Clinical disease in dogs:
Probably only about 10% of infected dogs develop clinical disease.
Signs of leishmaniasis develop after a very prolonged incubation
period of months to years. When evident, clinical signs include:
- exfoliative
dermatitis (with ulceration, pustules, hyperkeratosis, hypopigmentation
and alopecia; generally non-pruritic; occurs in over 90% of clinical
cases)
- lymphadenopathy
- weight loss
- arthritis
- epistaxis and other forms of hemorrhage
- deformed claws
- splenomegaly
- ocular disease
- In a recent review of canine cases, 15% had only ocular disease
(uveitis, blepharospasm, keratoconjunctivitis most commonly)
at the time of presentation. (See Pena et al. 2000)
- renal failure
- The prognosis with renal involvement is very poor.
Clinical illness in a given animal appears to be related to
that animal's predisposition to develop a humoral rather than
a cell mediated immune response.This is largely an immune-mediated
disease due to an excessive, non-protective immunoglobulin response
(reflected frequently by hypergammaglobulinemia). Immune-complex
deposition leads to arthritis, glomerulonephritis, vasculitis,
uveitis and/or thrombocytopenia (which can lead to a hemorrhagic
diathesis). In addition, an infection-induced suppression of T
cells and the inability of macrophages to kill the organism contribute
to its persistence in a host.
Diagnosis in dogs:
- identification of the organism in blood
smears, skin biopsies, or lymph node or bone marrow aspirates
(esp. in monocytes/macrophages) (~30-60% success rate)
- culture or PCR detection of the organism from bone marrow,
blood, lymph node aspirates or skin biopsies (Historically it
had been suggested that bone marrow was the most sensitive sample
to test, but a recent study found the organism more often in
skin biopsies.)
- serology (IFA with a 1:64 cut-off for positivity) - But caution:
Leishmania and Trypanosoma cruzi may cross-react
in serologic assays.
Treatment in dogs:
- meglumine antimonate (Glucantime) or sodium stibogluconate
(Pentostam)
- These are compounds that inhibit protozoal enzymes involved
in glycolysis and fatty acid metabolism.
- They are not readily available commercially. Glucantime is
not available in the U.S. and Pentostam can only be obtinaed
from the CDC.
- The injections are very expensive and also painful.
- Treatment failures and relapses are not unusual. Dogs appear
to be more resistant to treatment than humans.
- There is a report of a dog being treated successfully and
without side-effects using allopurinol. (See J.A.V.M.A. 209:615,
1996) This drug has also been combined with stibogluconate in
humans.
- Amphotericin B and paromycin have also been used; these may
reduce clinical signs but are unlikely to eliminate the organism.
- A new drug, miltefosine (Impavido®), that has broad anti-parasitic
and anti-cancer properties has recently been shown to be effective
against Leishmania, even when given orally. ((See the
article by Sundar et al. and http://www.who.int/inf/en/pr-2002-46.html)
Prevention of infection in dogs:
- In enzootic areas, dogs should be housed in sandfly-free
kennels from just before sunset to just after sunrise.
- AN EFFECTIVE VACCINE IS SOUGHT, BOTH TO PREVENT THE
DISEASE IN DOGS AND TO REDUCE THEIR COMPETENCE AS A RESERVOIR
FOR INFECTION OF PEOPLE.
- Interestingly, in the case of cutaneous leishmaniasis, a
recent report suggests that protection from Leishmania
infection may be conferred by delayed-type hypersensitivity responses
that the body mounts against salivary proteins in the bite of
uninfected sand flies.
