Bio Pathogens Short Answer

Definition: Infectious Disease & Pathogen

Infectious Disease: A disease caused by an invading microorganism or agent (pathogen) that disrupts normal body functions. Pathogen: A disease-causing agent, such as a bacterium, virus, fungus, protist, oomycete, or prion.

Definition: Zoonosis & Vector

Zoonotic Disease: An infectious disease that can be naturally transmitted from vertebrate animals to humans. Biological Vector: An organism (e.g., mosquito, mite) that actively transmits a pathogen from one host to another, often acting as an intermediate host for the pathogen's lifecycle.

Definition: Host, Reservoir & Fomite

Host: An organism that harbors a pathogen. Reservoir: A living host or environmental habitat (soil/water) where a pathogen normally lives, multiplies, and persists. Fomite: An inanimate object (e.g., clothing, equipment, doorknob) that carries infectious material.

Definition: Direct vs. Indirect Transmission

Direct Transmission: Immediate transfer of a pathogen from a reservoir/host to a susceptible host via physical contact, droplet spread (close range), or vertical transmission. Indirect Transmission: Transfer via an intermediate vehicle, such as air (airborne), inanimate objects (fomites), water/soil (environmental), or biological vectors.

Definition: Hyperplasia, Hypertrophy & Necrosis

Hyperplasia: Abnormal increase in the number of plant/animal cells leading to swelling. Hypertrophy: Abnormal increase in the size of individual cells. Necrosis: Unprogrammed or premature death of living cells/tissue (e.g., caseous necrosis in TB, plant tissue necrosis).

What are Koch's Postulates and what is it used for?

1. The microorganism must be present in every case of the disease, but absent from healthy organisms.
   
   

2. The microorganism must be isolated from the diseased organism and grown in a pure culture in vitro.
   
   

3. the cultured microorganism must cause the specific disease when inoculated into a healthy, susceptible host.
   
   

4. The same microorganism must be re-isolated from the experimentally infected host and identified as identical to the original pathogen.
   
   It is four basic rules used to prove that a specific microbe causes a specific disease

Koch's Postulates: Purpose & Limitations

Purpose: Used to establish a direct causal link between a specific pathogen and a specific infectious disease. Limitations: Cannot be applied to obligate intracellular pathogens that cannot grow in pure culture (e.g., viruses like Ross River, DWV, or Influenza), pathogens that infect only humans (ethical constraints), or asymptomatic carriers.

Tuberculosis: Pathogen Type, Scientific Name & Zoonotic Status

Type: Gram-positive, non-motile bacillus bacterium. Scientific Name: Mycobacterium tuberculosis (and M. bovis). Zoonotic: Yes (Y) (M. bovis infects cattle and humans; M. tuberculosis primarily infects humans).

Tuberculosis: Modes of Transmission / Transport

Indirect Airborne Transmission: Respiratory droplets containing bacteria are expelled during coughing, sneezing, or speaking, suspended in air currents, and inhaled into the lower respiratory tract of a susceptible host. Direct Transmission: Rare, via direct mucous membrane or broken skin contact with infected fluid.

Tuberculosis: Host Range / Organisms Infected

Humans, non-human primates, cattle, badgers, and other domestic and wild mammals.

Tuberculosis: Structure, Major Effects & Harm to Host

Inhaled bacteria infect alveolar macrophages, triggering granuloma (tubercle) formation. Caseous necrosis causes pulmonary tissue cavitation, persistent bloody cough (hemoptysis), chest pain, high fever, night sweats, and severe weight loss (wasting).

Tuberculosis: Detailed Lifecycle

1. Inhalation: Droplet nuclei containing bacteria reach alveoli.

2. Phagocytosis: Alveolar macrophages engulf bacteria, but bacteria inhibit phagolysosome fusion and replicate intracellularly.

3. Granuloma Formation: Immune cells surround infected macrophages, creating a tubercle to wall off infection (latent TB).

4. Reactivation & Necrosis: Granuloma centre undergoes caseous necrosis and liquefies.

5. Cavitation & Dissemination: Tubercles rupture into bronchial tubes, releasing active bacteria into air via cough and spreading throughout lungs/body.

Tuberculosis: Specific Australian Control & Management Efforts

Mandatory notification to state public health units; contact tracing; screening high-risk migrants via chest X-rays; BCG vaccination for selective high-risk groups; isolation of active cases in negative-pressure hospital wards; and strict compliance with 6–9 month combination antibiotics (Isoniazid, Rifampicin, Ethambutol, Pyrazinamide).

