Microbe-Human interactions_Lecture 2.pdf

Microbe-Human Interactions: Infection and Disease James Otabil [email protected] 1 What is host-microbe interaction? The host-microbe interaction is defined as how microbes sustain themselves within host organisms on a molecular, cellular...

Microbe-Human Interactions: Infection and Disease James Otabil [email protected] 1 What is host-microbe interaction? The host-microbe interaction is defined as how microbes sustain themselves within host organisms on a molecular, cellular/ population level. A pathogen refers to disease-causing microorganisms although they may not cause illness in all hosts. Host any organism that harbours another organism or particle (virus/prion). 2 Types of pathogens True pathogens – capable of causing disease in healthy persons with normal immune defenses eg. Influenza virus, plague bacillus, malarial protozoan Opportunistic pathogens – cause disease when the host’s defenses are compromised or when they grow in a part of the body that is not natural to them. eg Pseudomonas spp. & Candida albicans 3  Bacteria: These one-celled organisms are responsible for illnesses such as strep, throat, urinary tract infection, and tuberculosis. Viruses: Smaller than bacteria, viruses cause a plethora of diseases ranging from the common cold to AIDS. Fungi: Many skin diseases, such as ringworm and athlete’s foot, are caused by fungi. Other types of fungi can infect your lungs or nervous system (eg. Aspergillus, Histoplasma). 4 Parasites: Organisms depending on one another for survival, nutrients, etc Malaria is caused by a tiny parasite that is transmitted by a mosquito bite. Other parasites may be transmitted to humans from animal feces (eg., Hookworm, tapeworm, etc.). 5  Infectious diaseases Several different factors influence a microorganism’s relationship to its host and level of severity. These include; 1. Pathogenicity- The ability to produce disease in a host organism 2. Virulence-The degree of pathogenicity of a microorganism. ✓Virulence for a pathogen includes a pathogen’s genetic, biochemical or structural features. 3. Infectivity-The level at which a microorganism is able to infect or invade a host. 4. Transmissibility-the measure of a microorganism's ability to spread from one host to the next. 6 The body’s normal flora The body contains two types of normal flora; 1. resident flora (survive for extended periods). Eg., Candida spp, S. epidermidis, E. coli. 2. transient flora (temporary). Eg., E. coli, Proteus mirabilis, M. tuberculosis Normal flora helps to provide defense against invading pathogens by covering adherence sites, producing compounds toxic to other organisms, and preventing pathogens from consuming available nutrients. For disease to occur there must be a change in the body’s environment, which, in turn, allows the pathogen to overcome the normal flora. This can occur through a change in the pH of the body or elimination of normal flora due to antibiotics. 7 Host defenses ✓ A microorganism will not be able to invade unless it overcomes the host defenses. Host defenses may include: Skin and mucosal secretions Non-specific local responses.(eg. pH) Non-specific inflammatory responses Specific immune responses(eg. lymphocytes) 8 Pathogen defenses Pathogens contain virulence factors that promote disease formation and provide the opportunity for a microbe to infect and cause disease. The greater the virulence, the more likely disease will occur. Such factors include: ✓ Ability to adhere to a host ✓ Ability to colonize (overcome) a host ✓ Ability to evade host defenses 9 Mechanisms of pathogenesis Pathogenesis is the process by which a disease can develop. This can occur through food-borne intoxication where the causative agent produces toxins in the body (eg., botulism). Another route is the colonization of an invading pathogen on the host surface, which allows the pathogen to increase in numbers and produce toxins that are damaging to the host’s cells(eg., Corynebacterium). The relationship between a host and a pathogen is dynamic. Production of disease occurs through a process of steps. 10 11 1. Transmission Contact transmission vehicle/fomite transmission Vector-borne transmission 12 Contact transmission Direct: ✓ person to person, through direct physical contact (skin to skin/body fluids) eg; STD’s & cold sores. Indirect: ✓ pathogens or agents transferred via intermediate items, organisms etc, to susceptible hosts Vehicle or fomite transmission Airborne: ✓ pathogen suspended in droplets or dust; can remain in air for hours to days. eg, cold virus travels in droplets when person sneezes & talks. 13 Vehicle borne: ✓ pathogen transmitted from source to susceptible individual via intermediate object (fomite). eg, contaminated medical equipment. Food or waterborne: ✓ pathogen transmitted to susceptible individuals via food /water. Ingestion: ✓ ingestion of pathogenic organism that grows in the GI tract. Eg, V. cholerae transmitted in water sources, E. coli in hamburgers, Salmonella. 