Article Contents
Article Contents

# Investigating the effects of intervention strategies in a spatio-temporal anthrax model

• In this paper, we extend our previous work on optimal control applied in an anthrax outbreak in wild animals. We use a system of ordinary differential equation (ODE) and partial differential equations (PDEs) to track the change in susceptible, infected and vaccinated animals as well as the infected carcasses. In addition to the assumption that the infected animals and the infected carcasses are the main source of infection, we consider the animal movement by diffusion and see its effects in disease transmission. Two controls: vaccinating susceptible animals and disposing infected carcasses properly are applied in the model and these controls depend on both space and time. We formulate an optimal control problem to investigate the effect of intervention strategies in our spatio-temporal model in controlling the outbreak at minimum cost. Finally some numerical results for the optimal control problem are presented.

Mathematics Subject Classification: Primary: 58F15, 58F17; Secondary: 53C35.

 Citation:

• Figure 1.  Simulation results for model (1)-(4) without control $u_1 = u_2 = 0$. The initial population of susceptible and infected animals are considered to be uniformly distributed in $1\le x\le 34$ and $27\le x\le 31$ respectively while only one initial carcass is considered near an end of the domain, $29\le x\le 30$. The figures in the first row show the plots for susceptible (left) and infected (right) animals; and the figure in the second row represents the carcasses

Figure 2.  Simulation results for model (1)-(4) with optimal rates of vaccination and optimal carcass disposal rates $0\le u_1(x,t)\le 0.027,\; \; \text{and}\; \; 0\le u_2(x,t)\le 0.5.$. The initial population of susceptible and infected animals are considered to be uniformly distributed in $1\le x\le 34$ and $27\le x\le 31$ respectively while only one initial carcass is considered near an end of the domain, $29\le x\le30$. The two plots in the first row represent the concentrations of susceptible(left) and infected (right) animals. The plots in the second row represents the concentrations of the infected carcasses(left) and the vaccinated animals(right). The last row represents the vaccination (left) and carcass disposal(right) rates

