What You Should Know About Avian Flu

This fact sheet provides general information about avian influenza (bird flu) and information about one type of bird flu, called avian influenza A (H5N1), that has caused infections in birds and in humans. Also see Questions and Answers on the CDC website and Frequently Asked Questions (FAQs) on the World Health Organization (WHO) website.

Avian Influenza (Bird Flu)

Avian influenza in birds

Avian influenza is an infection caused by avian (bird) influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, avian influenza is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them.

禽流感是一種由病毒感染引起的禽 （鳥）流行性感冒（流感）病毒。這些流感病毒在禽鳥中自然產生的。野生鳥類攜帶的病毒在世界範圍內的腸子，但通常不生病他們。不過，禽流感是鳥類中非常傳染性和可以做一些家養鳥類，包括雞，鴨和火雞，病得很重，殺死他們。

Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated secretions or excretions or with surfaces that are contaminated with secretions or excretions from infected birds. Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the virus.

流感病毒感染 的鳥棚在他們的唾液，鼻腔分泌物和糞便。易感鳥類受到感染時，他們已接觸受到污染的分泌 物或排泄物，或表面的分泌物或排泄物污染從受感染的鳥類。家養鳥類可能被感染禽流感病毒 通過直接接觸感染的水禽或其他被感染的家禽，或通過接觸表面（如灰塵或籠子）或材料（如水或飼料）已經被污染了該病毒。

Infection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The “low pathogenic” form may go undetected and usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the highly pathogenic form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours.

感染禽流感病毒在家禽中引起兩種主 要形式的疾病的特點是極端的高，低毒性。 “低致病性”可能不被發現，通常僅 導致輕微症狀（如羽毛凌亂和產蛋量下降）。但是，高致病性病毒傳播更加迅速通過成群的家禽。這種形式可能會導致多種疾病，影響到 內部器官，具有死亡率可達到 90-100％，通常在48小時。

Human infection with avian influenza viruses

There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds.

有許多不同的亞型 A型流感病毒。這些亞型的不同，因為在某些蛋白質的變化，表面上的流感病毒（血凝素[房屋]和神經氨酸酶[不適用]蛋白）。房委會有16個已知的亞型和9個已 知的北美流感病毒亞型。許多不同組合的HA和NA蛋白是可能的。每個組合都代表一個不同的亞型。所有已知的甲型流感病毒亞型中可以找到鳥類。

Usually, “avian influenza virus” refers to influenza A viruses found chiefly in birds, but infections with these viruses can occur in humans. The risk from avian influenza is generally low to most people, because the viruses do not usually infect humans. However, confirmed cases of human infection from several subtypes of avian influenza infection have been reported since 1997. Most cases of avian influenza infection in humans have resulted from contact with infected poultry (e.g., domesticated chicken, ducks, and turkeys) or surfaces contaminated with secretion/excretions from infected birds. The spread of avian influenza viruses from one ill person to another has been reported very rarely, and has been limited, inefficient and unsustained.

通常，“禽流感病 毒”是指A型流感病毒主要是在發現鳥類，但這些病毒可感染發生在人類身上。從禽流感的風險是一般人普遍偏低，因為病毒通常不會感染人類。但是，人類感染確診病例從幾個亞型 禽流感病毒自1997年以來已報告。多數情況下在人類感染禽流感已造成接觸受感染家禽（如家養的雞，鴨和火雞）或表面污染的分泌物/排泄物從受感染的鳥類。在傳播禽流感病毒從一個人到另一個 病人有報導很少，並且已經有限，效率低，不能持續。

“Human influenza virus” usually refers to those subtypes that spread widely among humans. There are only three known A subtypes of influenza viruses (H1N1, H1N2, and H3N2) currently circulating among humans. It is likely that some genetic parts of current human influenza A viruses came from birds originally. Influenza A viruses are constantly changing, and they might adapt over time to infect and spread among humans.

During an outbreak of avian influenza among poultry, there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with secretions or excretions from infected birds.

Symptoms of avian influenza in humans have ranged from typical human influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications. The symptoms of avian influenza may depend on which virus caused the infection.

