A spiral-shaped bacterium.
Spirochaetes cause syphilis, leptospirosis, relapsing fever, and Lyme disease.
Spirochaetes cause syphilis, leptospirosis, relapsing fever, and Lyme disease.
Bacteria are classi?ed according to their shape: BACILLUS (rod-like), coccus (spherical – see COCCI), SPIROCHAETE (corkscrew and spiral-shaped), VIBRIO (comma-shaped), and pleomorphic (variable shapes). Some are mobile, possessing slender hairs (?agellae) on the surfaces. As well as having characteristic shapes, the arrangement of the organisms is signi?cant: some occur in chains (streptococci) and some in pairs (see DIPLOCOCCUS), while a few have a ?lamentous grouping. The size of bacteria ranges from around 0.2 to 5 µm and the smallest (MYCOPLASMA) are roughly the same size as the largest viruses (poxviruses – see VIRUS). They are the smallest organisms capable of existing outside their hosts. The longest, rod-shaped bacilli are slightly smaller than the human erythrocyte blood cell (7 µm).
Bacterial cells are surrounded by an outer capsule within which lie the cell wall and plasma membrane; cytoplasm ?lls much of the interior and this contains genetic nucleoid structures containing DNA, mesosomes (invaginations of the cell wall) and ribosomes, containing RNA and proteins. (See illustration.)
Reproduction is usually asexual, each cell dividing into two, these two into four, and so on. In favourable conditions reproduction can be very rapid, with one bacterium multiplying to 250,000 within six hours. This means that bacteria can change their characteristics by evolution relatively quickly, and many bacteria, including Mycobacterium tuberculosis and Staphylococcus aureus, have developed resistance to successive generations of antibiotics produced by man. (METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA)) is a serious hazard in some hospitals.
Bacteria may live as single organisms or congregate in colonies. In arduous conditions some bacteria can convert to an inert, cystic state, remaining in their resting form until the environment becomes more favourable. Bacteria have recently been discovered in an inert state in ice estimated to have been formed 250 million years ago.
Bacteria were ?rst discovered by Antonj van Leewenhoek in the 17th century, but it was not until the middle of the 19th century that Louis Pasteur, the famous French scientist, identi?ed bacteria as the cause of many diseases. Some act as harmful PATHOGENS as soon as they enter a host; others may have a neutral or benign e?ect on the host unless the host’s natural immune defence system is damaged (see IMMUNOLOGY) so that it becomes vulnerable to any previously well-behaved parasites. Various benign bacteria that permanently reside in the human body are called normal ?ora and are found at certain sites, especially the SKIN, OROPHARYNX, COLON and VAGINA. The body’s internal organs are usually sterile, as are the blood and cerebrospinal ?uid.
Bacteria are responsible for many human diseases ranging from the relatively minor – for example, a boil or infected ?nger – to the potentially lethal such as CHOLERA, PLAGUE or TUBERCULOSIS. Infectious bacteria enter the body through broken skin or by its ori?ces: by nose and mouth into the lungs or intestinal tract; by the URETHRA into the URINARY TRACT and KIDNEYS; by the vagina into the UTERUS and FALLOPIAN TUBES. Harmful bacteria then cause disease by producing poisonous endotoxins or exotoxins, and by provoking INFLAMMATION in the tissues – for example, abscess or cellulitis. Many, but not all, bacterial infections are communicable – namely, spread from host to host. For example, tuberculosis is spread by airborne droplets, produced by coughing.
Infections caused by bacteria are commonly treated with antibiotics, which were widely introduced in the 1950s. However, the con?ict between science and harmful bacteria remains unresolved, with the overuse and misuse of antibiotics in medicine, veterinary medicine and the animal food industry contributing to the evolution of bacteria that are resistant to antibiotics. (See also MICROBIOLOGY.)... bacteria
Louse-borne relapsing fever is an EPIDEMIC disease, usually associated with wars and famines, which has occurred in practically every country in the world. For long confused with TYPHUS FEVER and typhoid fever (see ENTERIC FEVER), it was not until the 1870s that the causal organism was described by Obermeier. It is now known as the Borrelia recurrentis, a motile spiral organism 10–20 micrometres in length. The organism is transmitted from person to person by the louse, Pediculus humanus.
Symptoms The incubation period is up to 12 days (but usually seven). The onset is sudden, with high temperature, generalised aches and pains, and nose-bleeding. In about half of cases, a rash appears at an early stage, beginning in the neck and spreading down over the trunk and arms. JAUNDICE may occur; and both the LIVER and the SPLEEN are enlarged. The temperature subsides after ?ve or six days, to rise again in about a week. There may be up to four such relapses (see the introductory paragraph above).
