How does the body defend itself from yellow fever?

Answer 1

malaria parasite is injected in your body by infected female anopheles mosquito, while sucking your blood. There from the parasite enter your liver. Parasite multiply there and then enter your red blood cells to give you malaria.

Answer 2

Malaria is a chronic infection. So you get immunity for the same. Protozoa frequently come out of liver to boost the immunity. So you do not eradicate the infection from the liver. You give radical treatment for falciparum malaria, usually. It is either falciparum malaria or you and not both.

Answer 3

The human immune system has two defenses against intracellular pathogens likemalaria. The initial defense is a population of cells called NK or Natural Killer cells which seek out cells lacking specific markers (MHC complexes, a major protein often downregulated in infected cells) and destroy them along with whatever is infecting them. They require no priming. The slower but more specific and effective defense is a type of T cell known as CD8+ cytotoxic T lymphocytes which provide the same function, they search for cells presenting pathogen antigens (in this case malaria antigens) on there surface, and destroy them along with the malaria. Macrophages also have limited intracellular pathogen destroying capabilities, and clean up the dead cells and malaria after the call has apoptosed (died).

This system is effective and is why there are capable vaccines against malaria. Sadly though, for those that are not vaccinated, its possibe that the initial immune response will not be sufficient and the malaria will multiply out of control of the immune system and a back up with quinine will be needed.

Answer 4

What is yellow fever?

Yellow fever is transmitted by mosquitoes in tropical regions.

Yellow fever is a potentially fatal viral infection that's transmitted by mosquitoes in tropical regions. It has both an urban cycle and a jungle cycle that relies on monkeys as carriers (sylphic cycle').

In mild cases the symptoms are similar to influenza, but serious cases develop a high temperature and may have a series of after effects, such as internal bleeding, kidney failure and meningitis.

A classic feature of yellow fever is hepatitis, which is the reason for the yellow colouring of the skin (jaundice) and the name of the disease.

Yellow fever can cause sudden epidemics, with a mortality rate of almost 50 per cent. Although a safe, efficient vaccine has been available for the last 60 years, epidemics still occur, constituting a health risk in tropical regions.

The disease is covered by the International Health Regulations, which are taken very seriously by authorities everywhere. Therefore, the vaccine has to be administered by clinics registered as Yellow Fever Centres.

What causes yellow fever?

Yellow fever virus belongs to the Flaviviridae family, other members of which cause dengue fever and Japanese encephalitis.

The virus is introduced into the bloodstream via the saliva of the mosquito as it bites.

The virus can then be transported around the body, and it can reproduce itself in a variety of the body's cells -- usually the liver, kidneys and blood vessels. In serious cases, these cells may become damaged themselves.

In addition, the cells of the immune system are affected and release large quantities of signalling substances. These substances are the cause of the normal disease symptoms, such as muscular pain and fever, that are also observed in influenza.

How is yellow fever passed on?

The virus is transmitted among humans by a couple of species of mosquito, including Aides egyptii, which can also transmit dengue fever. It's an unexplained fact that, despite the presence of the Aides mosquito in Asia, yellow fever is limited to Africa and South America.

In its original jungle cycle, the mosquito sucks the blood of an infected monkey. The mosquito develops a permanent infection, in which the virus accumulates in its salivary glands. Then the mosquito bites another monkey, which then also becomes infected with the virus.

A person travelling through the jungle may also become infected by an infected mosquito. When this person returns to urban areas, a new cycle begins.

Urban cycles start when an infected traveller returns from the jungle. A mosquito bites the traveller, who then becomes infected and passes the virus on to other people, and either an epidemic breaks out or an endemic situation is perpetuated.

Where does yellow fever occur and how many people are affected?

The virus is permanently prevalent, with a more or less constant number of sufferers (ie it is endemic) in several tropical regions of Africa and on the continent of America.

In addition, there's an increasing number of epidemics, in which a large number of people suddenly develop yellow fever.

