277. Influenza

Influenza is an acute viral infection that spreads easily from person to person.
Influenza circulates worldwide and can affect anybody in any age group.
Influenza causes annual epidemics that peak during winter in temperate regions.
Influenza is a serious public health problem that causes severe illnesses and deaths for higher risk populations.
An epidemic can take an economic toll through lost workforce productivity, and strain health services.
Vaccination is the most effective way to prevent infection.



Overview

Seasonal influenza is an acute viral infection caused by an influenza virus.

There are three types of seasonal influenza – A, B and C. Type A influenza viruses are further typed into subtypes according to different kinds and combinations of virus surface proteins. Among many subtypes of influenza A viruses, currently influenza A(H1N1) and A(H3N2) subtypes are circulating among humans. Influenza viruses circulate in every part of the world. Type C influenza cases occur much less frequently than A and B. That is why only influenza A and B viruses are included in seasonal influenza vaccines.

Signs and symptoms

Seasonal influenza is characterized by a sudden onset of high fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and runny nose. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death in people at high risk (see below). The time from infection to illness, known as the incubation period, is about two days.

Who is at risk?

Yearly influenza epidemics can seriously affect all age groups, but the highest risk of complications occur among children younger than age two, adults age 65 or older, and people of any age with certain medical conditions, such as chronic heart, lung, kidney, liver, blood or metabolic diseases (such as diabetes), or weakened immune systems.

Transmission

Seasonal influenza spreads easily and can sweep through schools, nursing homes or businesses and towns. When an infected person coughs, infected droplets get into the air and another person can breath them in and be exposed. The virus can also be spread by hands infected with the virus. To prevent transmission, people should cover their mouth and nose with a tissue when coughing, and wash their hands regularly.

Treatment

Antiviral drugs for influenza are available in some countries and effectively prevent and treat the illness. There are two classes of such medicines, 1) adamantanes (amantadine and remantadine), and 2) inhibitors of influenza neuraminidase (oseltamivir and zanamivir). Some influenza viruses develop resistance to the antiviral medicines, limiting the effectiveness of treatment. WHO monitors antiviral susceptibility in the circulating influenza viruses.

Seasonal epidemics

Influenza epidemics occur yearly during autumn and winter in temperate regions. Illnesses result in hospitalizations and deaths mainly among high-risk groups (the very young, elderly or chronically ill). Worldwide, these annual epidemics result in about three to five million cases of severe illness, and about 250 000 to 500 000 deaths. Most deaths associated with influenza in industrialized countries occur among people age 65 or older. In some tropical countries, influenza viruses circulate throughout the year with one or two peaks during rainy seasons.

Disease effects

Influenza can cause serious public health and economic problems. In developed countries, epidemics can result in high levels of worker absenteeism and productivity losses. In communities, clinics and hospitals can be overwhelmed when large numbers of sick people appear for treatment during peak illness periods. While most people recover from a bout of influenza, there are large numbers of people who need hospital treatment and many who die from the disease every year. Little is known about the effects of influenza epidemics in developing countries.

Prevention

The most effective way to prevent the disease or severe outcomes from the illness is vaccination. Safe and effective vaccines have been available and used for more than 60 years. Among healthy adults, influenza vaccine can prevent 70% to 90% of influenza-specific illness. Among the elderly, the vaccine reduces severe illnesses and complications by up to 60%, and deaths by 80%.

Vaccination is especially important for people at higher risk of serious influenza complications, and for people who live with or care for high risk individuals.

WHO recommends annual vaccination for (in order of priority):
nursing-home residents (the elderly or disabled)
elderly individuals
people with chronic medical conditions
other groups such as pregnant women, health care workers, those with essential functions in society, as well as children from ages six months to two years.

Influenza vaccination is most effective when circulating viruses are well-matched with vaccine viruses. Influenza viruses are constantly changing, and the WHO Global Influenza Surveillance Network (GISN), a partnership of National Influenza Centres around the world, monitors the influenza viruses circulating in humans. WHO annually recommends a vaccine composition that targets the three most representative strains in circulation.

276. Hepatitis A

Hepatitis A is a viral liver disease that can cause mild to severe illness.
Globally, there are an estimated 1.4 million cases of hepatitis A every year.
The hepatitis A virus is transmitted through ingestion of contaminated food and water, or through direct contact with an infectious person.
Hepatitis A is associated with a lack of safe water and poor sanitation.
Epidemics can be explosive in growth and cause significant economic losses.
Improved sanitation and the hepatitis A vaccine are the most effective ways to combat the disease.



