NEW DIAGNOSTIC SEROLOGICAL TEST FOR CANINE LEISHMANIOSIS
What is canine Leishmania?
Leishmania is a disease caused by Leishmania infantum, a protozoal organism that is transmitted between dogs by sandflies. Vertical transmission and spread through contaminated blood products is also possible. Leishmania can be zoonotic; infection is usually transmitted from dogs to humans via sandflies. Leishmania is very common in many of the holiday destinations that UK owners take their dogs to using the Pet Travel Scheme e.g. countries surrounding the Mediterranean such as Spain, Italy and Greece. Since the incubation period for this disease can be very long (months to years), a recent history of travel is not a prerequisite for considering this disease as a differential diagnosis.
Many dogs infected with Leishmania are asymptomatic; the prevalence of infection in endemic areas is far higher than the prevalence of clinical disease. It is therefore important, in our patients, to differentiate confirming evidence of Leishmania infection compared to diagnosing disease due to Leishmania.
What clinical signs are common with clinical Leishmania infection?
- Skin lesions (scaling is common, also alopecia, ulceration) especially head and pressure points
- Weight loss & poor body condition
- Ocular signs (e.g. uveitis, conjunctivitis, keratoconjunctivitis sicca)
- Lymphadenopathy
What other clinical signs may be seen with clinical Leishmania?
- Epistaxis
- Splenomegaly
- SIgns of kidney disease (glomerulonephritis & interstitial nephritis can be seen); polyuria & polydipsia
- Abnormal nails
- Lameness due to polyarthritis
What clinicopathological changes can occur with clinical Leishmania?
The following non-specific changes are not infrequently seen with clinical Leishmania:-
- Hyperproteinaemia due to hyperglobulinaemia
- Hypoalbuminaemia
- Elevated renal parameters; urea & creatinine
- Elevated urine protein to creatinine ratio (≥ 0.5)
- Non-regenerative anaemia
How do I diagnose Leishmania infection in dogs?
IN DOGS WITH CLINICAL SIGNS AND/OR CLINICOPATHOLOGICAL ABNORMALITIES COMPATIBLE WITH CANINE LEISHMANIOSIS - TO DIAGNOSE DISEASE
Demonstration of Leishmania infantum organisms in samples
Finding Leishmania organisms on stained smears or sections prepared from fine needle aspirates or tissue biopsies from affected tissues is useful to confirm infection, although the examiner needs to be experienced in identifying organisms. Organisms can be scarse and only present in certain organs, reducing the sensitivity of this technique. Samples should only be obtained in dogs in which clinical Leishmania is suspected due to the presence of consistent clinical signs and/or clinicopathological changes. Suitable samples include bone marrow, lymph node, spleen, skin or joint fluid. Samples showing pathology consistent with Leishmania infection e.g. (pyo)granulomatous or lymphoplasmacytic inflammation or reactive hyperplasia, as well as organisms, are more likely to represent clinically significant Leishmania infection.
IN HEALTHY DOGS - TO DIAGNOSE INFECTION
&
IN DOGS WITH CLINICAL SIGNS AND/OR CLINICOPATHOLOGICAL ABNORMALITIES COMPATIBLE WITH CANINE LEISHMANIOSIS - TO DIAGNOSE DISEASE
i) Serology - antibody testing
The detection of Leishmania-specific serum IgG antibodies (Abs) in the serum of dogs using quantitative techniques is very useful in the diagnosis of Leishmania infection. Antibodies are typically detected by either ELISA or immunofluroescence. Although it can take a few months for dogs to seroconvert, the long incubation period with Leishmania means that most sick dogs are likely to be Ab positive. High Ab levels are consistent with clinical Leishmaniosis. Low Ab levels are not usually indicative of disease, although infection is implied, and in these cases further montoring (repeat serology every 3-6 months) and /or additional diagnostic tests such as PCR are indicated to help confirm or exclude clinical Leishmania disease. PCR results can also help determine when treatment courses can be completed.
A new Leishmania ELISA is being launched by Acarus, Langford Veterinary Services; this sensitive and specific quantitative ELISA will determine if Abs to Leishmania are present and, if they are, will determine whether high or low levels of Ab are present. This measurement will not only help vets determine the significance of any Leishmania infection present, but it will also help monitor changes in Ab level, such as during longer term treatment (when Ab levels should fall; negative or low Ab levels are recommended before stopping Leishmania treatment), or if a dog is being monitored for any increase in Ab levels consistent with the start of clinical disease
ii) Polymerase chain reaction (PCR)
PCR is a sensitive and specific technique that can amplify DNA from Leishmania infantum in various samples. PCRs based on amplifying Leishmania kinetoplast DNA (kDNA), such as the PCR offered by Acarus, Langford Veterinary Services, are particularly sensitive due to the many thousands of kDNA sequences present in each Leishmania organism. Real-time PCR, as offered by Acarus, additionally allows quantification of Leishmania DNA in the sample; thus the level of any Leishmania infection present can be determined (higher levels consistent with severe disease), and additionally response to treatment can be monitored (as Leishmania organism numbers should fall quite quickly with effective treatment). PCR results can also help determine when treatment courses can be completed (negative PCR results should be obtained before treatment is stopped).
Samples suitable for PCR include blood samples, bone marrow, lymph node, skin or splenic aspirates, or conjunctival swabs. PCR is more sensitive when performed on samples collected from affected tissues in sick animals, such as lymph node or bone marrow aspirates, than on blood samples. PCR on conjunctival swabs has also shown encouraging sensitivity.
Although blood is often positive by PCR in clinical Leishmania disease, a negative result cannot be used to rule out disease, and in these cases concurrent serology testing for Abs is helpful to determine if clinical Leishmania disease is likely in cases with consistent clinical signs and/or clinicopathological changes. Additionally PCR can sometimes generate positive results in dogs that are Leshmania infected but which do not have clinical disease, so again testing for Abs is helpful to determine if clinical Leishmania disease is likely.
Together with clinical signs and clinicopathological changes, combined Leishmania PCR and Ab testing gives the maximum information for helping you determine whether a dog is Leishmania infected and/or has Leishmania disease. Both of these tests can now be run at Acarus, Langford Veterinary Services.PCR requires submission of EDTA blood; this same sample can be used for Ab testing. Alternatively Ab testing can be run on plain blood samples.
Further details about Leishmania (including its treatment and monitoring) can be found here