Infectious Disease Treatment

What are Bacteria?

Bacteria are small infectious agents that fall into a category of living things called prokaryotes. Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment known as a nucleus. Bacteria are among the Earth's earliest forms of life. In fact, they are thought to have helped shape Earth's early environment, eventually creating atmospheric oxygen that enabled the development of other more complex life forms.

Classifying Bacteria

Bacteria are divided into thousands of different species but are broadly classified by their shape. Rod-shaped bacteria are termed bacilli, ball-shaped bacteria are called cocci and spiral-shaped bacteria are known as spirochetes. Bacterial cells are further grouped by whether they form clusters, chains or other groupings when examined microscopically.

Bacteria live on or in almost every surface, material and environment on Earth. Some bacteria possess long whip-like structures called flagellae that they rotate to move. Others secrete a slime layer to slowly move over surfaces, and still others are stationary. Some bacteria are photosynthetic, but most absorb nutrients from their environment in order to survive. A particular bacterium's ability to absorb nutrients and tolerate specific environmental conditions influences whether it is likely to colonize or infect humans.

Treating Bacterial Infections

A multitude of antibiotics have been developed to treat bacterial infections. Antibiotics work by preventing bacteria from performing essential functions such as putting their cell walls together, assembling essential cell proteins or making copies of their genetic material (DNA). In addition, highly effective vaccines have been developed to prevent bacterial infection. Examples of such vaccines include those directed against Streptococcus pneumoniae, the most common bacterial cause of pneumonia in adults, and Neisseria meningitidis, the most common cause of meningitis. Research is underway to develop vaccines to prevent the most common causes of hospital-acquired infections, which are often resistant to common antibiotics.

Over the past 25 years, Lyme disease has evolved from a mysterious focus of childhood illness in rural Connecticut to the most common tick-borne illness in the United States. A great deal has been learned, both about the cause and the clinical manifestations of Lyme disease, yet some of the mystery persists. Careful study has helped to dispel some of the confusion and anxiety surrounding this illness.

Lyme disease is caused by Borrelia burgdorferi, a spirochete that is carried by the deer tick, Ixodes scapularis. As suburban neighborhoods have reached further into wooded areas, deer and mice bring infected ticks into human contact. Most cases in the US have been concentrated along the northeast Atlantic coast, from Maryland to Maine, with another focus in Wisconsin. Beginning in springtime, deer tick nymphs, about the size of a period at the end of a sentence, can attach to a human host. If allowed to remain attached for more than 24 to 36 hours, they can feed on the human host’s blood and (if infected) transmit Lyme disease.

Lyme disease usually appears several days to two weeks after a tick bite. A large, red rash may accompany fever, muscle and joint aches, headache, and malaise. This is often described as donut- or ring-shaped, and typically appears at the site of the bite. The rash may be as small as 5cm (2 inches) in diameter, or may expand to cover the chest, abdomen, or an entire limb. Sometimes it will appear with multiple rings that may move around on the skin (erythema migrans). Untreated infection may resolve itself or progress to later stages of infection.

The most common long-term manifestation of Lyme disease is joint involvement, or arthritis. This can produce intermittent bouts of swelling and pain, usually in large joints, such as the knee. If untreated, some cases will become chronic. Less commonly, neurological infection can occur. This may cause meningitis (with headache, fever, and stiff neck) or a facial droop (Bell’s Palsy). Infection of the heart is fairly rare, but can cause a brief blockage of electrical conduction in the heart muscle. Each of these conditions is amenable to treatment with antibiotics.

Although Lyme disease can cause many conditions, complaints of common symptoms such as fatigue and aches are often incorrectly attributed to Lyme disease when another condition is to blame. When considering Lyme disease, it is important to assess three major issues: the likelihood of exposure to Lyme-infected ticks; whether a typical illness occurred; and the results of blood tests.

After infection with B. burgdorferi, two major types of antibody can be detected in blood. Immunoglobulin M (IgM) is a rapid-response antibody that typically appears within one to three weeks of infection and then disappears over the next three to six months. Immunoglobulin G (IgG) is a more long-lasting antibody, appearing several weeks into the infection and often lasting for years. Testing for these antibodies can help immensely, but requires the assistance of a reputable laboratory.

A screening test (EIA) is first used as a sensitive search for exposure to Borreliae. If this suggests there has been an antibody response, a more careful test (Western blot) is used to discern B. burgdorferi infection from cross-reacting antibodies. Scientists from the fields of infectious disease, rheumatology, and laboratory medicine have established standard criteria for diagnosing and interpreting these tests. Although most cases of Lyme disease produce clear-cut antibody results, testing too early in the course of illness (e.g., when a rash first appears) will not detect infection about half the time. In contrast, antibody responses in later disease, such as arthritis or neurological infection, are almost always positive.

Typically, Lyme disease is easily treated with an oral antibiotic. Infection involving the central nervous system or the heart usually requires more intensive intravenous antibiotic therapy. Rash and fever respond quickly to two weeks of therapy, whereas arthritis and meningitis require a four week treatment period.