IHepatitis A is a liver disease caused by the hepatitis A virus. The virus is primarily spread when an uninfected (and unvaccinated) person ingests food or water that is contaminated with the faeces of an infected person. The disease is closely associated with a lack of safe water, inadequate sanitation and poor personal hygiene.

Unlike hepatitis B and C, hepatitis A infection does not cause chronic liver disease and is rarely fatal, but it can cause debilitating symptoms and fulminant hepatitis (acute liver failure), which is associated with high mortality.

Hepatitis A occurs sporadically and in epidemics worldwide, with a tendency for cyclic recurrences. Every year there are an estimated 1.4 million cases of hepatitis A worldwide.

The hepatitis A virus is one of the most frequent causes of foodborne infection. Epidemics related to contaminated food or water can erupt explosively, such as the epidemic in Shanghai in 1988 that affected about 300 000 people. Hepatitis A viruses persist in the environment and can resist food-production processes routinely used to inactivate and/or control bacterial pathogens.

The disease can lead to significant economic and social consequences in communities. It can take weeks or months for people recovering from the illness to return to work, school or daily life. The impact on food establishments identified with the virus, and local productivity in general, can be substantial.

Geographical distribution

Geographical distribution areas can be characterized as having high, intermediate or low levels of hepatitis A infection.

Areas with high levels of infection

In developing countries with very poor sanitary conditions and hygienic practices, most children (90%) have been infected with the hepatitis A virus before the age of 10. Those infected in childhood do not experience any noticeable symptoms. Epidemics are uncommon because older children and adults are generally immune. Symptomatic diseases rates in these areas are low and outbreaks are rare.

Areas with intermediate levels of infection

In developing countries, countries with transitional economies and regions where sanitary conditions are variable, children often escape infection in early childhood. Ironically, these improved economic and sanitary conditions may lead to a higher susceptibility in older age groups and higher disease rates, as infections occur in adolescents and adults, and large outbreaks can occur.

Areas with low levels of infection

In developed countries with good sanitary and hygienic conditions, infection rates are low. Disease may occur among adolescents and adults in high-risk groups, such as injecting-drug users, men who have sex with men, people travelling to areas of high endemicity, and in isolated populations such as closed religious communities.

Transmission

The hepatitis A virus is transmitted primarily by the faecal-oral route. This is when an uninfected person ingests food or water that has been contaminated with the faeces of an infected person. Waterborne outbreaks, though infrequent, are usually associated with sewage-contaminated or inadequately treated water.

The virus can also be transmitted through close physical contact with an infectious person, although casual contact among people does not spread the virus.

Symptoms

The incubation period of hepatitis A is usually 14–28 days.

Symptoms of hepatitis A range from mild to severe, and can include fever, malaise, loss of appetite, diarrhoea, nausea, abdominal discomfort, dark-coloured urine and jaundice (a yellowing of the skin and whites of the eyes). Not everyone who is infected will have all of the symptoms.

Adults have signs and symptoms of illness more often than children, and the severity of disease and mortality increases in older age groups. Infected children under six years of age do not usually experience noticeable symptoms, and only 10% develop jaundice. Among older children and adults, infection usually causes more severe symptoms, with jaundice occurring in more than 70% of cases.

Who is at risk?

Anyone who has not been vaccinated or previously infected can contract hepatitis A. In areas where the virus is widespread (high endemicity), most hepatitis A infections occur during early childhood. Risk factors include:
poor sanitation
lack of safe water
injecting drugs
living in a household with an infected person
being a sexual partner of someone with acute hepatitis A infection
travelling to areas of high endemicity without being immunized.

Treatment

There is no specific treatment for hepatitis A. Recovery from symptoms following infection may be slow and may take several weeks or months. Therapy is aimed at maintaining comfort and adequate nutritional balance, including replacement of fluids that are lost from vomiting and diarrhoea.

Prevention

Improved sanitation, food safety and immunization are the most effective ways to combat hepatitis A.

The spread of hepatitis A can be reduced by:
adequate supplies of safe drinking water
proper disposal of sewage within communities
personal hygiene practices such as regular hand-washing with safe water.

