Epidemic and Murine Typhus: Lice, Fleas, and Bacteria
What Is Typhus?
Typhus is a group of closely related diseases caused by bacteria in the Rickettsiaceae family. The bacteria are spread by lice and flea bites. The two most common types of typhus are the potentially serious epidemic typhus, which is transmitted by a louse, and the less serious but still unpleasant murine typhus, which is transmitted by a flea.
Historically, huge numbers of people have died from epidemic typhus. Fatalities are rarer today due to modern treatments, especially when the treatment is started soon after symptoms appear. Murine typhus is rarely fatal.
Despite its similar name, typhoid is a completely different disease from typhus. Typhoid is also called typhoid fever or enteric fever. It's caused by ingesting material contaminated with feces containing a bacterium named Salmonella typhi, which is not a member of the Rickettsiaceae family.
Rickettsia is a genus of non-motile bacteria that live as parasites inside the cells of animals and humans. The genus is responsible for a variety of human diseases, including the forms of typhus discussed in this article.
The Body Louse
Lice are wingless insects. A louse (singular of lice) has a small head, three pairs of legs and a flattened, oval body. The head bears a pair of antennae. Epidemic typhus is transmitted by the body louse. The bacterium that causes the disease is named Rickettsia prowazekii. It lives inside the digestive tract of the louse. The bacterium was named after two scientists, Howard Taylor Ricketts and Stanislaus von Prowazek, who both died after researching a typhus outbreak and becoming infected themselves.
Body and head lice are very closely related and are similar in structure and appearance. The body louse may be slightly bigger, however, reaching a maximum length of 3.6 mm as opposed to 3 mm for the head louse. Both animals feed on blood. Body lice move on to the skin to feed and then retreat to seams and folds in clothing. Head lice stay on the head, whether or not they are feeding. The scientific name of the body louse is Pediculus humanus humanus while that of the head louse is Pediculus humanus capitis.
The video below is an interesting look at a living head louse, which moves like a body louse. There is one error in the commentary, however. There are about four hundred species of sucking lice, the group that contains head and body lice, but there is only one species of head louse.
The Secret Life of Head Lice
Human infection with epidemic typhus takes place when a body louse bites someone in order to obtain its meal of blood and releases feces while it's eating. Since the bite itches, the person scratches the wound. This action crushes the louse and sends its contaminated feces into the wound. Bits of crushed lice may also enter the wound and transmit the bacteria. Symptoms of the bacterial infection don't appear until one or two weeks after the bite.
Once they are inside their host’s blood, the typhus bacteria enter the cells lining the smaller blood vessels. The infected cells become swollen as the bacteria multiply. The cells eventually burst, releasing bacteria which can then infect more cells.
When an uninfected louse feeds on an infected human, typhus bacteria from the person’s blood enter the louse’s digestive system and the cycle is ready to begin again.
Stages in Body Louse Development
Incidence of Disease
The incidence of epidemic typhus rises in areas of poor sanitation where people are crowded together, such as in war zones and refugee camps. The body louse population increases under these conditions. People may have no choice but to share clothing and blankets that have attached lice. In addition, people may be huddled so close together that lice can easily travel from one person to another. Lice can’t fly or jump. Instead, they crawl from clothing to people’s skin, where they reproduce.
In the past, epidemic typhus was sometimes called “jail fever” because it occurred in crowded jail conditions. Epidemic typhus spread through the Bergen-Belsen concentration camp in 1945, killing Anne Frank and many other people. Today the disease is rare in North America but still occurs in some parts of the world.
The symptoms of epidemic typhus listed below may indicate the presence of a different disorder. In addition, patients not may have all of the symptoms listed. Some may have symptoms that aren't listed. A doctor must be consulted for a correct diagnosis and for appropriate treatment.
Possible Symptoms of Epidemic Typhus
Symptoms of epidemic typhus may include:
- a high fever
- an intense headache
- muscle and joint pain
- a cough
- sensitivity to light
- a general feeling of illness (a condition known as malaise)
A few days after the symptoms begin, a petechial rash may appear. This rash appears as small pink or red spots on the skin. In severe cases of epidemic typhus there may be low blood pressure, delirium, stupor or a coma. In untreated cases, necrosis (tissue death) may occur.
