JWSS Biology Chapter 10 Infectious Disease

4 G3 Science(Biology) Chapter 8 Notes JURONG WEST SECONDARY SCHOOL SECONDARY FOUR – SCIENCE (BIOLOGY) Chapter 8: INFECTIOUS DISEASES Learning Outcomes: Candidates should be able to: (a) state that infectious diseases can be spread from person to person whereas non-infectious diseases cannot and identify examples of each (b) explain that infectious diseases are caused by pathogens such as bacteria and viruses and can be spread from person to person through body fluids , food and water (knowledge of the structure of bacteria and viruses is not required) (c) state the signs and symptoms of: • influenza – caused by the influenza virus • pneumococcal disease – caused by the bacteria, pneumococcus (d) describe the transmission and methods to reduce the transmission of: • influenza virus • pneumococcus (e) state that vaccines contain an agent that resembles a pathogen and prevent infectious diseases by stimulating white blood cells to quickly produce antibodies when the pathogen invades (f) state that antibiotics kill bacteria and are ineffective against viruses (g) explain that the misuse and overuse of antibiotics may accelerate the emergence of antibiotic resistant bacteria (a) State that infectious diseases can be spread from person to person whereas non-infectious diseases cannot and identify examples of each Infectious diseases are transmissible diseases that can be spread from one person to another via various methods. • Causes: Pathogens What are Pathogens? o They are disease-causing organisms o Eg: Bacteria and Viruses o Different types of pathogens give rise to different types of diseases, for example SARS-CoV-2 Virus results in COVID-19, Vibrio Cholerae bacteria results in Cholera The COVID-19 Outbreak resulted in approximately 2.6 million cases and 1800 deaths around the world. Today, 15 million people have been vaccinated against the disease. Cholera is a water-borne disease caused by contaminated water that

contains the Vibrio Cholerae bacteria. Think about what countries or conditions is Cholera the most common? 4G3 Science(Biology) Chapter 8 Notes Non-Infectious Diseases are non-transmissible diseases that cannot be spread from one person to another and are not caused by pathogens. • Causes: Inherited , lifestyle or environmental conditions o Eg. Sickle-cell anemia patients would have inherited 2 faulty haemoglobin genes from their parents o Eg. Excessive alcohol consumption may cause liver cirrhosis over time o Eg. Air Pollution may lead to pulmonary diseases Infectious Diseases Non-infectious diseases Transmissibility Can be transmitted from person to person Cannot be transmitted from person to person Mode of Transmission a) Droplets of water in air b) Direct Contact c) Contaminated Food and Water May be inherited or caused by environmental factors / lifestyle changes Pathogen-causing Caused by pathogens Not caused by pathogens Examples COVID-19, Influenza, Chicken Pox, Herpes, Cholera Diabetes, coronary heart diseases, sickle-cell anaemia Let’s Think! What is the difference between infectious and contagious? An infectious disease means that it can be spread from one person to another, however something that is contagious focuses more on the fact that it can be spread via contact with another person (as a mode of transmission). So, when something is contagious, it is also infectious as it would mean that one would have to be in contact with the infectious agent to get the disease. Something infectious however, may not always ben contagious. For example, Sinusitis, Sinus Infection is infectious but not contagious. Mosquito borne diseases are also infectious but not contagious. On the other hand, COVID-19 and stomach flu are both infectious and very contagious as well. A disease is a condition in that causes the body to function less effectively . Diseases produce specific signs or symptoms . A sign of a disease can be observed or measured . E.g., Rashes, fever, coughing or vomiting. A symptom of a disease can be described or felt by the patient. E.g., Headache, fatigue, and nausea (b) Explain that infectious diseases are caused by pathogens such as bacteria and viruses and can be spread from person to person through

body fluids, food and water How are Infectious Diseases transmitted? 1. Droplets of water in the Air (bodily fluids) 2. Direct Contact (bodily fluids) 3. Contaminated Food and water 2 4G3 Science(Biology) Chapter 8 Notes 1. Droplets of water • When a person sneezes or coughs, many respiratory droplets are expelled from the person’s mouth or nose. • These respiratory droplets may contain pathogens . • Hence when someone nearby inhales these respiratory droplets, they also inhale these pathogens which can then enter their respiratory system and infect them. Think about how wearing a mask and practicing social distancing can help protect us against viruses. A mask acts as a protective layer and reduces the amount of pathogens released from a person into the air. Hence, reducing the chance of someone nearby inhaling these pathogen-containing respiratory droplets and getting infected. Respiratory droplets can usually travel 2-3m away from the infected person. By keeping a distance away from the infected person, the likelihood of inhaling these pathogen-containing respiratory droplets is reduced , thus protecting one from being infected. 2. Direct Contact • An infected person may exchange bodily fluids or blood with another person via direct physical contact with them, for example during sexual intercourse . • Examples: o Sexually transmitted diseases (STIs) such as Human deficiency Virus (HIV) can be transmitted during sexual intercourse. o Hepatitis B and Syphilis can be transmitted from mother to child during breastfeeding. o HIV, Hepatitis B and C can also be transmitted via the blood of an infected person to someone uninfected. ▪ Through open wounds/ break in the skin, mucous membranes , or even infected needles . 3. Contaminated Food and Water • When food and water are not handled or stored properly , they end up being contaminated by pathogens . • The diseases that result from the transmission of contaminated food/water are called food-borne / water-borne diseases. • Examples : o Cholera – A water-borne disease common in underdeveloped countries with the lack of proper water supplied and sewage disposal , resulting in the consumption of Cholera bacteria -containing water. o Salmonella Infection – A food-borne disease that may occur when flies deposit salmonella onto our food. • Methods to prevent and control the spread: o Practice g