaplasma phagocytophilum Antigen in Ovine Buffy Coat Smears

Diagnosis of anaplasmosis is challenging considering the great variation in clinical signs and the limitations of the available diagnostic assays, while the detection of carrier animals that play a significant role in disease epidemiology as reservoirs is of great significance. In this study, we evaluated the diagnostic accuracy of a newly developed indirect immunofluorescent assay (Ag-IFAT) for the detection of A. phagocytophilum antigens in buffy coat specimens, alone and in combination with cytology, using PCR as a reference. Blood samples were collected from 138 sheep of the Chios breed from six farms in Greece. A buffy coat was extruded from the centrifuged blood. Buffy coat smears were used for cytological examination and the Ag-IFAT assay. The Ag-IFAT assay presented excellent specificity (100%) and high sensitivity (85.4%) for the detection of A. phagocytophilum antigens in buffy coats, and it has an almost perfect agreement with PCR and cytology (κ value = 0.88 and 0.85, respectively). A. phagocytophilum antigens are likely to be detected using Ag-IFAT in a PCR-positive animal, as indicated by the good performance of the assay. Overall, this assay presents high diagnostic accuracy, and it could be used for the detection of animals during the early stage of infection.

Quantitative and Morphological Blood Cell Findings Associated with the Presence of Antigen and/or Antibodies Against Anaplasma phagocytophilum in Sheep

Anaplasma phagocytophilum is the causative agent of a disease known as tick borne fever in sheep, although fever is not always present. Due to inconclusive clinical signs, diagnosis is based on the cytological or molecular detection of the microorganism in blood and/or the determination of antibodies against A. phagocytophilum. The aim of the study was to determine the alterations caused by the presence of antibodies and/or the antigen of A. phagocytophilum in the blood cell count and morphology in sheep. Cytology and indirect immunofluorescence assay were performed for detection of antibodies and the antigen of A. phagocytophilum, respectively. The samples were divided into four groups depending on the result of the antigen and antibody detection. The samples that were only positive for antigen detection had mild anemia, leukopenia (lymphopenia), and thrombocytopenia. The samples that were positive in both assays had anemia, leukopenia (neutropenia and lymphopenia), and thrombocytopenia. Samples that were positive only for antibody detection had mild leukopenia. Morphological findings in infected sheep included band neutrophils, toxic neutrophils, reactive lymphocytes, and activated monocytes. The hematological findings along with cytological and serological tests can contribute to the assessment of the stage of the disease. A combination of leukopenia and thrombocytopenia raises a strong suspicion of the disease. When the microorganism and antibodies are simultaneously present, sheep are more susceptible to secondary complications. The first reported morphological findings and the quantitative hematological alterations are indicative of an inflammatory reaction, antigenic stimulation, and stress.

Clinical and immunological responses in sheep after inoculation with Himar1-transformed Anaplasma phagocytophilum and subsequent challenge with a virulent strain of the bacterium

In Norway, the tick-transmitted bacterium Anaplasma phagocytophilum is estimated to cause tick-borne fever (TBF) in 300 000 lambs on pastures each year, resulting in economic and animal welfare consequences. Today, prophylactic measures mainly involve the use of acaricides, but a vaccine has been requested by farmers and veterinarians for decades. Several attempts have been made to produce a vaccine against A. phagocytophilum including antigenic surface proteins, inactivated whole cell vaccines and challenge followed by treatment. In the current study, a virulent wild type strain of A. phagocytophilum named Ap.Norvar1 (16S rRNA sequence partial identical to sequence in GenBank acc.no M73220) was subject to genetic transformation with a Himar1-transposon, which resulted in three bacterial mutants, capable of propagation in a tick cell line (ISE6). In order to test the immunogenicity and pathogenicity of the live, mutated bacteria, these were clinically tested in an inoculation- and challenge study in sheep. One group was inoculated with the Ap.Norvar1 as an infection control. After inoculation, the sheep inoculated with mutated bacteria and the Ap.Norvar1 developed typical clinical signs of infection and humoral immune response. After challenge with Ap.Norvar1, 28 days later all groups inoculated with mutated bacteria showed clinical signs of tick-borne fever and bacteremia while the group initially inoculated with the Ap.Norvar1, showed protection against clinical disease. The current study shows a weak, but partial protection against infection in animals inoculated with mutated bacteria, while animals that received Ap.Norvar1 both for inoculation and challenge, responded with homologues protection.

