Archive for repellent

Dengue Fever

Posted in Health/Diseases, Latest of Asienreisender with tags , , , , , , , , , , , , , , , , , , , , , on August 7, 2013 by Thim Kwai

In difference to malaria, which vector is a parasite, dengue fever is a viral disease. It’s hosts are exclusively primates, mostly humans and some kinds of mosquitoes of the family aedes, who transfer it. There are four different subspecies of the virus.

Mosquito larvas in a washing basin in Cambodia. Images by Asienreisender, 2013

Dengue fever is a very dangerous and painful disease. It is also an emerging disease, in fact the fastest dispersing disease in the world transfered by mosquitoes. In the fifty years between 1960 and 2010 dengue cases rose up thirty fold worldwide. In the ten years between 2000 and 2010 the number of cases doubled. That has to do with the expansion of the vector mosquito, what is in Southeast Asia (mostly) the Asian tiger mosquito, in general mosquitoes of the aedes family. This mosquito kind thrives in urban regions, and it’s very adaptable. Since urbanisation is rampant in Southeast Asia, the Asian tiger mosquito has a rapidly growing habitat. But it’s also worldwide spreading out. Globalization promotes the outspread of the tiger mosquito and the disease. Increased mobility as travel activities, population growth and global warming play a role as well.

Particularly the Philippines and Laos are in the center of the emerge, but also Thailand, Malaysia, Singapore and Vietnam have all reported an increase in cases.

The World Health Organization (WHO) estimates between 50 to 100 million annual cases of dengue worldwide, of whome half a million suffer a heavy course of disease and 22.000 people die; most of the victims are children. In Asia more than 90% of the heavy course of the disease hit children. The magazine ‘Nature’ wrote in it’s April 2013 issue that even 390 million people get infected annually, referring to the studies of the scientific authors of the article.

Dengue is endemic in 110 countries in the tropical and subtropical regions of the earth; 75% of the dengue cases appear in the Asia/Pacific region.

Dengue fever is commonly also called the ‘breakbone disease’ or ‘dandy fever’.

Transfer

The disease is mostly transfered by the Egyptian tiger mosquito, also known as dengue mosquito or yellow-fever mosquito and, here in Southeast Asia, by the Asian tiger mosquito (lat. Stegomyia albopicta, aedes albopictus). There are some other mosquitoes who transfer the disease, particularly in New Guinea and in the south Pacific (the Polynesian tiger mosquito).

The circle of reproduction is similar to those of other mosquito-born diseases. A female mosquito sucks blood from an infected person and gets the virus in it’s stomach. If the virus concentration is high enough, it can befall the mosquito’s stomach cells and reach it’s own blood circulation and contamine the mosquito’s saliva. The extrinsic incubation time inside the mosquito is eight to ten days, means that the virus is then mature and harmful. Next time when it’s biting someone, the infection is transfered to him or her. That’s because at any bite a mosquito does, first it’s injecting some saliva into the victims blood. A single bite of an infected mosquito is sufficient to transfer the disease, but not necessarily does. The virus can also be transfered from the mosquito to it’s lavaes.

Although the mosquito gets itself infected by the dengue virus, there are no harming effects for the mosquito.

Dengue can’t spread directly from one person to another one. But, if there is someone around who has dengue fever it is most important to protect everybody from the mosquitoes around, particularly the patient. They can transfer the virus from the infected person to other people around.

Dengue can also be transfered by blood transfusions and organ donations if the donator was infected himself.

The risk of an infection is highest in the rainy season (monsoon), for the mosquitoes then find the most breeding places and florish. The tiger mosquitoes prefer living indoor in urban regions and their daily peak periods of biting are around sunrise and up to two hours later and around sunset. Though, it can bite at any time of the day.

Course of the Disease

After getting bitten by a mosquito and infected, dengue has a latent period between three and fourteen days. Most of the cases are mild and not to distinguish from a normal flu. One get’s fever (up to 40 degree C) with ague, headache, eye- muscle- and limbpains. It comes together with a rash. After three to seven days it’s easing off. Though, in two to four percent of the cases the course of disease continues heavy. A ‘dengue hemorrhagic fever’ (DHF), also called ‘dengue shock syndrome’ can appear. One to five percent of the heavy cases are lethal.

