MAP Super-shedders

Another Factor in the Control of Johne's Disease

Abstract

Traditionally, fecal cultures were either positive or negative for growth of Mycobacterium paratuberculosis (MAP). Nearly all culture-positive cattle were judged to be infected, shedding MAP, thus a threat to spread the disease to susceptible cattle and were culled from the herd as quickly as possible. Over time it was recognized that differences in MAP shedding existed among culture-positive cattle. Cattle were classified as low, moderate or high shedders based on the visible colonies of MAP on the surface of solid media, typically Herrold's egg yolk media (HEYM). Rarely did authors provide the estimated MAP colony forming units (cfu) per gram of manure. Additionally, culture methods were not standardized among diagnostic laboratories in the US, which made it difficult to compare results from one laboratory to another. Laboratories rarely used internal quality control fecal samples. As the infection and disease progressed, the intensity of fecal shedding of MAP increased, culminating in clinical disease which was associated with the greatest numbers of MAP present in manure. Since cattle with clinical signs lose weight and have decreased milk production causing them to be unprofitable, they are soon culled from the herd. If not culled from the herd, they would continue to lose weight and become emaciated with muscle weakness, leading to recumbency requiring euthanasia. The fewest colonies reported is one colony on one of four tubes ofHEYM, which translates into approximately six cfu/gram of feces, assuming the original sample was two grams; 5 ml was transferred from the fecal water tube to the second decontamination tube with HPC. That centrifugation technique was used and the pellet was re-suspended in 1 ml of antibiotic brew, with 200 ul of the re-suspended pellet inoculated onto each of four tubes of HEYM, all with mycobactin J. Low shedders typically had less than 10 colonies on the four tubes ofHEYM. Moderate shedders ranged from 11 to approximately 70 colonies of MAP, while high shedders had more than 70 colonies on any of the four tubes. Calculated on MAP cfu per gram of feces this would be up to 60 cfu for low shedders, 61 to 300 cfu per gram for moderate shedders and more than 300 cfu per gram for heavy shedders.

Over the past five years most laboratories in the US report the number of visible MAP colonies on each tube of HEYM, but rarely enumerate above 50 to 70 colonies per tube. Accounting for sample preparation, 50 colonies on each of four tubes represents an estimated 1,050 colony forming units of MAP per gram of manure. The objective of this study was to determine the range of MAP cfu/gram of manure in cattle classified as heavy shedders.