Lice infestation: Description
A lice infestation is usually very annoying for those affected, but generally less dangerous. For a better understanding of the disease, the biology of lice is first explained in more detail here.
What are lice?
Lice are parasitic insects and as such are always dependent on a host to feed on. Parasites can either live in or on their host – if the latter is the case, the parasites are referred to as ectoparasites. In addition to lice, this group also includes fleas, ticks and leeches, for example. Lice live permanently on their host and generally do not leave it, except in the case of a direct transfer to another host (transmission).
Colonization with parasites that do not reproduce in their host is correctly referred to as infestation, although the term “infection” is often used in connection with lice infestations.
The different species of animal lice each prefer certain hosts and are adapted to them. For example, there are dog lice, seal lice, pig lice and human lice. Transmission of lice between different animal species or between humans and animals is very rare. Therefore, only human lice come into question for a lice infestation in humans (called pediculosis). They come from the Pediculidae group.
Within the Pediculidae, there are three representatives that can be a problem for humans. The best known and most common is the head louse (Pediculus humanus capitis). There are also the felt lice (Pthirus pubis), which are much rarer in this country, and the clothes lice (Pediculus humanus humanus). It has not yet been clarified whether the clothes louse and the head louse are separate species or merely two different subspecies of the human louse. However, this is irrelevant for the diagnosis and treatment of lice infestations.
Lifestyle and reproduction of human lice
Like all so-called “real” animal lice, human lice feed on the blood of their host. To do this, they are equipped with special mouthparts that enable them to penetrate the host’s skin and suck its blood. They also release some saliva into the bite canal, which ensures that the blood does not clot (like mosquitoes). It triggers the typical symptoms of a lice infestation. A louse takes a blood meal several times a day and can only survive for a few days without a host.
The eggs of human lice are coated in a solid chitinous shell and are attached by the lice to the hair of the host or textile fibers of clothing – insoluble in water, which is why the eggs cannot simply be washed out in the event of a lice infestation. The term “nits” sometimes refers to the eggs, but sometimes only to the chitin shells left behind after the young have hatched.
The newly hatched lice larvae, also known as nymphs, already resemble adult animals on the outside, but are much smaller and can hardly be seen with the naked eye. They go through various stages of development until they are sexually mature after about ten days.
Who is affected by a lice infestation?
In principle, anyone can be infested with lice. However, hygienic conditions play a major role in the spread of crabs and clothes lice in particular, meaning that they are mainly found in poorer countries and in crisis areas. In Western Europe, clothes lice are only rarely the cause of lice infestations. The situation is different with head lice, where hygiene has little influence on infection. This is why they are still widespread in our climes, although it is mainly children who are infested.
Lice infestation: symptoms
Apart from the unpleasant symptoms and the psychological stress that often accompanies them, lice infestations do not in themselves pose any health risks. However, clothes lice are possible carriers of various bacteria, which can sometimes lead to severe fevers.
Lice infestation: causes and risk factors
As human lice are virtually non-existent in animals, infection occurs almost exclusively from person to person or, in the case of clothes lice, via infested items of clothing. Direct physical contact is necessary for transmission, as the lice do not usually leave the host body.
The longer the physical contact lasts, the greater the risk of transmission. Lice need a certain amount of time to crawl from one host to another. Such transmission does not normally occur through brief contact.
Lice infestation: examination and diagnosis
A lice infestation is usually detected by inspection, i.e. by recognizing the lice or eggs with the naked eye. To do this, hair or items of clothing must be searched thoroughly. Tools such as a magnifying glass or a lice comb make the search easier.
Conversely, nits left behind after hatching are not sufficient proof of an active lice infestation. This is because it is possible that all the lice have already been killed with a chemical or physical treatment, but the egg cases are still in the hair because they have not been removed. However, if empty eggs are found in the hair but no treatment has been carried out beforehand, it can be assumed that there is a lice infestation – the parasites do not normally disappear on their own.