Several hepatitis A vaccines are available internationally. All are similar in terms of how well they protect people from the virus and their side-effects. No vaccine is licensed for children younger than one year of age.

Nearly 100% of people develop protective levels of antibodies to the virus within one month after a single dose of the vaccine. Even after exposure to the virus, a single dose of the vaccine within two weeks of contact with the virus has protective effects. Still, manufacturers recommend two vaccine doses to ensure a longer-term protection of about five to eight years after vaccination.

Millions of people have been immunized worldwide with no serious adverse events. The vaccine can be given as part of regular childhood immunizations programmes and also with other vaccines for travellers.

Immunization efforts

Vaccination against hepatitis A should be part of a comprehensive plan for the prevention and control of viral hepatitis. Planning for large-scale immunization programmes should involve careful economic evaluations and consider alternative or additional prevention methods, such as improved sanitation, and health education for improved hygiene practices.

Whether or not to include the vaccine in routine childhood immunizations depends on the local context, including the proportion of susceptible people in the population and the level of exposure to the virus. Several countries, including Argentina, China, Israel and the United States of America have introduced the vaccine in routine childhood immunizations.

While the two-dose regimen of inactivated hepatitis A vaccine is used in many countries, other countries may consider inclusion of a single-dose inactivated hepatitis A vaccine in their immunization schedules. Some countries also recommend the vaccine for people at increased risk of hepatitis A, including:
travellers to countries where the virus is endemic;
men who have sex with men;
people with chronic liver disease (because of their increased risk of serious complications if they acquire hepatitis A infection).

Regarding immunization for outbreak response, recommendations for hepatitis A vaccination should also be site-specific, including the feasibility of rapidly implementing a widespread immunization campaign.

Vaccination to control community-wide outbreaks is most successful in small communities, when the campaign is started early and when high coverage of multiple age groups is achieved. Vaccination efforts should be supplemented by health education to improve sanitation, hygiene practices and food safety.

275. MONKEYPOX

The monkeypox virus can cause a fatal disease in humans; it is similar to human smallpox, although typically much less serious.
Monkeypox occurs primarily in remote villages in Central and West Africa, near tropical rainforests.
The monkeypox virus is transmitted to people from a variety of wild animals and it spreads in human population through human-to-human transmission.
There is no treatment or vaccine available although smallpox vaccination has proven to be 85% effective in preventing monkeypox.



Monkeypox is a viral zoonosis with symptoms in humans similar to those seen in the past in smallpox patients. However, smallpox no longer occurs, following its worldwide eradication in 1980, whereas monkeypox still occurs sporadically in parts of Africa.

Monkeypox is a member of the Orthopoxvirus genus in the family Poxviridae.

The virus was first identified in the State Serum Institute in Copenhagen, Denmark, in 1958 during an investigation into a pox-like disease among monkeys.

Outbreaks

Human monkeypox was first identified in humans in 1970 in the Democratic Republic of Congo. Since then, the majority of cases have been reported in rural regions of the Congo Basin and western Africa, particularly in the Democratic Republic of Congo. In 1996-97, a major outbreak occurred in the Democratic Republic of Congo. In the spring of 2003, monkeypox cases were confirmed in the Midwest of the United States of America, marking the first reported occurrence of the disease outside of the African continent. More recently, monkeypox has been reported in Unity, Sudan.

Transmission

Infections of index cases result from direct contact with the blood, bodily fluids, or rashes of infected animals. In Africa, human infections have been documented through the handling of infected monkeys, Gambian rats or squirrels.

Secondary transmission is human-to-human, resulting from close contact with infected respiratory tract excretions, with the skin lesions of an infected person or with recently contaminated objects. Transmission via droplet respiratory particles has also been documented. Transmission can also occur by inoculation or via the placenta (congenital monkeypox). There is no evidence to date that person-to-person transmission alone can sustain monkeypox in the human population.

Signs and symptoms

The incubation period (interval from infection to onset of symptoms) of monkeypox varies from 6 to 16 days.

The infection can be divided into two periods:
I.the invasion period (0-5 days) characterized by fever, intense headache, lymphadenopathy (swelling of the lymph node), back pain, myalgia (muscle ache) and an intense asthenia (lack of energy);
II.the skin eruption period where the various stages of the eruption appear on the face (in 95% of cases), on the palms of the hands and soles of the feet (75%) and on the body nearly simultaneously. Evolution of the rash from maculopapules (lesions with a flat bases) to vesicles (small fluid-filled blisters), pustules, followed by crusts occurs in approximately 10 days. Three weeks might be necessary before the complete elimination of the crusts.

