CPD Article | EQUINE
development of respiratory signs.
Subacute/cardiac form ('Dikkop')
• Fever for 3-6 days and severe depression.
• Peripheral edema of head (especially supraorbital
fossa, also cheeks, lips, tongue and laryngeal
region), neck, chest
and ventral abdomen. No
edema of lower limbs.
• Petechial hemorrhages may be evident on
conjunctival mucosa; ecchymoses on tongue.
• Death 4-8 days.
• Recovery can occur; if so, edema subsides over 3-8
days.
Diagnostic investigation
• Endemic area, season, clinical signs (supraorbital
swellings are characteristic).
• Establish presence of suitable insect vectors.
Hematology
• Thrombocytopenia.
Identification of the agent
Virus isolation
• Unclotted whole blood collected during early
febrile stage of the disease.
• At post-mortem small pieces of spleen, lung and
lymph nodes can be collected.
• Samples should be kept at 4°C/39.2°F during
transportation and short-term storage prior to
processing.
• Virus isolation can be performed on baby hamster
kidney (BHK-21), monkey stable (MS) and African
green monkey kidney (Vero) mammalian cell lines
or on Culicoides and mosquito insect cell lines.
Detection of AHSV nucleic acid
• Rapid, sensitive and versatile test, with no need for
live virus.
• Can detect AHSV prior to development of clinical
signs, approximately 7 days after exposure.
• May detect erythrocyte-bound viral RNA; horse is
not necessarily infectious.
• Conventional agarose gel-based RT-PCR can be
used or real-time RT-PCR (rRT-PCR).
• RT-LAMP assays have also been developed.
Serological tests
• Indirect and competitive blocking ELISA; both
ELISAs are prescribed tests for international trade.
• Immunoblotting test.
• Complement fixation test: this test is also a
prescribed test for international trade but its use
is decreasing. Largely been replaced by the ELISA
methods. Can be used in endemic regions to
detect group-specific IgM antibodies against AHSV
following recent infection or vaccination.
• Virus neutralization test: can be used to determine
serotype and used for epidemiological surveillance
and transmission in endemic regions.
Confirmation of diagnosis
Discriminatory diagnostic features
• History especially contact with insect vectors and
enzootic animals.
• Clinical signs especially peripheral edema, high
temperature and dyspnea.
• Diagnostics are done by specialist labs such as the
National Vet Services Lab (NVSL) in Ames, Iowa, USA
and The Pirbright Institute (UK).
• Volume 21 Issue 4 | December 2019 •
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