Causes Of Yellow Fever And Transmissions Biology Essay

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Later, the theory that yellow fever is transmitted by mosquito rather than direct human contact was first introduced by a Cuban physician, Dr. Carlos Finlay, in 1881. 10 years later in 1900, using earlier research from Dr. Finlay, U.S. Army Major Dr. Walter Reed and his team proved the "Mosquito Hypothesis"; that yellow fever was in fact transmitted by mosquitoes. This revolutionary idea was instrumental in leading to the following control of yellow fever in various regions. The virus responsible for yellow fever was later isolated in the late 1920s, and this breakthrough discovery allowed South African/American virologist Max Theiler to later develop the first vaccine against yellow fever in the 1930s. This successful vaccine helped control and eliminate yellow fever from various countries in Africa and South America during the mid 20th century. For his work Theiler received the 1951 Nobel Prize in Physiology or Medicine.

Enters host → eaten by a macrophage (white blood cell) → sheds envelope, disabling further digestion of the pathogen by the macrophage cell → macrophage cell continues with healthy virus to the lymph nodes where the virus begins replication → other macrophages are infected → the virus is eventually carried through the blood stream to the liver → Kupffer cells (specialised macrophages) lining blood-vessels in the liver are infected → infection and death of Kupffer cells damages surrounding hepatocytes (a cell of the main tissue of the liver) → formation of translucent "councilman hyaline bodies," the hallmark of yellow fever → Liver damage → jaundice (the yellowish pigmentation of the skin, due to increased levels of bilirubin in the blood) → virus becomes systemic → collected from the bloodstream by mosquitoes → begins its life cycle again.

Yellow fever is transmitted to humans by the bite of infected mosquitoes. In the jungle or rainforest the yellow fever virus is passed onto other mosquitoes that feed on infected monkeys. These infected mosquitoes bite humans that enter the forest, resulting in some cases of yellow fever.

In other circumstances urban yellow fever happens when infected people introduce the virus into areas with high human populations, resulting in mosquitoes carry the virus from person to person.

Host response:

Macrophages involved in the body's immune system try to counteract the virus but are infected in the process. The lymph nodes replicate the infected macrophages and eventually circulate around the bloodstream. Kupffer cells located in the liver are destroyed as well as sustained damage to the surrounding hepatocytes. The liver fails to function and later the kidneys are also rendered useless.

Major Symptoms:

Symptoms of yellow fever take 3 to 6 days to appear. Some infections can be mild but most lead to serious illness characterised by two stages.

In the first stage of yellow fever, muscle pain, nausea, vomiting, headache and muscular weakness occurs.

About 15 to 25 per cent of those with yellow fever progress to the second stage also known as the 'toxic' stage, of which half die within 10 to 14 days after onset of illness. Visible bleeding, jaundice (yellow pigmentation of the skin), kidney and liver failure can occur during the second stage.


People who aren't vaccinated will be severely affected by the virus. There is no specific treatment for yellow fever. However medicines can be used to relieve the symptoms and may improve the outcome for seriously ill patients. But in the event of kidney and liver failure renal and liver dialysis is needed until a transplant is available.


Vaccination is the best way to prevent yellow fever. The vaccine is safe and nearly 100% effective. Vaccination is recommended for all travellers to countries or areas where there is a risk of yellow fever transmission.

Avoiding mosquitoes that transmit yellow fever. The type of mosquito that transmits the disease is usually active during the day. People living in or travelling to countries that is affected by the disease are advised to avoid mosquitoes by:

Wearing mosquito repellent DEET or Picaridin

Wearing long sleeved bright coloured clothes outside

Avoid wearing perfume of cologne (some may attract mosquitoes)


Prevent mosquitoes entering your accommodation

Use a mosquito net at night-time over bed

Be aware of areas that may contain mosquitoes (swamps, rivers, humid areas)


Identify potential sources of infection (mosquitoes) and risk of infection from occupations/activities; e.g. unhygienic conditions and providing first aid.

Evaluate the risk of infection. Consider the modes of transmission and type and frequency of exposure.

Develop safe activity practices with controls to manage risks.

Provide appropriate personal protective equipment (mosquito repellent, long sleeved clothes)

Determine need and availability of vaccination

Educate people about the disease and people who are likely to go to countries infected by the disease

Process, analyse and present information from secondary sources to evaluate the effectiveness of vaccination programmes in preventing the spread and occurrence of once common diseases, INCLUDING small pox, diphtheria and polio.

Vaccination gives artificially acquired immunity from disease. Once common diseases such small pox, diphtheria and polio have now become rare due to vaccination programs. However vaccination can sometimes cause disease itself, so vaccines have to be administered properly to individuals and developed very carefully.