Dengue hemorrhagic fever is an acute shock syndrom with uncontrollable inner and outer bleedings; the blood circulation breaks down, abdominal pain, fever and headache, dehydration, brain caused spasms, coma, bloody vomiting, bleeding gums, a swollen liver and many more symptoms appear.

The shock occurs two to six days after infection with sudden collapses, cool clammy extremities, weak thready pulse and blueness around the mouth, blood spots in the skin, spitting blood, blood in the stool, bleeding gums and noise bleeding. It can lead to pneumonia and heart inflammation. The mortality rate at this stage is announced by the WHO by between 2.5% with proper medical treatment up to twenty percent, without. Letal cases are mostly among children.

The disease is very painful. The acute phase lasts between one to two weeks, but can extend much longer (four to six weeks). If the infection is survived, the patient is immune against all four dengue viruses for a short time and for the certain virus which caused the acute disease a live long.

When suffering the first typical symptoms it makes sense to have it checked by a doctor to make certain what it exactly is.

Diagnosis

Therapy

Prevention

Peculiarities

Know…

This is only a part of the illustrated article ‘Dengue Fever’. Read the whole article on Dengue Fever by Asienreisender.

Keep yourself up-to-date

Check the list of recently published articles on a great variety of Southeast Asian themes. All of them are richly illustrated: Asienreisender

Malaria by Asienreisender

Posted in Health/Diseases, Latest of Asienreisender with tags , , , , , , , , , , , , , , , , , , , , , , on July 29, 2013 by Thim Kwai

Malaria is an infectious parasitic disease. It’s naturally transfered by a female mosquito of the kind anopheles from man to man. Another way of transfer can be by blood transfusion or other injections (with used syringes) with parasite – containing blood. Smallest amounts of blood already allow a transfer. Pregnant mothers can in certain cases transfer malaria to their child, but it’s not necessarily so.

A poster warning before mosquitoes. Seen at a hospital in Chumpon, south Thailand. Image by Asienreisender, 2012

The development of the parasite happens exclusively inside anopheles mosquitoes and human bodies. There are three different kinds of malaria. Meaningful for travellers in Southeast Asia is malaria tropica, the most dangerous one. The others are malaria tertiana (which was widespread also in Europe, up to middle- and northern Europe until the first half of the 20th century) and malaria quartana.

Famous malaria patients of the European past were Albrecht Duerer, Oliver Cromwell and Friedrich Schiller. Malaria was finally extinct from Europe not before the 1960s due to the ‘Global Malaria Eradiction Program’ (see below).

A famous Asian malaria victim was Mohandas Gandhi (1869 – 1948), who suffered a severe attack in Aga Khan Palace in Pune in 1942, where he was held as a political prisoner.

All these three kinds of malaria are human-specific, means they don’t infect animals (apart from very few exceptions at monkeys, some of them observed at macaques in Southeast Asia).

Anopheles mosquitoes are (together with aedes und culex mosquitoes) among the most widespread mosquito kinds. There are 360 different kinds of anopheles mosquitoes alone in the world, of whom 45 potentially carry malaria. Their habitats are not limited to the tropes and subtropes, but spread out until the borders of arctic regions.

Around 40% of the global human population lives in areas infested with malaria, of whom 300 – 500 million people are infected (according to the Robert Koch Institute, Berlin). More than 80% of them live in tropical Africa, 13.8% live in Asia.

In mountainous areas above 1.500m, near the equator from 2.500m on anopheles mosquitoes do not appear anymore. Malaria is pandemic in almost whole Southeast Asia. Indonesia and Burma / Myanmar have here by distance the most cases in percentage of the population. A growing resistance to antimalarials are a challenge in the Greater Mekong Sub-Region.

The exciter for malaria tropica is the parasite plasmodium falciparum, the most lethal one among the four plasmodium parasites. Estimated 1.8 million people died in 2004 worldwide, 1.2 million in 2010 due to malaria.

Let’s assume that a biting mosquito is sucking blood. When the bitten human is malaria infected, the mosquito sucks with the blood the exciters which transfer within 8 to 16 days inside the mosquito into another phase and next to it’s final stage. When it gets injected then into another humans blood circulation, reaching there the human liver, it’s again breeding and spreading out into the vascular system. The perpetuation of the circle is then completed.

