Proceedings of the 10th International Colloquium on Paratuberculosis

animals may have occurred peri-parturient (sharing maternity pen facilities, colostrums sharing)
or from calf to calf in <strong>the</strong> first months <strong>of</strong> life. Infection would be transmitted by calves that were
infected by <strong>the</strong>ir dam in <strong>the</strong> first days. The third type is a birth cluster <strong>of</strong> future shedding cows
without any positive dams being present at <strong>the</strong> time <strong>the</strong> birth cluster occurred. Finding such
clusters suggests a contaminated calving area or calf to calf transmission in <strong>the</strong> first days,
weeks or even months <strong>of</strong> <strong>the</strong>ir lives.
In this longitudinal study on an eight year database <strong>of</strong> a New York dairy farm, we
attempted to evaluate whe<strong>the</strong>r cows who eventually become Map shedders, were more likely
born in clusters <strong>of</strong> shedders. The eventual objective <strong>of</strong> this study was to get a more in depth
understanding <strong>of</strong> Map transmission on dairy farms.
MATERIALS AND METHODS
The data set used in this study contains data <strong>of</strong> cows present at an Upstate New York dairy
farm during an intensive individual animal diagnostic testing period starting in 1995 and lasting
until 2002. A total <strong>of</strong> 2,788 cows have been at this farm in this period. The Johne’s status, JS, <strong>of</strong>
<strong>the</strong> individual cows is based on results <strong>of</strong> annual fecal culture testing <strong>of</strong> Map in <strong>the</strong> herd. The
fecal diagnostic tests were run in <strong>the</strong> Animal Health Diagnostic Center (AHDC), Cornell
University. The laboratory used initially a Herrold Egg Yolk Media system (HEYM), and later
switched to a liquid medium culture system where fecal cultures were grown for 35-42 days and
<strong>the</strong>n checked with an acid-fast stain. In <strong>the</strong> liquid culture system, bottles with acid-fast
organisms detected were confirmed using MAP PCR. Semi quantitative results were provided
based on days to positive culture. The specificity <strong>of</strong> <strong>the</strong> culture is assumed to be 100%, <strong>the</strong>
sensitivity is estimated at 30-40%. The JS was expressed as positive, negative or unknown. A
cow’s JS was considered positive when fecal culture results were at least once positive for Map.
A total <strong>of</strong> 1577 cows qualified with ei<strong>the</strong>r a positive or negative Johne’s status and were used in
this study. Cows with an unknown JS were not used in <strong>the</strong> cluster calculations.
Prevalence per year was calculated as <strong>the</strong> percentage <strong>of</strong> cows with a Johne’s status ever
(JSever) positive <strong>of</strong> all adult cows on <strong>the</strong> farm that year. The current Johne’s status (JScurrent)
is <strong>the</strong> percentage <strong>of</strong> fecal shedding positive cows in that year <strong>of</strong> all <strong>the</strong> adult cows present on
<strong>the</strong> farm that year. The incidence was calculated as <strong>the</strong> fraction <strong>of</strong> animals which were first
tested positive in that year <strong>of</strong> all cows tested in that year.
The SaTScan v 7.01 s<strong>of</strong>tware was used to scan for <strong>the</strong> birth clusters in this herd.
SaTScan is a s<strong>of</strong>tware program that analyzes spatial, temporal and space-time data using <strong>the</strong>
spatial, temporal, or space-time scan statistics (Kulldorff 1997). This program was designed to
use windows <strong>of</strong> different size to identify statistically significant clusters <strong>of</strong> events (p