Host Microorganisms relationship.pptxtso

Book analysis

1. Host–Microorganisms Relationship Richard Karing’uri Lecturer, KMTC-Kilifi Nursing Students’ Microbiology Lecture Notes

2. By the end of this lesson, nursing students shall be able to:- Define the common terms used in host-microorganism relationship. Describe various sources of microorganisms that cause infections. Describe various modes of transmission of microorganisms. Describe various stages of an infection. Learning Outcomes

3. Pathogen, virulence, infection and host’s resistance A microorganism that is capable of causing a disease is called a pathogen . The ability of the pathogen to cause disease is called pathogenicity. The degree of pathogenicity is called virulence. Virulence of a pathogen is determined by its virulence factors. The host’s ability to resist pathogens is called immunity. Under normal circumstances, a balance exist between pathogen’s virulence and host’s resistance. This is a dynamic equilibrium. When the host’s resistance is impaired, even the microorganisms that are a normal flora can cause a disease .

4. Balance Disease Health Increase Decrease Disease Health Increase Decrease Pathogen’s virulence Host’s resistance Figure 1 : An illustration of pathogen’s virulence and host’s resistance balance. Shift in balance causes either increase in health or disease .

5. Host resistance to infection The host immune system provides resistance against pathogens. Shall be covered under immunology.

6. Sources of Microorganisms These sources are also called the reservoirs. They can cause infections when introduced into susceptible host. The sources of microorganisms include:- Human Body Skin : Such as the armpits, groin, and hands e.g. Staphylococcus epidermidis and Corynebacterium species. Mouth and respiratory tract : Streptococcus spp, Neisseria spp , and Candida are commonly found in the mouth, nose, and throat. Gastrointestinal tract : e.g. Escherichia coli and Lactobacillus . Genital and urinary tract : e.g. Lactobacillus spp in the vagina, while the urethra harbors Staphylococcus saprophyticus .

7. Air Present in the air as aerosols or dust particles . Include bacteria, fungal spores, and viruses, e.g. Mycobacterium tuberculosis , Aspergillus and respiratory viruses like influenza. Water Natural water sources : e.g. Vibrio cholerae and Pseudomonas spp. Drinking water : Poorly treated or contaminated water supplies can harbor Salmonella spp , Escherichia coli , and Cryptosporidium spp . Hospital water systems : Legionella spp and Pseudomonas aeruginosa leading to nosocomial infections.

8. Soil Bacteria like Clostridium tetani and Bacillus anthracis Food Raw foods , e.g. meat, poultry, dairy products, and vegetables, can harbor Salmonella spp , Listeria monocytogenes , and E. coli . Spoiled food : Fungi and bacteria, e.g. Penicillium species and Clostridium botulinum , can grow in food, leading to food poisoning. Animals Zoonotic microorganisms : e.g. Rabies virus and Brucella spp , Ebola virus.

9. Vectors : e.g. mosquitoes and ticks can transmit Plasmodium spp, Borrelia burgdorferi and viruses like Dengue and Chikungunya Fomites (Inanimate Objects) E.g. Doorknobs, bed linens, medical equipment, and clothing. Contaminated fomites transmit infections through contact, e.g. Staphylococcus aureus can survive on surfaces and cause infections when transferred to wounds. Plants Can harbor microorganisms, particularly bacteria and fungi Molds, like Aspergillus , grow on decaying plant, release spores that cause respiratory illnesses.

10. Hospital Environment Sources of microorganisms-presence of sick patients, invasive procedures. Pathogens like Methicillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile , and Pseudomonas aeruginosa Insects and Arthropods E.g. flies and cockroaches -mechanical vectors, transferring microorganisms from feces or garbage to food and surfaces. Fleas, lice, and ticks can also transmit microorganisms such as Rickettsia (causes typhus) and Yersinia pestis (causes plague).

11. Mechanisms by which the microorganism is transferred from one person to another or from a reservoir to a new host . Transmission may be:- Direct transmission Immediate transfer of microorganism from an infected host or reservoir to an appropriate portal of entry . This could be: Vertical transmission: From mother to the foetus e.g. transplacental transmission of HIV, from mother to the baby. Horizontal transmission: Through kissing, touching, sex, droplet spread onto mucus membrane of eye, nose or mouth during sneezing coughing, spitting or talking. Limited to a distance of 1 meter or less Modes of transmission of microorganisms

12. Indirect transmission Vehicle-borne transmission : Contact with fomites like: Beddings, toys, handkerchiefs, soiled clothes, cooking or eating utensils, surgical instruments. Contaminated food and water. ƒ Biological products like blood, serum, plasma or IV-fluids. The agent may or may not multiply or develop in the vehicle before it is introduced into man. Vector-borne transmission: The microorganism is conveyed by a vector to a susceptible host. Mechanical transmission: The vector transports the agent by soiling its feet or proboscis , no multiplication or maturation of the microorganism in the vector e.g. Salmonenella . typhi by housefly.

