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Objective—To determine signalment, history, clinical signs, duration, seasonality, and response to various treatments reported by owners for headshaking in horses.

Design—Owner survey.

Animals—109 horses with headshaking.

Procedure—Owners of affected horses completed a survey questionnaire.

Results—78 affected horses were geldings, 29 were mares, and 2 were stallions. Mean age of onset was 9 years. Headshaking in 64 horses had a seasonal component, and for most horses, headshaking began in spring and ceased in late summer or fall. The most common clinical signs were shaking the head in a vertical plane, acting like an insect was flying up the nostril, snorting excessively, rubbing the muzzle on objects, having an anxious expression while headshaking, worsening of clinical signs with exposure to sunlight, and improvement of clinical signs at night. Treatment with antihistamines, nonsteroidal antiinflammatory drugs, corticosteroids, antimicrobials, fly control, chiropractic, and acupuncture had limited success. Sixty-one horses had been treated with cyproheptadine; 43 had moderate to substantial improvement.

Conclusions and Clinical Relevance—Headshaking may have many causes. A large subset of horses have similar clinical signs including shaking the head in a vertical plane, acting as if an insect were flying up the nostrils, and rubbing the muzzle on objects. Seasonality and worsening of clinical signs with exposure to light are also common features of this syndrome. Geldings and Thoroughbreds appear to be overrepresented. Cyproheptadine treatment was beneficial in more than two thirds of treated horses. (J Am Vet Med Assoc 2001;219:334–337)

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in Journal of the American Veterinary Medical Association


Objective—To assess spatial and temporal patterns of seroprevalence among dogs in California to the causative agent of granulocytic ehrlichiosis (GE).

Sample Population—Sera of 1,082 clinically normal dogs from 54 of 59 counties in California in 1997 to 1998.

Procedure—Serum-specific IgG reactivity to Ehrlichia equi was assessed by use of an immunofluorescent antibody assay, using E equi-infected horse neutrophils as substrate. Data were analyzed, using a geographic information system. Spatial analysis of seroprevalence included first order Bayesian analysis of seroprevalence and second order analysis of clustering by K-function and Cuzick-Edwards tests. Monthly seroprevalence among dogs was examined by use of regression on monthly densities of Ixodes pacificus adults and nymphs .

Results—Seroprevalence among dogs to E equi was 8.68%. Data were seasonally bimodal with highest prevalence in winter (when adult ticks were abundant) and a secondary peak in late spring (corresponding to nymphal ticks). Humboldt County had the highest seroprevalence (47.3%), and other northern coast range counties had seroprevalence from 15 to 30%.

Conclusion and Clinical Relevance—The patchy distribution of exposure to Ehrlichia organisms is a subset of the distribution of the tick vector. This may reflect enzootic cycles or climatic or historical factors that limited the range of the disease. Dogs, horses, and humans from north coast range counties in California are at increased risk of GE. These data provide a background for assessing risk of infection in horses and dogs, depending on geographic location. Dogs may be sentinels for assessing risk of GE in humans. (Am J Vet Res 2001;62:1599–1605)

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in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association


The prevalence of antibodies to Ehrlichia equi in horses from the foothill regions of northern California and from the Sacramento valley (non-foothill area) was determined, using an indirect fluorescent antibody test. Horses from foothill regions had a higher prevalence of seropositivity (10.4%) and higher titer (1:10 to 1:80) than did those from non-foothill regions (3.1%; titer ≤ 1:10). Fifty percent of healthy horses on a foothill farm enzootic for E equi had titer to E equi, suggesting that infection with E equi can be subclinical. Six veterinarians surveyed from northern California diagnosed clinical E equi infection in 38 horses during 1985-1986 based on clinical signs of infection and observation of E equi inclusion bodies in neutrophils on blood smears.

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in Journal of the American Veterinary Medical Association


Objective—To describe clinical and clinicopathologic findings and outcome of horses with meningitis and meningoencephalomyelitis.

Design—Retrospective case series.

Animals—28 horses.

Procedures—Medical records of horses admitted to the hospital during a 25-year period were reviewed. Horses with a definitive diagnosis of meningitis or meningoencephalomyelitis were included in this study. Information extracted from the medical records included signalment, history, reason for admission, clinical signs, results of clinicopathologic testing and diagnostic procedures, treatment, outcome, and necropsy findings.