Table 1.  The model parameters, their description, values and units

 Parm. Description Values Units $r$ Intrinsic growth rate of healthy animals $5.052\times 10^{-4}$ day$^{-1}$ $\gamma$ Disease induced death rate of infecteds $\frac{1}{7.5}$ day$^{-1}$ $\alpha$ Carcass feeding rate by scavengers $0$ animal$^{-1}$ day$^{-1}$ $K$ Carrying capacity of animals 2000 animal $p$ Carcass decay rate $0.02816$ day$^{-1}$ $d$ Diffusion rate of healthy animals $0.12$ $km^2$ day$^{-1}$ $d_1$ Diffusion rate of infected animals $0.024$ $km^2$ day$^{-1}$ $\theta_c$ Disease transmission rate from carcasses $1.65\times 10^{-3}$ carcass$^{-1}$ day$^{-1}$ $\theta_i$ Disease transmission rate from infected animals $2.05\times 10^{-2}$ animal$^{-1}$ day$^{-1}$
•  [1] S. Altizer, R. Bartel and B. A. Han, Animal migration and infectious disease risk, Science, 331 (2011), 296-302.  doi: 10.1126/science.1194694. [2] Animal Diversity Web, https://animaldiversity.org/, Accessed May 2018. [3] J. K. Blackburn, A. Curtis, T. L. Hadfield, B. O'Shea, M. A. Mitchell and M. E. Hugh-Jones, Confirmation of Bacillus anthracis from flesh-eating flies collected during a West Texas Anthrax Season, Journel of Wildlife Disease, 46 (2010), 918-922.  doi: 10.7589/0090-3558-46.3.918. [4] L. Busch, Bison herd suffers worst anthrax outbreak on record, Northern News Services Online, (2012), http://www.nnsl.com/frames/newspapers/2012-08/aug13\_12bs.html. [5] J. R. Castello, Bovids of World: Antelopes, Gazelles, Cattle, Goats, Sheep and Relatives, Prinston University Press, 2016. doi: 10.1515/9781400880652. [6] S. Chawla and S. M. Lenhart, Application of optimal control theory to bioremediation, Journal of Computational and Applied Mathematics, 114 (2000), 81-102.  doi: 10.1016/S0377-0427(99)00290-3. [7] S. Clegg. P. Turnbull, C. Foggin and P. Lindeque, Massive Outbreak of anthrex in wildlife in the Malilangwe Wildlife Reserve, Zimbabwe, The Veterinary Record, 160 (2007), 113-118. [8] Department of Agriculture Forestry and Fisheries, Republic of South Africa, http://http://gadi.agric.za/articles/Furstenburg\_D, Accessed, 2018. [9] D. C. Dragon and B. T. Elkin, An overview of early Anthrax Outbreaks in Northern canada: Field reports of the Health of Animals Branch, Agriculture canada 1962-71, Arctic, 54 (2001), 1-104.  doi: 10.14430/arctic761. [10] D. Dragon and R. Rennie, The ecology of anthrax spores: Tough but not invincible, Canadian Veterinary Journal, 36 (1995), 295-301. [11] P. van den Driessche and J. Watmough, Reproduction number and sub-threshold endemic equilibria for compartmental models of disease transmission, Mathematical Bioscience, 180 (2002), 29-48.  doi: 10.1016/S0025-5564(02)00108-6. [12] L. C. Evans, Partial Differential Equations, Graduate Studies in Mathematics, 19. American Mathematical Society, Providence, RI, 1998. [13] Experience Zimbabwe, http://www.experiencezimbabwe.com/experience/attractions/malilangwe-wildlife-reserve, Accessed, 2018. [14] A. Fasanella, D. Galante, G. Garofolo and M. Hugh-Jones, Anthrax under valued zoonosis, Veterinary Microbiology, 140 (2010), 318-331. [15] E. M. Fevre, B. M. de C. Bronsvoort, K. A. Hamilton and S. Cleaveland, Animal movements and the spread of infectious diseases, Trends in Microbiology, 14 (2006), 125-131.  doi: 10.1016/j.tim.2006.01.004. [16] P. R. Furniss and B. D. Hahn, A mathematical model of an anthrax epizootic in the Kruger National Park, Applied Math Modeling, 5 (1981), 130-136.  doi: 10.1016/0307-904X(81)90034-2. [17] K. R. Fister, S. Lenhart and J. McNally, Optimizing chemotherapy in an HIV model, Electronic Journal of Differential Equations, 1998 (1998), 12 pp. [18] A. Friedman and A.-A. Yakubu, Anthrax epizootic and migration: Persistence or extinction, Mathematical Bioscience, 241 (2013), 137-144.  doi: 10.1016/j.mbs.2012.10.004. [19] W. Hackbusch, A numerical method for solving parabolic equations with opposite orientations, Computing, 20 (1978), 229-240.  doi: 10.1007/BF02251947. [20] B. D. Hahn and P. R. Furniss, A deterministic model of and anthrax epizootic: Threshold results, Ecological Modelling, 20 (1983), 233-241.  