Principles of disease control/ epidemiology of zoonoses

• An infectious disease can be defined as an illness due to a pathogen or its toxic product, which arises through transmission from an infected person, an infected animal, or a contaminated inanimate object to a susceptible host
• Reservoir host:

  • A host that serves to sustain an infectious pathogen as a potential source of infection for transmission to humans
  • A reservoir host will not succumb to infection
• Vehicles:

  • Inanimate objects that serve as an intermediate in the indirect transmission of a pathogen from a reservoir or infected host to a susceptible host
  • Examples include food, water, and fomites such as doorknobs, surgical instruments, and used needles
• Environmental factors determine if a host will become exposed to one of these agents, and subsequent interactions between the agent and host will determine the exposure outcome
• An infectious disease results from a combination of agent (pathogen), host, and environmental factors
• Agent Factors:

  • Infectivity: likelihood that an agent will infect a host when the host is exposed to the agent
  • Pathogenicity: ability of an agent to cause disease
  • Virulence: likelihood of causing severe disease among those with the disease
  • Infectivity and pathogenicity can be measured by the attack rate, the number of exposed individuals who develop the disease
• Host Factors:

  • Susceptibility refers to the ability of an exposed individual to resist infection or limit disease as a result of their biological makeup
  • Factors influencing susceptibility include innate, genetic factors and acquired factors such as specific immunity that develops following exposure or vaccination
• Host Factors 2:

  • Susceptibility is also affected by extremes of age, stress, pregnancy, nutritional status, and underlying diseases
  • Mechanical and chemical surface barriers such as the skin, tears, mucus, and gastric acid act as the first host obstacles to infection
  • Microbiome-resident bacteria can confer host protection by preventing pathogenic bacteria from taking up residence
• Environmental Factors:

  • Environmental determinants of vulnerability to infectious diseases include physical, social, behavioral, cultural, political, and economic factors
  • Environmental influences can increase the risk of exposure to an infectious agent and susceptibility to infection by inducing physiological changes in an individual
• The chain of infection:

  • Represents the process of infection where microorganisms are passed from a source to a vulnerable person
  • Starts with the infectious agent residing and multiplying in a natural reservoir, then moves to a susceptible host through a portal of exit and a mode of transmission to reach a portal of entry
• Opportunities to break the chain of infection:

  • Breaking a link at any point in the chain controls the risk of infection by preventing the onward transmission of microorganisms
  • Transmission may be interrupted by eliminating, inactivating, or preventing the survival of the infectious agent
  • Early diagnosis, treatment, contact tracing, and quarantine are key strategies
• Principles of control:

  • Control measures may be aimed at various points along the chain of infection
  • Understanding how infections occur and spread is crucial for prevention
  • Direct protection of hosts, reducing contact between agent and host, and reducing the amount of agent released are key actions
• Zoonosis can be defined as an infectious or communicable disease that is transmissible from vertebrate animals to human beings under natural conditions
• Transmission of Zoonotic Diseases:

  • Through the air
  • By eating contaminated meat or meat products
  • Through close contact with an infected animal
  • By touching an area or surface the infected animal has touched
  • Through insect bites such as mosquitoes, fleas, and ticks
• Presentations of zoonotic diseases range from short-term illness to major life-threatening presentations, some of which can cause death
• Zoonotic diseases can be caused by viruses, bacteria, fungi, protozoa, helminths, and rickettsiae
• Reservoir of infection is the natural habitat of an infectious agent where it normally lives and multiplies, which could be a person, animal, arthropod, plant, or soil
• Types of Zoonotic Diseases include:

  • Animal Flu
  • Anthrax
  • Avian Flu
  • Swine Flu
  • Bovine Tuberculosis
  • Brucellosis
  • Campylobacter infection
  • Cat scratch fever
  • Cryptosporidiosis
  • Dengue
  • Ebola Haemorrhagic Fever
  • Enzootic abortion
  • Fish tank granuloma
  • Giardiasis
  • Glanders
  • Haemorrhagic colitis
  • Hepatitis E
  • Hydatid disease
  • Leptospirosis
  • Lassa Fever
  • Malaria
  • Plague
  • Q fever
  • Ringworm
• Livestock farmers, family pet keepers, pregnant women, the elderly (65 years and above), those with HIV, those on chemotherapy, and immunocompromised people are at risk of zoonotic infections
• • Exclude animals regarded as pests from human habitations
  • Control vectors transmitting zoonoses, such as mosquitoes, fleas, and ticks
  • Implement surveillance, isolation, quarantine, and notification in deadly zoonotic diseases
  • Protect susceptible hosts by immunization/chemoprophylaxis
  • Treat infected persons
  • Provide health education
• Prevention and Control of Zoonoses:

  • Implement food safety regulations when the reservoir of infection is animals used for food
  • Wash hands diligently to prevent salmonellosis and E. coli infection
  • Cook food thoroughly, especially of animal origin, to safe temperatures
  • Thoroughly wash vegetables
  • Practice safe food handling
  • Maintain general housekeeping of abattoirs and slaughter slabs
  • Ensure good personal hygiene of animal handlers
  • Vaccinate pets and use gloves when handling sick animals
  • Keep clean and sanitary where pets are kept
• One Health concept:

  • One Health approach involves designing and implementing programs, policies, legislations, and research involving multiple sectors
  • Recognizes the interconnectedness of human health, animal health, and the environment