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Microbio 8-12
Microbio lectures 8-12 sam Kelleher Unimelb
| Term | Definition |
|---|---|
| Types of Symbiosis | Parasitism Mutualism Commensalism |
| Parasitism | One benefits, one harmed |
| Mutualism | Both benefit |
| Commensalism | One benefits, other unharmed |
| Life Cycle Terminology | IH: Intermediate host DH: Definitive host PH: Paratenic Host |
| Definitive Host | Harbours adult or sexually reproductive from |
| Intermediate Host | Supports immature or asexual stages |
| Paratenic Host | Transport hosts, aids transmission without development |
| Integrated Parasite Control (C=M+E+T) | Control = Management Epidemiology Treatment |
| Management (parasite control) | Reduce exposure (e.g. hygiene, stabling animals) |
| Epidemiology (parasite control) | Species-species factors, (climate, vectors, etc) |
| Treatment (parasite control) | Anthelmintics/ insecticides; resistance is rising |
| Parasite groups | Protists Nematodes Cestodes Trematodes Arthropods |
| Nematodes (round worms) | - Barber's pole worm (haemonchs contortus) - Costly for livestock industries - Lifecycle: egg -> L1 -> L2 -> L3 (infective stage) -> adult in host - Control via integrated strategies and anthelmintic use |
| Cestodes (tape worms) | - Often zoonotic - Lifecycle includes larval cysts in livestock and adults in dogs and humans - Examples: hyatid disease, beef/sheep measles, bladder worm |
| Trematodes (Flukes) | - Liver Fluke most significant - Lifecycle includes snail as IH and metacercariae on vegetation - Control: flukicides (resistance increasing), snail control, grazing management |
| Arthropods | Insecta or Arachnida - Ticks, mites, flies, fleas |
| Blowflies and Flystrike | Lucilia cuprina responsible for 90% of strikes - Lifecycle: eggs -> Larvae -> pupae -> adult - Seasonal peaks: spring/autumn |
| Blowfly/Flystrike Control | Animal management: crutching, breeding for resistance Environmental: carcase removal, traps Chemical control (resistance is a concern) |
| Giardia Lamblia | Protists - Cause diarrhoea, survives in water, tolerant to chlorine - Moves using flagella - Faecal oral transmission |
| Fasciola hepatica (trematode - Fluke) | - Adults in bile duct - eggs pass in faeces - Eggs hatch - miracadia released - Miracadia affects snails (IH) - Attach with vegetation - metcercariae (infective) - Eaten by hosts - Excyst in intestine, penetrate intestinal wall, liver |
| Features of Ticks | - Obligate parasites; need blood meals (so females can lay eggs) - Most of life cycle spent off host - Variable host specificity |
| Ixodes holycyclus | Paralysis Tick - 3 host lifecycle - 18 month life cycle - males rarely found on host |
| Ixodes holycyclus (effect on host) | - All stages cause irritation and paralysis - Sheep, dogs, cats most susceptible; 1 female tick will kill a dog - Can effect humans - Females engorge for up to 21 days - Signs develop on days 5-6 |
| Blowflies, flesh flies, and screw worm flies | Family: Calliphoridae - Important environmentally - Breed in decaying organic matter - Adults feed on decaying organic material or nectar - Faculative parasites |
| Types of Parasitism | Obligate, Facultative, Permanent, Intermittent |
| Obligate Parasites | Must have a host to survive (fleas) |
| Facultative Parasites | Can survive without a host (flies) |
| Permanent Parasites | On host at all times (lice) |
| Intermittent Parasites | Visit host periodically (mosquitos) |
| Detection methods for infectious agents | -Direct identification of the agent - Indirect identification |
| Direct Identification | - Culture of the Agent - In presence or absence of host cells - Visualisation of samples/ tissues - Detection of Nucleic acids (molecular methods) - Presence of an antigen, toxin detection |
| Indirect Identification | - Response of host against agent - Immune response |
| Culture of Agent (detection method) | - Requires viable and culturable microbes - Viable but non cultural bacteria (VBNC) - Microbe may lose viability during transport - OHS risk - Contamination of sample |
| Host Cell-Free Culture | - Detects some bacteria (but not all) - Doesn't detect viruses - Can use broth culture or agar plates |
| Host Cell-Free Culture (Agar Plates) | - Isolates single colony ("pure culture") - Testing ( for identification, antimicrobial resistance, etc) - Enumerate colony forming units (CFU) e.g., faecal coliforms have CFU limits for water |
| Growth Conditions (for detecting infectious agents) | Different nutrient and energy sources, pH, temperature and atmospheric conditions |
| Host Cell Culture | - All viruses and some bacteria - Less common for diagnosis in the common era |
| Host Cell Lines (examples) | - Immortal cell lines e.g. HeLa cells - Primary cell lines - Embryonated eggs (flu viruses) - Animal hosts (non-culturable microbes) |
