MOSQUITOES AND YELLOW FEVER
Yellow fever is a disease, principally of seaport towns, from which the
United States has suffered more than any other country. It is endemic
only in tropical regions but is often carried to subtropical, sometimes
even to temperate zones where, if the proper mosquitoes exist, it may
rage until frost.
Vera Cruz, Havana, Rio de Janeiro, and the west coast of Africa were
long regarded as permanent endemic foci, the disease appearing there in
epidemic form from time to time, often spreading to other ports in more
or less close communication with such places. In the United States the
Gulf states have been the greatest sufferers from the disease, although
it has spread as far as Baltimore, Philadelphia and Washington, where at
rare intervals it was most serious, abating its ravages only when frost
came.
The last severe outbreak occurred in New Orleans in 1905 when eight
thousand cases and nine hundred deaths occurred. At that time there was
waged one of the most remarkable warfares against death in its most
terrifying form that the world has ever known. And, thanks to the
achievements of science, particularly to the investigations of three
men, one of whom gave his life to the cause, the fight was successful
and this dreadful outbreak was checked just at the time when according
to all precedent it should have been at its height.
This result which at other times and under other conditions would have
been considered miraculous was achieved not by the usual custom of
isolation, quarantine, etc., but by a direct, we may almost say hand to
hand, conflict with mosquitoes: the mosquitoes belonging to a particular
genus and species, _Stegomyia calopus_ (_fasciata_).
Before taking up a discussion of this achievement in New Orleans let us
consider first the work of the men that made such results possible.
For many years the cause and methods of dissemination of this disease
had been a puzzle to physicians and scientists. Very early it was
believed that it might be transmitted through the air, and the fact that
infection usually occurred in the vicinity of the water and in the
tropics or in midsummer led to the belief that the disease was due to
fermentation. This theory received strong support in the fact that
serious outbreaks of the fever often followed the coming into port of
vessels from the tropics with the water in their holds in an offensive
condition. When it was discovered that bacteria were the cause of
fermentation and also of many diseases this theory was considered
abundantly proven. From time to time, announcements have been made that
the particular species of bacteria that causes the disease has been
isolated, but there has always been something lacking in the final
proof.
Yellow fever has always been regarded as a very highly contagious as
well as infectious disease, and the utmost precaution has been taken to
isolate the patients when possible and in recent years strict
quarantines have been established against infected localities and no
person or commerce or even the mails were allowed to come from such
places without thorough fumigations. But all these things proved
unsatisfactory. The disease could not ordinarily be checked by simply
isolating the patients. Many people became sick without ever having been
near a yellow fever patient, while others worked in direct daily contact
with the disease and did not suffer from it. Those who had once had it
and recovered became practically immune, rarely suffering from a second
attack. Negroes may suffer from the disease, but are usually regarded as
practically immune.
[Illustration: FIG. 104--Yellow-fever mosquito (_Stegomyia calopus_).
(R. Newstead, del.)]
It was early observed, too, that the danger zone might be quite well
defined and that outside this zone one would be safe. More than a
century ago the British troops and other inhabitants of Jamaica found
that by retreating to the mountains during the warm weather the
non-immunes could escape the fever. It was also observed that those who
slept on the first floor were more apt to take the disease than those on
the second floor.
THE YELLOW FEVER COMMISSION
In 1900, during the American occupation of Cuba, yellow fever became
very prevalent there. A board of medical officers was ordered to meet in
Havana for the purpose of studying the disease under the favorable
opportunities thus afforded. This board, which came to be known as the
Yellow Fever Commission, was composed of Drs. Walter Reed, James
Carroll, Jessie W. Lazear and Aristides Agramonte of the United States
Army. Agramonte was a Cuban and an immune, the others were non-immunes.