14 Vector-borne transmission Pathogen transmitted to susceptible individuals via animal or insect. ✓ Mechanical transmission (external)-use a host for transport. e.g., a fly landing on food at a picnic after it picked up some E. coli. ✓ Biological transmission (internal)- carried inside vector; use vector part of the life cycle. e.g., malaria parasite, Plasmodium in blood ingested by Anopheles mosquito after bite. 15 Mechanism of microbial pathogenicity 16 Microbial interaction An association between two species (“living together’’). Sometimes beneficial and sometimes harmful. One organism can be located on the surface of another organism as an ‘ectobiont’ (Eg., S. epidermidis) or located within another organism as an ‘endobiont’ (Plasmodium spp). The interaction may be positive and negative such as, ✓ Positive- mutualism, commensalism. ✓ Negative- parasitism, amensalism, competition. 17 Positive relationship Mutualism- the relationship in which each organism in interaction gets benefits from association. Eg., S. epidermidis on the skin, Bifidobacterium in gut. Commensalism- it is a relationship in which one organism in the association is benefited while another organism (host) of the association is neither benefited nor harmed. eg, Bacillus spp on skin 18 Negative relationship Parasitism- one population (parasites) benefits and derives its nutrition from another population (host) in the association that is harmed. - Long periods of contact may be physical or metabolic. Eg, viruses. Competition: microbial population in which both populations are adversely affected with respect to their survival and growth. It occurs when both populations use the same resources such as the same space or the same nutrition. Eg., Clostridioides difficile, Methicillin-resistant Staphylococcus aureus (MRSA). The overuse of antibiotics sometimes eliminates the body’s normal flora giving room for resistant strains to thrive 19  Amensalism- one microbial population produces substances that are inhibitory to another population. The 1st population which produces inhibitory substances is unaffected while other populations get inhibited. This chemical inhibition is known as antibiosis. Eg., Staphylococcus epidermidis vs. Staphylococcus aureus 20 Infection- a condition in which pathogenic Overview of infection microbes penetrate host defenses, enter tissues & multiply. Disease – any deviation from health, disruption of a tissue or organ caused by microbes or their products. 21 Portals of entry skin gastrointestinal tract respiratory tract urogenital tract 22 Portals of exit Respiratory, saliva Skin, scales Fecal exit Urogenital tract Removal of blood 23 Patterns of infection localized infection– microbes enter the body & remain confined to a specific tissue Systemic infection– infection spreads to several sites and tissue fluids usually in the bloodstream Focal infection– when an infectious agent breaks loose from a local infection and is carried to other tissues Mixed infection – several microbes grow simultaneously at the infected site Primary infection – first instance of an infection by a pathogen Secondary infection – a subsequent infection during or after a primary infection caused by a different microbe. Eg., someone may contract pneumonia after a flu 24 Patterns of infection 25 Hospital Acquired (Nosocomial) infections Diseases that are acquired during a hospital stay For most bacterial infections, the typical incubation time is 48 hours. However, different pathogens may have varying incubation times due to underlying patients’ conditions. Some nosocomial infections may not even manifest until the patient is discharged. Most affected areas include the urinary tract, respiratory tract, & surgical incisions. Most common organisms include E. coli, Pseudomonas spp., Staphylococcus spp. 26 Nosocomial infections 27 Factors Influencing the Risk of Transmission of HAIs 1. Patient Characteristics ✓ Increased susceptibility to infections 2. Type of Healthcare Facility (HCF) or Clinical Unit ✓ Acute care eg people who require constant checking of vitals ✓ Intensive care eg people who require constant checking of vitals ✓ Long-term care eg people with cognitive impairment ✓ Surgical units ✓ Oncology or transplant units ✓ Burns or trauma care units 28 3. Type and Frequency of Use of Indwelling Devices 4. Intensity of Care 5. Exposure to Environmental Sources 6. Length of Stay 7. Frequency of Interaction with Healthcare Workers (HCWs) 29 Causes of Infections in Hospitalized Patients Systems and processes of patient care Eg., improper hand hygiene Economic constraints Eg., budgetary issues leading to a high patient-staff ratio Priorities of the institution and country Human behaviour 30 Preventive Measures for Infections in Special Scenarios Burns Predisposing Causes, Sources, and Types of Infections Large area of damaged skin and exposed tissues provides a portal of entry for airborne or contact infection. Measures: Care for patients in the burns unit ✓ Physically separate, single isolation rooms with filtered air at positive pressure into rooms. ✓ Air from rooms should be extracted to the exterior. ✓ Practise stringent hand hygiene between patient contacts. ✓ Don appropriate PPE (gowns, gloves, etc.). ✓ Isolation Precautions are needed in patients with >30% total body surface involvement. 