The Zimbabwean Gardener Issue 12 Autumn 2015 High res | Page 50

Pests in the home

What are dust mites?
BY ANGUS MEIKLE

The house dust mite is a cosmopolitan pyroglyphidea,
known by the Latin name Dermatophagoides
pteronyssinus, but you don’t need to know that. What
you do need to know is that dust mites are the biggest
cause of allergens in the household.
So what are dust mites? The common
house dust mite is a microscopic
organism, invisible to the naked eye,
and thrives in the warm, humid indoor
environment provided by most homes.

Habitat and food

House dust mites consume minute
particles of organic matter. The organic
matter, commonly called ‘dander’, is
made up of dead skin cells and scales
shed by humans and their pets. The
average person sloughs off about 10
grams of dead skin in a week. Cats and
dogs create far more dander. That gives
the mites a lot to eat.
Dander is most often concentrated
in lounging areas, mattresses,
frequently used furniture, and
associated carpeted areas that end
up harbouring large numbers of these
microscopic mites; numbers like 100 –
500 mites/gram of dust. Mites survive
and reproduce particularly well in
mattresses and pillows, which take up
moisture from body contact.
Nearly 100,000 mites can live in just
under one square metre of carpet, and
a typical mattress may have anywhere
from 100,000 to 10 million mites inside
it: 10 percent of the weight of a two
year-old pillow may be composed of
mites and their droppings.

Cause of allergies

Dust mites are generally harmless
to most people. They don’t carry
diseases, but they can cause allergic
reactions in asthmatics and others
who are allergic to their faeces. This

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is because the mites’ gut contains
potent digestive enzymes that are
then excreted and are the major
inducers of allergic reactions. You
should be aware that in the average
mites’ 10 week life span, it will
produce approximately 2,000 faecal
particles and an even larger number
of partially-digested, enzyme-covered
dust particles.

How to recognise the
symptoms of allergies to
dust mites

When the proteins in dust mite
faeces are inhaled or touched by the
skin, mainly those who suffer from
allergies, they produce antibodies
in humans. The antibodies result
in the release of histamines, which
cause nasal congestion, swelling and
irritation of the upper respiratory
passage. The individual may
experience all or just some of the
following symptoms:
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Hay fever
Watering eyes, runny or itchy
nose and sneezing
Asthma/ difficulty in breathing
Infantile eczema
Facial pressure and pain
Frequent awakening
Swollen, blue-colored skin under
your eyes
In a child, frequent upward
rubbing of the nose

Eradication of mites

House dust mites reproduce quickly
enough that their effect on human
health can be significant. Since dust

mites depend on moisture to survive,
they are most often found in bedding
such as pillows and duvets. Existing
mites can be eradicated by regularly
cleaning and washing items that
harbour them and exposing them to
temperatures below 0 °C. An example
of this would be regularly washing
sheets and duvets and placing pillows
in the deep freeze for a couple of
hours.
Carpets should be regularly vacuumed
to reduce the amount of dander, or
food, available to the mites. In addition
to this, mattresses, carpets and the soft
furnishings should be professionally
cleaned at regular intervals, with
detergents specifically formulated to
eliminate the dust mites.

How often should you
get your furnishings
professionally cleaned?

This varies considerably from home
to home, depending on the size
of the home, the amount of traffic
through the home, and if there are
allergy sufferers, but here are some
guidelines from some of the world’s
leading carpet and upholstery
cleaners:
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Singles or couples every 12
months
Singles or couples with two or
more pets every 6 months
Couples with a baby and one pet
every 3 months
Families with two kids and two or
more pets every 2 months