Crown Gall: Pathogen Type, Scientific Name & Zoonotic Status

Type: Gram-negative, flagellated rod-shaped soil bacterium. Scientific Name: Agrobacterium tumefaciens. Zoonotic: No (N) (plant pathogen only).

Crown Gall: Modes of Transmission / Transport

Direct Transmission: Root-to-root contact between infected and healthy host plants. Indirect Transmission: Soil-borne transport (movement of contaminated soil/water), entry through physical wound sites caused by pruning, grafting, or soil insects, and contaminated gardening tools (fomites).

Crown Gall: Host Range / Organisms Infected

Over 140 species of broad-leaved dicotyledonous plants, including fruit trees (apples, stone fruits), walnuts, grapevines, roses, and ornamental woody plants.

Crown Gall: Structure, Major Effects & Harm to Host

Transfer of T-DNA from the bacterial Ti plasmid triggers overproduction of auxins and cytokinins, driving uncontrolled cell division (hyperplasia) and expansion (hypertrophy). This forms rough galls (tumours) on roots and stems that crush xylem/phloem, leading to blocked transport, stunted growth, nutrient deficiency, wilting, and plant death.

Crown Gall: Detailed Lifecycle

1. Soil Survival: Bacteria survive as free-living saprophytes in soil.

2. Host Attraction: Wounded plant roots release phenolic compounds (acetosyringone), attracting bacteria via chemotaxis.

3. Attachment: Bacterial surface proteins attach to host plant cell walls.

4. T-DNA Integration: Virulence (vir) genes induce transfer of T-DNA from bacterial Ti plasmid into host plant cell genome. 5. Gall Formation: Plant cells express T-DNA, overproducing auxins/cytokinins (uncontrolled cell growth) and opines (bacterial nutrients). 6. Bacterial Multiplication: Bacteria feed on opines, multiply inside galls, and shed back into soil.

Crown Gall: Specific Australian Control & Management Efforts

Strict nursery biosecurity and quarantine inspections of rootstock; sterilising grafting/pruning tools with chemical disinfectants; physical removal and burning of infected plants; avoiding root damage during cultivation; and biological control using Agrobacterium radiobacter (Strain K84), which secretes agrocin 84 to kill pathogenic strains.

Influenza: Pathogen Type, Scientific Name & Zoonotic Status

Type: Enveloped single-stranded RNA virus. Scientific Name: Influenza A virus / Influenza B virus. Zoonotic: Yes (Y) (Influenza A strains originate and circulate in birds, pigs, and humans).

Influenza: Modes of Transmission / Transport

Direct Transmission: Direct physical contact with an infected individual or breathing in large droplets from close-range coughing/sneezing. Indirect Transmission: Airborne aerosol transmission over longer distances and surface/fomite contamination (touching contaminated surfaces then touching mouth, nose, or eyes).

Influenza: Host Range / Organisms Infected

Humans, wild aquatic birds, poultry, pigs, horses, seals, and domestic animals.

Influenza: Structure, Major Effects & Harm to Host

Viral hemagglutinin attaches to sialic acid on respiratory epithelial cells, invading and replicating to cause host cell lysis and widespread mucosal inflammation. Symptoms include sudden high fever, chills, severe myalgia (muscle body aches), fatigue, sore throat, dry cough, and secondary bacterial pneumonia.

Influenza: Detailed Lifecycle

1. Adsorption: Viral hemagglutinin (HA) surface protein binds to sialic acid receptors on respiratory epithelial cells. 2. Endocytosis: Host cell engulfs virus via receptor-mediated endocytosis. 3. Uncoating: Low endosomal pH triggers membrane fusion and release of viral RNA into host cytoplasm. 4. Transcription & Replication: Viral RNA enters cell nucleus, hijacking host machinery to synthesize viral vRNA and mRNA. 5. Assembly & Budding: Viral proteins assemble at plasma membrane. 6. Release: Neuraminidase (NA) cleaves sialic acid receptors, releasing newly formed virions to infect adjacent cells and lysing the host cell.

Influenza: Specific Australian Control & Management Efforts

Annual National Immunisation Program (NIP) tailored to updated circulating strains; nationwide disease surveillance via the Australian Sentinel Practices Research Network (ASPRN); public health campaigns promoting respiratory hygiene; prescription of antivirals like Oseltamivir (Tamiflu); and strict biosecurity measures against Avian Influenza strains.

