Biology Extended Response

For Phytophthora Dieback - What is the disease name, pathogen, and scientific classification of Phytophthora Dieback?

Disease: Phytophthora Dieback. Pathogen: Phytophthora cinnamomi, classified as a protist (specifically an oomycete or 'water mould').

For Phytophthora Dieback - Why is Phytophthora cinnamomi classified as a protist rather than a true fungus?

Its cell wall is mainly cellulose (not chitin), it produces motile zoospores with flagella, and genetic evidence links it closer to algae.

For Phytophthora Dieback - What are the main structural features of Phytophthora cinnamomi?

It contains thread-like hyphae (which form mycelium networks), sporangia (spore-producing structures), zoospores (motile spores), and chlamydospores (survival spores).

For Phytophthora Dieback - What role do chlamydospores play in survival and germination?

They are thick-walled dormant spores that survive dry conditions in soil without a host; warm, moist soil after rain triggers them to germinate into sporangia.

For Phytophthora Dieback - How are zoospores produced, released, and attracted to host plants?

Zoospores are produced asexually in sporangia, released into soil water, and swim using flagella toward chemical compounds released by host root tips.

For Phytophthora Dieback - What is the portal of entry for Phytophthora cinnamomi and how does infection occur?

The intact root tip is the portal of entry (no wound required); zoospores attach, penetrate root cells with hyphae, and absorb nutrients.

For Phytophthora Dieback - What is the primary mode of reproduction for Phytophthora cinnamomi in Australia?

It reproduces predominantly asexually via sporangia and zoospores (though sexual oospores occasionally form).

For Phytophthora Dieback - How does Phytophthora cinnamomi cause plant symptoms like wilting and dieback?

Hyphae expand into a mycelium network that rots the root system, severely impairing the plant's capacity to absorb water and nutrients.

For Phytophthora Dieback - What are the individual plant symptoms of Phytophthora Dieback?

Root rot, yellowing leaves, wilting, branch dieback, and eventual death.

For Phytophthora Dieback - What is the host range and portal of exit for Phytophthora cinnamomi?

Over 2,000 plant species worldwide (>40% of native WA plants, e.g., Banksia, Jarrah, Grasstrees); sporangia on infected roots act as the portal of exit by releasing new zoospores.

For Phytophthora Dieback - What are the primary modes of transmission for Phytophthora Dieback?

Contaminated soil/mud/gravel, human equipment (footwear, tyres, machinery), and water movement (groundwater, runoff, drainage).

For Phytophthora Dieback - What are the broader ecosystem impacts of Phytophthora Dieback?

Loss of biodiversity, destruction of vulnerable plant communities, reduced habitat availability, and altered ecosystem functioning.

For Phytophthora Dieback - What are the four main management strategies for Phytophthora Dieback?

Hygiene (wash-down stations), Chemical treatments (phosphite sprays), Quarantine (soil access restriction), and Monitoring (surveillance/mapping).

For Phytophthora Dieback - How does phosphite treatment help manage Phytophthora Dieback?

It boosts the plant's natural immune response/resistance and slows disease progression.

For Phytophthora Dieback - Why is Phytophthora cinnamomi practically impossible to eradicate from soil?

Its thick-walled chlamydospores can remain dormant in soil without a host for years and restart the cycle when moisture returns.

For Phytophthora Dieback - What is the main goal of WA management programs for Phytophthora Dieback?

Because there is no known cure, programs focus on containment, hygiene, and preventing spread rather than eradication.

For Phytophthora Dieback - What features do oomycetes share as a biological group?

They are eukaryotic, have nuclei and membrane-bound organelles, possess cellulose cell walls, form hyphae, produce spores, and require moisture for dispersal.

For Phytophthora Dieback - How does the soil act as a reservoir in the disease cycle?

Soil holds both dormant chlamydospores during drought and active zoospores in water-filled pores, maintaining the pathogen population indefinitely.

For Ross River Virus - What is the disease name, pathogen, and scientific classification of Ross River Virus disease?

Disease: Ross River Virus Disease (Ross River Fever). Pathogen: Ross River Virus (RRV), a single-stranded positive-sense RNA alphavirus (family Togaviridae).

For Ross River Virus - Why is Ross River virus classified as a virus rather than a cellular organism?

It is non-cellular, lacks independent metabolic machinery, and requires a living host cell to replicate.

For Ross River Virus - What are the primary structural features of the Ross River virus particle?

A single-stranded RNA genome inside an icosahedral protein capsid, surrounded by a lipid envelope containing glycoprotein spikes.

