| NEW DISEASE ABOUT VIRUS
New diseases and renewed threats During the past 20 years, at least 30 new diseases have emerged, for many of which there is no treatment, cure or vaccine, or the possibility of effective prevention or control.
In addition, the uncontrolled and inappropriate use of antibiotics has resulted in increased antimicrobial resistance and is seriously threatening drug control strategies against such common diseases as tuberculosis, malaria, cholera, dysentery and pneumonia.
EMERGING infectious diseases are those whose incidence in humans has increased during the last two decades or which threatens to increase in the near future.
The term also refers to newly-appearing infectious diseases, or diseases that are spreading to new geographical areas - such as cholera in South America and yellow fever in Kenya.
It refers also to diseases that were easily controlled by chemotherapy and antibiotics, but which have developed anti-microbial resistance. The diseases in question involve all the major modes of transmission - they are spread either from person to person, by insects or animals, or through contaminated water or food.
The most dramatic example of a new disease is AIDS, caused by the human immunodeficiency virus (HIV). The existence of the virus was unknown until 15 years ago, but it has since then infected an estimated 24 million adults worldwide, and that number could grow to a cumulative total of 40 million by the year 2000. 
The origins of HIV are unknown, but it is related to viruses which cause AIDS-like illness in monkeys. Microorganisms constantly undergo changes that enable them to cope with an increasingly hostile environment in their hosts. 
For example, HIV exploits weaknesses in the host's defences by damaging the human immune system, thereby allowing other 'opportunistic' infections to take advantage. A new breed of deadly haemorrhagic fevers, of which Ebola is the most notorious, has struck in Africa, Asia, the United States and Latin America.
Ebola appeared for the first time in Zaire and Sudan in 1976; it has since struck in Cote d'Ivoire in 1994 and 1995, Liberia in 1995 and again in Zaire in 1995, where it was fatal in 77% of cases.
The United States has seen the emergence of hantavirus pulmonary syndrome, characterised by respiratory failure and a case fatality rate of over 50%.
Since it was first recognised in 1993, this type of hantavirus infection has been detected in more than 20 states in that country, and has also surfaced in Argentina and Brazil.
This hantavirus is carried by rodents, particularly deer mice, and other hantaviruses have been recognised for many years in Asia, where they cause haemorrhagic fever with renal involvement in humans. Epidemics of food-borne and water-borne diseases due to new organisms such as cryptosporidium or new strains of bacteria such as Escherichia coli have hit industrialised and developing countries alike.
The O157:H7 strain of E.coli was first reported in 1982 and has since then been implicated in many serious outbreaks of diarrhoeal illness, sometimes leading to kidney failure. The strain has been linked to undercooked hamburger beef and unpasteurised milk. A completely new strain of cholera, 0139, appeared in south-eastern India in 1992 and has since spread north and west to other areas of India, into western China, Thailand and other parts of South-East Asia. The threat of a new global influenza pandemic is increasing. Major shifts in the make-up of influenza viruses occur every 20 years or so, triggering large epidemics in many parts of the world, and causing many thousands of deaths. The next such shift is expected to take place very soon. 
Epidemic strains of influenza viruses originate from China. The influenza virus is carried by ducks, chickens and pigs raised in close proximity to one another on farms. The exchange of genetic material between these viruses produces new strains, leading to epidemics of human influenza, each epidemic being due to a different strain. New strains such as those of cholera and influenza do not follow the usual pattern of being more common in younger people. They affect all age groups, since older people have not acquired immunity to them from previous infection. The emergence of drug-resistant strains of microorganisms or parasites is promoted by treatments that do not result in cure. The increasing use of antimicrobials worldwide, often in subtherapeutic doses and sometimes in counterfeit form, guarantees that this problem will increase in the foreseeable future.... Changes in lifestyle, behaviour (including injecting and non-injecting drug use) and cultural or social values are behind the emergence of some infectious diseases such as syphilis. Increases in the number of sexual partners have been the main factor in the spread of HIV infection and other sexually transmitted diseases.
Travel, including tourism, also plays a role. The spread of syphilis in the 18th and 19th centuries was related to the movement of armies.
, the introduction of HIV in many parts of the world is due to greatly increased human mobility. Studies show that whereas only a few generations ago most people in their lifetime travelled no further than 40 kilometres from their birthplace, many today go up to 1,000 times further, travelling the whole world.\
The practices of modern medicine also contribute. The spread of viral hepatitis is related in part to techniques such as kidney dialysis and multiple blood transfusions, as well as to other forms of transmission.
KIDNEY
Relaxation in immunisation practices can quickly result in the resurgence of diseases, as, for example, the recent spread of diphtheria in the Russian Federation and other former republics of the USSR. New animal diseases pose potential food-borne risks to human health that are sometimes difficult to evaluate or predict. An example that has caused much public concern in Europe is bovine spongiform encephalopathy ('mad cow disease').
Fears have grown that the infectious agent responsible may be passed through the food chain to cause a variant of the incurable Creutzfeldt-Jakob disease in humans, in which the brain is attacked. The British beef market has been seriously affected and stringent public health safeguards have been introduced. The reasons for outbreaks of new diseases, or sharp increases in those once believed to be under control, are complex and still not fully understood. The fact is however that national health has become an international challenge. An outbreak anywhere must now be seen as a threat to virtually all countries, especially those that serve as major hubs of international travel. Despite the emergence of new diseases in the last 20 years, there is still a lack of national and international political will and resources to develop and support the systems that are necessary to detect them and stop their spread.
Without doubt diseases as yet unknown, but with the potential to be the AIDS of tomorrow, lurk in the shadows. Antimicrobial resistance Resistance by disease-causing organisms to antimicrobial drugs and other agents is a major public health problem worldwide.
It is making a growing number of infections virtually untreatable, both in hospitals (as discussed in the later section on hospital infections) and in the general community.
It is having a deadly impact on the control of diseases such as tuberculosis, malaria, cholera, dysentery and pneumonia. Antimicrobial resistance is not a new problem, but it has worsened dramatically in the last decade. During that time, the pace of development of new antimicrobials has slowed down while the prevalence of resistance has grown at an alarming rate. The increase in the number of drug-resistant bacteria is no longer matched by a parallel expansion in the arsenal of agents used to treat infections. | 