Studies done in laboratories suggest that some of the prescription medicines approved in the United States for human influenza viruses should work in treating avian influenza infection in humans. However, influenza viruses can become resistant to these drugs, so these medications may not always work. Additional studies are needed to demonstrate the effectiveness of these medicines.

Avian Influenza A (H5N1)

Influenza A (H5N1) virus – also called “H5N1 virus” – is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to them. H5N1 virus does not usually infect people, but infections with these viruses have occurred in humans. Most of these cases have resulted from people having direct or close contact with H5N1-infected poultry or H5N1-contaminated surfaces.

Avian influenza A (H5N1) outbreaks

For current information about avian influenza A (H5N1) outbreaks, see the CDC's Outbreaks page.

Human health risks during the H5N1 outbreak

Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans. However, it is possible that those cases in the most severely ill people are more likely to be diagnosed and reported, while milder cases go unreported. For the most current information about avian influenza and cumulative case numbers, see the World Health Organization (WHO) avian influenza website.

Of the human cases associated with the ongoing H5N1 outbreaks in poultry and wild birds in Asia and parts of Europe, the Near East and Africa, more than half of those people reported infected with the virus have died. Most cases have occurred in previously healthy children and young adults and have resulted from direct or close contact with H5N1-infected poultry or H5N1-contaminated surfaces. In general, H5N1 remains a very rare disease in people. The H5N1 virus does not infect humans easily, and if a person is infected, it is very difficult for the virus to spread to another person.

While there has been some human-to-human spread of H5N1, it has been limited, inefficient and unsustained. For example, in 2004 in Thailand, probable human-to-human spread in a family resulting from prolonged and very close contact between an ill child and her mother was reported. Most recently, in June 2006, WHO reported evidence of human-to-human spread in Indonesia. In this situation, 8 people in one family were infected. The first family member is thought to have become ill through contact with infected poultry. This person then infected six family members. One of those six people (a child) then infected another family member (his father). No further spread outside of the exposed family was documented or suspected.

Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. If H5N1 virus were to gain the capacity to spread easily from person to person, an influenza pandemic (worldwide outbreak of disease) could begin. For more information about influenza pandemics, see PandemicFlu.gov.

No one can predict when a pandemic might occur. However, experts from around the world are watching the H5N1 situation in Asia and Europe very closely and are preparing for the possibility that the virus may begin to spread more easily and widely from person to person.

Treatment and vaccination for H5N1 virus in humans

The H5N1 virus that has caused human illness and death in Asia is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat influenza caused by H5N1 virus, but additional studies still need to be done to demonstrate their effectiveness.

For information about H5N1 vaccines, visithttp://www.cdc.gov/flu/avian/gen-info/qa.htm.

Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus. (SOURCE: Center for Disease Control and Prevention, USA)

Q. What is dengue hemorrhagic fever (DHF)?
A. DHF is a more severe form of dengue. It can be fatal if unrecognized and not properly treated. DHF is caused by infection with the same viruses that cause dengue. With good medical management, mortality due to DHF can be less than 1%.

Q. How are dengue and dengue hemorrhagic fever (DHF) spread?
A. Dengue is transmitted to people by the bite of an Aedes mosquito that is infected with a dengue virus. The mosquito becomes infected with dengue virus when it bites a person who has dengue or DHF and after about a week can transmit the virus while biting a healthy person. Dengue cannot be spread directly from person to person.

Q. What are the symptoms of the disease?
A. The principal symptoms of dengue are high fever, severe headache, backache, joint pains, nausea and vomiting, eye pain, and rash. Generally, younger children have a milder illness than older children and adults.

Dengue hemorrhagic fever is characterized by a fever that lasts from 2 to 7 days, with general signs and symptoms that could occur with many other illnesses (e.g., nausea, vomiting, abdominal pain, and headache). This stage is followed by hemorrhagic manifestations, tendency to bruise easily or other types of skin hemorrhages, bleeding nose or gums, and possibly internal bleeding. The smallest blood vessels (capillaries) become excessively permeable (“leaky”), allowing the fluid component to escape from the blood vessels. This may lead to failure of the circulatory system and shock, followed by death, if circulatory failure is not corrected.

