Worldwide Insect
Borne Diseases.
Of
the many diseases spread by insects, very few are actually
caused by the insects themselves but raher, by other
organisms passed on when they feed or bite.
Insects are capable of spreading diseases
caused by many different types of micro-organisms including
bacteria, viruses, protozoans, etc. In these instances
it is the micro-organism that is the pathogen (disease
causer) and the insect involved is known as the vector.
Biting insects are active at all times of the
day and night. However, some prefer different times
of day eg.the mosquitoes that spread malaria are mainly
active after dark but the mosquitoes that spread yellow
fever and dengue fever are active during daylight hours.
The following table illustrates the global distribution
of the more well known insect borne diseases:-
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Table
of Insect Borne Diseases
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Disease
|
Vector
|
Endemic
Zone
|
For
More Info |
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Malaria
|
Mosquitoes
|
Global
tropical and subtropical areas.
| | |
Yellow
Fever
|
Mosquitoes
|
Tropical
areas of Africa and Central and South America
| | |
Dengue
Fever
|
Mosquitoes
|
Tropical
Africa, South East Asia, South America and
the Pacific.
|
Japanese
B
Encephalitis
|
Mosquitoes,
Ticks
|
The
Far East and South East Asia. Forested areas
of Central & Eastern Europe, Scandinavia
and former USSR.
| |
Filariasis
|
Mosquitoes,
Blackflies
|
Global
tropical and subtropical areas.
| | |
Lyme
Disease
|
Ticks
|
Europe
(inc. UK), USA, Australia, China & Japan.
| |
Leishmaniasis
|
Sandflies
|
Global
tropical and subtropical areas including the
Mediterranean.
| |
Sleeping
Sickness
|
Tsetse
Flies
|
East,
West and Central Southern Africa.
| |
Chagas
Disease
|
Assassin
Bugs
|
Tropical
South and Central America.
| |
Typhus
Fever
|
Ticks
& Lice
|
World-wide |
|
Plague
|
Fleas
|
World-wide.
|
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When
entering a region where
any of the above diseases are endemic, you should
always take the following precautions:
- Avoid
bites after sunset by wearing long-sleeved
clothing and long trousers.
- Most
insects can bite through thin clothing, so
spray an insecticide or repellent on them.
An insect repellent should also be used on
any exposed skin.
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- Spraying
insecticides in the room, burning pyrethroid
coils and heating insecticide impregnated
tablets all help to control mosquitoes.
- If
sleeping in an unscreened room, or out of
doors, a mosquito net (impregnated with insecticide)
is a sensible precaution. Portable, lightweight
nets are available.
- Things
like Garlic, Vitamin B and ultrasound devices
do not prevent bites.
|
 Filariasis
Filariasis
is a worm infestation confined mainly to the tropics
and spread from person to person by the bites of mosquitoes.
Many types of mosquito are involved in transmission.
The severity of the disease depends on the number of
worms present.
Filariasis affects an estimated
120 million persons in tropical areas of the world,
including sub-Saharan Africa, Egypt, southern Asia,
the western Pacific islands, the northeastern coasts
of South and Central America, and the Caribbean Islands.
The disease is caused by long thread like worms up to
50cm in length which live under the skin and in lymphatic
tissues. The female worms release larvae that circulate
in the peripheral blood vessels and are ingested by
mosquitoes; thus, infected mosquitoes transmit the infection
from person to person. Filarial worms can live up to
twenty years in humans producing larvae that infect
insects but the worms do not multiply in the body.
 Short-term
travelers to endemic areas are at low risk of contracting
filariasis. However, travelers who visit endemic areas
for extended periods of time and who are intensively
exposed to infected mosquitoes can become infected.
No vaccine is available.
Protective measures include avoidance of mosquito bites
through the use of personal protection measures
Symptoms vary widely between individuals but severe
cases include inflammatory swelling of the arms and
legs. Some forms of the disease can cause blindness.
In all cases, drug treatment is effective if given before
the disease becomes advanced.
 Lyme
Disease
An infectious disease caused
by a bacterium which is spread to humans by tick bites.
It is characterised initially by an expanding red rash
at the site of the bite often accompanied by headache,
muscle and joint aches and fever.
Lyme disease occurs in temperate forested regions of
Europe (including the UK) and Asia and in the northeastern,
north central, and Pacific coastal regions of North
America, Australia, China and Japan. It is not transmitted
in the tropics.
Travelers to endemic areas who have frequent or prolonged
exposure to tick habitats could be at increased risk
for Lyme disease and should be advised to avoid tick
habitats if possible. If exposure to tick habitats cannot
be avoided, the application of repellents to skin and
clothing, as well as regular daily checks for any attached
ticks, can reduce the risk of infection. Prompt removal
of any attached ticks will help prevent infection.
 Repellents
containing DEET have been found to be useful but if
an embedded tick is discovered, slowly pulling it out
with tweezers is the best method of removal and the
affected person should remain alert to the development
of any symptoms. If a rash appears at the site of attachment,
immediate medical attention should be sought. Lyme disease
is effectively treated with oral penicillin or tetracyclines.
A safe and efficacious vaccine was, until recently (Feb
2002), available for protection from Lyme disease. However,
production of the vaccine was discontinued by the manufacturer
because of low demand and is no longer commercially
available.
 Leishmaniasis
Is caused by single celled organisms called
leishmania which are passed on to humans by the bite
of the sand fly (phlebotomus). There are two forms of
the disease: Cutaneous Leishmaniasis (oriental sore)
and Visceral Leishmaniasis (kala azar).