Ross River Virus: Pathogen Type, Scientific Name & Zoonotic Status

Type: Enveloped single-stranded RNA Alphavirus. Scientific Name: Ross River virus. Zoonotic: Yes (Y) (transmitted between animal reservoirs and humans via vectors).

Ross River Virus: Modes of Transmission / Transport

Indirect Vector Transmission: Biological transmission via the bite of an infected female mosquito vector (primarily Aedes vigilax, Aedes camptorhynchus, or Culex annulirostris). Direct human-to-human transmission does not occur.

Ross River Virus: Host Range / Organisms Infected

Humans, native Australian marsupials (macropods like kangaroos and wallabies), horses, and flying foxes.

Ross River Virus: Structure, Major Effects & Harm to Host

Virus infects skeletal muscle, joint synovial tissue, and macrophages. Triggers inflammatory destruction of synovial membranes resulting in severe joint pain and swelling (polyarthritis), debilitating fatigue, muscle aches (myalgia), fever, and a raised maculopapular skin rash.

Ross River Virus: Detailed Lifecycle

1. Ingestion: Female mosquito feeds on viremic reservoir host (macropod). 2. Vector Replication: Virus infects mosquito midgut, multiplies, and migrates to salivary glands. 3. Vector Injection: Infected mosquito bites human, injecting viral saliva into bloodstream. 4. Host Invasion: Virus targets and replicates within skeletal muscle cells, joint synovial cells, and macrophages. 5. Inflammation: Replication triggers intense immune response causing joint tissue damage. 6. Transmission Cycle: Uninfected mosquito bites a viremic animal/human host, maintaining transmission.

Ross River Virus: Specific Australian Control & Management Efforts

Vector management programs using aerial larvicides (e.g., Bacillus thuringiensis israelensis) and fogging; state public health surveillance of mosquito populations; public warnings during flood/high tide events; personal protection campaigns (DEET repellent, loose clothing, flyscreens); and symptomatic pain management using NSAIDs (e.g., ibuprofen).

Honeybee Viral Diseases: Pathogen Type, Scientific Name & Zoonotic Status

Type: Non-enveloped, positive-sense single-stranded RNA viruses. Scientific Name: Deformed wing virus (DWV) and Sacbrood virus (SBV). Zoonotic: No (N) (insect pathogens only).

Honeybee Viral Diseases: Modes of Transmission / Transport

Indirect Vector Transmission: Mechanical/biological vector transmission via parasitic Varroa destructor mites (for DWV). Direct Transmission: Horizontal transmission via shared larval food/royal jelly from nurse bees, cannibalism of infected larvae, and vertical transmission from queen to eggs.

Honeybee Viral Diseases: Host Range / Organisms Infected

European honeybees (Apis mellifera), native bumblebees, and allied pollinating insects.

Honeybee Viral Diseases: Structure, Major Effects & Harm to Host

DWV: Replicates in pupae, causing emerging adult bees to display crumpled, non-functional wings, stunted bodies, and early death. Sacbrood: Prevents larvae from shedding cuticles during ecdysis; fluid builds up under skin creating a fluid-filled sac that kills larvae prior to pupation.

Honeybee Viral Diseases: Detailed Lifecycle

1. Entry: Virus enters larvae/pupae through infected nurse bee jelly (oral ingestion) or Varroa mite feeding bites. 2. Tissue Replication: Viral RNA replicates inside host abdominal tissues, head tissues, and wing buds. 3. Developmental Disruption: High viral load disrupts pupal morphogenesis (causing deformed wings) or halts larval ecdysis (causing fluid accumulation under larval cuticle). 4. Mortality/Emergence: Affected larvae die before pupation (Sacbrood) or emerge as malformed, short-lived adults (DWV). 5. Hive Propagation: Sick adults shed virus into hive wax, pollen, and honey, or mites transmit virus between pupae.

Honeybee Viral Diseases: Specific Australian Control & Management Efforts

Strict national biosecurity quarantine measures; the National Sentinel Hive Program monitoring major Australian ports for invasive Varroa destructor vectors; mandatory reporting of hive abnormalities; re-queening affected hives; applying synthetic miticides (e.g., flumethrin); and culling infected hives during outbreak responses.

Chytridiomycosis: Pathogen Type, Scientific Name & Zoonotic Status

Type: Parasitic chytrid fungus. Scientific Name: Batrachochytrium dendrobatidis (Bd). Zoonotic: No (N) (amphibian pathogen only).

Chytridiomycosis: Modes of Transmission / Transport

Indirect Transmission: Waterborne transmission via motile flagellated zoospores swimming through aquatic habitats, and environmental contact with damp soil/submitting substrates. Direct Transmission: Direct physical skin-to-skin contact between infected and healthy amphibians.