Dr. Manson in his lectures on Tropical Medicines says of them:
"I cannot pass on, however, to what I have to say in connection
with this work without a word of admiration for the insight, the
energy, the skill, the courage, and withal the modesty and
simplicity of the leader of that remarkable band of workers. If any
man deserved a monument to his memory, it was Reed. If any band of
men deserve recognition at the hands of their countrymen, it is
Reed's colleagues."
Their first work was to determine whether any of the germs that had been
claimed to be the cause of yellow fever were really responsible for the
disease. _Bacillus icteroides_ that for some time and by some
investigators had been named as the offender was particularly
investigated, but was proved to be a secondary invader only.
Dr. Charles Finlay of Havana had been claiming for some years that the
yellow fever was transmitted by means of the mosquito and possibly by
other insects also. He even claimed to have proved this theory
experimentally. We know now, however, that there must have been errors
in his experiments and that his patients became infected from sources
other than those he was dealing with.
The Yellow Fever Commission decided to put this theory to the test and
secured a number of volunteers for the experiments. The first thing was
to let an infected mosquito bite some non-immune person. How this was
done and the results, may be told in Dr. Carroll's own words.
EXPERIMENTS
"Two separate lines of work now presented: one, the study of the
bacterial flora of the intestine and anaërobic cultures from the
blood and various organs; the other, the theory of the transmission
of the disease by the mosquito, which had been advanced by Dr.
Carlos Finlay in 1881. After due consideration it was decided to
investigate the latter first. Then arose the question of the
tremendous responsibility involved in the use of human beings for
experimental purposes. It was concluded that the results
themselves, if positive, would be sufficient justification of the
undertaking. It was suggested that we subject ourselves to the same
risk and this suggestion was accepted by Dr. Reed and Dr. Lazear.
It became necessary for Dr. Reed to return to the United States and
the work was begun by Dr. Lazear, who applied infected mosquitoes
to a number of persons, himself included, without result. On the
afternoon of July 27, 1900, I submitted myself to the bite of an
infected mosquito applied by Dr. Lazear. The insect had been reared
and hatched in the laboratory, had been caused to feed upon four
cases of yellow fever, two of them severe, and two mild. The first
patient, a severe case, was bitten twelve days before; the second,
third and fourth patients had been bitten six, four and two days
previously, and were in character mild, severe and mild
respectively. In writing to Dr. Reed that night of the incident, I
remarked jokingly that if there was anything in the mosquito
theory, I should have a good dose. And so it happened. After having
slight premonitory symptoms for two days, I was taken sick on
August 31, and on September 1, I was carried to the yellow fever
camp. My life was in the balance for three days, and my chart shows
that on the fifth, sixth and seventh days my urine contained
eighth-tenths and nine-tenths of moist albumin. On the day I was
taken sick, August 31, 1900, Dr. Lazear applied the same mosquito,
with three others, to another individual who suffered a
comparatively mild attack and was well before I had left my bed. It
so happened that I was the first person in whom the mosquito was
proved to convey the disease.
"On the eighteenth of September, five days after I was permitted to
leave my bed, Dr. Lazear was stricken, and died in convulsions just
one week later, after several days of delirium with black vomit.
Such is yellow fever.
"He was bitten by a stray mosquito while applying the other insects
to a patient in one of the city hospitals. He did not recognize it
as a _Stegomyia_, and thought it was a _Culex_. It was permitted to
take its fill and he attached no importance to the bite until after
he was taken sick, when he related the incident to me. I shall
never forget the expression of alarm in his eyes when I last saw
him alive in the third or fourth day of his illness. The spasmodic
contractions of his diaphragm indicated that black vomit was
impending, and he fully appreciated their significance. The
dreaded vomit soon appeared. I was too weak to see him again in
that condition, and there was nothing that I could do to help him.
"Dr. Lazear left a wife and two young children, one of whom he had
never seen."
These experiments and many others like them conducted on soldiers and
Spanish immigrants proved that this particular mosquito would transmit
the disease under certain conditions.
1. The mosquito must bite the patient during the first three days of the
fever; after that a yellow fever patient cannot infect a mosquito.
