Open AccessEvalution of the “Iceberg Phenomenon” in Johne's Disease through Mathematical Modelling
Author(s) -
Gesham Magombedze,
Calistus N. Ngonghala,
Cristina Lanzas
Publication year - 2013
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0076636
Subject(s) - paratuberculosis , subclinical infection , disease , iceberg , stage (stratigraphy) , clinical disease , transmission (telecommunications) , biology , medicine , mycobacterium , pathology , tuberculosis , sea ice , paleontology , oceanography , engineering , electrical engineering , geology
Johne's disease (JD) is a chronic, enteric disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Disease progression follows four distinct stages: silent, subclinical, clinical and advanced. Available diagnostic tests have poor sensitivity and cannot detect early stages of the infection; as a result, only animals in the clinical and advanced stages, which represent the tip of the ‘iceberg’, are identified through testing. The Iceberg Phenomenon is then applied to provide estimates for JD prevalence. For one animal in the advanced stage, it is assumed that there are one to two in the clinical stage, four to eight in the subclinical stage, and ten to fourteen in the silent stage. These ratios, however, are based on little evidence. To evaluate the ratios, we developed a deterministic ordinary differential equation model of JD transmission and disease progression dynamics. When duration periods associated with the natural course of the disease progression are used, the above ratios do not hold. The ratios used to estimate JD prevalence need to be further investigated.