Smallpox was the first disease in which a vaccine was developed. Edward Jenner did this in 1796. Smallpox was a horrific disease which in most cases caused lesions and rashes on the skin. The World Health Organisation (WHO) started vaccination programs for smallpox in the 1960s until eradication was declared in December of 1979. Vaccination against smallpox worked well due to smallpox being only a human disease in which the virus could be transmitted. Currently, people are not vaccinated against smallpox because there is no risk of getting the disease.

Diphtheria is a highly contagious and serious disease which kills 35-90% of infected people. The infection causes deterioration of the myelin sheaths (electrically insulating material around the axon of a neuron) of the central and peripheral nervous system which in turns leads to degeneration of motoring skills and coordination skills accompanied with loss of touch. The Diphtheria vaccine is given as part of a triple antigen injection that protects against diphtheria, tetanus and whooping cough. Vaccination began globally in the 1920s however Australia began in the 1930's and 40's after which there was a rapid drop in the disease. The last known case of diphtheria in Australia was in 1992. With mass vaccination of children diphtheria is no longer considered to be a major killer of children under the age of 14. However it has not yet been eliminated and there have been outbreaks of this disease in some countries so vaccination is still important. Booster shots should be given during adulthood as the effect of vaccination wears off with time, this should be done especially when diphtheria prone countries.

Polio is a disease that can damage the nervous system and cause paralysis. The polio virus lives in the throat and intestines of infected persons. The virus enters the body through the mouth, usually from hands contaminated of an infected person. Objects, such as eating utensils, can also spread the virus.

Vaccination was introduced in 1955 but was changed to an oral vaccine in the 1960s (The oral vaccine is not wildly used in developed countries because it had a small chance to cause Polio). Vaccination programs in Australia began in 1956, the last cause of paralytic polio in Australia was in 1977. World incidence of polio has dropped significantly from infecting nearly around 4 - 6 thousand people a year in the 1980s to fewer than 2 thousand cases a year in 2004 and onwards. Children usually receive four doses of the polio vaccine for effective protection.

Discuss the role of quarantine in preventing the spread of disease in plants and animals into Australia and across regions of Australia (discuss how quarantine is enforced in Australia)

Quarantine is a strict isolation imposed to prevent the spread of disease.

Australian quarantine seeks to prevent the entry of harmful diseases into Australia and to stop the spread of diseases within Australia. Because of Australia's geographical isolation we have been fortunate in preventing the spread of plant and animal disease from other parts of the world. However in recent years travel and trade has increased and our isolation as a continent is becoming less relevant from the harmful spread of diseases. The role of quarantine is to protect the health of the human, animal and plant populations.

Australia has more than 60,000 kilometres of coastline, offering a variety of pathways for exotic pests and diseases to infiltrate our country. AQIS (Australian Quarantine and Inspection Service) is a government organisation which manages and enforces quarantine controls and laws at Australia's borders to minimise the risk of exotic pests and diseases entering the country. These laws prohibit the entry of items that are considered a risk, as well as enforcing the isolation of plants and animals. Because of Australia's strict laws, Australian plants and animals do not have some of the serious diseases found in other countries such as foot-and-mouth disease, mad cow disease and fruit fly.

Types of quarantine procedures that AQIS implement are:

Border control- clearance by quarantine officers

Animal Quarantine- all animals must spend a term in specially equipped quarantine stations

Plant quarantine- all plants and plant material, including wood products must be examined by officers

Human quarantine- a continuous check is kept on all passengers to ensure that they are not carrying infectious diseases

AQIS quarantine inspectors are on duty 24 hours a day seven days a week to screen, inspect and clear people, mail parcels, baggage, ships, animals, plants and cargo containers entering Australia through airports, seaports and international mail centres. The AQIS uses sophisticated technologies such as X-ray machines, surveillance, and detector dogs in search for quarantine risk material during border control processes, to help prevent the introduction and spread of disease

AQIS also provides inspection and certification for a range of agricultural products exported from Australia, to ensure compliance with overseas countries importation requirements. For example FSANZ (Food Standards Australia and New Zealand), AQIS administers the Imported Food Programme, which ensures that food commercially imported into Australia meets Australia's Quarantine Standards and the Food Standards Code.

Process and analyse information from secondary sources to evaluate the effectiveness of quarantine in preventing the spread of at least ONE plant and at least ONE animal disease into Australia or across regions of Australia

Citrus Canker:

What is it?

It is a disease affecting citrus species that is caused by the bacterium Xanthomonas axonopodis.

Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit.

While not harmful to humans, canker significantly affects the vitality of citrus trees, causing leaves and fruit to drop prematurely; a fruit infected with canker is safe to eat but too unsightly to be sold.

Initial Infection:

Australia's physical isolation is an effective barrier to this disease, but it appears likely that this outbreak was from importing infected stock.