The number of the lesions varies from a few to several thousand, affecting oral mucous membranes (in 70% of cases), genitalia (30%), and conjunctivae (eyelid) (20%), as well as the cornea (eyeball).

Some patients develop severe lymphadenopathy (swollen lymph nodes) before the appearance of the rash. The presence of lymphadenopathy can help identify the disease as monkeypox since it is not characteristic of either smallpox or chickenpox.

The symptoms of monkeypox usually last from 14 to 21 days.

The case fatality has varied widely between epidemics but, has been less than 10% in documented cases. Most fatalities occur in young children. In addition, children may be more susceptible to monkeypox due to the termination of regular smallpox vaccinations following the worldwide eradication of the disease in 1980.

Diagnosis

The differential diagnoses include usually smallpox, chickenpox, measles, bacterial skin infections, scabies, medicamentous allergies and syphilis.

Monkeypox can only be diagnosed definitively in the laboratory where the infection can be diagnosed by a number of different tests:
enzyme-linked immunosorbent assay (ELISA)
antigen detection tests
polymerase chain reaction (PCR) assay
virus isolation by cell culture.

Treatment and vaccine

There are no drugs or vaccines available for monkeypox, although vaccination against smallpox has been proven to be 85% effective in preventing monkeypox in the past.

Natural host of monkeypox virus

In Africa, monkeypox infection has been found in many animal species: rope squirrels, tree squirrels, Gambian rats, striped mice, doormice and primates. Doubts persist on the natural history of the virus and further studies are needed to identify the exact reservoir of the monkeypox virus and how it is maintained in nature.

In the USA, the virus is thought to have been transmitted from African animals to a number of susceptible non-African species (like prairie dogs) with which they were co-housed.

Prevention

Preventing monkeypox expansion through animal trade

Restricting or banning the movement of small African mammals and monkeys may be effective in slowing the expansion of the virus outside Africa.

Captive animals should not be inoculated against smallpox. Instead, infected animals should be isolated from other animals and placed into immediate quarantine. Any animals that might have come into contact with an infected animal should be quarantined and observed for monkeypox symptoms for 30 days.

Reducing the risk of infection in people

During monkeypox outbreaks, close contact with other patients is the most significant risk factor for monkeypox virus infection. In the absence of specific treatment and a vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.

Public health educational messages should focus on the following risks.
Reducing the risk of human-to-human transmission. Close physical contact with monkeypox infected people should be avoided. Gloves and protective equipment should be worn when taking care of ill people. Regular hand washing should be carried out after caring for or visiting sick people.
Reducing the risk of animal-to-human transmission. Efforts to prevent transmission in endemic regions should focus on thoroughly cooking all animal products (blood, meat) before eating. Gloves and other appropriate protective clothing should be worn while handling sick animals or their infected tissues, and during slaughtering procedures.

Controlling infection in health-care settings

Health-care workers caring for patients with suspected or confirmed monkeypox virus infection, or handling specimens from them, should implement standard infection control precautions (see the "Related links" section for more information on "standard precautions in health care").

Healthcare workers and those treating or exposed to patients with monkeypox or their samples should consider being immunized against smallpox. However, the smallpox vaccination should not be administered to people with comprised immune systems.

Samples taken from people and animals with suspected monkeypox virus infection should be handled by trained staff working in suitably equipped laboratories.

274. Botulism

Clostridium botulinum is a bacterium that produces dangerous toxins (botulinum toxins) under low-oxygen conditions.
Botulinum toxins are one of the most lethal substances known.
Botulinum toxins block nerve functions and can lead to respiratory and muscular paralysis.
Human botulism, caused by ingestion of contaminated food, is a rare but potentially fatal disease if not diagnosed rapidly and treated with antitoxin.
Foodborne botulism is often caused by eating improperly processed food. Homemade canned, preserved or fermented foodstuffs require extra caution.



Overview

Human botulism is a serious, potentially fatal disease. However, it is relatively rare. It is an intoxication usually caused by ingestion of potent neurotoxins in contaminated foods. Person to person transmission of botulism does not occur.