Treatment Preventive measures are the same as those for typhus. Rest in bed is essential, as are good nursing and a light, nourishing diet. There is usually a quick response to PENICILLIN; the TETRACYCLINES and CHLORAMPHENICOL are also e?ective. Following such treatment the incidence of relapse is about 15 per cent. The mortality rate is low, except in a starved population.
Tick-borne relapsing fever is an ENDEMIC disease which occurs in most tropical and sub-tropical countries. The causative organism is Borrelia duttoni, which is transmitted by a tick, Ornithodorus moubata. David Livingstone suggested that it was a tick-borne disease, but it was not until 1905 that Dutton and Todd produced the de?nitive evidence.
Symptoms The main di?erences from the louse-borne disease are: (a) the incubation period is usually shorter, 3–6 days (but may be as short as two days or as long as 12); (b) the febrile period is usually shorter, and the afebrile periods are more variable in duration, sometimes only lasting for a day or two; (c) relapses are much more numerous.
Treatment Preventive measures are more di?cult to carry out than in the case of the louse-borne infection. Protective clothing should always be worn in ‘tick country’, and old, heavily infected houses should be destroyed. Curative treatment is the same as for the louse-borne infection.... relapsing fever
It is also known as Weil’s disease.
Symptoms include fever, chills, headache, severe muscle aches, and a skin rash.
Kidney and liver damage are also common.
Antibiotic drugs are effective treatment but kidney and liver function may recover only slowly.
The nervous system may also be affected, often producing signs of meningitis.... leptospirosis
In?ammation of the liver, or HEPATITIS, may occur as part of a generalised infection or may be a localised condition. Infectious hepatitis, which is the result of infection with a virus, is one of the most common forms. Many di?erent viruses can cause hepatitis, including that responsible for glandular fever (see MONONUCLEOSIS). Certain spirochaetes may also be the cause, particularly that responsible for LEPTOSPIROSIS, as can many drugs. Hepatitis may also occur if there is obstruction of the BILE DUCT, as by a gall-stone.
Cirrhosis of the liver A disorder caused by chronic damage to liver cells. The liver develops areas of ?brosis or scarring; in response, the remaining normal liver cells increase and form regeneration nodules. Those islands of normality, however, suffer from inadequate blood supply, thus adversely affecting liver function. Alcohol is the most common cause of cirrhosis in the United Kingdom and the USA, and the incidence of the disorder among women in the UK has recently risen sharply as a consequence of greater consumption of alcohol by young women in the latter decades of the 20th century. In Africa and many parts of Asia, infection with hepatitis B virus is a common cause. Certain drugs – for example, PARACETAMOL – may damage the liver if taken in excess. Unusual causes of cirrhosis include defects of the bile ducts, HAEMOCHROMATOSIS (raised iron absorption from the gut), CYSTIC FIBROSIS, cardiac cirrhosis (the result of heart failure causing circulatory congestion in the liver), and WILSON’S DISEASE (raised copper absorption).
Symptoms Some people with cirrhosis have no signs or symptoms and the disease may be diagnosed at a routine medical examination. Others may develop jaundice, OEDEMA (including ascites – ?uid in the abdomen), fever, confusion, HAEMATEMESIS (vomiting blood), loss of appetite and lethargy. On examination, cirrhotic patients often have an enlarged liver and/ or SPLEEN, and HYPERTENSION. Liver function tests, cholangiography (X-ray examination of the bile ducts) and biopsy of liver tissue will help to reach a diagnosis.
Treatment Nothing can be done to repair a cirrhosed organ, but the cause, if known, must be removed and further advance of the process thus prevented. In the case of the liver, a high-protein, high-carbohydrate, low-fat diet is given, supplemented by liver extract and vitamins B and K. The consumption of alcohol should be banned. In patients with liver failure and a poor prognosis, liver TRANSPLANTATION is worthwhile but only after careful consideration.
Abscess of the liver When an ABSCESS develops in the liver, it is usually a result of amoebic DYSENTERY, appearing sometimes late in the disease – even after the diarrhoea is cured (see below). It may also follow upon in?ammation of the liver due to other causes. In the case of an amoebic abscess, treatment consists of oral metronidazole.
Acute hepatic necrosis is a destructive and often fatal disease of the liver which is very rare. It may be due to chemical poisons, such as carbontetrachloride, chloroform, phosphorus and industrial solvents derived from benzene. It may also be the cause of death in cases of poisoning with fungi. Very occasionally, it may be a complication of acute infectious hepatitis.