Every year about 200,000 cases of yellow fever are recorded, and 30,000 of these die, but the figures are underestimated because of poor record-keeping.

In total, yellow fever occurs in 33 countries and more than 500 million people are at risk of catching the disease.

As yet, there's no yellow fever in Asia. But it's feared that the high level of international travel could introduce the virus by means of infected people. Mosquitoes do live here, and they could potentially transmit the disease and create a new reservoir.

Consequently, the countries of Asia have strict quarantine regulations that apply if you arrive without a valid vaccination certificate travelling from areas in Africa and Latin America, where yellow fever occurs.

What are the symptoms of the disease?

The incubation period from infection to developing yellow fever is 3 to 16 days.

Yellow fever varies in severity. The infection has an incubation period of three to six days.

Initial symptoms include muscle aches, fever, headache, anorexia, nausea, and vomiting. In many patients there will be improvement in symptoms and gradual recovery occurring three to four days after the onset of symptoms.

But within 24 hours of an apparent recovery, up to a quarter of patients progress to a more serious illness and of these up to half may die.

The danger signals

Various systems in the body are affected during this phase. Anaemia (lack of red blood cells) develops, as well as liver inflammation, hepatitis and jaundice.

The kidneys are also affected and bleeding from the mouth, nose and stomach may occur, which leads to blood in vomit and faeces.

The majority of patients who experience bleeding die in a short space of time.

What can you do yourself?

There's a vaccine that's very effective against yellow fever.

It protects you from 10 days after the vaccination, which is administered in a single injection. Current advice is to have it repeated every 10 years.

In recent years awareness has risen of vaccine side-effects in two main groups:

• those over 60 years of age (usually those who have never previously had yellow fever vaccination)
• those born with or who have developed problems with a gland called the thymus.

It's recommended for all areas where the disease occurs. But new guidance and maps are being developed as outbreaks occur.

Requirement for yellow fever vaccination

In some countries where there are mosquitoes that could transmit the virus: actual documentation is required, stating that you have been vaccinated against yellow fever before you can obtain permission to enter the country.

This can be provided by a stamp in the yellow international vaccination card issued by a World Health Organisation (WHO) recognised vaccination centre.

To be on the safe side, it's been agreed internationally that the vaccination provides protection for 10 years. After that you have to be vaccinated again, even though the first vaccination may still be effective for a little while longer.

Preventing mosquito bites

Apart from vaccination, prevention of mosquito bites is the best way of avoiding yellow fever. But because the disease is so dangerous, taking a chance and going without vaccination is absolutely not recommended.

In many poor countries, where for one reason or another vaccination is not available, bite avoidance may be the only method of protecting the local population.

How is the disease diagnosed?

The disease may be difficult to distinguish from other illnesses, especially in the early stages. To confirm any suspicions, from the case history and information on the patient's journeys abroad, the doctor has to take a blood sample.

In the laboratory, specific yellow fever virus antibodies can be detected in the blood.

What treatment is there for yellow fever?

There are no medicines that are effective against this virus.

Serious cases of yellow fever always need hospital treatment. As there are no products that combat the virus itself, the doctor can only treat the symptoms.

If there's a lack of fluid in the body, leading to disturbances in the electrolyte balance, this can be remedied by administration of fluids by intravenous drip.

In mild cases, the pain may be relieved with simple painkillers. High temperatures can be treated by cooling the patient and giving them appropriate medicines to lower the temperature, such as aspirin (eg Disprin) or ibuprofen (eg Nurofen).

Paracetamol (eg Panadol) is probably best avoided if there is already evidence of liver damage.

Answer 5

Malaria parasites attack your liver first. Then they attack your red blood cells to give you haemolytic anaemia. This will trigger enlargement of spleen. The Plasmodium falciparum may present as a case of acute bronchitis or acute gastroenteritis. It can affect your brain to give you cerebral malaria, which an be fatal.

Answer 6

Immune system from you body notes that malaria parasite is a foreign pathogen. You get humeral as well as cell mediated immunity against the malaria parasite over the weeks.