Page 972 - Clinical Small Animal Internal Medicine

910 Section 9 Infectious Disease

Table 93.3 (Continued)
VetBooks.ir Assay Advantages Disadvantages Recommended testing time

Spinning‐disc ● Detects antibodies against E. canis ● Cannot be performed in Currently unknown.
interferometry and A. phagocytophilum practice Recommended after 3–4
serology: Accuplex4 ● May detect E. canis antibodies ● Indicates exposure, not infection weeks post infection
Bio‐CD earlier than the ELISA ● Does not quantify antibody
response
● May have less accuracy and
reproducibility than the ELISA
for Anaplasma spp.
● Unclear if detects antibodies
against A. platys, E. chaffeensis,
E. ewingii, Panola Mountain
Ehrlichia, and E. muris
Western ● Detects specific antibody response ● Cannot be performed in Subclinical or chronic phases
immunoblotting to ehrlichial species practice
● Less cross‐reactivity among species ● Technically difficult
than other serology methods ● Not widely available
● Primarily used on research
Polymerase chain ● Early detection of active infection ● Cannot be performed in Acute phase.
reaction ● Highly sensitive for acute phase practice May detect carrier state and
● Identifies pathogens at the species ● Procedure not standardized chronically infected, but
sensitivity ranges from 25%
level, and even new species or strains among veterinary laboratories to 68%
● Can test a wide variety of samples ● Sensitivity and specificity
(whole blood, buffy coat, cavitary depend on assay design
effusions, synovial liquid, tissue ● Risk of false‐positive results if
aspirates or fragments, and laboratory quality control is not
ectoparasites) implemented
● Can test frozen historical samples ● Limited sensitivity for chronic
● Widely available infection
● Negative results do not rule out
infection, even after therapy, as
bacteria levels may be lower
than limit of detection of assay
● Not recommended as a single
screening test for blood donors
ELISA, enzyme‐linked immunosorbent assay; IFA, immunofluorescent antibody.

Visualization of morulae in blood smears using light and other potential differential diagnosis. A single posi-
microscopy can facilitate diagnosis, but it is insensitive. tive serology result in a healthy dog with no clinical,
In addition, stain artifacts or basophilic precipitates can hematologic or biochemical abnormalities or proteinu-
be confused with inclusions so other diagnostic tech- ria may not require therapy. Because serology depends
niques are recommended. Serology based on assays upon production of specific antibodies, false‐negative
such as immunofluorescent antibody (IFA), enzyme‐ results may occur in the first 1–2 weeks post infection.
linked immunosorbent assay (ELISA), spinning‐disc Seronegative dogs with compatible clinical signs should
interferometry or western blotting is the most common be retested 2–3 weeks later to demonstrate seroconver-
method used for diagnosis. Most of the serology meth- sion, and alternative methodologies, including poly-
ods cannot precisely identify the species of Ehrlichia or merase chain reaction (PCR), should be utilized.
Anaplasma involved due to serologic cross‐reactivity. Continuous decrease in antibody titers after antibiotic
Serology only documents exposure to, not infection therapy may suggest clearance of infection; however, it
with, one or more organisms, so previous exposure or may take several months to years for titers to decrease.
self‐limiting infection should be considered in a patient In addition, dogs with chronic infection may be seron-
with a positive result. Results of serology should be inter- egative due to the ability of the pathogen to evade the
preted in light of clinical signs, laboratory abnormalities, immune system.