ABSTRACT
After the 1999 outbreak of West Nile (WN) encephalitis in New York horses, a case definition was developed that specified the clinical signs, coupled with laboratory test results, required to classify cases of WN encephalitis in equines as either probable or confirmed. In 2000, 60 horses from seven states met the criteria for a confirmed case. The cumulative experience from clinical observations and diagnostic testing during the 1999 and 2000 outbreaks of WN encephalitis in horses will contribute to further refinement of diagnostic criteria.
Subject(s)
Disease Outbreaks , Horse Diseases/physiopathology , West Nile Fever/veterinary , West Nile virus/physiology , Animals , Antibodies, Viral/blood , Antibodies, Viral/cerebrospinal fluid , Brain/pathology , Brain/virology , Chlorocebus aethiops , DNA, Viral/analysis , Horse Diseases/classification , Horse Diseases/epidemiology , Horse Diseases/immunology , Horses , Rabbits , Reverse Transcriptase Polymerase Chain Reaction , United States/epidemiology , Vero Cells , West Nile Fever/classification , West Nile Fever/epidemiology , West Nile Fever/physiopathology , West Nile virus/genetics , West Nile virus/immunology , West Nile virus/isolation & purificationABSTRACT
A traditional single-stage reverse transcription-polymerase chain reaction (RT-PCR) procedure is effective in determining West Nile (WN) virus in avian tissue and infected cell cultures. However, the procedure lacks the sensitivity to detect WN virus in equine tissue. We describe an RT-nested PCR (RT-nPCR) procedure that identifies the North American strain of WN virus directly in equine and avian tissues.
Subject(s)
Bird Diseases/virology , Disease Reservoirs/veterinary , Horse Diseases/virology , West Nile Fever/veterinary , West Nile virus/isolation & purification , Animals , Bird Diseases/epidemiology , Bird Diseases/pathology , Birds/virology , Brain/pathology , Brain/virology , Horse Diseases/epidemiology , Horse Diseases/pathology , Horses/virology , New York/epidemiology , North America , RNA, Viral/analysis , Reverse Transcriptase Polymerase Chain Reaction , Sensitivity and Specificity , West Nile Fever/epidemiology , West Nile Fever/pathology , West Nile Fever/virology , West Nile virus/geneticsABSTRACT
Immunoglobulin M (IgM) and G (IgG) capture enzyme-linked immunosorbent assays (ELISAs) were used as possible adjuncts to hemagglutination inhibition (HI) and virus neutralization (VN) tests to differentiate between reaction to recent exposure to eastern equine encephalomyelitis (EEE) virus and those due to prior vaccination. Serum samples were evaluated by the IgM-capture ELISA, and the results were compared with those of HI and VN tests. Of 381 serum samples, 51% (195 samples) were positive by HI test (> or = 1:40) and 54% (205 samples) were positive by VN test (> or = 1:10), but only 35% (132 samples) were positive by IgM-capture ELISA (> or = 1:100). With only a few exceptions, the sera with IgG ELISA titers had a VN titer of > or = 1:100. When EEE virus isolation and serology were compared, the EEE cases were divided into three categories: 1) peracute cases--the serum was negative for EEE IgM and IgG by the ELISA, negative for VN antibody, but HI antibody positive; 2) acute cases--IgM and HI antibody positive but negative for IgG and VN antibody; and 3) transitional cases--positive for IgM and IgG antibodies, HI titers of 1:40-1:160, and VN titers of > or = 1:100. IgM antibodies of EEE virus were monospecific and did not cross-react with western or Venezuelan equine encephalomyelitis viral antigens by the ELISA.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Antibodies, Viral/blood , Brain/microbiology , Encephalitis Virus, Eastern Equine , Encephalomyelitis, Equine/veterinary , Horse Diseases , Immunoglobulin G/blood , Immunoglobulin M/blood , Animals , Antigens, Viral/immunology , Cross Reactions , Diagnosis, Differential , Encephalitis Virus, Eastern Equine/immunology , Encephalitis Virus, Eastern Equine/isolation & purification , Encephalomyelitis, Equine/diagnosis , Encephalomyelitis, Equine/immunology , Enzyme-Linked Immunosorbent Assay/methods , Hemagglutination Inhibition Tests/methods , Horses , Neutralization Tests/methods , Viral VaccinesABSTRACT
An influenza virus, A/equine/Alaska/1/91 (H3N8), was isolated from horses from Alaska with an acute respiratory infection. Pathogenic and serologic studies revealed that this virus is similar to previously isolated equine H3N8 influenza viruses. Antigenic analyses utilizing hemagglutination inhibition and neuraminidase inhibition assays indicated an antigenic drift from the prototype equine H3N8 influenza virus, A/equine/Miami/1/63. Partial sequence analysis of the A/equine/Alaska influenza virus indicated that each of 8 gene sequences are of equine origin.
