1.3 – Disease and Agricultural Production Research - ANSWERS Students: 1.3 assess the causes and effects of diseases on agricultural production, including but not limited to: 1.3 a – plant diseases 1.3b – animal diseases Foot-and-mouth disease 1. Identify the pathogen that causes the disease and the species it affects. Foot and mouth disease (FMD) is caused by the foot and mouth disease virus. There are seven types of the virus: A, O, C, SAT1, SAT2, SAT3 and Asia1. These are further subdivided into more than 60 strains. FMD affects cloven-hoofed animals (those with divided hoofs), including cattle, buffalo, camels, sheep, goats, deer and pigs. 2. Outline status of the disease in Australia (i.e. is it currently present in Australia? Have there been outbreaks in the past? If so, when?) Australia is currently free of foot and mouth disease. Minor outbreaks of possible FMD are believed to have occurred in Australia in 1801, 1804, 1871 and 1872. 3. Outline the symptoms of the disease. Symptoms include fever, followed by the appearance of fluid-filled blisters on the lips, tongue and palate, between the toes and on the heels, and on mammary glands. These erupt to leave raw, painful ulcers that take up to 10 days to heal. Foot lesions leave animals lame and unable to walk to feed or water. Tongue and mouth lesions are very painful and cause animals to drool and stop eating. Adults usually begin eating again after a few days, but young animals may weaken and die, or be left with foot deformities or damage to the mammary glands. 4. Outline the host response to the presence of this pathogen. Similarly to a human immune response, animals affected by foot and mouth disease will mount an adaptive immune response against the virus. This involves innate responses, including the ingestion of the virus by phagocytic cells, and the adaptive immune response, involving the recognition of the antigens via MHC by the helper T cells, the production of antibodies by B cells and the destruction of infected cells by T cells. 5. Assess the effects (or potential effects) of the disease on agricultural production in Australia. FMD results in high morbidity, which can cause serious production losses in livestock and livestock products. Countries without the disease, which include many of Australia’s major trading partners, do not import from, or severely restrict imports from FMD-infected countries. A 2001 outbreak in the United Kingdom caused losses of more than 8 billion pounds (approximately $AUD 19 billion). Australia estimates that a small FMD outbreak, controlled in 3 months, could cost around $AUD 7.1 billion, while a large 12 month outbreak would cost $AUD 16 billion. 6. Describe methods that are implemented to prevent or control this disease. Australia has invested heavily in the World Animal Health Organisation (OIE) Southeast Asia and China FMD Campaign (SEACFMD), which aims to eradicate the disease from nearby countries. Australia also maintains a strong biosecurity program at the border to manage FMD risks, and also undertakes extensive planning and preparedness activities to ensure that should an incursion occur, the disease can be contained and controlled as quickly as possible. This plan includes a vaccination program, a hotline for reporting suspected cases, and a system for the humane destruction of any infected animals. Citrus Canker 1. Identify the pathogen that causes the disease and the species it affects. Citrus canker is caused by the bacteria Xanthomonas citri, and affects all types of citrus, including lemon, lime, orange, grapefruit and mandarin. 2. Outline status of the disease in Australia (i.e. is it currently present in Australia? Have there been outbreaks in the past? If so, when? Australia has had outbreaks of citrus canker in the Northern Territory in 1912, 1984, 2004 and 2018, and WA in 2018. The most recent outbreak in the Northern Territory was eradicated in April 2021. 3. Outline the symptoms of the disease. Symptoms of the disease include blister-like lesions called ‘cankers’ on both sides of the leaves, twigs, shoots and fruits. These sports are raised and ‘warty’, tan to brown in colour. On the leaves they are surrounded by an oily, water-soaked margin and a yellow ring or halo. Other symptoms include premature fruit drop, defoliation and tree death. 4. Outline the host response to the presence of this pathogen. In an attempt to prevent the bacterial infection from spreading, a tree infected with citrus canker will lose its affected fruit and leaves, confining the infection. 5. Assess the effects (or potential effects) of the disease on agricultural production in Australia. The latest outbreak of citrus canker in the NT took three years to control.Outside of where the disease was first detected, 16 properties were infected, so this was considered to be a small outbreak. Despite this, eradication involved a national ban placed on NT citrus products, the destruction of over 6,000 plants, and millions of dollars in costs to the citrus and nursery industries. 6. Describe methods that are implemented to prevent or control this disease. In the most recent outbreak, tens of thousands of plants from hundreds of properties were inspected. Infected plants or crops were destroyed or quarantined. Any farm that has been found to be infected with citrus canker bacteria became a restricted area, in which there was no movement of plants, and limited movement of people and vehicles. Follow up surveillance is still occurring, with thousands of properties being routinely inspected. Bibliography Department of Agriculture, Water and the Environment (2021), Citrus Canker Fact Sheet. Retrieved 01/07/21 from https://www.agriculture.gov.au/pests-diseases-weeds/plant/citrus-canker Department of Agriculture, Water and the Environment (2020), Foot-and-mouth Disease Fact Sheet Retrieved 01/08/21 from https://www.agriculture.gov.au/pests-diseases-weeds/animal/fmd#what-is-footandmouth-disease Fitzgerald, D. (2021) Citrus canker plant disease gone from Australia after NT eradication. ABC Rural. Retrieved 01/08/21 from https://www.abc.net.au/news/rural/2021-04-12/citrus-canker-eradicated-from-australia-after-nt-campaig n/100064068 Grubman, M. J., Moraes, M. P., Diaz-San Segundo, F., Pena, L., De Los Santos, T. (2008), Evading the host immune response: how foot-and-mouth disease virus has become an effective pathogen, FEMS Immunology & Medical Microbiology, 53(1): 8–17. Retrieved 01.08.21 from https://academic.oup.com/femspd/article/53/1/8/490101.
