The white blood cell count is a valuable parameter for detecting ClassicalSwine Fever

In this paper we describe a study of the use of the white blood cell count (wbcc) as a parameter for detecting outbreaks of Classical Swine Fever (CSF ). Meta-analysis of the results of challenge experiments revealed that oron asal infection of SPF-pigs with the virulent CSF virus (CSFV) strains Bresc ia or NL9201 resulted in a significant decrease in the average white blood cell count during the first week after inoculation of the virus. Challenge of conventional finishing pigs and sows with the moderately virulent strain Paderborn also resulted in a significant decrease in the average wbcc. How ever, this decrease was not observed after inoculation of SPF pigs with the mildly virulent CSFV strains Henken, Zoelen, or Bergen. The usefulness of clinical inspection in combination with wbcc to detect CS F outbreaks in the field was examined using the results of 214 EDTA blood s pecimens collected from 22 infected herds and 7250 EDTA blood specimens col lected from 1450 non-infected herds. Half of the infected herds had been in fected with the moderately virulent CSFV strain Venhorst (closely related t o strain Paderborn) during the 1997-98 epidemic in the Netherlands. The oth er half had been infected with the moderately virulent CSFV strain Loraine. Using these data as a starting point, 1000 samples of one to ten specimens were generated by Monte Carlo simulation. These simulated samples and the samples of the non-infected herds were analysed by use of Receiver Operatin g Characteristic curves. On the basis of that analysis, the optimal number of animals whose wbcc needed to be determined to detect a CSF outbreak was five. With this number of animals, in conjunction with the threshold of 800 0 white blood cells per mm(3) (meaning that a herd is designated as CSF sus pect if one or more of the five specimens has a white blood cell count of 8 000 leukocytes/mm(3) or less), the test procedure had a herd sensitivity (H SE) of 94.5% and a herd specificity (HSP) of 97.2%). The HSE is defined as the percentage of samples of infected herds with a positive result of the t est procedure; HSP is defined as the percentage of uninfected herds with a negative result of the test procedure. We conclude that the wbcc can help the veterinary practitioner to detect ou tbreaks of CSF caused by (moderately) virulent CSFV strains; However, for t he detection of outbreaks caused by mildly virulent CSFV strains, the contr ibution of the wbcc is doubtful Development of additional tools that can im prove the clinical diagnosis of the veterinary practitioner remains desirab le.