Q. What is the treatment for dengue?
A. There is no specific medication for treatment of a dengue infection. Persons who think they have dengue should use analgesics (pain relievers) with acetaminophen and avoid those containing aspirin. They should also rest, drink plenty of fluids, and consult a physician.

Q. Is there an effective treatment for dengue hemorrhagic fever (DHF)?
A. As with dengue, there is no specific medication for DHF. It can however be effectively treated by fluid replacement therapy if an early clinical diagnosis is made. Hospitalization is frequently required in order to adequately manage DHF. Physicians who suspect that a patient has DHF may want to consult the Dengue Branch at CDC, for more information.

Q. Where can outbreaks of dengue occur?
A. Outbreaks of dengue occur primarily in areas where Aedes aegypti (sometimes also Aedes albopictus) mosquitoes live. This includes most tropical urban areas of the world. Dengue viruses may be introduced into areas by travelers who become infected while visiting other areas of the tropics where dengue commonly exists.

In the America region, all dengue virus serotypes are now present. DEN-3 was reintroduced into Central America in 1994 and is now found in several countries in the region. Since this serotype has been absent from the Americas for almost 20 years, the population has a low level of immunity and the virus is expected to spread rapidly.

Q. What can be done to reduce the risk of acquiring dengue?
A. There is no vaccine for preventing dengue. The best preventive measure for residents living in areas infested with Aedes aegypti is to eliminate the places where the mosquito lays her eggs, primarily artificial containers that hold water.

Items that collect rainwater or are used to store water (for example, plastic containers, 55-gallon drums, buckets, or used automobile tires) should be covered or properly discarded. Pet and animal watering containers and vases with fresh flowers should be emptied and scoured at least once a week. This will eliminate the mosquito eggs and larvae and reduce the number of mosquitoes present in these areas.

For travelers to areas with dengue, a well as people living in areas with dengue, the risk of being bitten by mosquitoes indoors is reduced by utilization of air conditioning or windows and doors that are screened. Proper application of mosquito repellents containing 20% to 30% DEET as the active ingredient on exposed skin and clothing decreases the risk of being bitten by mosquitoes. The risk of dengue infection for international travelers appears to be small, unless an epidemic is in progress.

Q. How can we prevent epidemics of dengue hemorrhagic fever (DHF)?
A. The emphasis for dengue prevention is on sustainable, community-based, integrated mosquito control, with limited reliance on insecticides (chemical larvicides and adulticides). Preventing epidemic disease requires a coordinated community effort to increase awareness about dengue/DHF, how to recognize it, and how to control the mosquito that transmits it. Residents are responsible for keeping their yards and patios free of sites where mosquitoes can be produced.

Questions and Answers about Dengue Fever and Dengue Hemorrhagic Fever. (SOURCE: Center for Disease Control and Prevention, USA)

Food

To avoid illness, travelers should be advised to select food with care. All raw food is subject to contamination. Particularly in areas where hygiene and sanitation are inadequate, the traveler should be advised to avoid salads, uncooked vegetables, and unpasteurized milk and milk products such as cheese, and to eat only food that has been cooked and is still hot or fruit that has been washed in clean water and then peeled by the traveler personally. Undercooked and raw meat, fish, and shellfish can carry various intestinal pathogens. Cooked food that has been allowed to stand for several hours at ambient temperature can provide a fer-tile medium for bacterial growth or be recontaminated by food-handling techniques so should be thoroughly reheated before serving. Consumption of food and beverages obtained from street vendors has been associated with an increased risk of illness. Travelers should be advised that these recommendations also include eating eggs that have been thoroughly cooked, alone or in sauces, and washing their own hands or using hand gel with more than 60% alcohol prior to eating, after using the bathroom or changing diapers and after direct contact with preschool children, animals or any feces.

The easiest way to guarantee a safe food source for an infant younger than 6 months of age is to have the infant breastfeed. If the infant has already been weaned from the breast, formula prepared from commercial powder and boiled water is the safest and most practical food.