2. A period of twelve days must elapse before the mosquito is able to
infect another person. After that she may infect anyone she may bite;
that is, the germs remain virulent during the rest of the mosquito's
life. The French Yellow Fever Commission working in Rio de Janeiro claim
that the first generation of offspring from such an infected mosquito is
capable of causing the disease after they are fourteen days in the adult
condition.
The next step was to ascertain whether the disease could be contracted
in any other way than by the bites of infected mosquitoes. A camp named
Camp Lazear was established and the following tests made: A
mosquito-proof building of one room was completely divided by a wire
screen from floor to ceiling. In one room fifteen mosquitoes that had
previously bitten yellow fever patients and had undergone the proper
period of incubation were liberated. In this room a non-immune exposed
himself so that he was bitten by several of the insects. A little later
the same day and again the next day the mosquitoes were allowed to feed
on him for a few minutes. Five days later, the usual incubation period,
he developed yellow fever.
At the same time that he entered the building two other non-immunes
entered the other compartment where they slept for eighteen nights
separated from the mosquitoes by the wire screen. They showed no signs
of taking the fever.
In another mosquito-proof house two soldiers and a surgeon, all
non-immunes, lived for twenty-one days. From time to time they were
supplied with soiled articles of bedding, clothing, etc., direct from
the yellow fever hospital in the city. These articles had been soiled by
the urine, fecal matter and black vomit obtained from fatal and other
cases of yellow fever. These articles were handled and shaken daily, but
no disease developed among the men and at the end of the twenty-one
days, two other non-immunes relieved them and handled a new supply of
clothing in the same way, sleeping between the same sheets that had
been used by a patient dying of yellow fever and exposing themselves in
every possible way to the soiled clothing. But no disease developed.
That these men were susceptible was shown later by inoculating some of
them, when they developed the disease.
In another experiment certain men in a camp allowed themselves to be
bitten by mosquitoes that had passed through the proper period of
incubation and every one of them and no others contracted the disease.
It was also shown that a mosquito was capable of communicating the
disease as long as fifty-seven days after it had bitten a yellow fever
patient. Another set of experiments showed that a subcutaneous injection
into a non-immune of a very small quantity of blood from the veins of a
yellow fever patient in the first two or three days of the disease would
produce the fever.
SUMMARY OF RESULTS
Since that time much other work has been done by independent workers as
well as by French and English Commissions both working at Rio de
Janeiro. The results of their investigation are practically the same and
may be summed up as follows:
1. The virus of the yellow fever is in the blood-plasma, not in the
corpuscles, for these may be removed and the plasma still be infective.
2. The virus is conveyed from one patient to another by the yellow fever
mosquito, _Stegomyia calopus_, and in no other way except by
experimental injections.
3. The patient is a source of infection only during the first three or
four days of the disease (this after the three to six days of
incubation).
4. The virus must undergo an incubation period of twelve to fourteen
days in the mosquito before she is capable of transmitting the disease.
5. The parasite, whatever it is, has never been seen. It is probably too
small to be seen by any of our present microscopes, even the recently
invented ultramicroscope. It is probably not a bacterial parasite but
very likely a Protozoan, and certain specialists have even shown by the
study of all the available data that it almost certainly belongs to the
Sporozoan genus _Spirocheta_.
Now what does all this mean? It means the saving of hundreds of human
lives annually. It means the banishing from many localities and possibly
very soon from the face of the earth of a disease that since the
earliest settlements on this continent has been a source of terror. It
means the making habitable of certain places which heretofore a white
man has entered only at the risk of his life. It means that quarantines
need no longer be established when yellow fever breaks out in a
district; quarantines which have inevitably caused the loss of millions
of dollars to the world of commerce.