Chytridiomycosis: Host Range / Organisms Infected

Amphibians worldwide, including frogs, toads, salamanders, and newts.

Chytridiomycosis: Structure, Major Effects & Harm to Host

Zoospores invade keratinised epidermal cells, developing into sporangia and causing hyperkeratosis (skin thickening), excessive sloughing, lethargy, loss of righting reflex, and disruption of cutaneous respiration and osmoregulation leading to fatal hypokalemia (cardiac arrest).

Chytridiomycosis: Detailed Lifecycle

1. Zoospore Stage: Flagellated, uniflagellate zoospores swim through water toward host chemical cues. 2. Encystment & Penetration: Zoospore attaches to keratinised amphibian skin (adult outer skin or tadpole mouthparts), sheds flagellum, and forms a germ tube to penetrate epidermal cells. 3. Thallus & Sporangium Growth: Inside host cells, fungus grows into a thallus and develops into a walled zoosporangium. 4. Maturation: Zoosporangium produces new internal zoospores through cleavage. 5. Release: Discharge papilla forms, bursting through skin surface to release zoospores into water or adjacent skin tissue, causing hyperkeratosis.

Chytridiomycosis: Specific Australian Control & Management Efforts

National Threat Abatement Plan for Chytridiomycosis; field hygiene protocols requiring researchers and bushwalkers to clean and disinfect gear/boots with Virkon or benzalkonium chloride; captive breeding "assurance colonies" for critically endangered native species (e.g., Corroboree frog); and antifungal bath treatments (Itraconazole) for captive individuals.

Malaria: Pathogen Type, Scientific Name & Zoonotic Status

Type: Unicellular protozoan parasite (protist). Scientific Name: Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, Plasmodium ovale. Zoonotic: Generally No (N) for main human strains (though P. knowlesi is zoonotic from macaques).

Malaria: Modes of Transmission / Transport

Indirect Vector Transmission: Biological vector transmission through the bite of an infected female Anopheles mosquito. Direct Transmission: Rare, via contaminated blood product transfusions, needle sharing, or congenital transmission across placenta from mother to fetus.

Malaria: Host Range / Organisms Infected

Humans, non-human primates, and female Anopheles mosquitoes.

Malaria: Structure, Major Effects & Harm to Host

Parasites invade and rupture liver cells (hepatocytes) and red blood cells (erythrocytes). Synchronised erythrocyte lysis releases toxins and hemozoin, driving paroxysmal fever spikes, chills, severe hemolytic anaemia, jaundice, microvascular blockage, organ failure, and cerebral malaria.

Malaria: Detailed Lifecycle

1. Human Inoculation: Mosquito bites human, injecting motile sporozoites into blood. 2. Exo-erythrocytic Phase: Sporozoites travel to liver, infect hepatocytes, and replicate into merozoites. 3. Erythrocytic Phase: Liver cells rupture, merozoites enter blood, invade red blood cells (RBCs), form trophozoites/schizonts, and cyclically lyse RBCs every 48-72 hrs. 4. Gametogony: Some merozoites differentiate into sexual gametocytes. 5. Mosquito Stage: Mosquito ingests gametocytes during blood meal; fertilization occurs in mosquito midgut forming an ookinete -> oocyst -> releasing sporozoites that migrate to salivary glands.

Malaria: Specific Australian Control & Management Efforts

Australia was declared malaria-free in 1981; current efforts focus on preventing re-establishment: strict border biosecurity; mosquito surveillance and control around northern ports/airports (e.g., Torres Strait); prophylactic antimalarial prescriptions for Australian travellers; and rapid treatment of imported cases using Artemisinin-based Combination Therapies (ACTs) or Chloroquine.

Phytophthora Dieback: Pathogen Type, Scientific Name & Zoonotic Status

Type: Soil-borne water mould / Oomycete (protist). Scientific Name: Phytophthora cinnamomi. Zoonotic: No (N) (plant pathogen only).

Phytophthora Dieback: Modes of Transmission / Transport

Indirect Transmission: Waterborne/soil-borne movement of flagellated zoospores swimming through soil water, transport of infested soil on vehicle tires, footwear, machinery, and earthmoving equipment, or infected nursery stock. Direct Transmission: Root-to-root contact between infected and healthy host plants.

Phytophthora Dieback: Host Range / Organisms Infected

Over 40% of native Australian plant species, including Jarrah (Eucalyptus marginata), Banksia, Xanthorrhoea (grass trees), and agricultural crops (avocados, macadamias).

