Yellow fever is a viral illness which is spread by the
bite of a mosquito. The species of mosquito that is responsible
for spreading yellow fever is Aedes Aegypti
and is a different species from the anopheles mosquito
that transmits malaria.
Essentially yellow fever is a disease
of monkeys living in tropical rain forests. The virus which
causes the disease is one of a group of viruses known as arboviruses.
Humans are infected by being bitten by rain forest mosquitos
carrying the yellow fever virus.
their name implies "arboviruses" are transmitted to humans
by insects (arthropod borne virus). The mosquito in particular
is well suited to the transport and spread of the infection
due to its wide distribution throughout the tropics.
The peak biting times for many mosquito species is dusk to
dawn. However, Aedes aegypti that transmits yellow
fever virus, feeds during the daytime.
The geographical distribution
of yellow fever is confined to Equatorial Africa and Central
South America as shown on the maps as shown.
Strangely, yellow fever is unknown in Asia despite
the presence of mosquitos capable of spreading the virus.
Arbovirus illnesses usually have two characteristic
phases, the first when the virus is invading the host cells,
and the second a few days later when the body's immune system
is fighting the infection.
The antibodies produced during the second phase of
illness can cause damage to the blood vessels which explains
why arboviruses often cause bleeding.
Many yellow fever infections are mild and go unrecognised
but severe and life threatening illness is not uncommon. After
an incubation period of about three to six days fever, headache,
abdominal pain and vomiting develop. After a brief recovery
period, shock, bleeding and signs of liver and kidney failure
develop. Liver failure is associated with jaundice hence the
name "yellow fever".
is no drug available to cure yellow fever hence treatment
is aimed at symptomatic relief. Overall about 5% of patients
die. Those who recover do so completely and are immune thereafter.
Fortunately yellow fever is
one of the few arboviruses for which a vaccination is available.
A single injection of a live, weakened (and harmless) virus
stimulates the body's immune defences and confers effective
immunity for ten years.
a list of clinics in the UK where you can obtain yellow fever
& other vaccines:-
In general, all travellers
going to an endemic area require a yellow fever vaccination
certificate and travellers going to some parts of Asia from
an endemic region will also require a certificate.
This is an unusual arbovirus infection since no other
animals except humans and mosquitoes play a significant part
in perpetuating the infection. It is present in Africa, South
East Asia, the Pacific area and northern South America.
The disease is spread to humans by the bite of a mosquito
(Aedes aegypti) and after about five days incubation period
there is a sudden onset of fever, headache and severe joint
and muscle pains. The initial fever resolves after about three
to five days only to recur with the appearance of a rash consisting
of small white spots which starts on the trunk and spreads
to the limbs and face. Within a few days the fever subsides
and recovery follows.
With more than one-third of the worlds population
living in areas at risk for infection, dengue virus is a leading
cause of illness and death in the tropics and subtropics.
As many as 400 million people are infected yearly.
is caused by any one of four related viruses transmitted
by mosquitoes. There are not yet any vaccines to prevent infection
with dengue virus and the most effective protective measures
are those that avoid mosquito bites. When infected, early
recognition and prompt supportive treatment can substantially
lower the risk of medical complications and death.
There is no specific treatment for Dengue but in terms
of management, sufferers are advised to take paracetamol and
Although dengue is a very unpleasant illness, complications
are uncommon and recovery is usually complete.
There is also a more severe and life threatening haemorrhagic
form of the disease which has appeared with dramatic outbreaks.
Fortunately this form occurs only rarely.
This is thought to be the
result of a second infection where there is some remaining
immunity from a first attack causing a vigorous immunological
response in which severe blood vessel damage occurs.
to infection does not last long and subsequent attacks are
possible. There is no vaccine available. Prevention is by
avoiding mosquito bites.
Note: The Aedes mosquito responsible for transmitting
Dengue Fever is a day time feeding species.
first vaccine against the Dengue virus
approved in Mexico
first vaccine to prevent dengue fever has been approved
for use in Mexico by the countrys drugs regulator.
The decision by the Federal Commission for the Protection
against Sanitary Risk (COFEPRIS) was based on the results
of more than 25 clinical trials conducted by vaccine
manufacturer Sanofi Pasteur in 15 countries including
Mexico which involved more than 40,000 volunteers.
Dengvaxia is a vaccine developed for prevention
of disease caused by all four dengue virus serotypes
and is made from attenuated dengue. The product is authorised
for use in populations where dengue is endemic.
COFEPRIS says the vaccine has an average efficacy of
60% for preventing infection and 93% efficacy for preventing
severe dengue infection in patients aged 945 years.
