|
Important information about Yellow Fever
>General
points
>Clinical signs
>Laboratory Diagnosis
>Control Measures
>>Vaccination
>>Notification
>General points
Yellow Fever is a viral disease which has caused widespread epidemics
throughout history in Africa and the Americas. In the Americas, it is
endemic in nine countries of South America and in a number of Caribbean
islands. Brazil, together with Colombia, Venezuela, Bolivia, Ecuador
and Peru are considered to the countries most at risk from transmission
of the disease.
The disease can occur in two different environmental contexts - urban
and in the wild. Urban yellow fever is transmitted to human beings through
Aedes aegypti mosquito bites, infected after biting other humans. This
type of yellow fever was a serious problem in Brazil but thanks to the
work and dedication of scientists such as Oswaldo Cruz, it was eradicated
and only now, almost a hundred years later, we are now living with the
threat of the disease making a reappearance in our cities and towns.
"Wild" yellow fever is transmitted by the bite of the Haemagogus
mosquito that can be found in bush areas, woods, forests and jungles
and are infected after feeding on the blood of infected animals, generally
monkeys. Since it is transmitted by mosquitoes, yellow fever is known
as an arbovirosis (from the English Anthropod Born Viruses). Elimination
of wild yellow fever is impossible since we have no control over the
mosquito transmitter, nor over their hosts (monkeys).
Yellow Fever in human beings, whether of the urban or wild variety,
is presented in different degrees of seriousness, from light moderate
infection to serious or very serious versions.
Although a safe and effective vaccine exists, used with success for
over 60 years, the increase in the number of people infected with the
disease is now a sign that yellow fever is returning as a serious public
health problem.
>Clinical
signs
Yellow Fever is an acute infectious disease that can present in
its early stages a clinical picture little different from that of many
other viruses, but later it develops more serious clinical manifestations.
The disease has an incubation period of between three and six days with
no apparent symptoms and can present in two different clinical forms-
light or non-apparent (in 90% of all cases) or the most serious form:
fulgurant yellow fever.
In the initial phase of the symptoms, the clinical picture of yellow
fever is signaled by fever, shivering, headaches, widespread body pains,
general exhaustion accompanied by nausea and vomiting. These signs and
symptoms last between 3 and 4 days and during this period natural evolution
towards cure and recovery can take place or, after a period of regression,
the more serious phase appears which presents itself in the patient
with signs and symptoms of failure of the principal body systems and
organs, mainly the liver and kidneys.
When the liver is attacked, the patient presents several types of hemorrhaging
of the gums, the nose, the ears, the mouth, (vomiting, haematemesis
(vomiting with blood) and of the intestine. Skin turns yellow (jaundice).
When the kidneys are affected, the patient presents a decrease in the
volume of the urine and can cease urinating altogether .A further characteristic
of the disease is a slow pulse, even with high fever (paroxysmal pulse).
These occurrences take place over a three to five day period. If the
patient is properly treated in hospital recovery is likely. Unfortunately,
around 15% of patients with the most serious forms of yellow fever can
enter terminal stage and die within 24 hours.
In the case of yellow fever, early diagnosis (done quickly and precisely),
as well as the availability of good quality medical attention, can mean
the difference between life and death.
Since it can be easily confused with other diseases, diagnosis of yellow
fever depends on the information supplied by the patient and his or
her family. The most useful information is that relating to the actual
areas where the patient has been recently (epidemiological information).
Diseases such as malaria, leptospirosis, fulgurant hepatititis etc can
be confused with yellow fever (differential diagnosis). Other hemorrhagic
fevers of viral origin also exist and these should be borne in mind
during diagnosis. One of them is hemorrhagic dengue.
Diagnosis of yellow fever must be confirmed by laboratory tests so that
appropriate measures can be implemented to protect public health.
>Laboratory
Diagnosis
Diagnosis is made with a single blood sample, taken after the sixth
day of the disease. This test (serology) will permit detection of the
presence of recent antibodies against the yellow fever virus (Immunoglobuline
M - IgM) and confirm the yellow fever diagnosis. This is a relatively
sensitive test and when carried out with blood samples taken at the
correct time, has a crucial effect on the result.
Another key test in public health terms is isolation of the virus. No
opportunity should be missed to extract a blood sample or a liver fragment
(in a life and death situation), during the first six days of the disease
in order to carry out this test. Isolating the virus can permit one
to confirm
the diagnosis one hundred per cent.
Other tests can also be carried out depending on the situation, and
the place and time that the case was notified. For example, if the health
authorities are informed of a case suspected after death of being yellow
fever, a post mortem can be carried out which will make possible a histopathological
examination of liver and kidney tissue. This procedure will confirm
the existence of a yellow fever case. It will also establish the differential
diagnosis with other similar diseases already mentioned.
