Human BiOlogy.

[Deadly_king]

Thanks muallima, master key and deadly king 
How about the house fly?

Explain why one contact with an infected mosquito can lead to malaria but repeated larval contacts are needed to produce symptoms of schistosomiasis.

I think i got it now.

Schistosomiasis is caused by larval forms of the parasite which penetrates the body. However our body and defensive system is highly beneficial against these parasites. Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely

Therefore malaria is more dangerous to humans than schistosomiasis since the latter is transmitted more easily and the body's defence mechanism cannot prevent it from entering the body. Our immune system will only respond to it when the parasite is already in the body.

For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria

Ref : http://www.who.int/topics/schistosomiasis/en/

[Deadly_king]

Since when do common house flys suck blood from a person ? They dont have the hypodermic needle like thing that mosquitoes have....

Oops..........i have been mistaken......My bad 

You have a point there

Indeed houseflies do not suck blood. Sorry for the confusion

House flies can become a vector of certain diseases since they are always attracted to sites of bacteria such as feaces or vomit.

Hence the bacteria may get attached to its hairs or other parts of the body. When the fly lands up on a person, the bacteria has a chance to penetrate the latter's body through the nose, ears, mouth and other parts.

One likely disease transmitted in this way is cholera.

[iluvme]

I think i got it now.

Schistosomiasis is caused by larval forms of the parasite which penetrates the body. However our body and defensive system is highly beneficial against these parasites. Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely

Therefore malaria is more dangerous to humans than schistosomiasis since the latter is transmitted more easily and the body's defence mechanism cannot prevent it from entering the body. Our immune system will only respond to it when the parasite is already in the body.

For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria

Ref : http://www.who.int/topics/schistosomiasis/en/

I'm confused.

[Deadly_king]

I'm confused.

Would you mind telling me what's confusing you

I'll try my best to clear your doubt

[iluvme]

This schistosomiasis thing, is spread by the larval forms of a parasite. From what I've read in Google, it is spread through water like cholera.

Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely

Where does the skin come into this? Did you mean like when the skin is cut and when water enters?

I think i got it now.
For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria

It is spread by water isn't it? So why is there a very little chance of the larval forms entering the body?
It is very similar to cholera isn't it?

[Deadly_king]

This schistosomiasis thing, is spread by the larval forms of a parasite. From what I've read in Google, it is spread through water like cholera.

Where does the skin come into this? Did you mean like when the skin is cut and when water enters?

It is spread by water isn't it? So why is there a very little chance of the larval forms entering the body?
It is very similar to cholera isn't it?

This disease is most commonly found in Asia, Africa, and South America, especially in areas where the water contains numerous freshwater snails, which may carry the parasite.

So it is the snails or larvae which carry the disease. Water is just a medium which is favourable to the carriers.

I took the skin as an example since the latter is involved in the defence mechanism of the human body.

Penetration of the human skin occurs after the cercaria have attached to and explored the skin. The parasite secretes enzymes that break down the skin's protein to enable penetration of the cercarial head through the skin. As the cercaria penetrates the skin it transforms into a migrating schistosomulum stage.

So it's not really spread by water.

Ref : http://en.wikipedia.org/wiki/File:Schistosomiasis_Life_Cycle.png

If you have any other questions, feel free to ask. I'll not leave you unless you have understood