For Ross River Virus - Who are the main vectors and primary reservoir hosts for Ross River virus?

Vectors: Female mosquitoes (e.g., Ochlerotatus vigilax, Culex annulirostris). Reservoirs: Native Australian marsupials (kangaroos and wallabies).

For Ross River Virus - How do weather conditions and stagnant water impact vector populations?

Warm temperatures and rainfall/flooding increase stagnant water bodies, providing essential egg-laying sites that trigger mosquito population surges.

For Ross River Virus - How does a mosquito acquire and transmit Ross River virus?

A female mosquito ingests the virus from an infected reservoir during a blood meal; glycoprotein spikes then allow the virus to bind and enter host cells.

For Ross River Virus - What is transovarial transmission in Ross River virus vectors?

Infected female mosquitoes pass the virus to their offspring through eggs, allowing the virus to survive dry spells in dormant mosquito eggs.

For Ross River Virus - What is the portal of entry and immediate progression of Ross River virus in humans?

The portal of entry is skin via an infected mosquito bite; the virus enters the bloodstream (viremia) and targets skeletal muscle, skin, and joint synovial tissues.

For Ross River Virus - How does Ross River virus replicate inside host cells?

Via obligate intracellular replication: it enters through receptor-mediated endocytosis, uncoats its RNA, uses host ribosomes to build viral parts, and releases new virions.

For Ross River Virus - How does viral replication lead to clinical symptoms in humans?

Replication inside joint, muscle, and skin tissues triggers an inflammatory immune response, causing tissue damage and localized swelling.

For Ross River Virus - What are the primary symptoms and incubation period for Ross River virus?

Incubation takes 7–9 days (range 3–21); symptoms include polyarthralgia (joint pain/swelling), fever, fatigue, myalgia (muscle pain), and a rash (30–50% are symptomatic).

For Ross River Virus - What is the portal of exit for Ross River virus to complete its life cycle?

The host's bloodstream, where an uninfected female mosquito ingests virions during a blood meal.

For Ross River Virus - What are the primary modes of transmission for Ross River virus?

Vector-borne transmission via mosquito bites (it is an arbovirus and cannot spread directly person-to-person through casual contact).

For Ross River Virus - What are the public health and socio-economic impacts of Ross River virus?

Workplace productivity loss from prolonged fatigue/joint pain, increased healthcare system costs, and disruption of outdoor community activities.

For Ross River Virus - What five key management strategies are used against Ross River virus?

Vector control (larvicides), personal protection (repellents/clothing), breeding site elimination, public education, and health surveillance.

For Ross River Virus - How do personal protection measures like DEET repellent and long clothing work?

They provide chemical and physical barriers that prevent mosquitoes from biting and transmitting virions into the skin portal of entry.

For Ross River Virus - Why is Ross River virus impossible to eradicate from the environment?

It relies on wild native animal reservoirs (macropods) and drought-resistant mosquito eggs that preserve the pathogen indefinitely.

For Ross River Virus - What is the primary focus of public health programs for Ross River virus in Australia?

Focus is on vector monitoring, reducing mosquito breeding sites, and community education, as there is currently no human vaccine or specific antiviral cure.

For Ross River Virus - Describe the step-by-step life cycle of Ross River virus.

1. Reservoir: Virus circulates in native marsupials (macropods).
2. Vector Blood Feed: Mosquito takes a blood meal containing viruses from an infected marsupial.
3. Vector Replication: Virus replicates inside mosquito and travels to its salivary glands.
4. Host Infection: Female mosquito vector takes a blood meal on a human host, injecting saliva containing viruses into the bloodstream.
5. Primary Replication: Primary replication occurs in human skeletal muscles/joints.
6. Cycle Continuation: Human-to-mosquito transmission is rare but possible, while mosquitoes continue to pass the virus back to marsupials.

For Phytophthora Dieback - Describe the step-by-step life cycle of Phytophthora cinnamomi.

1. Attraction & Penetration: Zoospores are attracted to and penetrate the roots of a healthy host plant.
2. Infection & Growth: Mycelium grows in and on infected root tissue, rotting the root system and creating a diseased plant.
3. Spore Formation: Spore sacs (sporangia) and thick-walled chlamydospores grow on the mycelium.
4. Survival Phase: Chlamydospores await favourable environmental conditions in soil.
5. Germination: Chlamydospores germinate when conditions improve, releasing zoospores directly or via sporangia.
6. Release & Spread: Zoospores are released into soil water to infect new plant roots.