History of Yellow Fever Outbreaks

Yellow fever is a disease of warm lands that is found mainly along the shores of the Atlantic ocean ,  It was first noticed in the Americas , but may well have come from Africa and reach the new world with or soon after  Columbus . Until about 70 years ago , Yellow fever was still one of the most feared diseases in the United States , where many died of repeated outbreak .

An outbreak which was to lead to surprising development was one that happened in Cuba during the Spanish-American war.

As a result , an army group under Major Walter Reed was sent there in June 1900 with orders to give special attention to question concerning the cause and prevention of yellow fever .

In a daring group of experiments using human beings , Major Reed proved the truth of an idea  advanced in 1881 by a Cuban doctor , that the city  type of mosquito passed on the disease .
The successful result of these experiments gave birth to another and still more important idea   , kill off the city type of mosquitoes and there will be no more yellow fever .

Fortunately these mosquitoes are one of the easiest type to destroy .

They are born in pool of quiet , warm water , within a short distance of people's homes .
So to Havana came a general with orders from the United States Government to dry up these pools .
He caried out his task so well that the mosquitoes disappeared .
With them went yellow fever , never to return to Havana . A few years later , the same general successfully repeated this operation in Panama Canal.

Its all seemed so simple . End the mosquitoes , end the diseases
Man even began to dream of getting rid of yellow fever from the world .
Meanwhile one question still remained unanswered .

The city type of mosquitoes carried the fever , without doubt , but how ?
After many experiments , a member of the United States Army Yellow Fever Commission decided that the disease must be carried by something too small to be seen .

Of his own free will , this devoted scientist decided to allow himself to be bitten by an infected mosquito  , then taking some of his own infected blood , he injected it into three other members of the group who wanted to help.

Two of the three got yellow fever and recovered , this showed that the disease was carried by a virus too small to be seen through the microscope of the day.
Hopes for victory over the disease of yellow fever were raised still further when one of the team Rockefeller doctor , studying yellow fever in Ghana , scored a major victory in the summer of 1927 .

Visiting a village where there was an outbreak, the doctor took the blood from a good looking African young man , Asibi by name , who had a mild touch of fever .

The doctor now injected some of this blood into four animal including one monkey that had just arrived from India , only the monkey went down with yellow fever , for the first time the the virus of the disease had been passed on to an animal other than man .

Having animals that could be given the disease opened the way to new line of experiments .
The Asibi virus was kept going from Monkey to Monkey . In this way , they gradually developed a virus whose power to make people ill had been greatly lowered .

But still it had enough strength to develop resistance in  human beings , so from the blood of the West African a vaccine was finally developed that now protects millions of people from yellow fever .
Such , then , was the point reached in 1932 . Yellow fever appeared to be on the way out , at least in the Americas .
Then there occurred an outbreak in a country district in Brazil .

This was strange , since yellow fever had always been believed to be a disease of the city , one that people caught by being bitten in their own homes by the city type of mosquitoes , bred within the hundred yards of their housed . Something much more surprising , however , was in store for the members of the Brazilian Yellow Fever Service  , when they reached the area .
There was yellow fever in the district , without doubt .

The service found it was present by all the standard test , But there were no city type mosquitoes , not one.
One morning , a doctor went into the jungle with some woodcutters ,  he wanted to collect mosquitoes , but they weren't biting.

The doctor was just ready to leave , when one of the men shouted that the tree was about to fall .
He stood back and watched the great mass come down , sunlight streamed through  the hole made in the roof of the jungle and from the upper branches of the fallen tree rose a cloud of blue mosquitoes which circled around the men .

So it was learned that these blue mosquitoes , relatively rare on the floor of the jungle , exist in great numbers in the tree top .
there too , the monkey live , This discovery completed a chain of fact about the way jungle yellow fever is caught and spread .

It is mainly a disease of monkeys in the jungle tree-top , they are infected by the bites of several kind of mosquitoes  , blue mosquito being one of the most common attackers .

The pattern is carried on from  monkey to mosquito and back to mosquito , but men going into the jungle may also get the disease , particularly if their work disturbs the roof of the jungle .
If the man bitten by an infected mosquito then return to a city where there are mosquitoes of the city type , he may start again the pattern of man to mosquito to man .

Dr Pedro Galindo was working on the difficult problem of trying to learn how  the yellow fever  virus can live on in the forest during the dry season .

Blue mosquitoes live in tree holes in pools of water , they lay their eggs above the water line and these somehow live through the dry season  , until the rains make the water rise to the level of the eggs , at that time , they float free and the baby mosquito is born .

Galindo learned that one other mosquito , a big , bright colored insect with yellow markings , we always present in Panama where there was yellow fever  but in such small numbers that is not likely to be a carrier , Galindo decided to keep a group of this insects and study them .

We had a two years battle , trying to get the giant mosquitoes  to lay eggs , Dr Galindo has said , no one had ever made them feel at home away from their natural places , so the female simply will not lay eggs .

After repeated attempts to get his females to lay eggs , Pedro Galindo went to the forest to study them more carefully in nature , he found they laid their eggs in water that had gathered in holes in trees , the water had to last through the dry season  , so the giant mosquitoes always placed in the hole that had small opening at the top , then widened toward the bottom , this kept the water from drying up .
he decided to build a  copy of their natural eggs-laying place and after finishing it , put in the middle of the group of mosquitoes .

The mosquitoes now circled around with interest , then there came for Dr Galindo a time of pure joy , a female headed for the hole and went inside .

Now Dr Galindo told me , spreading his arm , 'we have thousand of them .'
From his mosquitoes , Dr Galindo learned that in the laboratory giant yellow mosquitoes may pass on yellow fever from monkey to monkey , and that the female has a life of five months or more .
'From what we have learned' , he said , we think it is possible that the giant mosquitoes is a poor but a strong carrier , she may live from one rainy season to the next , holding the virus in her body , It may be she who reinfected the monkeys or other animals at the start of the rainy season .

They then have the disease ready in their blood to pass on to the blue mosquitoes as they rise from the hole after the rain.

If this should prove to be the way it works , he said looking at the yellow striped mosquitoes , 'we see here what may be the weak spot of the virus and it chances to live on in the jungle , so we must learn more about these lovely mosquitoes.
   

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