Estimates are that the vaccine could help prevent 8,000
hospital admissions and 104 deaths every year from the
virus in Mexico, saving 1,100 million pesos in healthcare
costs. In 2014, Mexico recorded 32,100 cases of dengue
Manufacturer Sanofi Pasteur, has spent more than 20
years developing a vaccine. The company claims it has
the potential to reduce cases of dengue fever by 50%
within five years in populations where the disease is
Dengvaxia is the first vaccine approved to prevent dengue
fever and is a major innovation and a public health
breakthrough. It will be a critical addition to the
integrated dengue prevention and control efforts.
This is a rare
but serious arboviral infection with a 20% fatality rate.
It occurs in most of the Far East and South East Asia. The
endemic zone extends from India and Nepal across the whole
of South East Asia to Japan and Korea in the Far East.
The risk of infection is greatest in long term visitors
to rural areas, and the risk to short term visitors and visitors
to major cities is small. Precautions against mosquito bites
Japanese B Encephalitis is transmitted by rice field
breeding mosquitoes (of the Culex group) that become infected
with Japanese encephalitis virus.
become infected by feeding on domestic pigs and wild birds
infected with the Japanese encephalitis virus. Infected mosquitoes
then transmit the Japanese encephalitis virus to humans and
animals during the feeding process.
The incubation period is normally between 5 and 15 days.
The illness cannot be passed on from person to person.
There is no specific treatment. Intensive supportive therapy
Mild infections can sometimes
occur without apparent symptoms other than mild fever
with headache. More severe infection is marked by quick onset,
headache, high fever, neck stiffness, stupor, disorientation,
coma, tremors, occasional convulsions (especially in infants)
and spastic paralysis.
There is an effective vaccine
available in the UK on a named patient basis. It should
be considered by anyone travelling to Asia for more than a
month or visiting rural areas.
blood feeding external parasites of mammals, birds, and reptiles
throughout the world. Ticks are not insects like fleas, but
arachnids like mites, spiders and scorpions.
encephalitis (TBE), is a viral disease affecting the central
nervous system. The disease is most often manifest as meningitis
or encephalitis or sometimes, even meningoencephalitis. It
is caused by the tick-borne encephalitis virus (TBEV), a member
of the family Flaviviridae.
is endemic in many European countries, the former Soviet Union,
and Asia. It is found mainly in temperate regions. The natural
hosts of the virus are small rodents and deer, with humans
being accidental hosts. After attaching itself to the host,
an infected tick transfers the virus to the host during feeding.
showing TBE endemic areas
endemic areas, people with recreational or occupational exposure
to rural or outdoor settings such as; hunters, hikers, campers,
forest workers, farmers, etc. are potentially at risk of infection
by contact with the infected ticks.
no specific treatment for TBE. Meningitis, encephalitis, or
meningoencephalitis require hospitalisation and supportive care.
The incubation period of TBE is usually between 7 and 14 days.
A characteristic biphasic febrile illness follows, with an
initial phase that lasts two to four days. It is non-specific
with symptoms that may include fever, malaise, anorexia, muscle
aches, headache, nausea, and/or vomiting.
about eight days of remission, the second phase of the disease
occurs in twenty to thirty percent of patients and involves
the central nervous system with symptoms of meningitis (fever,
headache, and a stiff neck) or encephalitis (drowsiness, confusion,
sensory disturbances, and/or motor abnormalities such as paralysis)
or meningoencephalitis. TBE is more severe in adults than
Mortality is about two percent with deaths occurring five
to seven days after the onset of neurological signs.
Like other tick-borne infectious diseases, TBEV infection can
be prevented by using insect repellents and protective clothing
to prevent tick bites.
A vaccine is available in some disease endemic areas but adverse
vaccine reactions in children limit the use of the vaccine.
The vaccine involves two doses one month apart. If required
a booster is given after a year.
West Nile Virus
of West Nile Virus
of a mild infection: fever, headache, bodyaches,
skin rash, and swollen lymph glands
of a severe infection may be marked by: high fever,
severe headache, neck stiffness, stupor, disorientation,
tremors, convulsions, muscle weakness, paralysis,
your health care provider if you have concerns about
your health. If severe symptoms develop, see your
West Nile Virus is a flavivirus commonly found in Africa, West
Asia, the Middle East and the United States. The virus can infect
humans, birds, mosquitoes, horses and some other mammals.
The principal route of human infection with West Nile virus
is through the bite of an infected mosquito. Mosquitoes become
infected when they feed on infected birds, which circulate the
virus in their blood for a few days. The virus replicates in
the mosquito and spreads to the mosquito's salivary glands.
