Human louse-transmitted infectious diseases

What diseases are lice carriers of? What does head lice carry? What does paid lice carry?

Several of the infectious diseases associated with human lice are life-threatening, including epidemic typhus, relapsing fever, and trench fever, which are caused by Rickettsia prowazekii, Borrelia recurrentis, and Bartonella quintana, respectively. Although these diseases have been known for several centuries, they remain a major public health concern in populations living in poor-hygiene conditions because of war, social disruption, severe poverty, or gaps in public health management. Poor-hygiene conditions favour a higher prevalence of body lice, which are the main vectors for these diseases. Trench fever has been reported in both developing and developed countries in populations living in poor conditions, such as homeless individuals. In contrast, outbreaks of epidemic typhus and epidemic relapsing fever have occurred in jails and refugee camps in developing countries. However, reports of a significantly high seroprevalence for epidemic typhus and epidemic relapsing fever in the homeless populations of developed countries suggest that these populations remain at high risk for outbreaks of these diseases. Additionally, experimental laboratory studies have demonstrated that the body louse can transmit other emerging or re-emerging pathogens, such as Acinetobacter baumannii and Yersinia pestis. Therefore, a strict survey of louse-borne diseases and the implementation of efficient delousing strategies in these populations should be public health priorities.

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Article published online: 23 January 2012

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Entomology Today

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Why do Body Lice Spread Disease, While Head Lice do not?

The human head louse, left, and body louse, right, are the same species, but differ in their ability to transmit disease to their host.

University of Illinois entomology professor Barry Pittendrigh and his colleagues compared the sequences of all protein-coding genes in head and body lice and determined that the two belonged to the same species, despite the fact that body lice are bigger than head lice, cling to clothing instead of hair, and can transmit disease.

Why then do body lice spread diseases such as trench fever or typhus, while head lice do not? A new study published in the journal Insect Molecular Biology seeks to answer this question.

In the new study, Pittendrigh worked with John M. Clark, a professor of environmental toxicology and chemistry at the University of Massachusetts. Clark’s group infected head and body lice with Bartonella quintana, the bacterium that causes trench fever. Pittendrigh’s laboratory then looked at gene expression in each to see how the insects responded to the infection.

“Our experiments suggest that the head louse immune system is fairly effective in fighting off the bacteria that cause trench fever,” Pittendrigh said. “However, the body lice don’t seem to have as good an immune response.”

The researchers discovered that several immune genes were regulated differently in head and body lice after infection with the bacteria, and the infection progressed further in body lice over time.

“By eight days post-infection, head lice had killed or contained the invading B. quintana, whereas the bacteria were still proliferating and spreading in body lice,” the researchers reported.

The team cannot yet say why head and body louse immune responses differ from one another, but Pittendrigh hypothesizes that the body louse has a reason to be more tolerant of bacterial infection.

“Head and body lice have beneficial bacteria living inside them,” he said. “These bacteria make vitamins that the lice need to grow and survive. Body lice tend to grow larger than head lice. It may be that a suppressed immune system allows body lice to grow more of the bacteria that make the vitamins they need, and they grow larger.”

The body louse’s dampened immune response would allow other invading bacteria, such as those that cause disease in humans, to also survive in its gut, he said.

“So body lice may grow bigger, but they also are more likely to get sick with the trench fever bacteria and pass the disease to humans,” Pittendrigh said.

The study team also includes researchers from Purdue University, Seoul National University, the University of California at San Francisco, the University of Massachusetts and the University of Illinois department of animal biology.

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How to Disinfect a Vehicle of Head Lice

The Mayo Clinic notes that it’s rare to get infested with head lice in any other way than direct head-to-head contact 2. Head lice can’t live very long without a blood meal from a human host–only around two days. The louse’s eggs (nits) die when removed from a temperature that’s similar to that of the human head in about a week. But it’s still possible to become infested–or reinfested–with head lice if you come into contact with contaminated belongings and environments where live lice can linger. Disinfecting a vehicle of head lice errs on the side of safety.

Removing Head Lice from Cars

Remove all personal belongings from the vehicle that might have become infested with head lice, such as clothing, scarves, caps, brushes, and combs. Launderable items should be machine-washed in soapy water at at least 130 degrees F and dried on high heat, notes the Centers for Disease Control. Anything that cannot be washed and dried (such as stuffed animals and pillows) may be stored in plastic bins for up to two weeks. Soak items in hot water of at least 130 degrees F for between five and 10 minutes.

