Biting Insects

Biting insects feed on humans and animals by piercing skin to tap into a blood vessel. They actively seek a food source by using their various senses such as heat, smell and sight to find a suitable host. Some insects make a quick feed and leave while others prefer to find hidden areas of the body to stay till they are gorged and can only drop off when they are swollen with blood.

Whichever way they find a host and feed, however, biting insects can cause itching, inflammation, painful welts and in addition can transmit many serious diseases that affect millions of people across the world.

Why Do Insect Bites Itch?

Bites itch because your body reacts to the saliva injected by the insect while it is biting you.

Biting insects have a complex mouth structure that varies between species. It can include a needle-like part that pierces the skin and other parts that are serrated and saw through the flesh to find a blood vessel.

They also have a food canal to suck up blood and a canal that injects saliva containing anticoagulant and anaesthetic. The anticoagulant keeps the blood liquid to keep it flowing and the anaesthetic stops you from feeling the bite so you don’t disturb the feeding insect.

The body’s immune system recognises the foreign material injected into the bite and produces histamine as a defence mechanism. This causes localised inflammation and itching.

The Mouth Parts Of A Female Mosquito

Legend:
a — antennae
c — compound eye
lb — labium
lr — labrum
md — mandibles
mx — maxillae
hp — hypopharynx

Source: Wikimedia commons: Xavier Vázquez.

Reactions To Bites

People’s reactions to bites can vary greatly depending on the sensitivity of their immune system and whether they have been bitten before.

It can take hours or days for itching or redness to occur after being bitten, making it difficult to tell what bit you. In this case you will need other identifying factors to tell the source of the bite.

Mosquitoes

There are over 3,500 known species of mosquito worldwide and a large number of these transmit diseases that affect more than 700 million people each year, causing at least two million deaths.

Female v. Male Mosquitoes

Only the female mosquitoes need a blood meal, having the specialised mouth parts that can penetrate animal skin, though they can also feed on sweet plant juices.

Male mosquito mouth parts are adapted only to feed on nectar and plant juices and cannot penetrate skin. It is the females that transmit diseases to humans and animals.

The female mosquito finds a host by sensing carbon dioxide in breath, perspiration and body odours, and tends to feed in the evening and night time, though there are notable exceptions.

Mosquito Bites

Mosquito bites are characterised by itchy red bumps on the skin, with varying degrees of swelling, depending on the person’s immune response.

How to prevent mosquito bites:

• Cover skin: wear long sleeves, trousers, footwear and hats.
• Avoid bright colours: bright colours attract mosquitoes.
• Avoid strong scents: strong scents such as perfumes and deodorants attract mosquitoes; Use insect repellents: use gels and sprays containing DEET or other repellent for applying to exposed skin; lighting insect repellent coils or citronella candles can help keep mosquitoes away from an area;
• Avoid areas with still water: mosquitoes breed in slow moving or still/stagnant water, so removing these from around the home — even small containers — will reduce mosquito numbers by preventing their breeding.
• Avoid vegetation: Avoid areas with dense vegetation where mosquitoes congregate.
• Use mosquito nets for sleeping: when in remote or undeveloped areas these are a proven way to prevent bites while sleeping and they can also be impregnated with insecticide to kill the mosquitoes as they land on the net.

How to treat mosquito bites

Mosquito bites can be treated with some simple measures:

1. Clean the bite area with soap and water: this is the most important treatment for a mosquito bite.
2. Use a cold compress: swelling can be reduced immediately after a bite by covering it with a cold compress such as ice in a cloth (but do not hold ice directly on the skin).
3. Take anti-histamines: itchiness and swelling can be relieved with antihistamine creams. Oral anti-histamine can also help if you have multiple bites.
4. Do not scratch: avoid scratching as this will increase the itching and could lead to the bite becoming infected.

Mosquito Borne Diseases

One of the main concerns around mosquito bites, is their ability to spread the following diseases:

• Malaria
• Dengue
• Chikunguya
• Yellow Fever
• Japanese encephalitis
• Lymphatic filariasis/ elephantiasis

Find more information on insect-borne diseases.