Clostridium botulinum produces spores that are heat-resistant and exist widely in the environment, and in the absence of oxygen they germinate, grow and then excrete toxins. There are seven distinct forms of botulinum toxin, types A–G. Four of these (types A, B, E and rarely F) cause human botulism. Types C, D and E cause illness in other mammals, birds and fish.

Botulinum toxins are ingested through improperly processed food in which the bacteria or the spores survive and produce the toxins. Though mainly a foodborne intoxication, botulism can also be caused by intestinal infection in infants, wound infections, and by inhalation.

Symptoms

Early symptoms are marked fatigue, weakness and vertigo, usually followed by blurred vision, dry mouth and difficulty in swallowing and speaking. Vomiting, diarrhoea, constipation and abdominal swelling may also occur. The disease can progress to weakness in the neck and arms, after which the respiratory muscles and muscles of the lower body are affected. The paralysis may make breathing difficult. There is no fever and no loss of consciousness.

The symptoms are not caused by the bacterium itself, but by the toxin produced by the bacterium. Symptoms usually appear within 12 to 36 hours (within a minimum and maximum range of four hours to eight days) after exposure. Incidence of botulism is low, but the mortality rate is high if prompt diagnosis and appropriate, immediate treatment (early administration of antitoxin and intensive respiratory care) are not given. The disease can be fatal in 5 to 10% of cases.

Exposure and transmission

Foodborne botulism

Clostridium botulinum is an anaerobic bacterium, meaning it can only grow in the absence of oxygen. Foodborne botulism occurs when Clostridium botulinum grows and produces toxins in food prior to consumption. Clostridium botulinum produces spores and they exist widely in the environment including soil, river and sea water.

The growth of the bacteria and the formation of toxin occur in products with low oxygen content and certain combinations of storage temperature and preservative parameters. This happens most often in lightly preserved foods and in inadequately processed, home-canned or home-bottled foods.

Clostridium botulinum will not grow in acidic conditions (pH less than 4.6), and therefore the toxin will not be formed in acidic foods (however, a low pH will not degrade any pre-formed toxin). Combinations of low storage temperature and salt contents and/or pH are also used to prevent the growth of the bacteria or the formation of the toxin.

The botulinum toxin has been found in a variety of foods, including low-acid preserved vegetables, such as green beans, spinach, mushrooms, and beets; fish, including canned tuna, fermented, salted and smoked fish; and meat products, such as ham and sausage. The food implicated differs between countries and reflects local eating habits and food preservation procedures. Occasionally, commercially prepared foods are involved.

Though spores of Clostridium botulinum are heat-resistant, the toxin produced by bacteria growing out of the spores under anaerobic conditions is destroyed by boiling (for example, at internal temperature >85°C for five minutes or longer). Therefore, ready-to-eat foods in low oxygen-packaging are more frequently involved in botulism.

Food samples associated with suspect cases must be obtained immediately, stored in properly sealed containers, and sent to laboratories in order to identify the cause and to prevent further cases.

Infant botulism

Infant botulism occurs mostly in infants under six months of age. Different from foodborne botulism caused by ingestion of pre-formed toxins in food, it occurs when infants ingest Clostridium botulinum spores, which germinate into bacteria that colonize in the gut and release toxins. In most adults and children older than about six months, this would not happen because natural defences that develop over time prevent germination and growth of the bacterium.

Clostridium botulinum in infants include constipation, loss of appetite, weakness, an altered cry and a striking loss of head control. Although there are several possible sources of infection for infant botulism, spore-contaminated honey has been associated with a number of cases. Parents and caregivers are therefore warned not to feed honey to the infants before the age of one year1.

Wound botulism

Wound botulism is rare and occurs when the spores get into an open wound and are able to reproduce in an anaerobic environment. The symptoms are similar to the foodborne botulism, but may take up to two weeks to appear. This form of the disease has been associated with substance abuse, particularly when injecting black tar heroin.

Inhalation botulism

Inhalation botulism is rare and does not occur naturally, i.e. it is associated with accidental or intentional (e.g. bioterrorism) events which result in release of the toxins in aerosols. Inhalation botulism exhibits a similar clinical footprint to foodborne botulism. The median lethal dose for humans has been estimated at two nanograms of botulinum toxin per kilogram of bodyweight, which is approximately three times greater than in foodborne cases.