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Vacuum the vehicle well using a hand-held attachment, and pay close attention to the area where the lice-infested person sat. Otherwise, the CDC notes there’s no need to spend exorbitant amounts of money on cleaning products or services to avoid reinfestation.

Alternately, simply don’t enter the vehicle for at least two days, at which point live lice will have expired.

Handle clothing, bedding and other soft items in the home in a similar manner as described in Step 1. The CDC advises vacuuming if a person infested with head lice has had contact with your home environment.


Don’t use fogs or spray fumigants to kill head lice in any environment, warns the CDC. These can cause serious side effects when inhaled or absorbed through the skin.

The Mayo Clinic notes that it’s rare to get infested with head lice in any other way than direct head-to-head contact. Launderable items should be machine-washed in soapy water at at least 130 degrees F and dried on high heat, notes the Centers for Disease Control.

The Latest on Lice

Like many other parents, I’ve paid my dues when it comes to head lice. It was a while ago, back in day care, and there was a dress-up box with hats and crowns and helmets that was probably the smoking gun. We all had to do the whole routine, applying insecticide rinses to our children’s heads and washing sheets and pillow cases in hot water, and becoming somewhat fanatical about not sharing hats.

Meanwhile, my parents, who had grown up in New York tenements, were vaguely horrified that their affluent privileged grandchild was acknowledged to have what they thought of as a mark of disgrace, an infestation that went with poverty and dirt.

And yes, eventually I became convinced that my own head was itching, and bought my own bottle of rinse, though I suspect I was by that point treating phantom lice. Since then, I have checked many heads in the exam room, and I have seen kids with lice, kids with nits, and kids with nothing much going on in the lice department — and I have learned to suppress the phantom lice response; I wear gloves and I wash my hands.

One aspect of the confusion around head lice is that we may think of them as “infectious” because they are spread from person to person — but they do not actually carry infections. They’re just bugs, and technically, we call head lice an infestation rather than an infection, but that doesn’t necessarily make anyone feel any better. (Body lice are different — they can indeed spread infections, most famously typhus.)

So when it comes to head lice, the pediatric role in recent years has largely been to reassure, to beg for calm, and to try to get kids back to school as quickly as possible.

The American Academy of Pediatrics put out its latest clinical report on head lice in 2015, a joint project of the group that focuses on school health and the committee on infectious diseases. The report reiterated longtime pediatric positions, emphasizing the importance of careful diagnosis, by trained observers, and arguing first and foremost that children should not miss school because of head lice or nits.

“Misdiagnosis is really common, even with medical personnel,” said Dr. Mary Anne Jackson, the director of infectious disease and professor of pediatrics at Children’s Mercy Hospital in Kansas City, Mo., who works with the A.A.P. committee on infectious diseases.

She said administrators at one school she worked with worried that its football field might be a source of lice, and were concerned with fumigating or otherwise disinfecting it. But unless the players are sharing helmets they are unlikely to transmit head lice.

There are many misunderstandings about head lice, Dr. Jackson said, including the persistent idea that a child with head lice is evidence of an unclean home. (Head lice are, in fact, one of the great equalizers; just look at all the high end “salons” offering to pick your child’s nits for a hefty fee.)

It’s not necessary to treat all the children in a classroom, or all the people who live in the house, though anyone who shares a bed should get treated. We no longer use some of the more toxic insecticidal drugs that used to be employed, like lindane, which was a potential neurotoxin. The over-the-counter preparations that are available now are much safer, but there are concerns about resistance, so many people resort to prescription drugs. One that is commonly prescribed is topical ivermectin, a drug with what Dr. Jackson called “a strong safety portfolio,” but it can be expensive.

And there are many treatments out there that have no evidence to back them up. For example, Dr. Jackson said, there are clinics using heat on children’s hair, which may work under certain conditions, but there is no regulation of how it is being used “to quote unquote inactivate the lice,” she said. “I am skeptical.”