Cancer of the liver is not uncommon, although it is rare for the disease to begin in the liver – the involvement of this organ being usually secondary to disease situated somewhere in the stomach or bowels. Cancer originating in the liver is more common in Asia and Africa. It usually arises in a ?brotic (or cirrhotic) liver and in carriers of the hepatitis B virus. There is great emaciation, which increases as the disease progresses. The liver is much enlarged, and its margin and surface are rough, being studded with hard cancer masses of varying size, which can often be felt through the abdominal wall. Pain may be present. Jaundice and oedema often appear.... liver, diseases of
Today, around 40 million new cases are noti?ed annually in the world, and this is probably an underestimate. In the UK the annual incidence of new cases of syphilis diagnosed in NHS genito-urinary medicine clinics has risen from 8.8 to 9.7 per million of male population between 1991 and 1999; among women the ?gures were 4.0 to 4.5 per million. The infection is most common in homosexual men (see HOMOSEXUALITY).
Causes The causative organism is the Treponema pallidum, a long, thread-like wavy organism with pointed tapering ends. It is found in large numbers in the sores in the primary stage of the disease and in the skin lesions in the secondary stage.
Syphilis may be acquired from people already suffering from the disease, or it may be congenital. The acquired form is usually got by sexual intercourse, kissing or other intimate bodily contact. The epithelium covering the general surface of the skin seems to be an e?cient protection, but the infective material penetrates mucous membranes. The acquired form of the disease is infectious from contact with sores, both in its primary and secondary stages; infants suffering from the congenital form are also highly infectious. Accordingly, anyone frequently handling such an infant is at risk of infection, although the mother may handle the baby with impunity.
Symptoms The acquired form of the disease is commonly divided into three stages – primary, secondary, and tertiary (although the latter is much less common than it was 50 years ago). The clinical manifestations are varied and are sometimes confused with those of other diseases. There are several laboratory tests for con?rming the diagnosis.
The incubation period ranges from ten to 90 days, although most frequently it is around four weeks. Then, a small persistent ULCER appears at the site of infection, which is accompanied by a typical cartilaginous hardness of the tissues immediately around and beneath it. This, which is known as the primary sore (or chancre), may be very much in?amed, or it may be so small as to pass almost or quite unnoticed. A few days later, the lymphatic glands in its neighbourhood, and then those all over the body, become swollen and hard. This condition lasts for several weeks before the sore slowly heals and the glands subside. After a variable period – usually about two months from the date of infection – the secondary symptoms appear and resemble the symptoms of an ordinary FEVER, with pyrexia, loss of appetite, vague pains through the body, and a faint red rash seen best upon the front of the chest. People with syphilis are infectious in the primary and secondary stages but not in the latent or tertiary stages.
In untreated or inadequately treated cases, manifestations of the tertiary stage develop after the lapse of some months or even years: this is known as the latent period. These consist in the growth, at various sites throughout the body, of masses of granulation tissue known as gummas. These gummas may appear as hard nodules in the skin, or form tumour-like masses in the muscles, or produce thickening of bones. They may develop in the brain and spinal cord, where their presence causes very serious symptoms. Gummas yield readily, as a rule, to appropriate treatment, and generally disappear speedily.
Still later, effects are apt to follow, such as disease of the arteries, leading to ANEURYSM (see also ARTERIES, DISEASES OF), to STROKE, and to mental deterioration (see MENTAL ILLNESS); also certain nervous diseases, of which tabes dorsalis and general paralysis are the chief.
The congenital form of syphilis, now rare, may affect the child before birth, leading then as a rule to miscarriage or to a stillbirth if born at full time. Alternatively he (or she) may show the ?rst symptoms a few weeks after birth, the appearances then corresponding to the secondary manifestations of the acquired form.
Laboratory con?rmation of a clinical diagnosis is done by identifying active spirochaetes (see SPIROCHAETE) in a smear taken at the site of the initial chancre, and by blood tests such as the treponomal antibody absorption tests. These tests are strongly positive at the secondary stage, and in patients with neurosyphilis the tests may have to be done on CEREBROSPINAL FLUID.
Treatment Any person with syphilis is a source of infection, and should take precautions not to spread it. PENICILLIN is the drug of choice in the disease in all its stages, but resistant strains of the Treponema pallidum have emerged and are causing problems, especially in developing countries. Treatment must be instituted as soon as possible after infection is acquired: (1) a full course of treatment is essential in every case, no matter how mild the disease may appear to be; (2) periodic blood examinations must be carried out on every patient for at least two years after he or she has been apparently cured.
Prevention is important and promiscuous hetero- or homosexual intercourse involves a risk of infection. Condoms provide some, but not complete protection. Infection can be avoided by maintaining a monogamous relationship.... syphilis
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