Bed Bugs

You are most likely to pick up bed bugs from a hotel, where they can crawl into luggage and clothing. They can also catch a ride in bedding and furniture and spread through buildings by crawling through holes in walls, such as for electrical wiring, or along pipe work.

Bed Bug Bites

Bed bugs tend to feed at night but will search for a host at any time if they are starved. They find a host through an array of sensors that can detect warmth, carbon dioxide and body odours.

Bed bugs feed for only 5-10 minutes until they become engorged with blood, if not disturbed and may spend less than 20 minutes on a host. After feeding, they return to their shelter.

How to spot bed bug bites

• Small, flat, raised bumps on skin.
• Several bites tend to appear in a line or row along an exposed area of the skin. This is usually the arm or leg.
• Several groups of bed bug bites around the body could indicate multiple bed bugs feeding.

How to treat bed bug bites

Bed bugs do not carry diseases so the only treatment needed is to stop itching and rarely for inflammation. If the bites develop into very itchy bumps, general products available from a pharmacy to stop itching are suitable. For inflammation it is best to see a doctor who can prescribe the most suitable treatment. Many people do not react to bed bug bites so do not need any treatment.

How to prevent bed bug bites

If you are worried about bringing back bed bugs from your travels, then follow these steps to prevent bed bugs from entering your home and feeding upon you at night:

• Leave luggage in your garage or bathroom. Bed bugs don’t like tiles or concrete, and it is easier to spot them on a hard surface compared to carpet.
• If you are really worried take off your clothes in the garage or bathroom and place them straight into the wash.
• Wash and dry clothes on the highest possible temperatures. Bed bugs don’t like heat.
• Vacuum your home, and your furniture thoroughly. This will reduce the size of your bed bug problem by eliminating both the adults and the eggs.

Worried about bed bugs in your hotel or dorm? Follow these steps to prevent them from biting your guests:

• Train staff on how to identify bed bugs.
• Ensure thorough checking for bed bugs is part of your room cleaning process.

Flies

Midges and gnats

The term midge and gnat is a very general term for a wide range of flies, including the Sand fly and Black fly. Most are aquatic during the larval stage.

Biting Flies

It is important to note that not all flies bite, some go about their day to day lives without the need to feast on humans. However there are a few fly species which rely on our blood to survive, these are:

• Sandfly
• Blackfly
• Horse fly
• Highland midge

How to treat fly bites

1. Wash the bite with soap and warm water.
2. Use and apply either antiseptic cream or spray to the area after washing.
3. Apply ice to the bite for 15 minutes, several times a day.
4. Avoid scratching so you don’t break the skin and cause and infection.

The bites of some flies such as horse flies can bleed. In this case a simple plaster applied after the bite has been washed would help. If the bleeding doesn’t stop on its own, you should see a doctor.

How to prevent fly bites

• Avoid outdoor activities during the day when flies are more prevalent.
• Cover up - wear long sleeves when outside.
• Use an insect repellent before going outside.
• Empty out bins, and clean dirty cups and plates regularly - flies are attracted to decaying matter.
• Install window and door screens to keep flies out.

Head Louse

The head louse, or nit, is a single species of small wingless insect, Pediculus humanus capitis, which feeds only on human blood and has its complete life cycle on the human scalp.

Lice cannot jump or fly but can crawl from person to person in close contact. Head lice commonly affect children, but anyone with hair can catch them.

Head lice are considered harmless as they are not known to carry any disease and are regarded more as a cosmetic problem. They do cause itching of the scalp and secondary infections can result from scratching.

• Adults are up to 3mm long and grey in colour until they have fed on blood, after which they become reddish.
• The females lay 3-4 eggs per day near the base of a hair shaft, gluing the eggs to the hair. The eggs are oval and less than 1mm in length. They are transparent until hatched, after which they appear white.
• The eggs hatch in 6-9 days and the shell stays attached to the hair.
• The six legs of the louse each have a claw on the end to grab onto hair.