And then there are the “suffocation treatments,” from olive oil to mayonnaise, applied to the hair in hopes of killing off the insects without resorting to chemicals and insecticides. Some of these probably work some of the time but “all will work no matter how you place them if you don’t have lice,” Dr. Jackson said.

So diagnosis is key — someone experienced should look at the child’s head, looking for lice and not just for nits, since all kinds of debris in the hair can be mistaken for nits; everything from dandruff to dirt to drops of hair care products. And someone who knows the resistance patterns in your area should advise you about whether to use the over the counter preparations or the prescription medications.

The head louse life cycle takes about three weeks; the adult female, about the size and color of a sesame seed, lays about 10 eggs a day, and glues each one to a hair near the scalp. Eggs hatch in about nine days, warmed by body heat emanating from the scalp, and the larvae then leave the egg case (which remains glued to the hair, though it’s now empty) and go through several different developmental stages over the next nine to 12 days, before reaching adulthood and starting to lay their own eggs.

That’s why it can be helpful to treat more than once, usually after about nine days, if you are using a product that does not kill the eggs, or if you see live lice after a first treatment. And there are indeed some lice that are resistant to some insecticides, so it’s important to know what is common in your community.

Removing nits with a fine-toothed comb can be done after treating the child’s head, and usually is most effective when the hair is wet, though still not a short or simple process.

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From an infectious diseases point of view, Dr. Jackson compared head lice with pinworms, another parasitic infestation parents regard with fear and sometimes with shame, and which may be treated repeatedly without a firm diagnosis that establishes beyond question the presence of these unwanted passengers on the child’s head — or the child’s tail. People worry, kids get treated, sometimes repeatedly, and the treatments cost money and take time. We spend a billion dollars a year on treatments for head lice, according to the American Academy of Pediatrics.

The A.A.P. has fought hard against “no nit” policies in schools, in the interest of reducing the school absence associated with head lice; the C.D.C. agrees, and schools are increasingly unlikely to exclude children for nits, but still, in some schools, the policies persist.

“There should never be a case for a child with head lice spending days out of school,” Dr. Jackson said. “Families should be notified, they should be able to access topical medication and they should be able to re-enter the next day.”

7 Signs of Head Lice You Shouldn’t Ignore, According to Doctors

People don’t immediately start scratching when they get lice—here are the other symptoms to note.

It seems like you’d know if you or a loved one has lice. But, if you’ve never dealt with the creepy scalp crawlers in the past, it can be hard to know what you’re looking for. In fact, the signs and symptoms of lice can actually look and feel a lot like dandruff.

But head lice is in a whole league of its own. These tiny parasitic insects are about two to three millimeters long—and they feast on human blood, according to the Centers for Disease Control and Prevention (CDC). Lice can’t fly or hop—instead, they get around by crawling, says Patricia Garcia, MD, a pediatrician at Connecticut Children’s Medical Center.

In general, people get lice from direct head-to-head contact. “This contact needs to be prolonged,” Dr. Garcia says. “The distance from one head to another is quite large for lice and it will take them a while to physically cross that distance.” Usually, they spread via an infected person or their belongings, like clothes or a hairbrush.

Lice are typically found on the scalp or attached firmly to hair shafts, but they can appear on the eyebrows and eyelashes as well. Even though they’re not known to carry disease, they can be a major pain to deal with. Here, doctors explain exactly what to look for if you think you’re dealing with lice—and how to get rid of them ASAP.

What are the signs and symptoms of lice?

Some lice symptoms are more common and noticeable than others. But in general, these are the ones you want to keep an eye out for:

1. Intense itchiness

This is a classic sign of lice, Dr. Garcia says. Head lice can cause itchiness on any part of the scalp, but it’s usually behind the ears and at the hairline, she says. “The itchiness is caused by irritation of the skin and scalp by lice saliva,” Dr. Garcia explains. This is an important fact to know, because people don’t immediately start scratching when they get lice: It can take several days for the itchiness to develop, she says.

2. White dots on the hair

These can be tough to spot but, if you look closely at someone who has lice, you’ll often see nits (aka lice eggs) on their hair shafts, says Ashanti Woods, MD, a pediatrician at Baltimore’s Mercy Medical Center. “It sometimes resembles dandruff,” he says.

