Abstract
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.
Highlights
Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne’s disease (JD) in ruminants [1]
Model simulations Matlab solver ode45 was used to solve the model with parameters drawn from the JD literature (Table 2)
We developed a qualitative framework based on an ordinary differential equation (ODE) model to test the iceberg phenomenon and its application in JD to predict infection prevalence in a herd once a clinically infected animal is diagnosed
Summary
Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne’s disease (JD) in ruminants [1]. Paratuberculosis (MAP) is the etiological agent of Johne’s disease (JD) in ruminants [1]. MAP may be a zoonotic hazard, as it has been implicated as a probable cause of human Crohn’s disease [3,4]. MAP can be transmitted directly from cattle to cattle through infected semen when herds share a bull for breeding [6]. Disease progression follows four distinct stages: (i) silent or latent, (ii) subclinical, (iii) clinical and (iv) advanced [1,6,10,11]. Infected cattle begin shedding bacilli after an unpredictable but lengthy latent period, which ranges from 2 to 10 years, and shedding increases with disease progression. Animals shed minimal amounts of MAP bacteria, thereby contributing a steady stealthy contamination to the environment [5]
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