Decision support tools for clinical diagnosis of disease in cows with suspected bovine spongiform encephalopathy

Abstract

Reporting of clinically suspected cattle is currently the most common method for detecting cases of bovine spongiform encephalopathy (BSE). Improvement of clinical diagnosis and decision-making remains crucial. A comparison of clinical patterns, consisting of 25 signs, was made between all 30 BSE cases, confirmed in Belgium before October 2002, and 272 suspected cases that were subsequently determined to be histologically, immunohistochemically, and scrapie-associated-fiber negative. Seasonality in reporting suspected cases was observed, with more cases being reported during wintertime when animals were kept indoors. The median duration of illness was 30 days. The 10 most relevant signs of BSE were kicking in the milking parlor, hypersensitivity to touch and/or sound, head shyness, panic-stricken response, reluctance to enter in the milking parlor, abnormal ear movement or carriage, increased alertness behavior, reduced milk yield, teeth grinding, and temperament change. Ataxia did not appear to be a specific sign of BSE. A classification and regression tree was constructed by using the following four features: age of the animal, year of birth, number of relevant BSE signs noted, and number of clinical signs, typical for listeriosis, noted. The model had a sensitivity of 100% and a specificity of 85%. This approach allows the use of an interactive decision-support tool, based entirely on odds ratios, a statistic independent of disease prevalence.

FIG. 1.

Age pyramid of Belgian cattle in 2000. Bars: □, females; ▪, males.

FIG. 2.

Clinical BSE in Belgium. A diagram shows spatial distribution of the investigated cases, i.e., suspected cases with full clinical evaluation record. (A) BSE suspected cases and subsequently unconfirmed cases from 1998 to 2000 (n = 272); (B) all BSE confirmed cases before October 2002 (n = 30).

FIG. 3.

Age distribution of clinically suspected BSE cases in Belgium between 1998 and 2000 (n = 290), Bars: ▪, BSE; ▤, listeriosis; ▥, meningitis and/or encephalitis; □, others; ✽, bovines between 20 and 24 months.

FIG. 4.

Clinically suspected BSE cases in Belgium between 1998 and 2000 by birth cohort (n = 290). Bars: ▪, BSE; ▤, listeriosis; ▥, meningitis and/or encephalitis; □, others.

FIG. 5.

Receiver-operating-characteristic curve of the score of the 10 most relevant signs of BSE (area under the curve = 0.7290 s.e. [area] = 0.0503; 0, 1,…, 7, 8 = BSE sign score).

FIG. 6.

CART decision tree for clinically suspected BSE cases in Belgium.