Assessing the clinical and bacteriological outcomes of vaccination with recombinant Asp14 and OmpA against A. phagocytophilum in sheep

Anaplasma phagocytophilum is a tick borne bacterium, causing disease in sheep and other mammals, including humans. The bacterium has great economic and animal welfare implications for sheep husbandry in Northern Europe. With the prospect of a warmer and more humid climate, the vector availability will likely increase, resulting in a higher prevalence of A. phagocytophilum. The current preventive measures, as pyrethroids acting on ticks or long acting antibiotics controlling bacterial infection, are suboptimal for prevention of the disease in sheep. Recently, the increased awareness on antibiotic- and pyrethorid resistance, is driving the search for a new prophylactic approach in sheep against A. phagocytophilum. Previous studies have used an attenuated vaccine, which gave insufficient protection from challenge with live bacteria. Other studies have focused on bacterial membrane surface proteins like Asp14 and OmpA. An animal study using homologous proteins to Asp14 and OmpA of A. marginale, showed no protective effect in heifers. In the current study, recombinant proteins of Asp14 (rAsp14) and OmpA (rOmpA) of A. phagocytophilum were produced and prepared as a vaccine for sheep. Ten lambs were vaccinated twice with an adjuvant emulsified with rAsp14 or rOmpA, three weeks apart and challenged with a live strain of A. phagocytophilum (GenBank acc.nr M73220) on day 42. The control group consisted of five lambs injected twice with PBS and adjuvant. Hematology, real time qPCR, immunodiagnostics and flow cytometric analyses of peripheral blood mononuclear cells were performed. Vaccinated lambs responded with clinical signs of A.phagocytophilum infection after challenge and bacterial load in the vaccinated group was not reduced compared to the control group. rAsp14 vaccinated lambs generated an antibody response against the vaccine, but a clear specificity for rAsp14 could not be established. rOmpA-vaccinated lambs developed a strong specific antibody response on days 28 after vaccination and 14 days post-challenge. Immunofluorescent staining and flow cytometric analysis of peripheral blood mononuclear monocytes revealed no difference between the three groups, but the percentage of CD4⁺, CD8⁺, γδ TcR⁺, λ-Light chain⁺, CD11b⁺, CD14⁺ and MHC II⁺ cells, within the groups changed during the study, most likely due to the adjuvant or challenge with the bacterium. Although an antigen specific antibody response could be detected against rOmpA and possibly rAsp14, the vaccines seemed to be ineffective in reducing clinical signs and bacterial load caused by A. phagocytophilum. This is the first animal study with recombinant Asp14 and OmpA aimed at obtaining clinical protection against A. phagocytophilum in sheep.

Opening the black box of Anaplasma phagocytophilum diversity: current situation and future perspectives

Anaplasma phagocytophilum is a zoonotic obligate intracellular bacterium known to be transmitted by ticks belonging to the Ixodes persulcatus complex. This bacterium can infect several mammalian species, and is known to cause diseases with variable symptoms in many domestic animals. Specifically, it is the causative agent of tick-borne fever (TBF), a disease of important economic impact in European domestic ruminants, and human granulocytic anaplasmosis (HGA), an emerging zoonotic disease in Asia, USA and Europe. A. phagocytophilum epidemiological cycles are complex and involve different ecotypes, vectors, and mammalian host species. Moreover, the epidemiology of A. phagocytophilum infection differs greatly between Europe and the USA. These different epidemiological contexts are associated with considerable variations in bacterial strains. Until recently, few A. phagocytophilum molecular typing tools were available, generating difficulties in completely elucidating the epidemiological cycles of this bacterium. Over the last few years, many A. phagocytophilum typing techniques have been developed, permitting in-depth epidemiological exploration. Here, we review the current knowledge and future perspectives regarding A. phagocytophilum epidemiology and phylogeny, and then focus on the molecular typing tools available for studying A. phagocytophilum genetic diversity.

A comparative study of clinical manifestations, haematological and serological responses after experimental infection with Anaplasma phagocytophilum in two Norwegian sheep breeds

Background

It has been questioned if the old native Norwegian sheep breed, Old Norse Sheep (also called Norwegian Feral Sheep), normally distributed on coastal areas where ticks are abundant, is more protected against tick-borne infections than other Norwegian breeds due to a continuously high selection pressure on pasture. The aim of the present study was to test this hypothesis in an experimental infection study.