While it’s easy to confuse nits with dandruff, a key difference is that nits are hard to remove from hair, while dandruff usually flakes off easily, says Robert C. Hamilton, MD, a pediatrician at Providence Saint John’s Health Center in Santa Monica, Calif. Dandruff causes white (or even yellowish) flaking on the scalp directly, while lice often look like little grains of rice that are firmly attached to the hair follicle.

3. A tickling sensation in the scalp

Not everyone feels lice moving around on their scalp, but some people do. Dr. Garcia says that most of her patients say they “don’t feel anything,” but others may get a creepy, tickling sensation as lice move around their head.

4. Red bumps on the scalp

Again, the itchiness that lice cause is from the saliva they inject into the scalp when they bite. That can cause an allergic reaction and lead to a red rash or bumps on the skin, Dr. Woods says. Given that the bumps are hidden under hair, they can be tough to spot, though.

5. Actual bugs on the scalp and in the hair

Lice don’t like light and they’ll “move quickly to avoid it” so you might not be able to see them as you comb through hair, Dr. Garcia says. However, sometimes you’ll actually spot the critters if you’re fast enough. “You can sometimes see live lice running around,” Dr. Hamilton says.

6. Irritation

All that itchiness caused by lice bites can lead to scalp irritation. “A lot of times because people are itching their head, they scratch themselves up,” Dr. Hamilton says. That can cause scabbing and skin irritation, he says, such as redness or even sores.

7. Trouble sleeping

Lice tend to be more active at night, the CDC says, and they tend to feed and move around a lot during this time. That can keep a person awake, and make it hard to get quality sleep.

How to get rid of lice

Lice don’t usually go away on their own, Dr. Woods says. Couple that with the fact that an adult louse can lay up to 10 eggs a day and “it’s quite possible to have a very rapid population explosion every two to three weeks if lice is left untreated,” Dr. Garcia says.

Lice treatment usually involves over-the-counter shampoos that contain pest-killing permethrin or pyrethrins, per the CDC. Some of these treatments will kill the nits, but you may need to retreat the scalp. It’s also a good idea to use a fine-tooth lice comb to get rid of nits, as well as any remaining dead or live lice. And, if that doesn’t seem to work, your doctor may recommend you use a prescription medication like benzyl alcohol, ivermectin lotion, or malathion.

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Pubic lice

Pubic lice is a skin parasitic disease that is caused by pubic lice , small insects that are unable to live independently, apart from their natural “hosts”.

Lice feed on blood, and blood is their only food.

Pubic louses are radically different from other members of this order. These insects can live only on pubic hair , at least on the hair in the armpits. Children in the pubic region have no hair, so lice can, in some cases, live on eyelashes or eyebrows (in this case, they die quickly).

Pubic louses never settle on the scalp, as the hair there has a circular cross section, and lice are not able to hold onto them.

Ways to transfer pubic lice

The most common way of transmitting a pediculosis pubis is sexual. In fact, with regard to pubic lice, the «sexual» path has a somewhat unusual meaning, since the infection occurs through direct contact, without the participation of biological fluids. In fact, insects simply move between sexual partners.

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Lice nits (eggs) can persist in the environment for several days, so there are frequent cases of infection through bed linen and towels .

All other transmission routes for pubic lice, in view of the characteristics of their parasitism, are not typical.

Predisposing factors

There are many examples in the history of whole head lice epidemics. They always accompany wars, the need to be in large concentrations of people without the ability to fully maintain personal hygiene.

There are no specific factors that predispose to the development of pubic lice. This is not affected by immune reactivity, background diseases or the usual way of life: absolutely all groups of people are subject to lice. Of course, lice are more often seen in people living in adverse material and living conditions, but this is due solely to difficulties in maintaining hygiene and facilitating the transmission of the disease.

What happens during infection?

Pubic lice «crawl» from one person to another. Most often this happens directly during sexual intercourse, when using someone else’s laundry or personal items.

Insect attached to the hair at its base, plunging into the skin. There lice have access to small blood vessels, through which they feed. Pubic lice can stay in one place for a long time without moving, so they can be difficult to detect.

Eggs (nits) lice lay on the hair itself, «sticking» them with a sticky secret. Lice are very fertile, which causes the epidemic nature of lice and the difficulty of treating this disease.

