<?xml version="1.0" encoding="UTF-8"?>
<article article-type="Research Article">
  <front>
    <journal-meta>
      <journal-id journal-id-type="publisher">journal-of-interdisciplinary-mathematics</journal-id>
      <journal-title-group>
        <journal-title>Journal of Interdisciplinary Mathematics</journal-title>
      </journal-title-group>
      <issn publication-format="electronic">2169-012X</issn>
      <issn publication-format="print">0972-0502</issn>
      <publisher>
        <publisher-name>Taru Publications</publisher-name>
      </publisher>
    </journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.47974/JIM-2063</article-id>
      <title-group>
        <article-title>Optimal control analysis of malaria and typhoid fever co-dynamics</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author" corresp="yes">
          <name>
            <surname>Tchoumi</surname>
            <given-names>S. Y.</given-names>
          </name>
          <aff>Department of Mathematics and Computer Sciences, ENSAI, University of Ngaoundere, Ngaoundere, P. O. Box 455, Cameroon</aff>
          <aff>Department of Mathematics and Applied Mathematics, University of Pretoria, Pretoria, South Africa</aff>
        </contrib>
        <contrib contrib-type="author">
          <name>
            <surname>Chukwu</surname>
            <given-names>C. W.</given-names>
          </name>
          <aff>Department of Mathematical Sciences, 65 Georgia Ave, Georgia Southern University, Georgia, P.O. Box 8093, Statesboro, 30460, U.S.A.</aff>
        </contrib>
        <contrib contrib-type="author">
          <name>
            <surname>Diagne</surname>
            <given-names>M. L.</given-names>
          </name>
          <aff>Departement de Mathematiques, UFR des Sciences et Technologies, Universite de Thies, Thies, Senegal</aff>
        </contrib>
        <contrib contrib-type="author">
          <name>
            <surname>Rwezaura</surname>
            <given-names>H.</given-names>
          </name>
          <aff>Department of Mathematics, University of Dar es Salaam, Dar es Salaam, P. O. Box 35062, Tanzania</aff>
        </contrib>
        <contrib contrib-type="author">
          <name>
            <surname>Tchuenche</surname>
            <given-names>J. M.</given-names>
          </name>
          <aff>School of Computer Science and Applied Mathematics, Private Bag 3, Wits 2050, University of the Witwatersrand, Johannesburg, South Africa</aff>
          <aff>School of Computational and Communication Sciences and Engineering, Nelson Mandela African Institution of Science and Technology, Arusha, P. O. Box 447, Tanzania</aff>
        </contrib>
      </contrib-group>
      <volume>28</volume>
      <issue>7</issue>
      <fpage>2567</fpage>
      <lpage>2600</lpage>
      <pub-date date-type="pub">
        <day>19</day>
        <month>08</month>
        <year>2025</year>
      </pub-date>
      <abstract>
        <p>Malaria is an infectious vector-borne disease spread by infected mosquitoes, while typhoid fever is contracted by either drinking water or eating food contaminated with the  Salmonella typhoid bacteria. Both diseases affect millions of individuals every year, causing a great deal of morbidity and mortality. Previous mathematical models of the co-dynamics of these two diseases have not considered the interplay between symptomatic and asymptomatic individuals infected with typhoid. To fill this gap, we formulate a malaria and typhoid co-infection model explicitly including both of these classes and use standard theory of dynamical systems to analyze the model. The sub-models reproduction numbers are derived. Theoretical results show that the disease-free and endemic equilibria could co-exist (backward bifurcation) for both the typhoid only and malaria only sub-models when the respective reproduction number is less than unity. The potential impact of malaria on typhoid reveals that the increase in the number of cases due to malaria could lead to a decrease of the number of typhoid fever cases. To mitigate the spread of both malaria and typhoid fever, the model is extended to include three control measures: malaria prevention, typhoid vaccination and treatment. Numerical simulations are carried out and graphically depicted, and it is noted that reduction in the spread of typhoid greatly impacts the decrease in the number of malaria infectious individuals. Also, as expected, the most effective combination control strategy is the simultaneous implementation of malaria prevention, typhoid treatment and vaccination.</p>
      </abstract>
      <kwd-group>
        <kwd>Malaria</kwd>
        <kwd>Typhoid fever</kwd>
        <kwd>Co-infection</kwd>
        <kwd>Optimal control</kwd>
        <kwd>Mathematical model</kwd>
        <kwd>Basic reproduction number</kwd>
      </kwd-group>
      <custom-meta-group>
        <custom-meta>
          <meta-name>access</meta-name>
          <meta-value>open</meta-value>
        </custom-meta>
        <custom-meta>
          <meta-name>retracted</meta-name>
          <meta-value>no</meta-value>
        </custom-meta>
      </custom-meta-group>
    </article-meta>
  </front>
</article>