Read here more on the feeding habits of mosquitoes.

Know…

This is only the first chapter of the illustrated article ‘Malaria in Southeast Asia’. Read the whole article on Malaria in Southeast Asia by Asienreisender.

The following chapters are:

Malaria Prevention by Asienreisender
Malaria Immunity Asienreisender
Malaria Diagnosis by Asienreisender
Malaria Pathogenesis by Asienreisender
Malaria Therapy by Asienreisender
The ‘Global Malaria Eradiction Program’ by Asienreisender

Keep yourself up-to-date

Check the list of recently published articles on a great variety of Southeast Asian themes. All of them are richly illustrated: Asienreisender

Mosquitoes in Southeast Asia

Posted in Animals, Latest of Asienreisender with tags , , , , , , , , , , , , , , , , , , , , , on July 27, 2013 by Thim Kwai

Health Concerns

Tourists and Travellers who come to Southeast Asia are usually very concerned about safety and health. It’s generally more safe here than in most other parts of the world and generally easy to remain healthy; the dangers are mostly overestimated or self-caused.

Nevertheless I want to point out one potential threat here.

More dangerous than all the scary animals like tigers, cobras, king cobras, crocodiles and so on are the mosquitoes (Spanish / Portuguese for ‘little fly’), or at least a few certain kinds of mosquitoes who transfer dangerous diseases. The verymost kinds of mosquitoes do not transfer diseases, although, in more seldom cases, they can cause various other infections when transmitting bacterias, viruses or other parasites into the human body.

Various kinds of mosquito – transmitted tropical diseases are malaria, dengue fever, chikungunya fever, yellow fever, West-Nile fever, Rift-Valley fever, encephalitis and more. Some mosquitoes transfer parasitarian worms who can live in the human vascular system. Even HIV/AIDS can still not be completely excluded from the list of diseases transmitted by the nasty insects, but it’s at least considered highly unprobable.

Apart from these health threats mosquitoes are simply annoying and can spoil enjoying time or cause sleepless nights.

Mosquito Habits

The oldest known mosquito remain discovered until now is some 79 million years old. It’s imbedded into a piece of amber.

Although generally very small animals, some of them reach a size of more than 15mm.

The number of different kinds of mosquitoes in total vary between 2,500 and 3,500 species, they appear worldwide except in the polar regions and in deserts. They breed at waterplaces of all kind. In the swamps of Siberia, Canada and the north of Europe they appear in the summer month in masses and are much bigger and their bites leave a much bigger impact on the skin than the ones in Southeast Asia. Therefore they are much less dangerous in the north than in the tropical regions of the globe. Particularly the anopheles (malaria) mosquito is a very small representative of his kind. When sitting on walls or the skin it’s body shows a peculiar angle of some 45 degree to where it sits on, what makes it distinctive from other mosquito types.

Mosquitoes do not feed from blood, but from nectar and fruit juices. Only the females suck additionally blood. They need the containing proteins for their eggs. A ‘blood meal’ of a female mosquito is sufficient for around 100 eggs, who are layed two to three days after it. In their lifespan, which lasts several weeks, a female mosquito can produce 1,000 or more eggs in her life. Though, there are also kinds of mosquitoes who don’t bite humans but exclusively animals, and a few others who don’t bite at all.

They lay their eggs one by one on the surface of calm, preferable clear water. The development from egg via larva and pupa to a flying mosquito takes about two weeks.

Their rostrums contain two canals. One is injecting a protein containing saliva for a first, external digesting or preparation of the blood, through the other canal the mosquito sucks it’s meal up. The injected protein leads to a small allergic reaction and the well-known itching swelling. If the bite hits directly a nerve, the bit can trigger a small pain. It’s, by the way, said that the bite of a female anopheles (malaria) mosquito is particularly itchy.

Everybody made already the experience, that some people attract mosquitoes more than others do. That has to do with the human smell, which attracts the animals. The smell of lactic acid and other substances on the skin and in sweat serves for their orientation. When they are already close to humans, they also orientate visually and on body temperature.

That explains an observation frequently done while hiking in the jungle. Jungle trekking is a sweat-driving activity. Soon many mosquitoes are attracted and buzz around one’s head.

