7.1.3 - Assess causes and effects of diseases

Question 1

Disease definition

Answer 1

A condition that modifies or interrupts the vital functions of an organism

Question 2

Importance of agricultural production to Australia

Answer 2

• Agriculture is the cultivation of crops and livestocks to produce products for human consumption, including fibres, wood, and animal products
• Agricultural production accounts for 10.8% of Australia’s national goods and services export, and 5.9% of rural employment → nationally important industry
• Plant and animal diseases can reduce yield, damaging local and national economy

Question 3

Plant disease case study

Panama disease in bananas

Answer 3

• Panama disease tropical race 4 (TR4) is a soil-borne fungal infection caused by fusarium oxysporum f. sp. cubense, which can survive in soil for many years
• Causes wilting and death in bananas, particularly Cavendish strains, by starving the plant of water and nutrients
• Spreads by the movement of infected plants, and contaminated soil, vehicles, equipment, and clothing
• The fruit of infected plants is safe for human consumption, but TR4 drastically reduces the yield of banana crops as it results in plant deaths in the long-term
• As the fungus can survive in soil for many years, infected orchards become un-viable for replantation for years

Management

• No cure for TR4. Only way to prevent its spread is by containment. Strict trespassing laws prohibit unauthorised entry into banana plantations, as visitors may inadvertently be carrying the fungus.
• Biosecurity Queensland had a Panama TR4 Program that routinely surveyed impacted + at-risk farms througout Far North Queensland for early detection of the disease. Plants that show early signs of infection (yellowing of the entire leaf and browning and the margins) were destroyed
• Successfully contained to the Tully Valley Area

Question 4

Plant disease case study

Citrus canker

Answer 4

• Bacterial disease caused by Xanothomonas citri
• Causes defoliation, dieback, blemished fruit, and unripe fruit falling to the ground in all types of citrus
• Most severe in hot, wet areas as these conditions are favourable for the growth of the bacteria
• Transmission usually indirect, for example sap from the infected site is transferred from tree to tree by irrigation or rain splash. This allows the canker to spready quickly over long distances on infected fruits and leaves, and on people and equipment

Management

• The canker is incurable. Farmers are often forced to destroy infected trees and replant the entire orchard, costing an exorbitant sum of money
• Also damages farmers economically as trading partners are likely to reject any fruit that may carry the disease
• In 2018, citrus canker was found in Darwin, NT , and northern WA. The outbreak was eradicated from NT after the destruction of 6000+ plants and a national ban on NT citrus products
• As eradication is costly, prevention is critical. Maintaining high level of hygiene in farm equipment and clothing of visistors, vetting imported goods for the disease according to Australia’s biosecurity rules, and regulation of interstate transport of whole plants, fruits, or cuttings, is effective
• Infested plants must be reported immediately to the Exotic Plant Pest Hotline

Question 5

Effect of plant diseases

Answer 5

• Economic losses
• Increased use of pesticides and fungicides
• Export bans
• Food insecurity

Question 6

Animal disease case study

Mad cow disease

Answer 6

• Also known as bovine spongiform encephalopathy
• Neurdegenerative disorder caused by prions (misfolded forms of proteins)
• Symptoms include incoordination, extreme nervousness, or violence
• There is usually a long incubation period between infection and the development of symptoms. There is no reliable to test for BSE in a live cow, as most cows are usually found to have BSE when their brain tissue is examined under a microscope and found to have a spongy appearance
• May be caused by feeding catle meat-and-bone meal containing prion-infected products from cows or sheep
• UK was severely hit by BSE, causing more than 184,000 cows to die of it between 1986-2015
• Can also be dangerous to humans: human ingestion of prion-infested products can cause variant Creutzfeldt-Jakob disease (vCJD), a fatal brain disorder that causes rapid, progressive dementia and neuromuscular disturbances

Management

• BSE has never been detected in Australia due to strict BSE policies. Australian BSE Food Safety Assessment Committee vets imports according to a BSE food safety assessment to ensure that BSE-contaminated material does not enter te country
• Most beef-producing countries have a ban on feeding mammalian protein to cattle, and stringent slaughtering practices prevent high-risk tissues from entering the human food chain or stock feed systems

Question 7

African swine fever

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Answer 7

• Contagious viral disease, caused by the African swine fever virus
• Causes hemorrhagic fever in wilde and domestic pigs, with a mortality rate that can reach 100%
• Transmission is primarily through direct contact between infected and non-infected pigs. But can also be transmitted indirectly through the movement of people/objects that have been in contact with infected pigs or the use of contaminated swill for feeding
• ASF virus can survive for long periods in uncooked, frozen, or cured pig0meat products. Can also persist in contaminated pig pens for at least 30 days
• First documented in sub-Saharan Africa in 1921, and has since spread to the EU and Asia
• Can devastate economies, especially family-run pig farms
• Can affect food security worldwide, as pork meat is one of the main sources of animal proteins, accounting for more than 35% of global meat intake
• Also threatens biodiversity as it kills wild boars and native pig breeds as well

Management

• No effective treatment is readily available. Management practices mostly concerned with containment, through killing infected pigs, and export bans
• Australia does not permit the import of pigmeat, either by companies or by incoming international passengers. Commercially imported pork products must be canned and cured under specific conditions to inactivate viruses, or be sourced from countries that the government has recognised as ASF-free