건강과 대안 » 전염

[구제역] Foot and Mouth Disease(Fiebre Aftosa)

건강과대안 — Fri, 31 Dec 2010 11:31:48 +0000

미국 주류학계의 구제역에 대한 입장을 잘 정리한 자료입니다.

마지막 인간에게 미치는 영향(공중보건, Public Health)을 기술한 부분을 보면… 구제역이 인수공통전염병(zoonosis)라는 사실 자체는 부정하지 않고… 인체에 전염된 사례가 40건 정도 있긴 하지만 공중보건 상 고려해야 할 정도는 아니라는 입장을 개진하고 있습니다.

“구제역은 공중보건 상 문제가 될 것으로 고려되지 않는다. 인간에게 구제역 바이러스가 감염된 것은 1921년 후 40건 정도가 진단될 정도로 아주 드물다. (감염된 인간에서는) 병변 부위에 수포가 생기고, 인플루엔자와 유사한 증상이 나타날 수 있다. 이 질병은 일반적으로 약하게 증상이 나타나고, 바이러스가 인체에서 생존하는 기간이 짧으며, 인간대 인간 전염이 이루어지지 않아 감염이 제한적이다.(Foot-and-mouth disease is not considered to be a public health problem. FMDV infections in humans are very rare, with approximately 40 cases diagnosed since 1921. Vesicular lesions and influenza-like symptoms can be seen; the disease is generally mild, short-lived and self-limiting.)”

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Foot and Mouth Disease

Fiebre Aftosa

Last Updated: September 24, 2007

Importance
Foot-and-mouth disease (FMD) is a highly contagious viral disease that primarily affects cloven-hooved livestock and wildlife. Although adult animals generally recover, the morbidity rate is very high in naïve populations, and significant pain and distress occur in some species. Sequelae may include decreased milk yield, permanent hoof damage and chronic mastitis. High mortality rates can be seen in young animals. Although foot-and-mouth disease was once found worldwide, it has been eradicated from some regions including North America and most of Europe. Where it is endemic, this disease is a major constraint to the international livestock trade. Unless strict precautions are followed, FMD can be readily re-introduced into disease-free livestock. Once this occurs, the disease can spread rapidly through a region, particularly if detection is delayed. Outbreaks can severely disrupt livestock production, result in embargoes by trade partners, and require significant resources to control. Direct and indirect economic losses equivalent to several billion US dollars are not uncommon. Since 1997, a PanAsia lineage virus has caused a series of outbreaks in Asia, Africa, the Middle East and Europe. Some outbreaks, particularly those in Taiwan and the United Kingdom, have been devastating.

Etiology
The foot-and-mouth disease virus (FMDV) is a member of the genus Aphthovirus in the family Picornaviridae. There are seven immunologically distinct serotypes – O, A, C, SAT 1, SAT 2, SAT 3 and Asia 1 – and over 60 strains within these serotypes. New strains occasionally develop spontaneously.
FMDV serotypes and strains vary within each geographic region. Serotype O is the most common serotype worldwide. This serotype is responsible for a pan-Asian epidemic that began in 1990 and has affected many countries throughout the world. Other serotypes also cause serious outbreaks. Immunity to one serotype does not provide any cross-protection to other serotypes. Cross-protection against other strains varies with their antigenic similarity.

Transmission
FMDV can be found in all secretions and excretions from acutely infected animals, including expired air, saliva, milk, urine, feces and semen. Pigs, in particular, produce large quantities of aerosolized virus. Animals can shed FMDV for up to four days before the onset of symptoms. This virus is also found in large quantities in vesicle fluid, and peak transmission usually occurs when vesicles rupture. Transmission can occur by direct or indirect contact with infected animals and contaminated fomites; routes of spread include inhalation of aerosolized virus, ingestion of contaminated feed, and entry of the virus through skin abrasions or mucous membranes. The importance of each of these routes varies with the species. For example, pigs are less susceptible to aerosolized virus than cattle or sheep. Sheep may have less obvious symptoms than other species, and have been important in disseminating the virus in some outbreaks. Sexual transmission could be a significant route of spread for the SAT type viruses in African buffalo populations.
Some animals carry FMDV for prolonged periods after recovering from acute disease. Animals with natural or vaccine-induced immunity can also become carriers if they are later exposed to virus; these animals can remain asymptomatic.

FMDV can persist for up to nine months in sheep and up to four months in goats. Most cattle carry this virus for six months or less, but some animals remain persistently infected for up to 3.5 years. Individual African buffalo have been shown to be carriers for at least five years, and the virus can persist in a herd of African buffalo for at least 24 years. Llamas do not become carriers. A single study suggested that pigs may become carriers, but many other studies have found that this species cleared the infection within 3 to 4 weeks. In carriers, FMDV is found only in the esophageal-pharyngeal fluid.