Male mosquitoes are in average 20% smaller than females, and they have bushy tentacles. As already mentioned males are not able to bite.

Most active mosquitoes get at warm, calm days without direct sunlight. When it gets too windy, they can not navigate anymore. That’s why they have problems with ventilators. When it’s too cool (10 degree or less) they get numb and paralized. They particularly dislike air conditioners.

Mosquitoes can fly over distances of several kilometers. Their speed can be considerable; it’s sometimes remarkable how quick they can disappear when being hunted. They manage to fly closely along walls, tree stams etc. to get cover and their trajectory is often very twisting and unpredictable. If the wind is favourable mosquitoes can fly as high as a hundred meters.

Mosquitoes are generally most active in the evening around sunset, sometimes in the morning, but can additionally appear at all times at day and night. Malaria mosquitoes are night active, while the ones transferring dengue are day active.

Mosquito Control and Practical Prevention

Fighting mosquitoes has a long tradition. For example the drainage of swamps detracts the basic for mosquito reproduction. An oil-film on breeding-waters stifles the mosquito larvaes. But it’s damaging the ecosystem as well, as many other approaches do. The problem of chemical treatments is always that not only the targeted mosquitoes but a lot of other species are also affected, if not whole biotopes. In many Southeast Asian countries DDT is still in use, while it is abolished in western countries since years (Stockholm Convention) and well known for it’s desastrous side-effects.

Another problem of chemical treatments are the growing resistances. DDT, supposed to be a superior mean against malaria in the 1950s, lost more and more effeciency over the following years being used.

Gentechnical approaches try to modify mosquito genes so that they can not reproduce anymore. Another approach is to make the mosquitoes themselves disease resistant, so that they can not serve as a host and transfer diseases as malaria and dengue fever anymore.

Dragonflies are very effective, hunting and eating mosquitoes at all stages of their development (eggs, larvaes, pupaes and adults). A number of other animals, insects, amphibians and fish eat mosquitoes or their spawn.

In Thailand I have seen the application of pesticides (presumably DDT containing) in great scale by troops of communal workers who used massive sprayers all along the river banks of the Mekong River and the inner town of Chiang Khong. Considered that all the housings, kitchens and restaurants are mostly open, it’s a very brutal way of dealing with mosquitoes. Not to mention that the pesticides get into the drainage system and the river later. Besides I didn’t see a relief in the mosquito plague in the following days.

There are many methods to prevent and fight mosquitoes in all-day-life, but still many people don’t care for that. First it’s helpful to avoid standing waters like little pools, flowerpots, tyres and so on catching rain water whenever possible, or to set little fish (like guppies) in them who eat their larvaes. It’s good to keep kitchen and kitchen surroundings clean, particularly from rotting fruits or fruit remains.

Above all one needs is to carry always a repellent in the pocket. Repellents are available in many shops in most places for small money. If you see mosquitoes around or you get a bite already, it’s best to use it immediately. The beasts target mostly for the ankles. At nighttime it’s best to apply a repellent on all parts of uncovered skin.

The most repellents are based on DEET. DEET is a chemical which is in use against mosquitoes since 1946 (developed by the US army, used much in the American Vietnam War) and since 1965 sold in the civil sector. The repellents I find in Southeast Asia are often pretty weak, containing 7%, 11% or 13% DEET. In western countries repellents contain 30%, sometimes up to 50%.

It’s yet not completely clear why actually DEET repels mosquitoes, but it has to do with the smell. Either the part of the human smell which attracts the mosquitoes is blocked in their reception, or the smell of the DEET itself causes the insects to stay away.

Side effects of DEET are possibly allergic reaction, insomnia, erratic mood swings and receptional irritations. It’s recommended not to be used by pregnant women and babies (below two years old).

One does not necessarily need a mosquito net. At warm nights a mosquito net queues the air and causes stifling air. On the other hand a mosquito net prevents from more than mosquitos – namely other animals who may creep around and might find the way into ones bed.

Know…

This is only a part of the illustrated article ‘Mosquitoes in Southeast Asia’. Read the whole article on Mosquitoes in Southeast Asia by Asienreisender.

Keep yourself up-to-date

Check the list of recently published articles on a great variety of Southeast Asian themes. All of them are richly illustrated: Asienreisender