Cutaneous: the infection is restricted to the
skin at the site of the bite where it manifests as skin
nodules on the face, arms and legs which may form ulcers.
The disease is normally self limiting but can leave
the victim with disfiguring scars. The disease is found
throughout North Africa, the Middle East, Asiatic Russia,
Iran and tourist resorts around the Mediterranean.
 Visceral:
in this instance the parasites invade the liver, spleen
and bone marrow causing serious illness, which, if untreated
can lead to death. The main problem being failure in
diagnosis. It is sometimes misdiagnosed as leukaemia
or lymphoma due to enlargement of the spleen, anaemia
and weight loss. It occurs in the same regions as the
cutaneous form but is more widespread in parts of Africa,
India and South America. Children are especially at
risk.
Most cases of leishmaniasis respond well to treatment
with an antimony drug (sodium stibogluconate) if diagnosed
early enough.
 Sleeping
Sickness
Also known as African Trypanosomiasis is caused
by tiny organisms called trypanosomes which are spread
by the bites of infected tsetse flies and is confined
to areas of tropical Africa.
Tsetse flies breed alongside rivers and transmit the
disease between wild animals, cattle and humans. It
is also responsible for deaths amongst livestock and
is therefore of economic significance. Epidemics usually
occur after outbreaks of social or political turmoil.
The first sign of the illness is a boil-like swelling
which arises five or more days at the site of the bite
(any sooner is probably an allergic reaction). Fever
follows within two or three weeks and a serious illness
follows which unless treated, affects the nervous system
resulting in the characteristic daytime drowsiness.
 Due
to the unfamiliarity of the disease it can remain undiagnosed
for some time. Travellers who become unwell after returning
home from an endemic area must inform their doctor of
their itinerary.
People on wildlife safaris are most at risk. The flies
are less attracted to persons on foot than on horseback
and then they are more likely to attack the horse than
the rider. They will even follow vehicles travelling
slowly through infested areas so windows should be kept
closed and any insects that enter should be killed with
a knock down insecticide spray.
There is no vaccine available and prophylactic drugs
are not recommended since they mask symptoms. Prevention
depends largely on avoidance of bites. Effective drug
treatment is hazardous and highly specialised.
 Chagas
Disease
Also known as American Trypanosomiasis, Chagas
is a potentially serious disease also caused by trypanosomes
which is endemic to South and Central America which
is spread by biting bugs called assassin bugs or kissing
bugs.
 The
disease is present in most rural areas particularly
where there is a human presence. This is because the
bugs that spread the disease live in the walls of mud
huts where they venture out, only at night to feed.
Travellers to these areas are most at risk but avoidance
is straightforward. True jungle areas of the Amazon
are mainly free of the disease and visitors to cities
or remote jungle ruins are not at risk.
 The
bugs become infected by feeding on the blood of someone
who has the disease. They then excrete infective trypanosomes
in their faeces which enter the blood of a subsequent
victim through the bite wound.
Chickens, dogs and opossums also harbour the disease.
Symptoms include swelling around the site of the bite
followed by enlargement of the lymph glands and fever.
Long term symptoms include damage to the heart causing
sudden death and paralysis of the gut causing difficulty
in swallowing and severe constipation.
 There
is no vaccine or preventative drug treatment available
and treatment of the disease is difficult since no drug
is currently able to kill the parasites without harming
the host.
Avoidance of the bites is the best strategy. When travelling
through an endemic region try not to sleep in adobe
huts where the locals sleep, keep away from walls when
sleeping and use mosquito nets. Spraying the insides
of rooms with an insecticide spray is also a good idea.
 Typhus
There are several varieties of typhus all of
which cause fever, severe headache and a skin rash and
the severity of the illness varies greatly among the
different types. In the past, outbreaks of typhus fever
have been responsible for thousands of deaths.
All forms of typhus fever are caused by tiny organisms
called rickettsiae which are passed on to humans by
various types of insects including lice (epidemic),
fleas (endemic), mites (scrub) and ticks.
 The
illness exists world-wide but nowadays, most cases of
typhus are confined to areas of Central and Southern
Africa, South America and Central and South East Asia.
Epidemic typhus is only likely to affect volunteer workers
who come into close contact with locals.
People who walk through tropical bush should inspect
their skin for any attached ticks and carefully remove
them. There are no vaccines available for any form of
typhus.
Symptoms of the disease include; severe headache, fever
and skin rashes. The severity of the illness depends
on the variety of typhus. The disease can be fatal but
responds well to antibiotic therapy using tetracyclines
if given early enough.
 Plague
Otherwise
known as The Black Death, this disease is one of the
oldest known and is found world-wide including the USA.
In the fourteenth century it spread across Europe and
was responsible for wiping out one third of the population.
The causative organism is a bacterium (Yersinia Pestis)
and it is primarily a disease of rodents especially
rats. The infection is spread to humans by the bite
of the rat flea (Xenopsylla cheopis).
Fleas become infected by feeding on the blood of an
infected rodent. When the rodents die the fleas go in
search of a new host. They can then transmit the disease
to humans who become their hosts.
The disease manifests itself in two forms; bubonic plague
and pneumonic plague:-
 The
symptoms of bubonic plague appear suddenly about seven
days after exposure and include high fever, headache,muscular
aches,shaking chills and pain in the groin and armpits
due to the formation of buboes or swollen lymph nodes.
Untreated, the disease can spread rapidly throughout
the body via the lymphatic system. When the lungs become
infected an infectious pneumonia may develop.
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