Canine Ehrlichiosis: An update on Diagnosis
Shraddha Sinha, S.K. Maiti
Department of Teaching Veterinary Clinical Complex
Dau Shri Vasudev Chandrakar Kamdhenu Vishwavidyalaya,
Anjora, Durg- 491001 (C.G.)
Introduction
Ehrlichiosis was first discovered in Algeria in 1935 followed by in United States in 1963 but in the 1970’s it was recognized as an important disease due to the illness and death of many military dogs, who returned from the Vietnam war. Canine ehrlichiosis is an infectious tick- borne disease of dogs caused by different species of Ehrlichia such as Ehrlichia canis, E chaffeensis and E ewingii and E. platys. Ehrlichia , an obligate intracellular bacteria which primarily affects cells of immune system of dogs, and cats is also known as canine haemorrhagic fever, canine typhus, canine tracker disease, and tropical canine pancytopenia.
The disease is characterized by a sudden reduction in different cellular components of blood most commonly anaemia and or thrombocytopenia, though course of clinicopathological effects varies depending on the Ehrlichia species.
Clinical presentations:
There are three stages/phages of Ehrlichiosis in dogs namely acute stage, sub clinical stage and chronic stage. So, clinical signs in Ehrlichiosis depends on in which stage the dog is. Many dogs experience self-limiting infection; however, some may develop a secondary quiescent phase of disease followed by a severe and life-threatening third chronic stage. In endemic area, coinfection with other tick borne infection may complicate the clinical diagnosis.
The most common typical clinical signs of acute ehrlichiosis are:
Fever, anorexia, lethargy, widespread lymphadenopathy, splenomegaly, bleeding tendencies, ocular lesions and pale conjunctival mucose. Presence of ticks on the body may be there.
On the other hand, variable anorexia, depression, fatigue, stiffness and unwillingness to walk, oedema of the limbs or scrotum, stomatitis, nervos signs like in-coordinated gait, seizure, coughing or dyspnea etc have been reported in chronic form of the disease. Bilateral epistaxis is more common and severe in this stage.
The most severe instances are observed during the warmer months, which also happen to be when the tick vector is most active. Chronic conditions can appear at any time of the year. Ocular lesions mainly uveitis is the most common manifestation though ocular discharge,conjunctivitis, scleral haemorrhage may be there. Although the clinical course of other ehrlichial infections produced by E chaffeensis, E ewingii, resembles acute E canis infection, it is typically milder and more self-limiting.
Haematological examination:
A CBC is an important screening test since the most consistent change in hemogram is thrombocytopenia, that occurs more than 80% cases of ehrlichiosis. Haemgram may be typically normal during the acute phase of E canis infection in dogs, but it may also show mild normocytic, normochromic anaemia. Other changes include leukopenia, or mild leukocytosis, lymphopenia or mild lymphocytosis and pancytopenia. A mild to moderate thrombocytopenia and or anaemia are most important haematological changes in chronic ehrlichiosis.
Cytological/blood smear examination:
Demonstration of Ehrlichia organism inside monocytes, neutrophils, lymphocytes or platelets, which are visible as intracytoplasmic inclusion structures called morulae, in Romanowsky stained smears from blood , buffy coat is very useful to confirm definitive diagnosis. E canis and E chaffeensis most commonly infect monocytes whereas E ewingii infects granulocytes. Due to the difficulty in demonstrating tiny numbers of organisms, this method of diagnosis lacks sensitivity. However, sensitivity of this technique can be increased by examining a concentrated buffy coat smear and the feathered edges of blood slides. Diagnostic sensitivity of buffy coat, lymph node or their combination has been reported to be 66%, 61% and 74% respectively. But cytological/blood smear examination technique is insensitive in subclinical and chronic infection of Ehrlichia infection. Lymph node aspiration reveals hyperplasia An immune-mediated thrombocytopenia and bleeding risk are brought on by vasculitis.
Blood biochemistry
Common biochemical abnormalities in ehrlichiosis include hyperproteinemia, hyperglobulinemia, hypoalbuminemia, and moderately increased alkaline phosphatase and alanine aminotransferase activities. Comparatively to non-pancytopenic dogs, pancytopenic dogs typically have lower quantities of total protein, total globulin, and gamma -globulin. Liver illness in the myelosuppressive CME might be either primary or due to hypoxia, intrahepatic haemorrhage, or septicemia. Some dogs may have increased levels of creatinine while also having glomerular proteinuria caused by glomerulonephritis with or without immune-complex deposition in the chronic and acute CME, respectively.
Serological test:
Currently, serology is the most important to confirm E. canis infection . The reference standard serological test for diagnosis of ehrlichiosis is indirect fluorescent antibody (IFA) assay for IgG although enzyme-linked immunosorbent assays (ELISA) are also being used. Most laboratories consider an IgG titer of 1:80 or higher to be indicative of prior exposure to an Ehrlichia spp. Antibodies don’t consistently correlate with the current carrier status, the length of the infection, or the presence and severity of clinical disease.
On the basis of immunofluorescent antibodies and enzyme immunoassays, serologic diagnostics for ehrlichiosis are available. The serology may be negative early in the course of the disease because the IgG antibody response to infection may be delayed for several weeks and IgM titers may be low. Additionally, as antibodies can last for months or even years after infection, serology might be difficult to use for the detection of clinically relevant infections,especially in locations with high enzootic activity where many dogs may already be immune to these agents from prior infections.
Strong serologic cross-reactivity exists between E canis, E chaffeensis, and E ewingii. The EML agent reacts cross-reactively to E chaffeensis in humans.
POLYMERASE CHAIN REACTION (PCR)
It is the most sensitive test for detection of early infection, molecular characterization, and quantification (real-time PCR) of the Ehrlichial organism. Blood, tissue aspirates, or biopsy specimens of reticuloendothelial organs such lymph nodes, spleen, liver, etc can be used for PCR. PCR may give false-positive result immediately after treatment since the test’s target is DNA, which may persist in the animals. Nested PCR and Multiplex PCR have also been developed targeting 16S rRNA and p30 genes to detect specifically E canis infection. The p30 genes based nested PCR has been found to be more sensitive than 16S rRNA based nested PCR for diagnosis of CME.
Commercial Diagnostic kits:
- VETSCAN® CANINE EHRLICHIA RAPID TEST by Zoetis
The VETSCAN Canine Ehrlichia Rapid Test is an easy-to-use test for the detection of antibodies to E. canis, E. chaffeensis, and E. ewingii in whole blood, serum or plasma.
- EHRLICHIA canis fastest kit by Vetlab
A quick immunochromatographic screening test for the detection of anti-Ehrlichia canis antibodies is the FASTest EHRLICHIA canis test kit. It can be utilised up to 28 days following infection using serum, plasma, or whole blood. The technique makes use of a special mixture of a labelled antigen that is adsorbed to the solid phase membrane and is conjugated on dye particles.
- SNAP4Dx KIT by IDEXX USA
The SNAP® 4Dx® Plus Test is an in vitro test for the detection of antigen to Dirofilaria immitis, antibodies to Borrelia burgdorferi, Anaplasma phagocytophilum, Anaplasma platys, Ehrlichia canis, and Ehrlichia ewingii in canine serum, plasma, or anticoagulated whole blood.
