Page 1505 - Small Animal Internal Medicine, 6th Edition

CHAPTER 95 Polysystemic Rickettsial Diseases 1477

can occur. Thus whether to treat seropositive healthy dogs Doxycycline given at 100 mg/dog/day was used successfully
is controversial. Arguments for and against testing or treat- as a chemopreventative (Davoust et al., 2005). Dogs used for
VetBooks.ir ing healthy dogs were reviewed by the ACVIM Infectious blood donors should be screened for E. canis infections by
serology and PCR assay; the ACVIM optimally recommends
Disease Study Group (Neer et al., 2002). The primary
reason to treat a seropositive healthy dog is to try to elimi-
et al., 2016). However, if PCR assay cannot be performed,
nate infection before development of chronic-phase disease. using only dogs that are negative in both tests (Wardrop
However, treatment of healthy dogs is controversial for at the minimal standard recommended was to use only sero-
least six reasons: (1) whether treatment halts progression to negative dogs as donors.
the chronic phase is unknown; (2) not all seropositive dogs Some countries have published guidelines to be used by
are infected; (3) not all seropositive dogs progress to the veterinarians to aid in the management of ehrlichiosis and
chronic phase; (4) whether treatment eliminates infection anaplasmosis (Neer et al., 2002; Sainz et al., 2015).
is unknown; (5) even if infection is eliminated, reinfection
can occur; and (6) treatment of healthy carriers may result
in antimicrobial resistance. Because further data are neces- FELINE MONOCYTOTROPIC
sary to make definitive recommendations, owners should EHRLICHIOSIS
be given the pros and cons and asked to make treatment
decisions. Etiology and Epidemiology
The prognosis is good for dogs with acute ehrlichiosis, Ehrlichia-like bodies or morulae have been detected in
and it is variable to guarded for those with chronic ehrlichio- peripheral lymphocytes or monocytes of naturally exposed
sis. Fever, petechiae, vomiting, diarrhea, epistaxis, and cats in a number of countries, including the United States,
thrombocytopenia often resolve within days after initiation Kenya, France, Brazil, and Thailand. DNA consistent with E.
of therapy in acute cases. Bone marrow suppression from canis has been amplified from blood of naturally infected
chronic-phase ehrlichiosis may not respond for weeks to cats in multiple surveys (Aguirre et al., 2004; Braga et al.,
months, if at all. Anabolic steroids and other bone marrow 2013; Braga et al., 2012; Breitschwerdt et al., 2002; de Oliveira
stimulants can be administered but are unlikely to be effec- et al., 2009; Hegarty et al., 2015). In Brazil, cats at high risk
tive because precursor cells are often lacking. Immune- for R. sanguineus infestation had a PCR-positive rate for E.
mediated events resulting in the destruction of red blood canis DNA of 9.4% (Braga et al., 2014). In addition, E.
cells or platelets are likely to occur with ehrlichiosis, leading chaffeensis DNA has been amplified from the blood of natu-
to the recommendation to administer antiinflammatory or rally exposed cats in the United States (Hegarty et al., 2015).
immunosuppressive doses of glucocorticoids to acutely In Europe, Ehrlichia canis DNA has been amplified from
affected animals. Prednisone (2.2 mg/kg PO divided q12h ticks collected from some cats (Pennisi et al., 2015). In the
during the first 3 to 4 days after diagnosis) may be beneficial United States, Amblyomma americanum removed from cats
in some cases, but controlled data are lacking. were shown to occasionally contain DNA of E. chaffeensis
(Little et al., 2018). Cats have also been shown to have anti-
Zoonotic Aspects and Prevention bodies that react to specific peptides of E. canis and E.
Dogs and human beings are both infected by E. canis and E. chaffeensis (Hegarty et al., 2015). These studies document
chaffeensis. Although people cannot acquire ehrlichiosis that cats can be exposed to mononuclear Ehrlichia spp. and
from handling an infected dog, dogs may be reservoirs for become infected. However, other studies of cats in endemic
these agents and may play a role in the human disease by areas (Arizona, Florida, Louisiana) have failed to amplify
bringing vectors into the human environment. Ticks should Ehrlichia spp. DNA from the blood of cats (Eberhardt et al.,
be removed and handled with care. Tick control should be 2006; Levy et al., 2011; Luria et al., 2004;). In one study of
maintained at all times; administration of fipronil was shown naturally exposed cats, E. canis DNA was amplified from the
to lessen transmission in one study (Davoust et al., 2003). In blood, but antibodies were never detected (Breitschwerdt
another study, administration of imidacloprid 10% and per- et al., 2002). Pathogenesis of disease associated with mono-
methrin 50% to young dogs lessened prevalence of E. canis cytotropic ehrlichiosis in cats is unknown but is likely to be
infections by 94.6% (Otranto et al., 2010). Because E. canis similar to that for E. canis infection of dogs. Guidelines for
is not passed transovarially in the tick, it can be eliminated cats with Ehrlichia spp. infections have been published in
in the environment by tick control or by treating all dogs Europe (Pennisi et al., 2017).
through a generation of ticks. Ehrlichia canis can be trans-
mitted within 3 hours of tick attachment so use of products Clinical Features
that repel or very quickly kill the ticks may be superior to All ages of cats have been infected; most cats were domestic
products with a slower kill rate (Jongejan et al., 2016). Rhipi- short-haired, and both males and females have been affected.
cephalus can only transmit E. canis for approximately 155 Anorexia, fever, inappetence, lethargy, weight loss, hyperes-
days; if tick control is not feasible tetracycline can be admin- thesia or joint pain, pale mucous membranes, splenomegaly,
istered (6.6 mg/kg PO daily for 200 days). During this time, dyspnea, and lymphadenopathy were the most common
infected dogs will not infect new ticks, and previously historic and physical examination abnormalities. Dyspnea,
infected ticks will lose the ability to transmit the organism. petechiae, retinal detachments, vitreous hemorrhages, and