Water

SWIMMING

A variety of infections (e.g., skin, ear, eye, respiratory, neurologic, and diarrheal infections) have been linked to wading or swimming in the ocean, freshwater lakes and rivers, and swimming pools, particularly if the swimmer’s head is sub-merged. Water may be contaminated by other swimmers and from sewage, animal waste, and wastewater run-off. Diarrhea and other serious waterborne infections can be spread when disease-causing organisms from human or animal feces are introduced into the water. Accidentally swallowing small amounts of fecally contaminated water can cause illness. Travelers should be warned to try to avoid swallowing water while engaging in aquatic activities. All travelers who have diarrhea should refrain from swimming to avoid contaminating recreational water.

Travelers who swim at freshwater or marine beaches should be advised to avoid swimming or wading 1) at beaches that may be contaminated with human sewage or animal feces (e.g., cattle, sheep, dogs); 2) near storm drains; 3) following heavy rainfall; 4) in freshwater streams, canals, and lakes in schistosomiasis-endemic areas of the Caribbean, South America, Africa, and Asia (see Map 4-11, Geographic distribution of schistosomiasis); 5) in bodies of water that may be contaminated with urine from animals infected with Leptospira; and 6) with open cuts or abrasions that might serve as entry points for pathogens. In certain areas where fatal primary amebic meningoencephalitis has occurred after swimming in warm freshwater lakes or rivers, thermally polluted areas around industrial complexes, and hot springs, travelers should avoid submerging the head and should wear nose plugs when entering untreated water to prevent water containing the pathogen from getting up the nose and causing infection.

Generally, for infectious disease prevention, pools that contain chlorinated water can be considered safe places to swim if the disinfectant levels and pH are properly maintained. However, some organisms are moderately (e.g., Giardia, hepatitis A, norovirus) to highly (i.e., Cryptosporidium) resistant to chlorine levels commonly found in chlorinated swimming pools, so travelers also should avoid swallowing chlorinated swimming pool water. Poorly maintained swimming pools or spas may not only spread disease from fellow swimmers but may allow amplification of environmental contaminants, such as Pseudomonas or Legionella, to levels that may cause disease (7). Travelers may choose to take test kits or strips to check pool chlorine and pH levels when traveling.

DRINKING

Water that has been adequately chlorinated according to the minimum recommended water treatment standards used in the United States will afford substantial protection against viral and bacterial waterborne diseases. However, chlorine treatment alone, as used in the routine disinfection of water, may not kill some enteric viruses and the parasitic organisms that cause giardiasis, amebiasis, and cryptosporidiosis. In areas where chlorinated tap water is not available or where hygiene and sanitation are poor, travelers should be advised that only the following may be safe to drink: beverages, such as tea and coffee, made with boiled water, canned or unopened bottled beverages, including water, carbonated mineral water, soft drinks, beer, and wine.

Where water might be contaminated, travelers should be advised that ice should also be considered contaminated and should not be used in beverages. If ice has been in contact with containers used for drinking, travelers should be advised to clean the containers thoroughly, preferably with soap and hot water, after the ice has been discarded.

It is safer to drink a beverage directly from the can or bottle than from a questionable container. However, water on the outside of beverage cans or bottles may also be contaminated. Therefore, travelers should be advised to dry wet cans or bottles before they are opened and to wipe clean surfaces with which the mouth will have direct contact. Where water may be contaminated, travelers should be advised to avoid brushing their teeth with tap water and that locally prepared fruit juice may also contain tap water.

Treatment of Drinking Water

Travelers should be advised of the following methods for treating water to make it safe for drinking and other purposes (8).

Boiling

Boiling is by far the most reliable method to make water of uncertain purity safe for drinking. Water should be brought to a vigorous rolling boil for 1 minute and allowed to cool to room temperature; ice should not be added. This procedure will kill all common waterborne pathogens. Adding a pinch of salt to each quart or pouring the water several times from one clean container to another will improve the taste.

Chemical Disinfection

Chlorine, in various forms, can also be used for chemical disinfection. However, its germicidal activity varies greatly with the pH, temperature, and organic content of the water to be purified; therefore, it can produce less consistent levels of disinfection depending on the water quality (e.g., turbid water). In addition, some forms of chlorine disinfectant may not be stable through long-term storage or at high temperatures.

