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Entomology

A zoological garden in the bed

Hundreds of thousands of bed bugs spread through mattresses and bring about asthma and rhinitis crises

CEME / UNIFESPUndesired inhabitants: the species Tyrophagus putrescentiae consumes food leftovers CEME / UNIFESP

The reason for these differences in concentration is unknown. The main suspect is that lower part of the mattresses concentrate more bugs because it is protected from light and less manipulated with each change of sheets. “Perhaps we’ll know this reason shortly when the results of Scottish studies come out that are attempting to reproduce in laboratory mattresses the environment in which the bugs live”, comments Prado.

Probably the cause of this preference for the bed is the same as that which allows the mites to proliferate freely on the sofa: food in abundance. The sofa accumulates the remains of food and human skin, whilst the bed, where the person spends around 8 hours per day, is a cellar of dead skin: each week a human being loses around 5 grams of skin that accumulates around the pillow and the mattress.

For this reason the best thing is to protect the mattress with cloth cover covered with a material that blocks the passage of mites. Without this protection, four months are sufficient for a brand new mattress to become infested, since each female produces around 200 offspring during its one hundred days of life. In the remainder of the house, the most efficient manner of eliminating these animals is cleaning with a vacuum cleaner – keeping the environment ventilated and free of excessive humidity also helps.

Allergies
Although they are related to spiders and scorpions, the class of arachnids, animals with eight legs and a head and thorax fixed into one single organ, the cephalothorax, the house dust mites are not just simply harmful to human beings – they have besides an important biological role in the control of insects and in the fertilization of the soil. The allergic reactions that they bring about are set off by proteins found in their skeleton and their feces. Discovered during the decade of the 1980’s by Thomas Platts Mills, from the University of Virginia, in the United States, one of these proteins named Der p1, acts upon cells of the human organism’s defense system and brings about an inflammation of the nostrils. For this reason it is used in very low concentrations in vaccines against bug allergy, indicated for those who do not improve with the treatment based on anti-allergic compounds not with the control of mites in the environment.

Students of these animals since their post graduation course, when they met and got married, researchers Oliveira and Raquel today maintain their own breeding stock of bugs. In their own laboratory the couple cultivate, in special plastic bottles stored in incubators, four species: Dermatophagoides pteronyssinus, Dermatophagoides farinae, Tyrophagus putrescentiae and Suidasia pontificia. They intend to use protein extracts of these species in the production of a vaccine that is more efficient than the national ones already in existence.

In a study published during 2004 in the magazine Revista Brasileira de Alergia e Imunopatologia, researchers from the states of Sao Paulo, Parana, Rio de Janeiro and Minas Gerais tested eight anti-allergic vaccines produced starting from extracts of the mite D. pteronyssinus – seven of them were manufactured in the country. Not one of the national vaccines showed concentrations of Der p1 or Der p2 comparable to that of the imported extract. This is a sign that one should not produce the minimum immune response indicated by the World Health Organization.

How to get rid of bed bugs
Brought into residences probably by birds, the house dust mites adapt themselves well to the domestic environment, where they find favorable conditions for reproduction and development. It is not possible to eliminate all of them, but simple measures can help to reduce – and considerably – the number of these undesirable animals in the house.

1- Leave the mattress exposed to the sun for half an hour every 20 days and, if possible, change it after five years of use.
2- Protect pillows and the mattress with cotton covers or micro fibers covered with latex or vinyl and change the bed linen at least once per week.
3- Carry out daily cleaning of the house with a vacuum cleaner and damp clothes and prefer ceramic floorings to rugs and carpets.
4- Maintain the environment well ventilated for at least half an hour per day and avoid the use of air humidifiers.
5- Avoid the consumption of food and the presence of domestic animals, plants or furry animals in the front room or bedroom.
6- Store clothes that will remain unused for a long period of time in plastic bags and prefer clothes of natural fibers to furs or wool.

They are everywhere: on land, in the air and even in water. But it is in the home that the house dust mite really becomes bothersome. More precisely in bed. With only a few months of use, mattresses are the home to hundreds of thousands of these animals, kin to spiders and ticks, enough to cause allergies and to set off rhinitis, asthma or conjunctivitis crises. In general, smaller than the point of a needle, the house dust mites find in the bedroom and in other parts of the house a true paradise. There the temperature is stable, food is abundant and the humidity of the air oscillates little. Under such favorable conditions, in a short time they infest curtains, carpets, sofas and, to the despair of allergic people, the bed, as was verified by a team led by the entomologist Angelo Pires do Prado, from the State University of Campinas (Unicamp).

With a vacuum cleaner in their hands,  Prado, the biologist Raquel Binotti and the medical allergy specialist Celso Henrique Oliveira set off on a scientific cleaning in front rooms, bedrooms and pantries of 58 residences in the city of Campinas, 100 kilometers from São  Paulo. Their goal was to identify which of the 20,000 species of known mites were most common therein. Motives were not lacking: it is estimated that the mites found in household dust brings about 90% of respiratory allergies – rhinitis, pharyngitis and asthma – that affect from 18 million to 30 million Brazilians. “Although this sample was not representative of the whole city, it gave us a good idea of the situation”, says Oliveira. And the situation is nothing good.

Searching through the collected dust, the Unicamp team verified that the residents housed a zoological garden of mites. Biologist Raquel identified 18 different species, which had spread themselves in varying quantities through the different household furnishings. The mites of the Dermatophagoides pteronyssinus and Dermatophagoides farinae species – that feed on fungi, bacteria and keratin, the protein that gives resistance to skin – were found in 88% of the dust samples collected from mattresses. Around 40% of mattresses had been infested by the predatory species Blomia tropicalis, which uses its pincers advantageously to suck out hemolymph – the fluid that at times is made of blood – of other mites, leaving them as dry as a raisin.

In the bedroom and living room – The mites are in lesser quantities in curtains and in food pantries. There was an average of 320 mites for every gram of room curtain dust, 350 in the bedroom and 450 in the food pantries, the preferred location of mites such as the Tyrophagus putrescentiae, shown on the following page, photographed by Edna Haapalainen’s team from the Federal University of Sao Paulo (UNIFESP).

On the other hand the carpets housed around 570 mites per gram of dust in the front room and 750 in the bedrooms, concentrations sufficient to cause allergy. “Around one hundred mites per gram of dust leave the immunological system sensitized, or that is to say, bring about an allergy”, advised professor Oliveira. “From 500 on , people begin to show allergic crises.” It is easy to understand why at times a person begins to sneeze only when touching the carpets or curtains in a house.

Detailed out in a series of scientific papers published from 2000 until the present time, this study’s data indicates that the preferred places for the mites are also ours: the sofa and the bed. Each gram of sofa dust contains around 900 mites. But the problem lies really in the bed. On the surface of the mattress in contact with the body this concentration went up to 950, while close to the bottom of the bed this index reached 3,900 – in an extreme case there were 40,000 mites in each gram of dust. Possibly this is the reason why anyone who suffers from rhinitis feels their nose blocked and anyone has asthma breathes with great difficulty as soon as they put their head on the pillow.

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