Detecting head lice

They are commonly found in the hair behind the ears and at the nape of the neck.

The remains of the white egg cases can also be seen attached to hairs.

The lice can be combed out of the hair onto a piece of white paper using a special nit comb that has very closely-spaced teeth to trap the lice.

Treating head lice

Repeated use of a nit comb can remove the lice, but larger infestation may only be effectively removed with medicated shampoos or lotions available from pharmacies. These contain insecticide so should be used carefully, especially on children.

Crab Or Pubic Louse

The crab louse (Pthirus pubis) feeds exclusively on blood and is only found on humans. It is distinct from the other two types of human louse in appearance, having a rounder and shorter body. It is usually found in pubic hair or other coarse hair such as eye lashes, beards and moustaches. It is mainly spread by close contact, sexual activity and shared use of towels, clothing and beds.

Chagas disease

It is classified by WHO as a neglected tropical disease, with 8 million people infected worldwide and an estimated 10,000 deaths caused by complications from the disease.

There are 150 species of the bug and more than 100 species of mammal carry the parasite, so it is considered impossible to completely eradicate the disease.

Originally a rural disease, socioeconomic changes, deforestation, rural migration and urbanisation have resulted in Chagas disease spreading more widely, according to WHO, and it is increasingly being detected in countries where it is non-endemic.

Nymphs And Adult Of The Triatomine Bug

Nymphs and adult of the triatomine bug Rhodnius prolixus
Source: Wikimedia Commons: Thierry Heger
https://commons.wikimedia.org/wiki/File:Rp-nymphs-adult.JPG

Bites

Triatomine bugs bite exposed areas such as the face, but it is not the bite that transmits the disease. After feeding, the bug defecates, which carries the protozoan onto the skin.

When the person inadvertently wipes their skin this can carry the protozoan into the bite, other broken skin, or the eyes and mouth.

Both the male and female adults and nymphs are blood sucking and carry the parasite in their faeces.

Control

The bugs live in cracks and crevices of poorly constructed homes, where they hide during daylight and emerge at night to feed. Fresh faeces contains live parasites, so infection can also occur after touching a place where they have defecated.

Spraying house interiors with insecticide, plastering walls to fill in hiding places, bed nets and hand hygiene are all effective means of control.

Arachnids

Arachnids are a separate Class from insects in the classification of the animal kingdom, distinguishable by their eight legs and two body sections: the abdomen and cepahlothorax.

The group is easily distinguished from insects, which have six legs, three body sections (head, thorax and abdomen) and one pair of antennae. They are both in the Arthropod phylum, however, which consists of animals having an exoskeleton.

The arachnids have many members that can be pests of humans: the ticks, mites, scorpions and spiders.

Mites

Mites are are closely related to ticks. There are nearly 50,000 known species, mostly microscopic, occupying a very diverse range of habitats. Many are pests of plants and animals such as bees and birds, but very few affect humans.

The house dust mite does not feed directly on humans but on shed skin particles and pet dander. The shed skins and faeces can cause allergic reactions in some people, similar to hay fever, asthma and eczema.

Scabies

The scabies mite, Sarcoptes scabiei, is a parasitic mite about 0.5mm long that burrows into the outer layer of skin to feed on skin cells. It lays 10-25 eggs that hatch and emerge from the skin after 3-4 days to travel to another part of the body and repeat the cycle.

The infection results in itching caused by the body’s reaction to secretions from the mites. This can take up to eight weeks to appear.

Scabies is highly contagious. People living in the same household are likely to become infected easily.

The most common treatments for scabies are the pesticides permethrin, malathion and lindane. However, these can have side effects and should be used with advice from a medical professional.

Rickettsialpox

Rickettsialpox is caused by the bacteria Rickettsia akari, which can be carried by house-mouse mites. They will seek new hosts, including humans, when the mice die off naturally or as a result of pest control. Infection is transmitted by the bite of the mite.

Rickettsialpox is regarded as a mild disease that takes 2-3 weeks to recover from. The first symptom is a bump around the bite that appears about a week after the bite, which turns into black crusty scab.