RESULTS IN HAVANA
The first practical work based on these findings was done in Havana. The
Yellow Fever Commission made their recommendations in 1900. In 1901 and
1902 they were put into effect. The following table of the death rate
there during a period of ten years shows graphically the results:
DEATHS IN HAVANA FROM YELLOW FEVER
-----+------+------+------+------+------+------+------+------+------+------
| 1893 | 1894 | 1895 | 1896 | 1897 | 1898 | 1899 | 1900 | 1901 | 1902
-----+------+------+------+------+------+------+------+------+------+------
Jan. | 15 | 7 | 15 | 10 | 69 | 7 | 1 | 8 | 7 | 0
Feb. | 6 | 4 | 4 | 7 | 24 | 1 | 0 | 9 | 5 | 0
Mar. | 4 | 2 | 2 | 3 | 30 | 2 | 1 | 4 | 1 | 0
Apr. | 8 | 4 | 6 | 14 | 71 | 1 | 2 | 0 | 0 | 0
May | 23 | 16 | 10 | 27 | 88 | 4 | 0 | 2 | 0 | 0
June | 69 | 31 | 16 | 46 | 174 | 3 | 1 | 8 | 0 | 0
July | 118 | 77 | 88 | 116 | 168 | 16 | 2 | 30 | 1 | 0
Aug. | 100 | 73 | 120 | 262 | 102 | 16 | 13 | 49 | 2 | 0
Sep. | 68 | 76 | 135 | 166 | 56 | 34 | 18 | 52 | 2 | 0
Oct. | 46 | 40 | 102 | 240 | 42 | 26 | 25 | 74 | 0 | 0
Nov. | 28 | 23 | 35 | 244 | 26 | 13 | 18 | 54 | 0 | 0
Dec. | 11 | 29 | 20 | 147 | 8 | 13 | 22 | 20 | 0 | 0
-----+------+------+------+------+------+------+------+------+------+------
As long as the United States held control at Havana the yellow fever
was kept in check by fighting the mosquitoes, when this vigilance was
relaxed the fever began to appear again and the Cubans found that it was
necessary to keep up the fight against the mosquitoes if the island was
to be kept free from the disease.
THE FIGHT IN NEW ORLEANS
In the summer of 1905 came another opportunity to put the knowledge
gained during these experiments to a practical test. Samuel Hopkins
Adams in his article in _McClure's Magazine_, June, 1906, says of the
beginning of this fight:
"Eight years before, the mosquito-plague had infected the great,
busy, joyous metropolis of the south. Ignorant of the real
processes of the infection, New Orleans had fought it blindly,
frantically, in an agony of panic, and when at last the frost put
an end to the helpless city's plight, she lay spent and prostrate.
The yellow fever of 1905 came with a more formidable and unexpected
suddenness than that of 1897. It sprang into life like a secret and
armed uprising in the midst of the city, full-fledged and terrible.
But there arose against it the trained fighting line of scientific
knowledge. Accepting, with a fine courage of faith that most
important preventive discovery since vaccination, the mosquito
dogma, the Crescent City marshaled her defenses. This time there
was no panic, no mob-rule of terrified thousands, no mad rushing
from stunned inertia to wildly impractical action; but instead the
enlistment of the whole city in an army of sanitation. Every
citizen became a soldier of the public health. And when, long
before the plague-killing frost came, the battle was over, New
Orleans had triumphed not only in the most brilliant hygienic
victory ever achieved in America, but in a principle for which the
whole nation owes her a debt of gratitude."
For some time the authorities had been trying to keep secret the fact
that the disease was prevalent, but the rapidity with which it spread
made them realize that only united action on the part of all the
community would be of any avail. The Citizens Volunteer Ward
Organizations were organized for the purpose of fighting the mosquitoes
which were everywhere. To many the fight looked hopeless. The miles of
open gutters, the thousands of cisterns and little pools of standing
water everywhere furnished abundant breeding-places for the mosquitoes.