Prevention of Lyme disease and other tick-borne infections includes wearing long sleeves and tucking in pants when in tick-infested areas. Careful inspection and removal of ticks as soon as possible prevents transmission. Insect repellents containing DEET are effective in repelling deer ticks. Lyme vaccine is no longer available for human use. It is notable that death from Lyme disease is exceedingly rare.

Other Tick-borne Infections

Other tick-borne infections may be found in the Northeastern United States, although less commonly than Lyme disease.

• Babesia microti is a protozoan that parasitizes red blood cells, causing anemia. This is generally a self-limited disease of low severity. However, bites from deer ticks infested simultaneously with both Lyme disease and Babesiosis can cause more severe symptoms. In addition, patients who have had a splenectomy are subject to more severe (occasionally fatal) illness.
• Ehrlichiosis occurs in two predominant forms; human granulocytic Anaplasmosis (HGA) and human monocytic Ehrlichiosis (HME). The latter is rare in the Northeast, where HGA is most common. Similar to Babesiosis, HGA can cause co-infection with Lyme disease, again associated with more severe symptoms. HGA alone can cause significant fever, aches, and prostration, sometimes with a fatal outcome. Prompt treatment with doxycycline is highly effective.
• Tularemia, caused by Francisella tularensis, can range from skin ulcers and swollen lymph nodes to severe pneumonia and a frequently fatal illness similar to typhoid fever. Tularemia is most often associated with contact with rabbits. Infection can occur by direct contact, through tick bite, or by inhalation.
• Rocky Mountain Spotted Fever (RMSF) is caused by Rickettsia rickettsii, a species of bacteria that is spread to humans by ixodid ticks. Initial signs and symptoms of the disease include sudden onset of fever, headache, and muscle pain, followed by development of rash. The disease can be difficult to diagnose in the early stages, and without prompt and appropriate treatment, it can be fatal.

Recommended Resources

• CDC Lyme Disease Home Page: Accurate information the disease agent, transmission, prevention and treatment; includes answers to common questions.
• The American Lyme Disease Foundation, Inc.: A proactive organization dedicated to the prevention, diagnosis, treatment and control of Lyme disease and other tick-borne infections. The Foundation supports critical scientific research and plays a key role in providing reliable and scientifically accurate information to the public, medical community and government agencies about tick-borne diseases and their potentially serious effects on our health and quality of life.
• Massachusetts Department of Public Health Information about Tickborne Diseases: Includes public health fact sheets for Babesiosis, Ehrlichiosis, Tularemia, and RMSF and links to other informative sites.
• Infectious Diseases Society of America 2006 Clinical Practice Guidelines for Assessment, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis (Ehrlichiosis), and Babesiosis

There are more than a million species of fungi, but only about 400 cause diseases in humans, animals or plants. Fungi are multicellular (eukaryotic) microorganisms whose genetic material is contained within a cell nucleus. Fungi require preformed organic compounds for energy and do not contain chlorophyll.

There are two broad groups of fungi: yeasts and molds. While these definitions are not mutually exclusive, mold spores germinate to produce the branching filaments known as hyphae. Yeasts are solitary rounded forms that reproduce by making more rounded forms through mechanisms such as budding or fission.

Recommended Resource

This is an excellent site primarily intended for physicians, but it includes introductory material written with minimal medical terminology, so it can be used by patients who wish to further their understanding of their illness.

Visit the DoctorFungus website.

Viruses are small infectious agents of genetic material (either DNA or RNA) contained in a protective protein covering called a capsid. Viruses cannot survive in a host on their own; rather they must use the host cell’s metabolic machinery to survive. Viruses are usually species or organ specific.

Virus particles use proteins in their capsid to attach to host cells through receptor molecules on the host cell surface. Once inside host cells, viruses take over the host cells’ metabolic machinery to multiply. Viruses may lie dormant for long periods of time, establish a persistent long-term infection without damaging the host cell, or kill host cells when they release daughter viruses.

Viruses may be transmitted to humans by direct transmission from person-to-person, as in contact with airborne droplets from a sneeze or cough, sexual contact, hand-to-eye or mouth contact, mouth-to-mouth contact, or via contaminated blood. Sometimes an insect vector is involved in transmission to humans, as in Yellow Fever or West Nile virus.

Examples of common viral diseases include the common cold, HIV, influenza, chickenpox (varicella virus), hepatitis viruses, infectious mononucleosis (Epstein Barr virus), mumps, and measles. In addition, some viral agents (such as smallpox) can be aerosolized and could be developed as bioterrorism agents.

Antibiotics used to treat bacteria are not effective for treating viruses. A number of antiviral agents have been developed to specifically treat certain viruses, most notably HIV, herpes viruses, and hepatitis B and C viruses. The primary means of treatment of viral infections is prevention through immunization. Vaccines are available for the prevention of several significant human diseases, including poliomyelitis, measles, mumps, rubella, tetanus, hepatitis B, influenza, rabies, and smallpox. Vaccines are made from live attenuated (virulence is radically diminished) or killed virus.