31 Burns ✓ Ensure appropriate wound care 1. Aseptic techniques and barrier precautions. 2. Clean and dress less infected areas first. 3. Monitor wound site by microbiological cultures. ✓ Ensure appropriate sterilization and disinfection of all equipment. ✓ Immunize staff against hepatitis B. ✓ Administer systemic antimicrobials according to the microbiological reports. 32 Dermatology Wards Predisposing Causes, Sources, and with broken skin. Types of Infections ✓ Dispose of contaminated dressings in ✓ Generalized desquamating lesions colonized appropriate bags. with: ✓ Use appropriate Personal Protective 1. Staphylococcus aureus Equipment (PPE). 2. Multi-drug resistant (MDR) pathogens Infection Control Measures ✓ Isolate patients with clinical sepsis. ✓ Place patients with diffuse desquamating lesions in single rooms. ✓ Ensure dressing rooms have an exhaust fan. ✓ Cover couches in dressing rooms with disposable paper/cloth covers; change between patients. ✓ Sterilize dressing materials that will contact 33 Emergency Departments Predisposing Causes, Sources, and ✓ Ensure appropriate management of Types of Infections biomedical waste. ✓ Many patients have open wounds or other ✓ Post appropriate signage for cough etiquette lesions. and other precautions in the ERs for patients ✓ Immunocompromised patients are especially and visitors. vulnerable. ✓ Many short surgical and endoscopic procedures are performed, increasing risks. Infection Control Measures ✓ Perform surgical procedures in mechanically ventilated rooms or Operating Rooms (ORs). ✓ Follow aseptic techniques. ✓ Ensure proper sterilization and disinfection of equipment and devices. ✓ Enforce hand hygiene and use of proper PPE. 34 Dialysis Unit Predisposing Causes, Sources, and Types ✓ Preferably use subcutaneous arteriovenous of Infections fistulae instead of external shunts to avoid open wounds and infections. ✓ Patients are at increased risk for blood- borne pathogens. ✓ The dialysis fluid carries risk for bacterial contamination with nosocomial pathogens. ✓ Vascular access sites, catheter exit sites, and peritoneum are prone to infection with nosocomial pathogens. Infection Control Measures ✓ Screen all patients for HIV, HBV, and HCV. ✓ Practice Standard Precautions (especially handwashing or use of alcohol hand rubs) during dialysis. ✓ Follow environmental hygiene and aseptic techniques strictly. 35 Transplant Recipients Predisposing Causes, Sources, and Types of Infections ✓ Underlying medical conditions ✓ Lack of specific immunity ✓ Prior colonization ✓ Administration of immunosuppressive agents ✓ Graft vs. host or host vs. graft reactions Infection Control Measures ✓ Administer prophylactic antimicrobials, as per specific indications. ✓ Practice Standard Precautions (especially handwashing or alcohol hand rubs). ✓ Ensure environmental management (cleaning and disinfection). ✓ Monitor and treat infections with appropriate antimicrobials. 36 Immunocompromised Patients Predisposing Causes, Sources, and Types of Infections ✓ Granulocytopaenia (predisposes to Gram-positive and Gram-negative bacterial infections) ✓ Damaged skin integrity (vascular catheter-related infections) ✓ Oral mucositis Infection Control Measures ✓ Administer prophylactic antimicrobials, as per specific indications. ✓ Practice Standard Precautions (especially handwashing or use of alcohol hand rubs). ✓ Ensure environmental management (cleaning and disinfection). ✓ Monitor and treat infections with appropriate antimicrobials. 37 Haematological Malignancies Predisposing Causes, Sources, and Types ✓ Immediately report spills, accidents, of Infections breaches of containment, or exposures to infectious materials to the laboratory ✓ Severe, prolonged neutropenia supervisor. ✓ Maintain an effective rodent and insect Infection Control Measures control program. ✓ Clean and decontaminate work surfaces with ✓ Ensure work surfaces are non-absorptive a suitable disinfectant at the end of the day and scratch, stain, chemical, and heat and after any spill of potentially resistant. biohazardous material ✓ Design windows to prevent the ingress of ✓ Appropriately decontaminate contaminated flying insects. materials and equipment. ✓ Ensure the availability of biosafety cabinets ✓ Monitor autoclaves regularly with biological and other necessary biosafety equipment. indicators. ✓ Decontaminate all contaminated materials before disposal or reuse. ✓ Discard biomedical waste in appropriate bags 38