The amount of virus is small, and it may be found only intermittently. Carriers might be able to transmit FMDV to other animals if they come in close contact; the importance of this route of transmission is controversial. Unequivocal evidence for transmission from carriers has been reported only from Africa, where African buffalo can spread the disease to cattle. With the exception of African buffalo, wildlife seems to be infected by contact with domesticated animals; FMDV disappears from the wildlife populations when outbreaks in livestock are controlled. Persistent infections have been reported in some experimentally infected wildlife including fallow (Dama dama) and sika deer (Cervus nippon) and kudu (Tragelaphus strepsiceros), and occasionally in red deer (Cervus elaphus). Deer could carry FMDV for up to 11 weeks.

FMDV can be transmitted on fomites including vehicles, as well as mechanically by animals and other living vectors. Airborne transmission can occur under favorable climatic conditions. FMDV is thought to have been transmitted via aerosols from Brittany to Jersey (approximately 30 miles or 48 km) and for approximately 70 miles (113 km) from Jersey to the Isle of Wight. There is limited information on the survival of FMDV in the environment, but most studies suggest that it remains viable, on average, for three months or less. In very cold climates, survival up to six months may be possible. Virus stability increases at lower temperatures; in cell culture medium at 4°C (39°F), this virus can remain viable for up to a year. It was reported to survive on bran and hay for more than three months in a laboratory. It can also remain viable for approximately two months on wool at 4°C, with significantly decreased survival when the temperature increases to 18°C (64°F), and for 2 to 3 months in bovine feces. Organic material protects the virus from drying, and enhances its survival on fomites. Virus survival is also enhanced when FMDV is protected from sunlight. FMDV is inactivated at pH below 6.5 or above 11. This virus can persist in meat and other animal products when the pH remains above 6.0,but it is inactivated by acidification of muscles during rigor mortis. It can survive for long periods in chilled or frozen lymph nodes or bone marrow.
In humans, FMDV may be carried in the nasal passages for a period of time. In one study, this virus was detected in the nasal passages of one of eight people 28 hours after exposure to infected animals, and from none of the eight at 48 hours. More recent studies have found that FMDV is not transmitted by people when personal hygiene and biosecurity protocols are followed, and suggest that nasal carriage of the virus may be unimportant. The discrepancy between these studies remains to be resolved.

Incubation Period
In cattle, the incubation period varies from two to 14 days, depending on the dose of the virus and route of infection. In pigs, the incubation period is usually two days or more, but can be as short as 18-24 hours. The incubation period in sheep is usually 3 to 8 days. Incubation periods as short as 24 hours and as long as 12 days have been reported in this species after experimental infection.

Good biosecurity measures should be practiced on uninfected farms to prevent entry of the virus.
Vaccination may be used to reduce the spread of FMDV or protect specific animals (e.g. those in zoological collections) during some outbreaks. The decision to use vaccination is complex, and varies with the scientific, economic, political and societal factors specific to the outbreak. Vaccines are also used in endemic regions to protect animals from clinical disease. FMDV vaccines must closely match the serotype and strain of the infecting strain. Vaccination with one serotype does not protect the animal against other serotypes, and may not protect the animal completely or at all from other strains of the same serotype. Currently, there is no universal FMD vaccine. Vaccine banks contain a wide variety of strains, particularly those judged to be the greatest threat of introduction, for use in an outbreak. Some countries maintain individual vaccine banks. There are also three international vaccine banks: the North American FMD Vaccine Bank (for Canada, the U.S. and Mexico), the E.U. Vaccine Bank (for all EU countries) and the International Vaccine Bank (for a variety of countries including Australia, New Zealand and some European nations).
Humans are thought to carry FMDV mechanically for a short period of time, based on a study that found this virus in the nasal passages of one of eight people 28 hours after they had been exposed to infected animals and none of the eight people at 48 hours. People who have been exposed to infected animals should avoid susceptible livestock for a designated period, usually a few days to a week. Some recent studies suggest that extended avoidance periods may not be necessary if good biosecurity practices, including effective personal hygiene protocols (showering or washing hands, and changing clothing), are followed. The discrepancy between these studies remains to be resolved, and government authorities should be consulted for the most recent waiting period recommendations.
Transmission of FMDV from wildlife in southern Africa is controlled by separating wildlife from domesticated livestock with fences, and by vaccination of livestock.

Public Health
Foot-and-mouth disease is not considered to be a public health problem. FMDV infections in humans are very rare, with approximately 40 cases diagnosed since 1921. Vesicular lesions and influenza-like symptoms can be seen; the disease is generally mild, short-lived and self-limiting.