The ditches and ponds were drained or salted, the cisterns were
screened, infected houses were fumigated, yet the fever continued to
spread. Rains refilled the ditches, winds tore the screens from the
cisterns, the ignorant people of the French quarter refused to
coöperate. At last the city in desperation appealed to the President for
aid. Surgeon J.H. White and a number of officers and men of the United
States Public Health and Marine Hospital Service soon took charge of the
work. This was continued along the same lines as before with the same
object in view. But with the coming of the regulars the work was more
systematically and thoroughly done. Every case of fever was treated as
though it was yellow fever and every precaution taken to prevent
mosquitoes from biting such a patient. The houses in which the fever
occurred were thoroughly fumigated to kill any mosquitoes that might be
there, and the neighborhood was thoroughly searched to find any places
where the mosquitoes might be breeding. So confident were the
authorities that the mosquito was the sole cause of the disease
spreading, that besides fighting it no other work was undertaken save to
make the sick as comfortable as possible.
Finally the results began to be apparent. The number of cases gradually
diminished, until long before frost came the city was free from the
great pest. Yellow fever will doubtless appear from time to time in New
Orleans and other cities, but there is, at least there should be, small
danger of another great epidemic, for the people now know how the
disease is caused and the remedy.
Not long since I had occasion to write to a prominent entomologist in
Louisiana for some specimens of the yellow fever mosquito for laboratory
work. The following extract from his reply will show something of the
work that is still being done there.
"I am afraid we cannot furnish specimens of _Stegomyia_, in spite
of the fact that Louisiana is _supposed_ to be the most favorable
home of this species in the South. Since the light occurrence of
yellow fever in this State in 1905, a very vigorous war has been
kept up against _Stegomyia_, and the ordinances of all Louisiana
cities and principal towns require the draining of all breeding
places of this mosquito and the constant oiling or screening of all
cisterns or other water containers. The result is this species is
very rare. Here in Baton Rouge I only see one once in a great
while, and it would require perhaps a good many days' work at the
present season to get as good specimens and as many of them as you
require."
IN THE PANAMA CANAL ZONE
Yellow fever was one of the worst obstacles that confronted the French
when they were attempting to build the Panama Canal. The story of the
suffering and death from this dread disease there is most pathetic.
Ship-load after ship-load of laborers were sent over, as those who had
gone earlier succumbed to the fever. The contractors were responsible
for their men while they were sick and in order to avoid having to pay
hospital expenses the men were often discharged as soon as they showed
signs of sickness. Many of them died along the roadside while
endeavoring to reach some place where they could obtain aid. The
hospitals were usually filled with yellow fever patients, a very large
percentage of whom died.
Not only the day laborers suffered but many of the engineers, doctors,
nurses and others sickened and died of the disease. It is reported that
eighteen young French engineers came over on one vessel and in a month
after their arrival all but one had died of the yellow fever. Out of
thirty-six nurses brought over at one time, twenty-four died of the
fever, and during one month nine members of the medical staff of one of
the hospitals succumbed.
One of the first things that the United States Government did in
beginning work in the canal zone was to take up the fight against the
yellow fever mosquito. In Panama where the water for domestic purposes
was kept in cisterns and water-barrels, inspectors were appointed to see
that all such receptacles and other possible breeding-places for
mosquitoes were kept covered. After the first inspection, 4,000
breeding-places were reported. About six months later there were less
than 400. Similar work was done in all the towns and settlements along
the route of the canal. In addition to this fight against the yellow
fever mosquito considerable attention was paid to the breeding-places of
the malarial mosquito. The results have been remarkable. Cases of yellow
fever are now rare throughout this zone, and there has been a very great
reduction in the extent of the malarial districts. The last case of
yellow fever occurred in May, 1906. Before this work was done a man took
his life in his hands when he went into this region. Now it is regarded
as a perfectly safe place to live. Indeed it is a much safer place than
many sections of our own country where proper sanitary measures have not
been taken to protect the health of the community.
