R. Fatzer

Targeted screening of high-risk cattle populations for BSE to augment mandatory reporting of clinical suspects

In Switzerland, the first case of bovine spongiform encephalopathy (BSE) was diagnosed in November 1990. Case numbers peaked in 1995, with a total of 352 BSE cases identified by 30 April 2000. Reporting of clinically suspect cattle is currently the most commonly used method world-wide to detect BSE cases. The effectiveness of mandatory reporting depends on a variety of factors; for other diseases passive surveillance underestimates the incidence of clinical cases. The efficiency of passive surveillance systems for BSE will remain unknown until screening tests able to identify clinically affected cattle have been applied in several countries. This paper provides the first detailed description of a targeted screening programme for BSE. Two populations of cows >24 months of age were included in the targeted screening: (i) cows found dead or culled on site where the carcass was submitted to rendering (fallen stock) and (ii) cows with health-related problems unfit for routine slaughter that were slaughtered under emergency procedures (emergency slaughter). Between 1992 and 1999, on average 81 clinical BSE suspects per year were reported to the veterinary authorities (passive surveillance), of which 43% were confirmed with BSE. A total of 30 clinical cases were captured by passive surveillance and an additional 20 BSE cases detected by targeted screening between May 1999 and April 2000. The odds of finding a BSE case was 49 times higher in the fallen stock and 58 times higher in emergency-slaughtered cattle when compared to passive surveillance. The targeted screening of fallen stock and emergency-slaughtered cattle considerably increased the number of detected cases in this 12-month period. Targeted-screening cases were on average 4 months younger than the clinical suspect cases. In conclusion, post-mortem testing of fallen stock and emergency-slaughtered cows >24 months for BSE is an important active surveillance element within a total surveillance system that principally is based on mandatory reporting of clinical suspect cases. Without ante-mortem screening tests to detect BSE-infected cattle during the incubation period, a combination of effectively functioning passive and active BSE surveillance strategies might be the only approach to assess the BSE situation reliably in a given country or region - and it is necessary to substantiate claims of freedom from the disease.

Necrosis of Hippocampus and Piriform Lobe in 38 Domestic Cats with Seizures: A Retrospective Study on Clinical and Pathologic Findings

The clinical records of 38 cats (1985-1995) with a neuropathologically confirmed diagnosis of necrosis of the hippocampus and occasionally the lobus piriformis were evaluated retrospectively. There was no sex or breed predisposition. Most cats were between 1 and 6 years of age (mean age 35 months) and had either generalized or complex-partial seizures of acute onset and rapid progression. The seizures had a tendency to become recurrent and to present as clusters or even status epilepticus later in the course of the disease. Fourteen cats died spontaneously, and 24 were euthanized. Histopathologic examination revealed bilateral lesions restricted to the hippocampus and occasionally the lobus piriformis. The lesions seemed to reflect different stages of the disease and consisted of acute neuronal degeneration to complete malacia, affecting mainly the layer of the large pyramidal cells but sometimes also the neurons of the dentate gyrus and the piriform lobe. The clinical, neuropathologic, and epidemiologic findings suggest that the seizures in these cats were triggered by primary structural brain damage, perhaps resulting from excitotoxicity. The cause remains unknown, but epidemiologic analysis suggests an environmental factor, probably a toxin.

Necrotizing Meningoencephalitis Associated with Cortical Hippocampal Hamartia in a Pekingese Dog

A 4-year-old male Pekingese dog was referred to the clinic with a history of recurrent seizures and progressive abnormal gait and behavior, which did not respond to treatment. At necropsy, a large cortical defect in the right temporo-parietal cortex, malacia of subcortical white matter, right basal nuclei, and capsula interna, as well as abnormalities of the right hippocampus were observed. Histological examination of the brain revealed moderate to severe nonsuppurative meningoencephalitis in the left cerebral hemisphere and extensive infarction-like lesions with milder inflammation in the right hemisphere. In the right hippocampus, the pyramidal cells were arranged in a gyrus-like pattern and intermingled with gemistocytic and fibrillary astrocytes. The histopathological features of the inflammatory lesions were consistent with necrotizing meningoencephalitis and resembled those described in so-called Pug dog encephalitis. The hippocampal changes were interpreted as dysplasia (monolateral hippocampal cortical hamartia), unrelated to clinical signs and necrotizing inflammatory lesions.

Modelling the expected numbers of preclinical and clinical cases of bovine spongiform encephalopathy in Switzerland

The objective of this study was to model the expected numbers of cattle incubating bovine spongiform encephalopathy (BSE) and the numbers of clinical cases of BSE in the Swiss cattle population between 1984 encephalopathy (BSE) and the numbers of clinical cases of BSE in the Swiss cattle population between 1984 and 2005. The results were compared with the observed number of clinical BSE cases and with the results of a culling and testing scheme on herdmates of cattle with BSE. The age distribution of the Swiss cattle population, the age-at-death distribution of the first 235 BSE cases and exposure information were used to calculate the expected number of infected cattle in each birth cohort and the resulting numbers of clinical cases and survivors incubating the disease for each year. The model which did not assume any underreporting of cases fitted the observed epidemic curve of clinical cases reasonably well, and predicted that the Swiss BSE epidemic would come to an end between 2003 and 2005. The age of survivors incubating BSE iS increasing. The higher than expected incidence of subclinical cases observed in animals from the culling scheme is most probably the result of the heterogeneous distribution of infected animals and affected herds in the population. The results of the model need to be taken into account when designing surveillance and testing schemes for BSE.

Trends in prevalence of BSE in Switzerland based on fallen stock and slaughter surveillance

nnnnn . TARGETED screening for bovine spongiform encephalopathy (BSE) was implemented in Switzerland at the beginning of 1999 on three categories of adult cattle: fallen stock, cattle subject to emergency slaughter and routinely slaughtered cattle (Doherr and others 1999, 2001). Switzerland has a total population of approximately 1-68 million cattle, including 0-8 million adult female cattle (over 24 months old) for breeding and dairy production. In total, over 38,000 adult female cattle leaving the population were examined between January 1, 1999 and December 31, 2000. Due to an increase in voluntary testing, over 32,000 samples were examined between January 1, 2001 and March 31, 2001. The objective of this short communication is to describe trends in the prevalence of cases detected since targeted screening began. In 1999, 25 targeted screening cases were detected by the Prionics Western blot, and six were detected in 2000. Between January 1, 2001 and March 31, 2001, an additional four screened cases were confirmed as being BSE. The odds of detecting a BSE case in 1999 and in 2000 were at least 40 times higher in the risk categories of emergency slaughtered cattle and fallen stock, when compared with the odds of detecting a BSE case by the reporting of clinical suspects (Table 1). This increase in odds is thought to be a combined effect of the higher prevalence of detectable cases, mainly in the fallen stock and emergency slaughter cohorts, and the higher sensitivity of the diagnostic screening test when compared with the clinical detection and reporting of BSE suspects in the field. Linear regression analysis assessing the change in monthly targeted screening prevalence (all categories combined) over