Chemical disinfection with iodine, which is not as sensitive as chlorine to pH shifts, is an alternative method of water treatment when it is not feasible to boil water. However, using iodine cannot be relied on to kill Cryptosporidium. Cloudy water should be strained through a clean cloth into a container to remove any sediment or floating matter, and then the water should be treated with iodine. Two well-tested methods for disinfection with iodine are the use of tincture of iodine (Table 2-2) and tetraglycine hydroperiodide tablets (e.g., Globaline, Potable-Aqua, or Coghlan’s). These tablets are available from pharmacies and sporting goods stores. The manufacturer’s instructions should be followed. If water is cloudy, the number of tablets used should be doubled; if water is extremely cold (<41°F), an attempt should be made to warm the water, and the recommended contact time should be increased to achieve reliable disinfection. Iodine treatment of water is intended for short-term use only to avoid over exposure to iodine (9). When the only water available is iodine treated, it should be used for only a few weeks.

Water Filters

Portable filters currently on the market will provide various degrees of protection against microbes but are generally meant to be used in conjunction with disinfection for greatest protection from pathogens. Reverse-osmosis filters provide protection against viruses, bacteria, and protozoa, but they are expensive and larger than most filters used by backpackers, and the small pores on this type of filter are rapidly plugged by muddy or cloudy water. In addition, the membranes in some filters can be damaged by chlorine in water. Microstrainer filters with pore sizes in the 0.1- to 0.3-µm range can remove bacteria and protozoa from drinking water, but they do not remove viruses. To kill viruses, travelers using microstrainer filters should be advised to disinfect the water with iodine or chlorine after filtration, as described previously. Some filtration kits come with an additional filter effective against viruses. Protozoa can be highly (Cryptosporidium) to moderately (Giardia) resistant to halogen treatment, particularly in cold or turbid water. As a result, filtration or boiling should be considered as a safer alternative to chemical disinfection. A travelers’ guide to buying water filters for preventing cryptosporidiosis and giardiasis can be found at URL: http://www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/factsht_crypto_prevent_water.htm. Increased protection can be obtained by using a filter that removes Giardia and Cryptosporidium that is combined with an iodine-impregnated resin which is more effective against bacteria and some viruses.

Filters that are designed to remove Cryptosporidium and Giardia carry one of the four messages below—verbatim—on the package label.

• Reverse osmosis
• Absolute pore size of ?1 micron
• Tested and certified by NSF International (formerly the National Sanitation Foundation) Standard 53 or NSF Standard 58 for cyst removal
• Tested and certified by NSF Standard 53 or NSF Standard 58 for cyst reduction

Filters may not be designed to remove Cryptosporidium and Giardia if they are labeled only with these words:

• Nominal pore size of ?1 micron
• One-micron filter
• Effective against Giardia
• Effective against parasites
• Carbon filter
• Water purifier
• Environmental Protection Agency (EPA)-approved (Caution: EPA does not approve or test filters.)
• EPA-registered (Caution: EPA does not register filters for Cryptosporidium removal)
• Activated carbon
• Removes chlorine
• Ultraviolet light
• Pentiodide resins
• Water softener

Filters collect organisms from water. Anyone changing cartridges should wash hands afterwards. Filters may not remove Cryptosporidium as well as boiling does, because even good brands of filters may sometimes have manufacturing flaws that allow small numbers of organisms to pass through the filter. In addition, poor filter maintenance or failure to replace filter cartridges as recommended by the manufacturer can cause a filter to fail.

Proper selection, operation, care, and maintenance of water filters are essential to producing safe water. The manufacturers’ instructions should be followed. NSF International, an independent testing company, tests and certifies water filters for their ability to remove protozoa, but not for their ability to remove bacteria or viruses. Few published scientific reports have evaluated the efficacy of specific brands or models of filters against bacteria and viruses in water.

Brief Information and Recommendations for Keeping Food and Water Healthful.  (SOURCE: Center for Disease Control and Prevention, USA)

What is hepatitis A?

General information, questions and answers about Hepatitis A.  (SOURCE: familydoctor.org, USA)

General information, questions and answers about Hepatitis B.  (SOURCE: familydoctor.org, USA)

General information, questions and answers about Hepatitis C.  (SOURCE: familydoctor.org, USA)

What is influenza?

General information, questions and answers about Influenza and the influenza vaccine.  (SOURCE: familydoctor.org, USA)