Methods

Five-months-old lambs of two Norwegian sheep breeds, Norwegian White (NW) sheep and Old Norse (ON) sheep, were experimentally infected with a 16S rRNA genetic variant of Anaplasma phagocytophilum (similar to GenBank accession number M73220). The experiment was repeated for two subsequent years, 2008 and 2009, with the use of 16 lambs of each breed annually. Ten lambs of each breed were inoculated intravenously each year with 0.4 ml A. phagocytophilum-infected blood containing approximately 0.5 × 10⁶ infected neutrophils/ml. Six lambs of each breed were used as uninfected controls. Half of the primary inoculated lambs in each breed were re-challenged with the same infectious dose at nine (2008) and twelve (2009) weeks after the first challenge. The clinical, haematological and serological responses to A. phagocytophilum infection were compared in the two sheep breeds.

Results

The present study indicates a difference in fever response and infection rate between breeds of Norwegian sheep after experimental infection with A. phagocytophilum.

Conclusion

Although clinical response seems to be less in ON-lambs compared to NW-lambs, further studies including more animals are needed to evaluate if the ON-breed is more protected against tick-borne infections than other Norwegian breeds.

Unidirectional suppression of Anaplasma phagocytophilum genotypes in infected lambs

Five-month-old lambs were simultaneously infected with different doses of two 16S rRNA genetic variants of Anaplasma phagocytophilum and thereafter followed for clinical observation and blood sampling. The result of the study indicates a unidirectional suppression of genotypes in infected lambs, at least during a certain period of an A. phagocytophilum infection.

Susceptibility of cattle to infection with Ehrlichia equi and the agent of human granulocytic ehrlichiosis

OBJECTIVE

To determine susceptibility of cattle to infection with Ehrlichia equi and the agent of human granulocytic ehrlichiosis (HGE).

DESIGN

Experimental disease and prevalence survey.

ANIMALS

6 cattle, 2 horses, and 2,725 serum samples from healthy cattle.

PROCEDURE

2 cattle and 1 horse were inoculated with E equi, 2 cattle and 1 horse were inoculated with the HGE agent, and 2 cattle served as sham-inoculated controls; inoculated animals were evaluated via clinical, hematologic, serologic, and real-time polymerase chain reaction tests. Prevalence of antibodies against E equi in 2,725 healthy cattle was determined by use of an indirect immunofluorescent technique.

RESULTS

No abnormal clinical or hematologic findings or inclusion bodies within granulocytes were observed in the cattle after inoculation, and results of all polymerase chain reaction tests were negative. Seroconversion in inoculated cattle developed 10 to 12 days after inoculation (reciprocal titers, 160). Both horses developed clinical signs of ehrlichiosis. Five of 2,725 (0.18%) cattle were seropositive for E equi, with titers ranging from 20 to 80. All seropositive cattle originated from the same tick-rich region in the Sierra Nevada foothills.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that cattle are not susceptible to infection with E equi or the agent of HGE and that prevalence of exposure to E equi in healthy cattle is low. Therefore, E equi and the agent of HGE are likely of negligible importance for cattle in North America.

The effect of two different oxytetracycline treatments in experimental Ehrlichia phagocytophila infected lambs

The effect of 2 different oxytetracycline treatments in acute E. phagocytophila infected lambs was investigated. Twenty 5-month-old lambs of the Dala and Rygja breeds were used. Ten lambs were inoculated intravenously with a stabilate of an ovine E. phagocytophila strain. On the third day of fever, 4 lambs were given long-acting oxytetracycline (Terramycin prolongatum vet, Pfizer) (20 mg/kg) intramuscularly and another 4 lambs were given short-acting oxytetracycline (Terramycin vet, Pfizer) (10 mg/kg) intravenously for 5 consecutive days. The lambs were examined for the presence of Ehrlichia infection by blood smear evaluation, polymerase chain reaction (PCR) and antibody titre against E. equi. One month after the last antibiotic treatment, 250 ml citrate blood from each of these lambs were inoculated into each of 10 susceptible lambs, which were observed during the following 6 weeks. The results indicate that oxytetracycline given in the acute stage of the infection may effectively terminate the development of fever, rickettsemia and weight reduction in E. phagocytophila infected lambs. No difference was observed between the 2 treatment groups. However, at least 3 of 8 antibiotic treated lambs (37.5%) were still infected with granulocytic Ehrlichia 3 months after treatment.