Billy Goat Weed (Ageratum conyzoides);



Plants and

Spread on the feet of birds that land on diseased plants.

People today are highly mobile, and with the amount of travel that occurs there is a lot more opportunity for disease outbreaks.

Outbreaks: There have been three outbreaks of Citrus Canker in Australia. The first occurred in the Northern Territory in 1912 and that took eleven years to eradicate.

Quarantine measures - The nationally agreed strategy for controlling and eradicating citrus canker in Australia included:

Surveillance and tracing to determine the extent of the outbreak and, if possible, locate the source

Removal and disposal of infected and potentially infected plant material

Strict quarantine and movement controls to prevent spread

Decontamination of people, equipment, vehicles and buildings

Surveillance to confirm pest freedom/eradication

On-farm biosecurity training and system development for commercial citrus growers in Queensland.

On 23 January 2009, citrus canker was officially declared eradicated in the Emerald Pest Quarantine Area (PQA). Therefore there have been effective quarantine measures.

Foot and Mouth Disease:

What is it? Foot and mouth disease (FMD) is one of the most serious livestock diseases caused by an apthovirus. It is found in most parts of the world;

It is highly contagious muscle-wasting disease of clover hoofed animals such as cows, sheep and camels.

Transmission: FMD is a viral disease that spreads rapidly between animals in breath, saliva, mucus, milk or faeces. It can also be spread on wool, hair, grass or straw, by the wind or by mud or manure sticking to footwear, clothing, livestock equipment or vehicle tyres.

Symptoms: fever, dribbling, blisters in mouth, lips and feet.

Outbreaks: Valuable lessons have been learnt from the 2001 outbreak in the UK. There has never been an outbreak in Australia, yet.

This virus is carried out by live animals and all associated meat and meat products as well as soil and equipment.

Quarantine regulations has prevented the entry of this disease - if an outbreak did occur, it would cost billions of dollars in loss.

Australia has tightened its border defence with more rigorous cargo container inspection and has developed an Emergency Animal Disease Response Agreement to increase Australia's capacity to prepare for and respond to emergency animal disease incursions.

The Australian Veterinary Plan or AUSVETPLAN is the central plan for controlling and eradicating an outbreak.

AQIS (Australian Quarantine and Inspection Service) inspects goods and organisms that are brought in or taken out of the country. For example, citrus canker is a bacterial disease found in Indonesia and New Guinea and hot, wet areas. It affects citrus fruits, e.g. oranges, lemons, grapefruit and limes. It attacks an above ground part such as leaves, twigs, shoots. It is important to keep the disease out of Australia as it could ruin the citrus industry in Australia. AQIS is also setting traps for Asian honey bees. These bees have tiny mites which could wipe out native bees and ruin the honey industry.

Within Australia there are different quarantine restrictions for different states depending on the plants and animals that are present or absent in that state. For example Phylloxera insects are a type of plant lice found on grapevines in the eastern states but not Western Australia or South Australia. There are restrictions taking vines into South Australia.

Gather and process information and use available evidence to discuss the changing methods of dealing with plant and animal diseases, including the shift in emphasis from treatment and control to management or prevention of disease.

The incidence of disease has more commonly been met with an emphasis on treatment and control. More recently however the emphasis has shifted to the importance and effectiveness of preventing and managing diseases instead, such as biological control.

→The following examples illustrate this:

Smallpox: Smallpox was a widespread disease that killed many in the 18th Century. Treatments were available, but were ineffective - many died. Prevention came in the form of vaccinations, and this has controlled the disease far more successfully than any treatments.

Cancers: With many diseases, such as cancer, there has been a shift from treatment and control to prevention. Current treatments for cancer such as chemotherapy, radiotherapy, combination therapy and surgical removals are quite successful, especially if detected early. However, they are not 100% successful and can cause physical trauma to the body (scars). Prevention campaigns (public health campaigns) such as "Slip, Slop, Slap, Seek, & Slide" and "There is nothing healthy about a tan", appear to be helping to reduce the incidence of skin cancer. And to prevent lung cancer cigarette packets, now, by law must have large photographs and warnings about the relationship between smoking and lung cancer

Asparagus rust: At first quarantine restrictions and fungicides were used to control the spread of fungus in asparagus crops. Control now involves management procedures by interrupting the life cycle of the fungus by burning infected material before the spring growth. Resistant varieties have also been developed.

Plant Diseases: These include disease such as fungal root infections, pests such as aphids and disease causing organisms. The usual treatment is spraying with pesticides. However, the use of pesticides may cause environmental problems, such as the accumulation of the pesticide in the food chain and the destruction of organisms other than the ones intended. Rather than treatment, preventative measures are used, especially quarantine measures, biological control (introducing species to control pests) and genetic engineering (to produce disease resistant plants and animals).