Symptoms such as itching and reddish patches of skin are not enough to diagnose a lice infestation. They can also have other causes, such as a flea infestation.
Lice infestation: treatment
There are basically three different therapeutic approaches available to treat a lice infestation:
- Mechanical removal of the lice using a special comb
- Treatment with chemical substances (these attack the lice’s nervous system and thus kill them)
- Treatment with physically effective substances (these close the insects’ breathing holes so that they suffocate)
In order to eliminate the lice infestation safely, the treatment must be carried out consistently and correctly according to the instructions. For example, it is important to repeat the drug treatment after about ten days, otherwise not all lice will be killed. You can find out more about the respective treatment in the sections on the different types of lice.
Head lice
Even in Germany, many children suffer from head lice at least once in their lives. You can find out everything you need to know about these widespread parasites and their treatment in the text Head lice.
Crabs
Pubic lice mainly infest the pubic hair, but in rare cases they can also occur on other parts of the body. You can read more about this and the correct treatment in the text Felt lice.
Clothes lice
An infestation with clothes lice (pediculosis corporis) only occurs under very poor hygienic conditions and is an absolute rarity in Western Europe. Occasionally, homeless people suffer from it if they wear their clothes for long periods of time and are unable to wash them.
Clothes lice are about 3 to 4 millimeters in size. They appear whitish to yellowish, sometimes slightly brownish. The white eggs of the parasites have a drop-like shape and are barely visible to the naked eye.
To feed, clothes lice move to the surface of the host’s body several times a day, where they pierce the skin and suck blood. The insects then return to their clothing. Among human lice, the clothes louse has the highest endurance capacity when there is a lack of food. They can survive up to four days without food at a temperature of around 23 degrees.
However, clothes lice are relatively sensitive to changes in temperature. Their optimum temperature is between 27 and 30 degrees. If the thermometer falls below 20 degrees, the development of the clothes lice comes to a complete standstill. Excessive heat is also a problem for the parasites. If the host’s body temperature rises (e.g. during a fever), they migrate to the outside of the clothing. Above temperatures of 47 degrees, both the clothes lice and their eggs are completely killed.
Reproduction of clothes lice
How are clothes lice transmitted?
Clothes lice can be transmitted from person to person through close and prolonged contact. However, it usually occurs through the exchange of infested, unwashed clothing. Sharing bed linen and towels can also lead to lice infestation.
What diseases can clothes lice transmit?
Numerous types of bacteria live in clothes lice. Some of them are dangerous pathogens for humans. The infectious diseases transmitted by clothes lice are
- Spotted fever, also known as lice spotted fever or war typhus. It causes high fever, severe aching limbs and the eponymous spots on the skin.
- Lice relapsing fever (relapsing fever). It causes several episodes of fever, between which there may be several symptom-free days.
- Volhynian fever, also known as five-day fever or trench fever. This causes sudden headaches, fever and sometimes even meningitis.
These infections can usually be well controlled with antibiotics. However, if left untreated, they can be severe and, in the worst case, even fatal.
How do you fight clothes lice?
At temperatures above 60 degrees, just one hour is enough to kill the lice. If the laundry is delicate and cannot be washed at 60 degrees, it should be disinfected instead.
The parasites can also be killed by a lack of food or cold. For example, contaminated textiles can be sealed in a plastic bag for at least four weeks or placed in a freezer for 24 hours.
Ointments and creams are available from pharmacies to treat the sometimes severe itching caused by clothes lice.
In the event of an infestation with clothes lice, a doctor should always be consulted and the relevant health authority should also be notified. Under certain circumstances, affected accommodation may also have to be cleaned by a state-approved pest control company, but only in the case of a very severe lice infestation.
Lice infestation: course of the disease and prognosis
As long as a lice infestation is not specially treated, the parasites can multiply undisturbed. Head lice and crabs cannot be deterred by simple washing or normal care products. Only clothes lice can be treated by washing clothes.