doi: 10.1016/0304-3800(83)90009-1. [21] L. Hartfield, Bad year for anthrax outbreaks in US livestock, Center for Infectious Disease Research and Policy (CIDRAP), University of Minnesota, (2005), http://www.cidrap.umn.edu/news-perspective/2005/08/bad-year-anthrax-outbreaks-us-livestock. [22] M. E. Hugh-Jones and V. De Vos, Anthrax and wildlife, Scientific and Technical Review of the Office International des Epizooties, 21 (2003), 359-383.  doi: 10.20506/rst.21.2.1336. [23] M. Kot,  Elements of Mathematical Ecology, Cambridge University Press, Cambridge, 2001.  doi: 10.1017/CBO9780511608520. [24] I. Kracalik, L. Malania, M. Broladze, A. Navdarashvili, P. mnadze, S. J. Rya and J. Blackburn, Changing livestock vaccination policy alters the epidemiology of human anthrax, Georgia, 2000-2013., Vaccine, 35 (2017), 6283-6289.  doi: 10.1016/j.vaccine.2017.09.081. [25] S. Lenhart and J. T. Workman, Optimal Control Applied to Biological Models, Chapman & Hall/CRC Mathematical and Computational Biology Series, Chapman & Hall/CRC, Boca Raton, FL, 2007. [26] C. Loehle, Social and behavioral barriers to pathogen transmission in wild animal populations, Clinical & Translational Immunology, 3 (1995), 1-6.  doi: 10.2172/666220. [27] D. L. Lukes,  Differential Equations: Classical to Controlled, Mathematics in Science and Engineering, 162. Academic Press, Inc., London-New York, 1982. [28] The MathWorks Inc, Global optimization toolbox user's guide, Release 2015a, 2015. [29] R. Miller Neilan and S. Lenhart, Optimal vaccine distribution in a spatiotemporal epidemic model with an application to rabies and raccoons, Journal of Mathematical Analysis and Applications, 378 (2011), 603-619.  doi: 10.1016/j.jmaa.2010.12.035. [30] J. S. Nishi, D. C. Dragon, B. T. Elkin, J. Mitchell, T. R. Ellsworth and M. E. Hugh-Jones, Emergency response planning for anthrax outbreaks in bison herds of northern canada, Annals of the New York Academy of Sciences, 969 (2002), 245-250.  doi: 10.1111/j.1749-6632.2002.tb04386.x. [31] B. Pantha, J. Day and S. Lenhart, Optimal control applied in an anthrax epizootic model, Journal of Biological Systems, 24 (2016), 495-517.  doi: 10.1142/S021833901650025X. [32] C. V. Pao,  Nonlinear Parabolic and Elliptic Equations, Plenum Press, New York, 1992.  doi: 10.1007/978-1-4615-3034-3. [33] C. M. Saad-Roy, P. van den Driessche and A.-A. Yakubu, A mathematical model of anthrax transmission in animal populations, Bulletin of Mathematical Biology, 79 (2017), 303-324.  doi: 10.1007/s11538-016-0238-1. [34] A. H. Seydack, C. C. Grant, I. P. Smit, W. J. Vermeulen, J. Baard and N. Zambatis, Large herbivore population performance and climate in a South African semi-arid Savanna, KOEDOE, 54 (2012), a1047. doi: 10.4102/koedoe.v54i1.1047. [35] S. V. Shadomy and T. L. Smith, Anthrax, Journal of the American Veterinary Medical Association, 233 (2008), 63-72.  doi: 10.2460/javma.233.1.63. [36] J. Simon, Compact sets in the space $L^p(0, T, B)$", Ann. Mat. Pura Appl., 146 (1987), 65-96.  doi: 10.1007/BF01762360. [37] J. Skellam,  The Formulation and Interpretation of Mathematical Models of Diffusionary Processes in Population Biology, The Mathematical Theory of the Dynamics of Biological Populations, Academic Press, 1973. [38] J. Tello and G. Van, The natural history of nyala, Tragelaphus angasi (Mammalia, Bovidae) in Mozambique, Bulletin of the AMNH, Bulletin of American Museum of Natural History, 155 (1975), 6283-6289. [39] Texas Animal Health Commission, Anthrax confirmed in Eadwards county Deer, (2014), http://www.ttha.com/ttha/news/2014/09/08/anthrax-confirmed-in-edwards-county-deer. [40] P. Turnbill,  Anthrax in Animals and Humans, WHO Press, Fourth edition, Geneva, 2008. [41] V. Vos, The ecology of anthrax in the Kruger National Park, Salisbury Medical Bulletin, 68 (1990), 9-23. [42] V. Vos, G. Rooyen and J. Kloppers, Anthrax immunizations of free ranging roan antelope hippotragus equinus in the Kruger National Park, KOEDOE, 16 (1973), 11-25.

Figures(2)

Tables(1)