13. Biological transmission: The microorganism reproduces or matures in the vector before it is transmitted to human e.g. plasmodium spp by mosquito. Air-borne transmission: Transfer of microorganisms by air to the respiratory tract either through:- Dust: small infectious particles of widely varying size that may arise from soil, clothes, bedding or contaminated floors and be resuspended by air currents. Droplet nuclei : Droplets emitted by an infected host. They usually remain suspended in the air for some time e.g. Mycobacterium tuberculosis.

14. Stages involved in development of an infection Help explain how infections progress and manifest. There are 5 typical stages involved:- Incubation period Prodromal stage Acute (illness) stage Decline stage Convalescence stage Incubation period The time between exposure to a pathogen and the appearance of the first symptoms. The pathogen is replicating, but the host may not yet experience any signs of illness. Varies depending on the type of microorganism , the dose of the pathogen, and the host's immune system .

15. In some cases, pathogens are still transmissible during this stage. Examples: Incubation period for the flu is 1-4 days. Incubation period for HIV is 3 months Prodromal Stage Early stage of infection, where nonspecific symptoms begin to appear, but they are often mild and generalized . Symptoms include fatigue , low-grade fever , malaise , and muscle aches . The pathogen is actively multiplying , and the host's immune system is starting to respond . In some infections, the pathogen is highly transmissible during this period.

16. Illness (Acute) Stage The infection reaches its peak, and the characteristic signs and s ymptoms appear. The immune response is at its most intense to fight the pathogen. Medical intervention is needed, if the disease is severe or life-threatening. Decline Stage Symptoms of the infection start to subside Pathogens numbers decrease due to the immune system’s activity or medical intervention . May still experience mild symptoms which gradually improve. If the immune system is weakened or treatment is incomplete, relapse or secondary infections may occur.

17. Convalescence (Recovery) Stage The patient recovers and returns to normal health. The pathogen has been eliminated. The host regains strength and health, though fatigue and weakness may persist for some time. In some cases, pathogens may still be present in small quantities but are no longer causing symptoms ( carriers ). Important notes Chronic Infections : In some cases, infections may not follow this pattern e.g. HIV and Hepatis B Latent Infections : Infections like herpes or TB can become latent , where the pathogen remains dormant in the body and can reactivate later. Asymptomatic Infections : Some infections never produce symptoms (subclinical infections), but the individual can still be a carrier and transmit the disease to others .

18. Review Questions Pathogenicity is the Invasion and multiplication of microorganisms in body tissues, which can result in a disease. Presence of microorganisms in or on a host without causing disease or symptoms. Ability of a microorganism to cause disease in a host. Presence of bacteria in the blood, which can be transient or lead to serious infections such as sepsis The general virulence factor of a bacteria that enable it breakdown host’s tissues is Adhesins Enzymes Toxins Capsule

19. Indicate whether the following statements about sources of microorganisms is TRUE or FALSE Sources of microorganisms are also called reservoirs. Human body is an important reservoir of microorganisms. It is possible to have microorganisms on the human body which do not cause any problem and in fact beneficial. Staphylococcus aureus is a common bacterium whose reservoir is usually water bodies. The reservoir for Clostridium tetani, the causative agent for tetanus is usually soil. All of the following microorganisms are zoonotic EXCEPT Rabies virus Bacillus antharacis Brucella Pseudomonas aeruginosa

20. An example of horizontal transmission of microorganism is Kissing Touching Sexual intercourse All of the above A fomite is An inanimate item contaminated with microorganism A vector e.g. housefly that mechanically carries microorganism. A vector e.g. a mosquito where microorganism undergoes sexual reproduction. Droplets emitted by an infected host during sneezing or coughing

21. The state of infection where nonspecific symptoms begin to appear, but they are often mild and generalized is Incubation period Prodromal stage Acute (illness) stage Decline stage Infections like herpes or tuberculosis which can become latent, where the pathogen remains dormant in the body and can reactivate later are called Chronic infections Latent infections Asymptomatic infections None of the above

22. End