Following inhalation, symptoms become visible between 1–3 days, with longer onset times for lower levels of intoxication. Symptoms proceed in a similar manner to ingestion of botulinum toxin and culminate in muscular paralysis and respiratory failure.

If exposure to the toxin via aerosol inhalation is suspected, additional exposure to the patient and others must be prevented. The patient's clothing must be removed and stored in plastic bags until it can be washed thoroughly with soap and water. The patient should shower and be decontaminated immediately.

Other types of intoxication

Waterborne botulism could theoretically result from the ingestion of the pre-formed toxin. However, as common water treatment processes (e.g. boiling, disinfection with 0.1% hypochlorite bleach solution) destroy the toxin, the risk is considered low.

Botulism of undetermined origin usually involves adult cases where no food or wound source can be identified. These cases are comparable to infant botulism and may occur when the normal gut flora has been altered as a result of surgical procedures or antibiotic therapy.

Adverse effects of the pure toxin have been reported as a result of its medical and/or cosmetic use in patients, see more on 'Botox' below.

Diagnosis and treatment

Diagnosis is usually based on clinical history and clinical examination followed by laboratory confirmation including demonstrating the presence of botulinum toxin in serum, stool or food, or a culture of Clostridium botulinum from stool, wound or food. Misdiagnosis of botulism sometimes occurs as it is often confused with stroke, Guillain-Barré syndrome or myasthenia gravis.

Antitoxin should be administered as soon as possible after a clinical diagnosis. Early administration is effective in reducing mortality rates. Severe botulism cases require supportive treatment, especially mechanical ventilation, which may be required for weeks or even months. Antibiotics are not required (except in the case of wound botulism). A vaccine against botulism exists but it is rarely used as its effectiveness has not been fully evaluated and it has demonstrated negative side effects.

Prevention

Prevention of foodborne botulism is based on good practice in food preparation particularly preservation and hygiene. Botulism may be prevented by the inactivation of the bacterial spores in heat-sterilized (e.g. retorted) or canned products or by inhibiting bacterial growth in other products. Commercial heat pasteurization (vacuum packed pasteurized products, hot smoked products) may not be sufficient to kill all spores and therefore the safety of these products must be based on preventing bacterial growth and toxin production. Refrigeration temperatures combined with salt content and/or acidic conditions will prevent the growth of the bacteria and formation of toxin.

The WHO Five Keys to Safer Food serve as the basis for educational programmes to train food handlers and educate the consumers. They are especially important in preventing food poisoning. The Five Keys are:
1.keep clean
2.separate raw and cooked
3.cook thoroughly
4.keep food at safe temperatures
5.use safe water and raw materials.

'Botox'

The bacterium Clostridium botulinum is the same bacterium that is used to produce Botox, a pharmaceutical product predominantly injected for clinical and cosmetic use. Botox treatments employ the purified and heavily diluted botulinum neurotoxin type A. Treatment is administered in the medical setting, tailored according to the needs of the patient and is usually well tolerated although occasional side effects are observed.

273. World Health Day 2014: small creatures, big threat

Vectors are small organisms such as mosquitoes, bugs, ticks and freshwater snails, that can carry disease from person to person and place to place. They can put our health at risk, at home and when we travel. The World Health Day 2014 campaign focuses on some of the main vectors and the diseases they cause and what we can all do to protect ourselves.

40% of the world's population is at risk from dengue.

Every 1 minute a child dies from malaria in Africa.

An estimated 1.3 million new cases of leishmaniasis occur annually.

272. Creutzfeld-Jakob disease (CJD)

Creutzfeld-Jakob disease (CJD) is a transmissible spongiform encephalopathy. Until the 1990s, three forms of CJD were recognized: sporadic disease, which accounted for the majority of cases and was of unknown origin; familial cases, associated with a gene mutation; and iatrogenic cases, caused by accidental transmission of the causative agent via contaminated instruments or certain transplants. Most cases were seen in people over 50 years of age, and were characterized by personality changes and progressive dementia. Death usually occurred within one year.

In the 1990s, a variant of CJD was recognized (vCJD), which was strongly linked to exposure – probably through food – to a disease of cattle, bovine spongiform encephalopathy. vCJD tends to affect younger patients than classical CJD, and to have a longer duration. Early symptoms include depression or, occasionally, a schizophrenia-like psychosis. As the disease progresses, patients develop more and more neurological signs, including unsteadiness, difficulty walking and involuntary movements