[돼지독감] 발열증상 사라진후 오랫동안 독감 바이러스 전염 가능

건강과대안 — Tue, 15 Sep 2009 10:59:30 +0000

돼지독감의 주요임상 증상 중 하나인 고열증상이 사라진 후에도 오랫동안 돼지독감 바이러스를 전염시킬 수 있다는 연구결과가 나왔습니다. 다시 말해 돼지독감에 감염된 환자가 회복된 후에도 바이러스를 퍼트릴 수 있다는 의미이며…이는 돼지에서 임상증상이 나타나지 않은 상태에서 최장 3개월 동안 바이러스를 퍼트릴 수 있다는 미국수의사회의 Fact sheet와 일맥상통하는 연구결과라고 생각합니다.

미국 질병관리본부는 현재 미국에서 100만 이상이 돼지독감 바이러스에 감염되었으며, 600명 이상이 사망한 것으로 추정하고 있습니다.

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Studies: Swine flu spreads long after fever stops

By MARILYNN MARCHIONE, AP Medical Writer Marilynn Marchione, Ap Medical Writer – 2 hrs 20 mins ago

출처 : AP통신 2009년 9월 15일 오전 7시 40분

SAN FRANCISCO – When the coughing stops is probably a better sign of when a swine flu patient is no longer contagious, experts said after seeing new research that suggests the virus can still spread many days after a fever goes away.

The federal Centers for Disease Control and Prevention has been telling people to stay home from work and school and avoid contact with others until a day after their fever breaks. The new research suggests they may need to be careful for longer — especially at home where the risk of spreading the germ is highest.

Swine flu also appears to be contagious longer than ordinary seasonal flu, several experts said.

“This study shows you’re not contagious for a day or two. You’re probably contagious for about a week,” said Gaston De Serres, a scientist at the Institute of Public Health in Quebec.

He presented one of the studies Monday at an American Society for Microbiology conference. It is the first big meeting of infectious disease experts since last spring’s emergence of swine flu, which now accounts for nearly all of the flu cases in the United States. More than 1 million Americans have been infected and nearly 600 have died from it, the CDC estimates.

It is unclear whether the new research will lead the CDC to rethink its advice on how long people with swine flu should hole up. Long breaks from school and work do not seem worth it for a virus that now seems to cause mostly mild illness, said the CDC’s flu chief, Nancy Cox. Swine flu is spreading so widely now that confining the sick does less good, she said.

“We tried to have our guidance balance out all of these factors,” she said. “It’s just virtually impossible not to have virus introduced into settings such as schools and universities.”

Doctors know that people can spread ordinary seasonal flu for a couple of days before and after symptoms start by studying virus that patients shed in mucus. The first such studies of swine flu are just coming out now, and they imply a longer contagious period for the novel bug.

“It’s probably realistic that this virus sheds much longer than seasonal flu,” said Dr. Jonathan McCullers, an infectious diseases specialist at St. Jude Children’s Research Hospital in Memphis, Tenn.

Three reports suggest this is so. De Serres and other researchers in Canada took nose and throat swabs from 43 patients with lab-confirmed flu and dozens of other sick family members.

On the eighth day after symptoms first appeared, 19 to 75 percent showed signs of virus remaining in their noses, depending on the type of test used.

“This proportion appears to be very big, and it is,” but it’s not clear how much virus is needed to actually spread flu, so the lower number is more reliable, he said.

Dr. David C. Lye reported on 70 patients treated at Tan Tock Seng Hospital in Singapore. Using a very sensitive test to detect virus in the nose or throat, he found that 80 percent had it five days after symptoms began, and 40 percent seven days after. Some still harbored virus as long as 16 days later. How soon they started on antiviral medicines such as Tamiflu made a difference in how much virus was found, but not whether virus was present at all.

A third report came from Dr. Guillermo Ruiz-Palacios of the National Institutes of Medical Science and Nutrition in Mexico, where the first cases of swine flu were detected.

Infected people “shed the virus for a very, very long time,” often for more than a week after the start of symptoms, he told the conference. This was especially true of obese people, and patients who started on medicines longer than two days after symptoms first appeared.

The new reports suggest a longer contagious period for swine flu, but how long is not clear, Cox said. Even with it in your nose, “you might not be shedding enough virus to infect other people,” she said.

That is why signs like coughing may matter more, De Serres said.

“Contagiousness varies, not only with the presence of the virus, but the other symptoms that would make you transmit,” he said.

Swine flu symptoms can include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue, and sometimes diarrhea and vomiting. Young children may be cranky, less playful or not eat as much as normal, the CDC advises.

The agency’s advice to stay home for a day after fever breaks does not apply to health care settings. There, confinement for seven days from the start of symptoms — or until they go away, whichever is longer — is still advised.

People who have had swine flu should cover their mouths when they cough or sneeze and wash their hands a lot once they do return to work and school, the CDC says.

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On the Net:

Swine flu info: http://www.flu.gov

CDC advice: http://www.cdc.gov/h1n1flu/guidance/exclusion.htm and http://www.cdc.gov/h1n1flu/qa.htm

Medical conference: http://www.icaac.org