Page 981 - Clinical Small Animal Internal Medicine

919

VetBooks.ir

96

Bartonellosis
Pedro P. Vissotto de Paiva Diniz, DVM, PhD

College of Veterinary Medicine, Western University of Health Sciences, Pomona, CA, USA

Etiology/Pathophysiology immune system. Other virulence factors also participate in
the pathogenesis of the infection. These include adhesion
Bartonellosis is a complex syndrome caused by gram‐ molecules, regulatory systems and a factor capable of inhib-
negative bacteria of the genus Bartonella, which are iting proinflammatory responses mediated by Toll‐like
transmitted by blood‐sucking arthropods and have tro- receptor IV. Bartonella spp. also infect dendritic cells,
pism for mammalian erythrocytes, endothelial cells, and microglial cells, monocytes, macrophages, and CD34+ pro-
bone marrow progenitor cells. There are at least 14 spe- genitor cells in the bone marrow. From these primary niches,
cies, subspecies or species candidatus of Bartonella Bartonella spp. are periodically shed into the bloodstream.
capable of infecting dogs, with at least six species capable Like bacteria belonging to the family Anaplasmataceae,
of infecting cats (Table 96.1). Bartonella spp. inhibit apoptosis of host cells. This allows
Most species of Bartonella reported from dogs and cats infected cells to remain in circulation longer, and increases
can also infect humans. Few Bartonella spp. are host specific, the likelihood of acquisition by a blood‐sucking arthropod
such as B. bacilliformis in people, with the vast majority of vector. The pathogen often establishes subclinical bactere-
species having a preferred host but being capable of infecting mia that can last from weeks to several months. It is still
other terrestrial mammals and even some marine animals. unclear why some dogs or cats may develop clinical manifes-
Bartonella spp. cause absent to minimal clinical manifesta- tations while other animals infected with the same Bartonella
tions in their preferred hosts. However, when a Bartonella sp. species are asymptomatic. Factors such as host immune
infects a nonadapted incidental host, clinical abnormalities response, species virulence, predisposing factors (congenital
are commonly seen. Severe illness is more frequently seen in valvular disease), infection chronicity, and concomitant
immunosuppressed hosts or when co‐infection with other infections may play a role in disease manifestation.
vector‐borne disease agents occurs. Bartonella causes
chronic infections in dogs, cats, and humans, many of which
are misdiagnosed and misreported. Epidemiology
Unlike some other vector‐borne disease agents, species of
Bartonella that infect dogs and cats do not form intracyto- Bartonella spp. can be transmitted by an increasing
plasmic morulae. Therefore, they cannot be seen on blood number of arthropod vectors. In dogs and cats, cat fleas
smears or cytologic specimens without the use of special (Ctenocephalides felis) have been well defined as the
staining. Based on genetic analysis and presence of virulent major mode of transmission. However, epidemiologic
factors, Bartonella spp. are divided into four lineages, with evidence also supports the role of ticks in transmission
B. bacilliformis being the ancestor of all other species. The to companion animals. Other suspected vectors include
vast majority of Bartonella spp. capable of infecting dogs Pulex flea species, lice, and biting flies.
and cats (lineages 3 and 4) have virulence factors that medi- The prevalence of Bartonella infection differs signifi-
ate erythrocyte adhesion in a host‐specific manner (Trw cantly between dogs and cats, being generally low in
type IV secretion system [T4SS]) and transfer effector pro- dogs and high in cats. There are also differences in infect-
teins into host cells (VirB T4SS) to promote chronic infec- ing species, with the most common species detected in
tion. Consequently, Bartonella can invade and multiply in dogs being B. henselae and B. vinsonii subsp. berkhoffii,
erythrocytes and endothelial cells and evade the host’s and the most common species in cats being B. henselae,

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical