DPC video Foodborne / Vector-Borne / Water Diseases: P
Module Overview
Focus on foodborne diseases and vector-borne, vermin-borne diseases.
Discuss prevention and control of communicable diseases—applying principles of epidemiology to public health interventions.
Objectives of the Module
At the end of the session, students should be able to:1. Explain core principles in the prevention and control of communicable diseases, focusing on breaking the links in the chain of infection, considering various modes of transmission.
Enumerate preventive measures related to proper food handling and preparation aligned with foodborne or vehicle-borne diseases control, emphasizing critical control points.
Discuss basic public health concerns on controlling vector-borne and vermin-related diseases regarding environmental health, including surveillance and response systems.
Identify common strategies of existing national health programs aimed at controlling and preventing priority communicable diseases, highlighting multi-sectoral collaboration and legislative frameworks.
Communicable Diseases Overview
Defined as illnesses caused by the transmission of an infectious agent (e.g., bacteria, viruses, fungi, protozoans, prions) from an infected person, animal, or reservoir to a susceptible host.
Transmission may occur directly (e.g., person-to-person contact, droplet spread within 1 meter) or indirectly (e.g., via an intermediate host like a vector, contaminated inanimate objects like fomites, or environmental sources like air or water).
Involves interactions among three components: agent, host, and environment (Ecologic Triad). This triad illustrates how changes in one component can affect the occurrence and spread of disease.
Agent: The pathogen itself, characterized by its infectivity (ability to invade and multiply), pathogenicity (ability to cause disease), virulence (severity of disease), and antigenicity (ability to induce an immune response).
Host: The human or animal that harbors the infectious agent, whose susceptibility is influenced by factors like age, immune status, genetic predisposition, and nutritional status.
Environment: External factors that influence the agent's survival, transmission, and the host's exposure, such as climate, housing, sanitation, and social conditions.
The interaction leads to diseases with varying presentation based on individual susceptibility and the characteristics of the infectious agent.
Carrier States
Individuals who harbor the infectious agent without showing signs of disease themselves but are capable of transmitting it to others.
Types of Carriers:
Chronic Carriers: Individuals who harbor an infectious agent for a prolonged period (months or years), often after an initial infection, without developing clinical symptoms or after recovering. E.g., Hepatitis B virus can remain dormant for years in chronic carriers, potentially leading to severe long-term complications like liver cirrhosis or hepatocellular carcinoma. This highlights the importance of universal vaccination for newborns and screening programs.
Convalescent Carriers: Individuals who are recovering from an illness but are still infectious and capable of transmitting the pathogen as they shed the agent. E.g., Varicella (Chickenpox); individuals are highly infectious during the recovery phase until all lesions have crusted over, even when symptoms are abating.
Incubatory Carriers: Individuals who can transmit the infection during the incubation period, before the onset of clinical symptoms. E.g., HIV; individuals without symptoms during the lengthy incubation period can transmit the infection, making control challenging due to the hidden nature of transmission.
Asymptomatic/Passive Carriers: Individuals who harbor the infectious agent but never develop clinical symptoms of the disease. They may be transiently or chronically colonized. E.g., Typhoid Mary (Mary Mallon); a historical example of an asymptomatic carrier of Salmonella Typhi who, as a cook, transmitted typhoid fever to numerous people, highlighting the critical importance of hygiene in food preparation and public health investigations.
Chain of Infection
Understanding the chain of infection is crucial for public health interventions aimed at breaking transmission links at any point to prevent the spread of disease. Breaking even one link can halt transmission.
Links in the Chain:
Agent: The pathogenic microorganism capable of causing disease (e.g., bacteria, viruses, fungi, protozoans, helminths). Factors like infectivity, virulence, and dose determine the agent's ability to cause disease.
Reservoir: The natural habitat where the agent lives, multiplies, and from which it can be transmitted. This can include humans (symptomatic cases, asymptomatic carriers), animals (zoonotic diseases), or the environment (soil, water, contaminated surfaces).
Portal of Exit: The way the infectious agent leaves the reservoir. Examples include respiratory tract secretions (coughing, sneezing), gastrointestinal tract (feces, vomit), genitourinary tract (urine, sexual fluids), skin/mucous membranes (open wounds, lesions), and blood.
Mode of Transmission: The mechanism by which the infectious agent is carried from the reservoir to a susceptible host.
Direct Transmission: Involves immediate transfer of the agent from a reservoir to a host.
Direct contact (e.g., touching, kissing, sexual intercourse).
Droplet spread (e.g., sneezing, coughing, talking, expelling droplets over short distances, generally less than 1 meter).
Indirect Transmission: Involves a common vehicle or vector, or airborne particles.
Airborne: Dissemination of droplet nuclei (< 5 micrometers) or dust particles containing the agent that remain suspended in air for longer periods and travel further.
Vehicle-borne: Through contaminated inanimate objects like food, water, biological products (blood), or fomites (inanimate objects like bedding, surgical instruments).
Vector-borne: Through living organisms (e.g., mosquitoes, ticks, fleas).
Portal of Entry: The route by which the infectious agent gains access into the new susceptible host. Examples include mucous membranes (respiratory, gastrointestinal, genitourinary tracts), skin breaks (cuts, abrasions, needle punctures), and parenteral routes.
Susceptible Host: Any person or animal who is at risk of infection. Factors contributing to a host's susceptibility include age (very young or elderly), nutritional status (malnutrition), immune status (immunocompromised individuals), presence of chronic diseases (diabetes, heart disease), genetic predisposition, and lack of previous exposure or vaccination.
Vehicle-Borne Diseases
Vehicle-borne diseases involve indirect transmission through inanimate carriers called 'vehicles' such as contaminated food, water, air, or biological products (e.g., blood, organs, tissues).
Contamination can occur at any stage—from production and harvesting to processing, distribution, and consumption.
Common Vehicle-Borne Diseases:
Foodborne diseases: Over 200 different diseases linked to contaminated food, causing significant morbidity and mortality globally, especially affecting low-income populations, children under 5 years, and the elderly. Common pathogens include Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, Campylobacter, and Norovirus, leading to symptoms ranging from mild gastroenteritis to severe neurological or kidney complications.
Waterborne diseases: Transmitted via consumption of contaminated water (e.g., Cholera, Giardiasis, Cryptosporidiosis).
Preventive Measures:
Maintain strict food hygiene practices: thorough handwashing, using clean utensils and surfaces.
Separate raw and cooked foods to prevent cross-contamination (e.g., using separate cutting boards and knives).
Adequately cook foods to kill pathogens (e.g., ensuring meats reach safe internal temperatures like 74^ ext{o}C (165^ ext{o}F) for poultry) and avoid the Temperature Danger Zone (5^ ext{o}C ext{ to } 60^ ext{o}C or 41^ ext{o}F ext{ to } 140^ ext{o}F) where bacteria multiply rapidly.
Chill foods promptly to inhibit bacterial growth.
Use safe water and raw materials.
Implement Hazard Analysis and Critical Control Points (HACCP) principles in food establishments.
Vector-Borne and Vermin-Borne Diseases
Vectors: Living organisms (often arthropods like mosquitoes, ticks, fleas, and flies) that carry and transmit infectious pathogens from an infected host to a susceptible host.
Biological vectors: The pathogen multiplies or develops within the vector before transmission (e.g., Anopheles mosquito for Malaria).
Mechanical vectors: The pathogen is simply carried on the exterior of the vector (e.g., flies carrying Shigella on their legs).
Vermin: Disgusting or obnoxious animals (e.g., rodents, cockroaches, flies) that are difficult to control and are typically associated with carrying diseases, contaminating food, or causing damage.
Health risks from vermin include direct transmission of pathogens (e.g., Hantavirus from rodents), food contamination through droppings, urine, or physical contact, and exacerbation of allergies (e.g., from cockroach allergens).
Common Vector-Borne Diseases in the Philippines
Malaria: Transmitted by female Anopheles mosquitoes.
Dengue: Transmitted by Aedes aegypti and Aedes albopictus mosquitoes.
Schistosomiasis: Transmitted by freshwater snails (Oncomelania hupensis for S. japonicum).
Lymphatic Filariasis (elephatiasis): Transmitted by several mosquito genera (Culex, Anopheles, Aedes). These are often neglected tropical diseases primarily affecting poor populations due to inadequate sanitation and limited access to healthcare.
Strategies to control these diseases include comprehensive vector surveillance, timely and accurate diagnoses, swift outbreak responses, continuous health education, and integrated environmental sanitation programs.
Key Concepts in Food Safety
Food Hygiene, Food Safety, and Food Sanitation:
Food Hygiene: Practices and conditions necessary for producers to ensure the safety of food at all stages of the food chain.
Food Safety: Assurance that food will not cause harm to the consumer when it is prepared and/or eaten according to its intended use.
Food Sanitation: Maintaining clean conditions to prevent contamination and ensure food is fit for consumption.
These concepts are focused on ensuring food is fit for consumption and free from physical, chemical, and biological contamination.
Food Contaminants Categories:
Biological: Microorganisms such as bacteria (e.g., Salmonella, E. coli), viruses (e.g., Norovirus, Hepatitis A), parasites (e.g., Giardia, Toxoplasma gondii), and fungi that can cause illness.
Chemical: Harmful substances that can get into food (e.g., pesticides, heavy metals like lead or mercury, cleaning agents, naturally occurring toxins like mycotoxins, or allergens that are not properly declared).
Physical: Foreign objects in food that can cause injury or disgust (e.g., glass shards, plastic pieces, metal fragments, hair, dirt, bone fragments).
Public Health Perspective on Foodborne Diseases
Affects primarily children under 5 years and immunocompromised individuals, leading to serious gastrointestinal issues such as severe dehydration, malnutrition, and potentially long-term complications like reactive arthritis, kidney failure, or neurological damage.
Statistics:
Non-typhoidal Salmonella is a major contributor to global foodborne illnesses, commonly associated with poultry, eggs, and raw milk products. It can lead to severe gastroenteritis and, in some cases, invasive disease.
The economic burden of foodborne diseases is substantial, including healthcare costs, lost productivity, and impaired social development.
Prevention of Vector-Borne Diseases
Public Health Initiatives for Vector Control:
Environmental sanitation and management: This involves source reduction (eliminating breeding sites such as stagnant water for mosquitoes), proper waste disposal, improved drainage systems, adequate housing (e.g., screening windows and doors), and proper land use planning.
Community health education and mobilization: Empowering communities with knowledge about disease transmission, preventive practices, and encouraging active participation in control efforts (e.g.,