During subsequent blood meals, the virus may be injected into
humans and animals, where it can multiply and possibly cause
At least 36 species of mosquito are known to be carriers of
West Nile Virus. The most common carrier of West Nile in the
United States is the Culex pipiens (Northern house) mosquito.
Nile fever is usually a case of mild disease characterized
by flu-like symptoms. It typically lasts only a few days and
does not appear to cause any long-term health effects.
More severe disease due to a person being infected with this
virus can be West Nile encephalitis, West Nile meningitis
or West Nile meningoencephalitis. Encephalitis refers to an
inflammation of the brain, meningitis is an inflammation of
the membrane around the brain and the spinal cord, and meningoencephalitis
refers to inflammation of the brain and the membrane surrounding
The incubation period is usually 3 to 14 days. Symptoms of
mild disease will generally last a few days. Symptoms of severe
disease may last several weeks, although neurological effects
may be permanent.
who are infected with the West Nile virus will not have any
type of illness. It is estimated that 20% of the people who
become infected will develop West Nile fever: mild symptoms,
including fever, headache, and body aches, occasionally with
a skin rash on the trunk of the body and swollen lymph glands.
symptoms of severe infection (West Nile encephalitis or meningitis)
include headache, high fever, neck stiffness, stupor, disorientation,
coma, tremors, convulsions, muscle weakness, and paralysis.
It is estimated that 1 in 150 persons infected with the West
Nile virus will develop a more severe form of disease.
There is no specific treatment for West Nile virus infection.
In more severe cases, intensive supportive therapy is indicated,
often involving hospitalization, intravenous fluids, airway
management, respiratory support (ventilator), prevention of
secondary infections (pneumonia, urinary tract, etc.), and
good nursing care.
When travelling to areas where the disease is endemic you
can reduce the risk of becoming infected with the virus by
employing preventive measures such as protecting yourself
from mosquito bites:-
insect rellent to your skin and clothes when going
possible, wear long-sleeved shirts and long pants
whenever you are outdoors.
mosquito netting over infant carriers when you are
outdoors with infants.
staying indoors at dawn, dusk, and in the early evening,
which are peak mosquito biting times.
sure any window and door screens are intact so that
mosquitoes cannot get indoors.
mosquito nets around beds at night while asleep.
of the mosquitoes that carry the West Nile virus are especially
likely to bite around dusk and dawn. If you are outdoors around
these times of the day, it is important to apply repellent.
But there are also mosquitoes that bite during the day, and
these mosquitoes have also been found to carry the West Nile
virus. The safest decision is to apply repellent whenever
you are outdoors
Apply insect repellent sparingly to exposed skin. The more
DEET a repellent contains the longer time it can protect you
from mosquito bites. A higher percentage of DEET in a repellent
does not mean that your protection is betterójust that it
will last longer. DEET concentrations higher than 50% do not
increase the length of protection. Choose a repellent that
provides protection for the amount of time that you will be
Chikungunya fever is another viral disease transmitted to
humans by the bite of infected mosquitoes. It is diagnosed
based on symptoms, physical findings (e.g., joint swelling),
laboratory testing, and the possibility of exposure to infected
Chikungunya typically starts with one or more of the following
symptoms - chills, fever, vomiting, nausea, head ache and
joint pain. The attack is sudden and sometimes it is accompanied
with rashes. Severe joint pain is the main and the most problematic
symptom of Chikungunya.
less commonly seen symptoms include mouth ulcers, loss of
taste and conjunctivitis. The fever usually subsides in a
couple of days, but other symptoms may last for a longer duration.
In some cases joint pain persisted for years.
There is no antiviral drug or medicine specifically for Chikungunya
fever; care is based on symptoms. Chikungunya infection is
not usually fatal and since chikungunya is cured by the immune
system in almost all cases there is no need to worry.
Steps to prevent infection with chikungunya virus include
use of insect repellent, protective clothing, and staying
in areas with screens.
Chikungunya virus was first isolated in Tanzania in 1953,
and has since been cited as the cause of numerous human epidemics
in India, Indonesia, Malaysia, Singapore, and Sri Lanka.
Chikungunya Distribution and Global Map
range of chikungunya virus is mainly in Africa and Asia. Given
the current large chikungunya virus epidemics and the worldwide
distribution of Aedes aegypti and Aedes albopictus
mosquitoes, there is a risk of importing chikungunya virus
into new areas through infected travellers.
where people have become infected with chikungunya virus