Symptoms of pubic lice

A persistent symptom of pediculosis is, of course, pruritus . It appears at the site of the parasite in the skin and around it, and it can be of very different intensity. The severity of this symptom depends on the sensitivity of the human skin: sometimes itching can be so severe that it requires the use of sedatives.

Pruritus is accompanied by scratching (and sometimes a person does not notice this, because scratching is a natural reaction to the feeling of itching). Trauma to the skin leads to its inflammation and, consequently, to even more severe itching.

When bite, the louse injects saliva under the skin, which has hemolytic properties. Because of this, bluish spots appear at the site of introduction, which, however, cannot be considered a reliable sign of pubic lice, a non-permanent symptom that is not observed in all patients and is rapidly passing.

A rash that can occur when infected with pubic lice can hardly be called a symptom of pediculosis, because it reflects, rather, the immune system’s response to the introduction of the parasite. However, several sources report that an allergic rash is a diagnostic sign of parasitizing pubic lice.

Diagnosis of pubic lice

For pediculosis, do not use any additional research methods other than microscopic. To make a diagnosis, it is enough to examine the patient — the detection of live or dead insects is an absolute diagnostic sign.

Nits, by virtue of their size, are detected by examination under a microscope. In normal examination, they resemble «dandruff», so the hair with such a «scale» is placed under a magnifying glass to clarify its nature.

Consequences of the disease

Unlike body lice, which are carriers of typhus and relapsing fever, pubic lice do not cause specific effects. Complications that may occur against the background of pubic lice, are reduced to infection of scratching on the skin.

If the infection gets into the damaged skin, pyoderma ( staphylococcal or streptococcal) may occur in the affected area. Pyoderma is a purulent inflammation of the skin, characterized by the appearance of pustules (vesicles filled with pus). Pyoderma are treated by prescribing antibacterial and anti-inflammatory drugs.

Often there is a pronounced allergic reaction , requiring the appointment of local antiallergic drugs. Allergy also leads to increased itching, which sometimes causes diagnostic errors (mainly during self-diagnosis).

Trauma to the skin leads to a weakening of local immunity, which facilitates the infection of venereal diseases. That is why such diseases are often detected simultaneously with head lice.

Treatment of pubic lice: how to «get» pubic lice?

The first and most important thing that must be done to eliminate pubic lice is thorough washing and disinfection of clothes and bed linen. Boiling clothes has a good effect — lice and nits die at a temperature of 100 ° C.

Pubic hair is recommended to shave, but it does not guarantee cure. It is mandatory to use local treatment with the help of various agents that affect both adult insects and their eggs.

Pediculosis medicines are available in various versions: in the form of ointments, shampoos, or simply solutions. Most of them need to be applied to the hair for a while so that the drug has time to act.

The most commonly used drugs are emulsions (Nittifor, Medifox, etc.): these drugs must be diluted in water. After application, the solution should be thoroughly rinsed with warm water — in no case should it be left for a long time.

After applying the medication to pubic hair, it is recommended to cover them with a cloth in order to increase the area of ​​contact with the solution and cover the entire surface of the pubis. This applies to shampoos and emulsions — for preparations in the form of soap (Vitar, Veda-2) such measures are not needed.

Treatment of pediculosis is carried out more than once , since one procedure, as a rule, is not enough. Usually the drug is used 3-4 times with an interval of 3 days to a week, until the signs of the disease disappear. The only reliable criterion for the effectiveness of treatment can be considered the absence of insects and nits in all parts of the body.

Prevention of pediculosis

Prevention of head lice infection is reduced to the need to adhere to elementary rules of personal hygiene. In any public places you need to use only personal things. The same goes for clothes and bed linen.

An important point — the exclusion of random sexual relations, which regularly become the cause of lice.

It should be remembered that washing with soap can not destroy the lice: they die only when using special disinfectants or boiling. Therefore, you should not hope for such a method of dealing with head lice — it is absolutely not effective.

Public prevention of pediculosis is the timely detection of the disease in children’s groups and hospitals (ie, in places of large concentrations of people). Upon admission to the hospital, each patient should be examined for the presence of pediculosis, and, in case of its detection, carry out the necessary measures aimed at his treatment.

In children, pubic lice usually affects the eyelashes and eyebrows, where insects can go unnoticed — these areas need to be examined very carefully.

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