A Nymph (Immature Stage) of a Body Louse
If epidemic typhus is not treated there is a ten to forty percent mortality rate. In people over fifty years of age, untreated epidemic typhus has a mortality rate of up to sixty percent. If antibiotics are taken in the early stages of the infection, however, the recovery rate is good.
People apparently cured of epidemic typhus may develop symptoms of the disease again, sometimes months or even years after the initial infection. This form of typhus is called Brill–Zinsser disease. The disease is usually milder than the person’s first bout of typhus. Scientists don’t know how the typhus bacteria manage to survive in the person’s body for so long, apparently inactive. The bacteria reactivate when a person is in a weakened state, such as when their body is fighting another infection.
In the eastern United States, a form of epidemic typhus called sylvatic typhus sometimes occurs when people come into contact with flying squirrels or their nests. The squirrel involved is the southern flying squirrel, or Glaucomys volans.
Although sylvatic typhus is caused by the same species of bacterium as the usual type of epidemic typhus, the symptoms of the infection are less severe. This strange observation hasn't been explained yet. It may be due to the existence of a different strain of the bacterium.
The infection mechanism isn’t known for certain, but possibilities include being bitten by fleas that live on infected flying squirrels or inhaling dust containing feces created by fleas or lice on the squirrels or in their nests. The disease generally responds well to antibiotics and there have been no recorded deaths from sylvatic typhus in the United States. There have been hospitalizations, however.
Like lice, fleas are wingless insects, but they have a different structure and belong to a different order. They are able to jump from place to place with the aid of their long and powerful hind legs. Some fleas are about the same size as lice while others are a bit smaller.
Murine Typhus and Fleas
Murine or endemic typhus is the most common type of typhus in the United States. It occurs in warm coastal areas of the southern U.S., including southern California and Texas, as well as in many other parts of the world. Its true incidence is unknown because its symptoms can be confused with those of other diseases.
The disease is caused by Rickettsia typhi. The bacterium is transmitted by fleas that have fed on infected rats and opossums. Cat fleas may transmit a related bacterium that causes similar symptoms to murine typhus. An infection results from a flea defecating as it eats, followed by the person scratching the wound and sending infected feces into their bloodstream.
The rat flea (Xenopsylla cheopis) is the most common cause of murine typhus. The video below shows the life cycle of a dog flea, which is similar to that of the rat flea.
Life Cycle of a Flea
Possible Symptoms and Treatment
The symptoms of murine typhus resemble epidemic typhus but are milder. Nevertheless, they can be very unpleasant. An infected person usually develops a fever and often has chills, a headache, and joint pain. The person may also develop a rash and experience a cough, nausea, vomiting and diarrhea. Some people experience weakness and confusion. Sensitivity to light is another possible symptom.
The symptoms of murine typhus generally don't develop until six to fourteen days after the initial infection. Since the symptoms are variable, the disease is sometimes misdiagnosed. A blood test can conform the presence of the disease.
Murine typhus is generally treated with antibiotics, which nearly always work well. Very few people die from the infection. As is the case with many bacterial diseases, elderly people or people with additional health problems are most likely to die after being infected.
The brown rat is the most common wild rat in many areas. It's sometimes involved in the transmission of murine typhus to humans.
Tips for Preventing Murine Typhus
If you live in an area susceptible to murine typhus, there are several steps that you can take to reduce the chance of developing an infection.
- Keep yards tidy and free of items that might hide rats or other animals. Remove brush and firewood and cut long grass.
- Pick up fruit that has fallen from trees or bushes.
- Keep garbage in a container with a secure lid.
- Don't leave pet food outside.
- If you have pets that could attract fleas, ask your vet about a safe flea prevention treatment for the pets.
- Don't allow pet cats to wander outdoors without supervision.
- Keep homes in good repair, especially parts such as crawl spaces which could be occupied by pests.
- Wear protective clothing and a mask when entering infested areas.
- Spray disinfectant in areas which pests have visited.
Keeping a garden and a community tidy is a good strategy for preventing other pest problems beside the appearance of animals that can transmit typhus. It's much better to protect ourselves from diseases than to experience them.
© 2010 Linda Crampton