IN RIO DE JANEIRO
In Rio de Janeiro they have as yet been unable to get rid of the
mosquitoes, although thousands of dollars are spent annually in fighting
them. But the non-immunes there protect themselves by doing their
business in Rio during the day and going back at night to Petropolis,
twenty-five miles inland and twenty-five hundred feet higher, where
they are safe, for no _Stegomyia_ have ever been found there.
They claim there that the yellow fever mosquito does not bite during the
daytime after she has laid her eggs, and that she will not lay her eggs
until about three days after she has fed on blood, therefore a
_Stegomyia_ that bites during the day will not carry the yellow fever
because she is too young. This seems to explain why the fever cannot be
contracted by being bitten by a mosquito in the daytime. Certain other
experiments, however, have given different results so that as far as we
know it is not safe to be bitten at any time by such a mosquito in a
region where the disease is endemic or where it is epidemic.
In the main the work of the French Yellow Fever Commission working in
Rio de Janeiro has confirmed the findings of the American Commission.
One interesting special thing that the French Commission seems to have
established is that the female may transmit the infecting power to her
offspring, so that it would be possible for a mosquito that had never
bitten a yellow fever patient to be capable of infecting a non-immune
person. While all this is very probable in the light of what we know of
the disease and the way in which other diseases caused by similar
organisms may be transmitted by the parent to the offspring, yet the
most conservative investigators are waiting for further proof.
HABITS OF STEGOMYIA
The whole fight against yellow fever, then is directed, as we have seen,
against the mosquito, _Stegomyia calopus_. The habits of this species
are such as to make it easy in some respects to combat. It is seldom
found far away from human habitation. The adults will not fly far. Once
in a house they usually stay there except when they leave to deposit
their eggs.
On the other hand, some of these same habits make it all the more
dangerous. It will breed in almost any kind of water, no matter how
filthy, and a very small amount will suffice. Thus any leaks from
water-pipes or drains, cisterns, small cans of water or any such places
may become dangerous breeding-places. If conditions are unfavorable
there will often be developed small individuals which can easily make
their way through ordinary mosquito-netting.
Dr. Manson has pointed out an interesting possible result of the crusade
that is now being waged against the yellow fever mosquitoes. The
immunity of the people native to the endemic regions is supposed to be
due to their having had mild attacks of the fever during childhood, for
the children in these regions are subject to certain fevers which are
probably very mild forms of yellow fever.
Now if we kill practically all of the _Stegomyia_ so that these children
do not have this fever there will be developed, in due time, a
population most of whom are non-immune.
This freedom from the disease for some time will allow us to grow
careless in regard to fighting the mosquitoes. They will be allowed to
increase and by some chance the yellow fever will again be introduced
and there will then be very grave danger of most extensive and
destructive epidemics.
DANGER OF THE DISEASE IN THE PACIFIC ISLANDS
I have already referred once or twice to the conditions in many of the
Pacific tropical islands. In some of these various species of
_Stegomyia_ are abundant, and in some _Stegomyia calopus_ is the most
abundant and troublesome form. All the natives of these islands are
non-immune because there has never been any yellow fever there. Unless
extraordinary care is taken the disease will be introduced there sooner
or later and the results are sure to be most appalling. The climatic and
sanitary conditions and the habits of the people are ideal for the
development and spread of the disease, and what I have seen of the
conditions on some of these islands convinces me that it would be almost
impossible to control the disease before it had a chance to kill a large
percentage of the population.
With the opening of the Panama Canal these things become more possible.
Heretofore, the shipping to these regions has not been from ports where
yellow fever was endemic or even likely to be epidemic. But unless the
yellow fever is kept out of the canal zone, the danger will be many fold
what it is now.
The white man has already carried enough misery to these island peoples
in the way of loathsome diseases, and it is to be hoped that this,
another great curse, will not be carried to them with our civilization,
the beneficial results of which have been so often very justly
questioned.
What I have said in regard to these islands applies with equal force and
in some instances with even greater force to parts of Asia, the Eastern
Archipelago and other places.