Sexually transmitted diseases (STDs) affect approximately 15 million new people annually in the United States, but most people remain unaware of the risks and consequences of all but the most prominent STD-HIV. Most prevalent among teenagers and young adults, many STDs are asymptomatic, especially in women. Due to the lack of noticeable symptoms, STDs are often not diagnosed, and even when they are, the diagnoses are underreported. Even when asymptomatic, STDs are infectious to sex partners, which is why periodic screening for all persons who have had multiple partners is recommended. The regular use of condoms decreases the transmission of most STDs.

What can you do to limit the spread of STDs?

•  Practice abstinence, the only sure way to avoid STDs.
• Try to limit your exposure to STDs. Unprotected sexual activity increases your chance of exposure and infection. If you or your partner has more than one sexual partner, this increases your chances of getting an STD.
• Use barrier protection such as a condom.
• Look at your partner for any noticeable signs of infection before having sex. If you see any signs such as rashes, sores, discharge or swelling, stop and talk about the importance of getting an STD test before having sex.
• If you think you may be infected with an STD, avoid any sexual contact and visit a local sexually transmitted disease clinic, hospital or your own primary care physician. If possible, bring your sex partner(s) with you so that they can be treated, if necessary.

Specific STDs

• Bacterial Vaginosis
• Chancroid
• Chlamydia
• Genital Herpes
• Genital Warts-Human Papilloma Virus (HPV)
• Gonorrhea
• Hepatitis B
• HIV
• Syphilis
• Trichomoniasis

Recommended Resource

The Massachusetts Department of Public Health’s Division of STD Prevention includes data on local prevalence, disease surveillance and fact sheets.

Not all infectious diseases require you to see an ID specialist. Your primary care physician can treat many common infections, but your doctor might refer you to an ID specialist in cases where an infection is difficult to diagnose, is accompanied by a high fever or does not respond to treatment. The specialized training and diagnostic tools of the ID specialist can help determine the cause of your infection and the best approach to treatment.

ID specialists also see healthy people who plan to travel to foreign countries or locations where infection risk is higher. In these cases, ID specialists can help determine whether special immunizations or other preventive measures are necessary to protect travelers from disease.

ID specialists are like medical detectives. They examine difficult cases, looking for clues to identify the culprit and solve the problem. If you are in the hospital or ICU with a severe illness, you may not be aware of your ID specialist's visits, constant attention and care. Much of their work is done behind the scenes. Examining germs carefully under the microscope, ID specialists make a diagnosis and coordinate a plan to treat your disease. They review your medical data, including X-rays and laboratory reports such as blood work and culture data, and may also perform a physical exam to help determine the cause of the problem.

ID specialists often order laboratory tests to examine samples of blood and other body fluids or cultures from wounds. A blood serum analysis can help the ID specialist detect antibodies that indicate the type of infection you have. Often these advanced studies can further explain the results of earlier tests, helping to pinpoint the problem.

Treatments consist of medicines-usually antibiotics-to help battle the infection and prevent it from returning. These medicines may be given to you orally (in the form of pills or liquids) or administered directly into your veins, via an IV tube. Many ID specialists have IV antibiotic therapy available in their offices, which decreases the likelihood that the patient will need to be hospitalized. ID specialists do not perform surgical procedures.

The ID specialist works with your personal physician to determine which diagnostic tests are appropriate. If treatment is necessary, your doctor and the ID specialist will work together to develop a treatment plan best suited to your needs. Often you will be asked to return to the ID specialist for a follow-up visit. This allows the specialist to check on your progress, confirm that the infection is gone, and help prevent it from coming back.

If you acquire an infection while in the hospital, the ID specialist will work with other hospital physicians to help direct your care. The specialist also might provide follow-up care after you go home.

Generally, your doctor will request a consultation with an infectious disease (ID) specialist due to the complicated nature of your illness. For your health and safety, you should follow your doctor's instructions to make this appointment.

If you are making your own appointment at Lahey Hospital & Medical Center, call the Appointment Office at 781-744-8000 (hours of operation: 7:45 am to 7:00 pm Monday through Thursday; and 7:45 am to 5:00 pm on Friday).

Some insurance plans require you to obtain a referral from your primary care physician prior to being seen by an ID specialist. This referral should be obtained after you make your appointment at Lahey and before you see the specialist.

Be sure to give your ID specialist all medical records related to your condition, including X-rays, laboratory reports, hospital discharge summary (if you were hospitalized) and immunization records. Often your personal physician will forward this information to the specialist before your scheduled appointment. You should also provide the ID specialist with a complete list of all medications you are taking and any allergies you have. This list should include over-the-counter (nonprescription) medications, as well. Also, be sure to tell the ID specialist if you are taking birth control pills; some antibiotics may interfere with the effectiveness of oral contraceptives.