Brazil is self-sufficient as far as diagnosis of yellow fever is concerned.
It does not need to depend on other countries to carry our confirmatory
diagnoses. We are lucky to have a network of public laboratories, coordinated
by the National Epidemiology Center of the National Health Foundation
(CENEPI/FUNASA). The latter can count on the assistance of the most
highly qualified laboratories in Brazil - Evandro Chagas/Funasa / PA
Institute, the Adolfo Lutz/SESA/SP Institute and the Oswaldo Cruz/FIOCRUZ/RJ
Institute - all of which are highly qualified and equipped to use the
latest techniques to identify the virus (genetic sequencing).
Those laboratories are recognized as Collaborating Centers by the World
Health Organization (WHO), and they serve as world class reference laboratories.
The laboratories in the Brazilian public network are equipped to meet
the requirements of epidemiological and sanitary surveillance in accordance
with their capabilities and area which they cover, as can be seen in
the Annex.
>Control Measures
>>Vaccination
The main strategy for controlling yellow fever is vaccination. The vaccine
is safe and provides almost 100% protection against the disease. Vaccination
is considered as obligatory by the World Health Organization for travelers
to areas with a transmission risk. According to the latest WHO publication
(January 2000), 124 countries require vaccination certificates for travelers
that visit or transit those countries. The format of the valid certificate
can be found at the Annex.
In endemic yellow fever areas, the vaccine is applied routinely in a
single dose in babies at nine months and reinforced at ten year intervals.
In endemic areas where there is very high transmission (Resolution 1/2000
of 24 February 2000), vaccination is recommended from six months of
age.
Protection is offered by the vaccine, after the first dose takes effect
after about 7 to 10 days. This is the length of time needed for protective
antibodies to form against the yellow fever virus.
The vaccine against yellow fever is contraindicated for people who have
life-long allergic reactions to chickens eggs (egg protein), for people
with immunodeficiency (congenital or acquired), especially those infected
by the HIV virus (symptomatic and asymptomatic). It is also contraindicated
for people who need to take continuously medicines based on corticosteroids
(corticoids) , for patients receiving chemotherapy, for those who have
had transplants, for pregnant women and for children under six months
old.
As with other vaccines, light and moderate adverse reactions to the
anti-yellow fever vaccination can occur. Between 2% and 5% of those
vaccinated experience headaches, muscular pain and low fever for up
to 5 to 10 days after being vaccinated. Reactions of immediate hypersensitivity
- itching and redness of the body skin and asthma are not common, occurring
in fewer than 1/1.000.000 of people, and mainly among people with a
history of allergic reaction to eggs.
Given the current situation in Brazil - the occurrence of cases of yellow
fever in some well defined areas - and the high rate of infestation
by the Aedes aegypti mosquito in many Brazilian municipal districts,
the National Immunization Programme has stepped up vaccination throughout
the country.
In addition to immunization, other measures to control the vectors of
the disease have been adopted to control the presence of the Aedes aegypti
in urban areas of Brazil. Among the key measures taken to reduce the
risk of transmission of yellow fever and dengue, attention needs to
be drawn to the need for efforts on the part of the population to reduce
the number of breeding grounds of mosquitoes: getting rid of disposable
containers, plant pots containing aquatic plants, water receptacles
without lids, old bottles and tires - and the carrying out of municipal
policies to ensure proper collection and disposal of solid residues
as part of urban cleansing programmes. In addition, chemical treatment
with insecticides is also recommended . The use of fumigation in urban
and periurban environments has been one of the main activities undertaken
by FUNASA. Responsibility for this activity is gradually being passed
to the States and municipal districts.
>>Notification
The need for careful, rapid and dynamic epidemiological surveillance
is extremely important for controlling the disease and protecting the
community.
Every unvaccinated individual coming from an area known to be infected
by the represents a risk of introducing the disease in an area infested
with the Aedes aegypti. It is for this reason that vaccination certificates
are required for all travelers going to endemic areas or moving between
one town and another where the where the disease does not exist or where
the Aedes aegypti vector is present.
Yellow Fever is an internationally notifiable disease in accordance
with the norms and regulations of the WHO and any suspected cases must
be communicated immediately to the Federal, state or municipal health
authorities by the fastest available means ( by fax, telex, telephone,
e-mail etc).
Once notified, the health authorities concerned must carry out, as a
matter of urgency, epidemiological investigation into each suspected
case in order to confirm or not the case and to start implementing individual
or collective control measures.
Epidemiological investigation requires speed of detection, early and
immediate care for the patient and the adoption of control measures.
In the case of death, immediate steps must be taken to clarify and confirm
the diagnosis through the employment of specific laboratory techniques.
|