Phytophthora Dieback: Structure, Major Effects & Harm to Host

Zoospores infect root tips and hyphae destroy root cortex tissues, preventing water and nutrient absorption. Symptoms include yellowing leaves, crown dieback starting from upper branches downward, severe wilting, primary root rot, and rapid plant death from starvation and dehydration.

Phytophthora Dieback: Detailed Lifecycle

1. Survival Phase: Thick-walled chlamydospores survive extended dry periods in soil or dead root material. 2. Germination: Warm, moist soil induces chlamydospores to germinate and produce sporangia. 3. Zoospore Release: Sporangia release motile, biflagellated zoospores into soil water. 4. Chemotaxis & Infection: Zoospores swim toward host root chemicals, attach, encyst, and germinate to form hyphae. 5. Tissue Destruction: Hyphae penetrate root cortex, secreting enzymes that destroy vascular tissue (xylem/phloem). 6. Sporulation: Hyphae produce new chlamydospores/sporangia within dying roots to repeat cycle.

Phytophthora Dieback: Specific Australian Control & Management Efforts

Establishment of Disease-Risk Areas (DRA) and strict quarantines; boot-cleaning and vehicle washdown stations at national park boundaries; seasonal track closures; aerial phosphite (phosphonate) spraying and trunk injections to boost host plant resistance; and strict biosecurity protocols for nursery trade.

Definition: Pathogen & Infectious Disease

Pathogen: A disease-causing agent, such as a bacterium, virus, fungus, protist, oomycete, or prion. Infectious Disease: A disease caused by an invading pathogen that can be transmitted between host organisms or from the environment, disrupting normal physiological function.

Definition: Transmission (Direct & Indirect)

Transmission: The transfer or mechanism by which a pathogen moves from an infected host or environmental reservoir to a susceptible host. Includes Direct Transmission (physical contact, close respiratory droplets, vertical transfer) and Indirect Transmission (airborne aerosols, fomites, soil/water vehicles, biological vectors).

Definition: Zoonosis (Zoonotic Disease)

Zoonosis: An infectious disease that can be naturally transmitted from vertebrate animals to humans (e.g., Influenza A, Ross River virus, Tuberculosis via M. bovis).

Definition: Incubation Period vs. Latent Period

Incubation Period: The time elapsed between initial exposure/infection by a pathogen and the first appearance of clinical signs or symptoms of the disease. Latent Period: The time interval between initial infection and when the host becomes capable of transmitting the pathogen to others.

Definition: Virulence & Pathogenicity

Pathogenicity: The qualitative ability of a pathogen to infect a host and cause disease. Virulence: The quantitative measure or degree of severity/damage a pathogen causes to its host (e.g., highly virulent pathogens cause severe illness or high mortality rates).

Definition: Population Density & Disease Spread

Population Density: The number of individuals of a host species living per unit of area or volume. High population density significantly increases the rate of host-to-host contact, accelerating the transmission and spread of contagious pathogens.

Definition: Globalisation & Pathogen Spread

Globalisation: The increasing interconnectedness of nations, human populations, and global economies through international trade, travel, and transport. Effects on disease: Rapid long-distance air travel allows infected hosts/vectors to bypass natural geographic barriers within hours (often before symptoms appear), while international shipping of soil, livestock, and produce facilitates the global transport of invasive vectors and plant pathogens.

Koch's Postulates (All 4 Postulates)

1. The microorganism must be present in every case of the disease, but absent from healthy organisms. 2. The microorganism must be isolated from the diseased host and grown in a pure culture in vitro. 3. The cultured microorganism must cause the specific disease when inoculated into a healthy, susceptible host. 4. The same microorganism must be re-isolated from the experimentally infected host and identified as identical to the original pathogen.

Koch's Postulates: Purpose & Key Limitations

Purpose: Used to establish a definitive causal relationship between a specific pathogen and a specific infectious disease. Limitations: Cannot be applied to obligate intracellular pathogens that cannot be grown in pure culture (e.g., viruses like Ross River, DWV, or Influenza), pathogens that infect only humans due to ethical restrictions, or asymptomatic carrier states.

Definition: Vector, Reservoir & Carrier State

Vector: An organism (e.g., mosquito, mite) that transmits a pathogen from one host to another. Reservoir: A living host or environmental substrate (soil, water) where a pathogen normally lives and multiplies. Asymptomatic Carrier: An infected host that harbors and sheds a pathogen without showing clinical symptoms.