Results—22 horses had confirmed infectious disease (19 bacterial, 2 parasitic, and 1 fungal), 4 had suspected infectious disease on the basis of CSF cytologic examination findings, and 2 had noninfectious meningitis or meningoencephalomyelitis. Trauma of the head and vertebral column with disruption of the blood-brain barrier and local ascending or hematogenous spread were the most common routes of infection. Common neurologic signs included abnormal mental status, cranial nerve deficits, vestibular dysfunction, ataxia, tetraparesis, and apparent neck pain. Common hematologic abnormalities included leukocytosis, neutrophilia, lymphopenia, and hyperfibrinogenemia. Cytologic examination of CSF samples revealed moderate to marked suppurative inflammation. Mortality rate was 96.4%. Microbial culture of CSF yielded bacterial growth in 15 of 23 horses (before death [2 horses], after death [11], and both [2]).

Conclusions and Clinical Relevance—Results suggested that meningitis and meningoencephalomyelitis are uncommon disorders in horses. Infectious disease was more common than noninfectious disease. Local trauma, ascending infection, or hematogenous spread of infection were the most common causes of meningitis or meningoencephalomyelitis. Neurologic deficits, neutrophilia, lymphopenia, hyperfibrinogenemia, and CSF with neutrophilic pleocytosis were common findings in affected horses.

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in Journal of the American Veterinary Medical Association


Intracranial pressure (icp) and cerebral perfusion pressure (cpp) were determined in 8 clinically normal neonatal foals. After the foals oriented themselves and nursed the mares, they were sedated as necessary, and local anesthesia was provided for making the skin incisions. Using a technique similar to that used in human beings, an indwelling subdural catheter was placed to measure icp. Carotid artery catheterization was used to measure arterial blood pressure. Cerebral perfusion pressure was calculated as the difference between mean arterial blood pressure and icp.

Intracranial pressure and cpp readings were taken twice during each 24-hour period, starting at 6 hours of age and continuing through 72 hours of age. Mean (± sd) icp were 5.83 ± 1.82, 8.81 ± 2.06, and 9.55 ± 1.55 mm of Hg (range, 2 to 15 mm of Hg), and mean cpp were 80.19 ± 10.34, 75.30 ± 10.86, and 76.80 ± 12.59 mm of Hg (range, 50 to 109 mm of Hg) for each of the first three 24-hour periods after birth, respectively. All 8 foals had physical and neurologic examinations, csf analysis, and computerized axial tomography evaluations. The foals manifested normal behavior during the interval of measurements, and adverse effects of the procedure were not detected during the monitoring period. Establishment of normal values for icp and cpp are important to clinicians who have the opportunity to apply this technique for monitoring and evaluating neonatal foals with signs of cns dysfunction.

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in American Journal of Veterinary Research


The original objective was to determine seroprevalence of Ehrlichia risticii antibody among horses in California. On the basis of the unexpected results of the survey, an investigation into the accuracy and reproducibility of results of the indirect fluorescent antibody ( ifa) test for E risticii was carried out.


Prospective, seroprevalence study.


Healthy horses (n = 655) and horses with clinical signs of equine monocytic ehrlichiosis ( eme; n = 514) from various regions of California.


The ifa test was performed. Results were compared with results of an elisa and with results of western immunoblot analysis.


Overall, 104 of 655 (15.9%) healthy horses had evidence of an antibody response. However, 84 of 514 (16.3%) horses with clinical signs of eme also had positive test results, and of the 8 seropositive diseased horses for which paired (acute and convalescent) samples had been submitted, only 1 had a rise in antibody titers between the acute and convalescent samples. Comparison of results for the ifa test, elisa, and western immunoblot analysis revealed a high rate of false-positive results for the ifa test. Subsequent studies suggested that routine vaccination of horses with non-E risticii vaccines may have contributed to the false-positive reactions.

Clinical Implications—

The data failed to provide conclusive evidence of E risticii infection among California horses. Owing to the high percentage of false-positive test results, caution is advised when using the ifa test to diagnose eme in horses or to determine the necessity for E risticii vaccination.

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in Journal of the American Veterinary Medical Association