| Cytopathic Effect | - Virus infection results in host cell death - Plaque assay - Can see effects under light microscope |
| Culture of the Agent (advantages) | - Antimicrobial susceptibility testing - Typing of the microbe - Storage of the microbe (so it can be used for further study) |
| Culture of the Agent (disadvantages) | - Must be viable and culturable - Takes time (overnight to months) - Requires specialised culture media, cell lines, equipment - Risk to lab staff (OHS) - Amplification of contaminating microbes |
| Visualisation of Microbe (bacteria) | - Light microscopy - Gram stain - Specific antibody stain |
| Visualisation of Microbe (bacteria or viruses) | - immunofluorescence - Confocal microscopy |
| Electron Microscopy | Identifies viruses that are too small for light microscopy |
| Visualisation of Microbe (advantages) | - Visualise organism - Further studies - host mechanism - Easy and fast (light microscopy only) - Less expensive (LM only) - Less expertise needed (LM only) |
| Visualisation of Microbe (disadvantages) | - Contamination from other bacteria - Secondary confirmation (culture first) - Electron microscope/fluorescence microscope requires special expertise, is expensive and time consuming |
| Detection of Nucleic Acids - Molecular Methods | - Amplification (PCR) - Quantitative PCR - Next Gen Sequencing |
| PCR amplification (detecting agents) | - Relatively specific - Shows presence or absence |
| qPCR amplification (detecting agents) | - Specific - Shows the amount of bacteria in a sample |
| Next Gen Sequencing (detecting agents) | - Thousands of reads - Whole genome sequencing - Data analysis is complex |
| Molecular Methods (advantages) | - Fast - Inexpensive (mostly) - No need for live organism - Low risk - Not affected by contamination (except PCR) - Confirm species level (except metagenomics) |
| Molecular Methods (disadvantages) | - Need specialised machines - Some methods still expensive - PCR can be misleading - Can't store microbes or characterise further (except possibly molecular typing) |
| Detection of antigen/toxin | Rapid Tests |
| Rapid Tests | - Detect antigen, e.g. surface protein, toxin - Useful in field testing |
| Rapid Tests (advantages) | - Fast - Practical and helpful for disease control - Inexpensive - No need for live organism - Low risk - Not affected by contamination |
| Rapid Tests (disadvantages) | Can't store microbe or characterise further |
| ELISA (Enzyme Linked Immunoabsorbent Assay) | - Indirect Method - Antibody response - Used in body fluids (e.g. milk, blood) |
| Indirect Methods (advantages) | - Fast (mostly) - Inexpensive (mostly) - No need of live organism - Low risk to staff - Not affected by microbial contamination - Can detect past and current infection |
| IgM | Current, acute infection (found using indirect method) |
| IgG | Past infection (found using indirect method) |
| Indirect Methods (disadvantages) | - Can't store microbe or characterise further as it only detects the response - Delayed response may give false negative - Cross - reaction may give false positive |
| Limitations of Tests | - False + - False - - Sensitivity - Specificity No test has 100% sensitivity or specificity |
| False Positives | Test is positive but microbe was not actually present in the animal |
| False Negatives | Test is negative but the microbe was present in the animal |
| Sensitivity | A tests ability to designate an individual with a disease as positive |
| Specificity | A tests ability to designate an individual who does not have a disease as negative |
| Sample Collection | - Collect from animals as early as possible after death (before they undergo autolysis) - Minimise contamination (aseptic technique) - Disinfect surface - Timing of sample (mid stream, etc) - Storage conditions - OHS -PPE |
| Sources of Microbes (dairy cow mastitis) | - Milker's hands - Mud - Urine - Milk splashes - Faeces |
| Types of Microbes | - Bacteria - Viruses - Parasites - Fungi - Algae - Protozoa - Prions |
| Where are microbes found? | - The environment - Other animals - The animal itself |
| Environmental Mastitis | - Develops with contact to soil organisms, water troughs, bedding etc - Contamination of environment by faeces - Eg coliform mastitis (E.coli) |
| Pathogens from own species | - Clinically affected animals - Subclinical infections - Latent infections - Normal flora (opportunistic pathogens) |
| Normal Flora (microbiota) | - Animals have a normal populations of microorganisms - In the gastrointestinal tract (essential for herbivores) - May protect against pathogenic agents (competition, inhibitory agents, altered environment) - Opportunistic pathogens |
| Association | - Statistical relationship between two variables - Specified health outcome that is more likely in animals with particular exposure - Two variables may be associated without a casual relationship |
