Article Contents
Article Contents

# Modeling environmental transmission of MAP infection in dairy cows

• * Corresponding author: Suzanne Lenhart
This work was partially supported by the National Institute for Mathematical Biological Synthesis, sponsored by the National Science Foundation Award NSF DBI-1300426.
• Johne's disease is caused by Mycobacterium avium subspecies paratuberculosis(MAP). It is a chronic, progressive, and inflammatory disease which has a long incubation period. One main problem with the disease is the reduction of milk production in infected dairy cows. In our study we develop a system of ordinary differential equations to describe the dynamics of MAP infection in a dairy farm. This model includes the progression of the disease and the age structure of the cows. To investigate the effect of persistence of this bacteria on the farm on transmission in our model, we include environmental compartments, representing the pathogen input in an explicit way. The effect of indirect transmission from the bacteria in the environment and the culling of high-shedding adults can be seen in the numerical simulations. Since culling usually only happens once a year, we include a novel feature in the simulations with a discrete action of removing high-shedding adults once a year. We conclude that with culling of high shedders even at a high rate, the infection will persist in the modeled farm setting.

Mathematics Subject Classification: Primary: 92B05; Secondary: 34B15.

 Citation:

• Figure 1.  Flow diagram of the transitions in our model (Sc, Sh, Sa -Susceptible calves, heifers, adults, Ec, Eh, Ea -Exposed calves, heifers, adults, Lh, La -Low shedding heifers, adults, Ha -High shedding adults, B1 -Bacteria in the heifer environment, B2 -Bacteria in the adult environment)

Figure 2.  Environmental transmission coefficient $f(B)$ with $K_1 = 1000$ and $K_2 = 100$

Figure 3.  Dynamics of the animals in each compartment with no testing or culling and with annual testing and culling

Figure 4.  Dynamics of the total animals in each disease class with no testing or culling and with annual testing and culling

Figure 5.  Number of exposed cows from the bacteria in the environment 1 and 2 when $p = 0.3 , r_1 = 0.06$, and $r_2 = 0.06$ with no testing or culling and with annual testing and culling

Figure 6.  Dynamics of the bacteria in the two environments with no testing or culling and with annual testing and culling

Figure 7.  Number of exposed cows due to different infection routes without testing or culling and with annual testing and culling

Table 1.  Initial number of animals in each compartment

 Variable Defining the variable Initial value Sc Number of susceptible calves 130 Sh Number of susceptible heifers 520 Sa Number of susceptible adults 650 Ec Number of exposed calves 70 Eh Number of exposed heifers 248 Ea Number of exposed adults 250 Lh Number of low-shedding heifers 32 La Number of low-shedding adults 80 Ha Number of high-shedding adults 20 B1 Amount of bacteria (MAP) in the environment 1(Scaled in 108) 0.2 B2 Amount of bacteria (MAP) in the environment 2(Scaled in 108) 590

Table 2.  Parameters and their values

Table 3.  Initial prevalence of the disease in each age class

 Susceptible Exposed Low-shedding High-shedding Calves 65% 35% 0% 0% Heifers 65% 31% 4% 0% Adults 65% 25% 8% 2%

Table 4.  Comparison of the number of animals in each compartment at the end of 10 years without culling and with annual culling

 Compartment Without culling With annual testing & culling Sc 26 42 Ec 53 32 Sh 196 530 Eh 349 244 Lh 301 208 Sa 5 90 Ea 321 388 La 456 424 Ha 284 10

Table 5.  Equilibrium values for the number of animals in each compartment at the end of 25 years without culling and the final values for the number of animals in each compartment at the end of 10 years with these equilibrium values as the initial values and annual culling

 Compartment Equilibrium values after 25 years without culling Final values with annual testing & culling Sc 25 40 Ec 54 33 Sh 184 498 Eh 349 252 Lh 311 230 Sa 4 67 Ea 308 370 La 455 439 Ha 296 11 B1 807×108 610×108 B2 3234523×108 786526×108
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