| Multifactorial Relationship of Disease Casualty | Includes: - Host (genetics, age) - Infectious agent (bacteria, virus) - Environment (climate, housing, etc) |
| Two Types of Cause | - Necessary cause - Sufficient cause |
| Necessary Cause | Condition/event/characteristic/agent that must be present for a disease to occur |
| Sufficient Cause | A set of minimal conditions/events that might produce a disease |
| Bovine Respiratory Disease (BRD) | - A complex multifactorial disease, common in feedlot cattle - A number of factors must interact to cause this disease such as: - Recent weaning - Transport - New introductions (stress) |
| Microbial Acquisition | Understanding where animals get their microbes from is crucial for studying host-microbe interactions and preventing disease |
| Balance is Key (host-microbe interactions) | Healthy microbial communities are vital for an animal's health, but disruption (e.g., pathogenic microbes) can lead to disease |
| Pathogenesis - How do microbes cause disease? | - Toxins (feed contamination) - Enter host and cause local damage - Spread throughout host - Can result in death, chronic infection or recovery |
| Botulism (clostridium botulinum) | - Spread by soil, water, intestinal tracts - Preformed toxin in food source - Vermin carcases, contaminated water, bone chewing |
| Entry of Microbes | - Skin - Respiratory tract - Gastrointestinal Tract - Genitourinary tract - Conjunctiva - Mammary - Umbilicus |
| Importance of Physical Barriers | Physical barriers are important to stop the entry of microbes, If the skin is broken, microbes will be able to enter the body more easily and spread |
| Following the entry of microbes: | Local multiplication begins, which can cause tissue damage |
| Absorption of toxins by the body can lead to: | - Toxin to act locally e.g., ETEC - Toxin to spread throughout the body e.g., tetanus |
| Viruses: | - Must replicate inside cells to survive - are prokaryotic - are not 'alive' |
| Bacteria may or may not: | - Enter cells passively or actively - Adhere to mucosal surfaces - Produce toxins |
| Spread within body: | - Inside or outside cells (immune cells) |
| Spread occurs via: | - Blood - Lymph - Nerves (neural spread) e.g. rabies |
| Host Immune Response | May be protective or contribute to the disease e.g. opportunistic pathogens within the body |
| Pathogens that avoid the immune system: | - Capsules (bacteria) - Mutations (virus) |
| Damage to the host includes: | - Cell death: agent replicating inside cell - Damage due to toxins, other virulence factors - Damage due to immune response |
| Recovery | Occurs when the virus or disease has cleared the organism completely |
| Persistent Infections | - Chronic infection - Latent (may reactivate and shed) e.g., herpesvirus - Shed or organism (always or intermittently) - No shedding |
| Contagious Diseases: | Diseases that spread from animal-animal |
| Non-Contagious Diseases: | - Not easily transmissible - Vector-borne infectious diseases e.g. bovine ephemeral fever (BEF) |
| Horizontal Transmission | Direct or indirect - Animal to animal - Fomies -Airborne -Vector-borne -Common vehicle - Zoonotic - Iatrogenic |
| Vertical Transmission | - Mother to offspring - Early postpartum by milk, fluids, placenta, birth canal, etc - In utero or in ovo - Can cause embryonic death, mummification, resorption or congenital defects |
| Direct Horizontal Transmission | - Animal to Animal transmission - Direct contact (licking, rubbing, biting, sexual contact) |
| Direct and Indirect Horizontal Transmission | - Airborne Transmission - Respiratory tract via droplet/aerosol - Droplets: direct contact - Aerosol: direct/indirect contact |
| Zoonotic Transmission | - Horizontal - Occurs through direct contact, contaminated food or water, or via vectors Animals and humans can be infected |
| Fomite Transmission | - Indirect horizontal transmission - Feed and water containers, bedding, dander, tack, clothes, etc |
| Common vehicle transmission | - Horizontal/indirect - One common source of transmission e.g., feed, water troughs, etc |
| Vector Borne Transmission | -Indirect/horizontal - Host to vector -> Vector to new host e.g. JEV, mosquitos will acquire the virus from infected pigs, and pass the disease to horses |
| Iatrogenic Transmission | - Indirect/horizontal - e.g. spread during medical care through infected equipment |
| Carrier state | Asymptomatic carriage May be contagious (sometimes or always) |
| Clinical Disease | A disease that has recognisable clinical signs and symptoms |
| Subclinical Disease | A disease that exists within the animal but does not show any symptoms. Animal is able to shed the disease and infect others but is not being harmed by the virus itself |
Created by:
sakelleher29
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