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Zoo tigers succumb to avian influenza
Newsdesk Zoo tigers succumb to avian influenza the virus spreads systemically in the birds. When an animal eats such infected birds, it is easy to envision that
Rights were not granted to include this image in electronic media. Please refer to the printed journal. Reuters
The Sriracha tiger zoo in Chonburi, Thailand, has been under quarantine since the middle of October, because of an outbreak of avian influenza in captive tigers (Panthera tigris) there. Among 441 tigers at the zoo, authorities identified 102 cases of avian influenza; almost half of the sick tigers were dead by the end of October. The cases ranged in age from 8 months to 2 years. Clinical signs in the tigers included lethargy, respiratory distress, and fever. Avian influenza-infected chicken carcasses are suspected to be the source of infection. One broker, who bought chicken from multiple slaughterhouses, has been identified as supplying the animal feed to the zoo, according to the October 29, 2004 report (http://www.oie.int) to the World Organisation for Animal Health (OIE). The trace-back investigation is ongoing. Virginia Hinshaw (Provost and Executive Vice Chancellor, University of California, Davis), is not surprised that tigers can be infected and even die from these influenza viruses. “Chickens infected with the virulent H5N1 virus contain large amounts of virus because
Even big cats have not got the stomach for flu
their respiratory tract would be exposed to virus during that process and result in infection”, Hinshaw told TLID. Healthy animals include tiger cubs (under 6 months of age) that were fed with chicken meat and pork. Hinshaw notes that because there is less genetic diversity among zoo animals, the level of virus exposure might explain the
difference in susceptibility to infection among the zoo tigers. Juan Lubroth (Infectious Disease Group, Food and Agriculture Organization of the United Nations, Rome, Italy), points out bad practice in the animal feed source. “As a veterinarian, any sick animal that is visibly sick and has died is not fit for animal consumption and should not enter into the animal food chain. We are not surprised that when you feed a nontypical host great quantities of virus they will become infected”, he told TLID. Outbreak control measures included separating sick and healthy tigers in the zoo, and feeding tigers well-cooked chicken carcasses or pork and beef, as well as treatment with an antiviral agent, oseltamivir. According to the OIE report: “19 other tigers presented clinical signs after the antiviral drug was no longer administered, with two deaths on October 27, and a further three deaths on October 28”. To date, no clinical disease or deaths have been seen in other animals housed at the zoo. Mary Quirk
Recombinant tuberculosis booster vaccine looks promising Booster vaccination with a recombinant tuberculosis vaccine could provide a “practical and efficient strategy for enhancing and pro longing antimycobacterial immunity”, according to Helen McShane (University of Oxford, UK) and colleagues (Nat Med 2004; 10: 1240–244). Vaccination with the BCG vaccine, an attenuated Mycobacterium bovis, provides protection against childhood tuberculosis but only for about 10 years, and repeated doses of BCG do not boost immunity. With the emergence of drug-resistant tuberculosis and the increased incidence of tuberculosis in Asia and Africa as a result of HIV infection, improved vaccination strategies are urgently needed. Because M tuberculosis is an intracellular pathogen, explains McShane,
716
“we need to induce a cellular immune response with vaccination. Although there are several ways to do this, in animal models repeated vaccinations with the same vaccine do not increase cellular immunity, in part because of immunity to the vaccine vector itself”. To circumvent this problem, McShane and her co-workers are using a heterologous prime-boost vaccination strategy in which the same antigen is given in two different vaccines. They have developed a recombinant modified vaccinia virus Ankara (MVA) expressing antigen 85A, an immunodominant antigen present in all mycobacteria. In their phase I trial, MVA85A vaccine alone in BCG-naive healthy volunteers induced a strong cellular response to mycobacterial proteins. In volunteers who had been vaccinated up to 38
years previously with BCG, MVA85 induced a 5–30-times higher cellular response than that seen in naive volunteers given BCG alone. If all goes to plan, explains McShane, “we aim to move to an efficacy trial in South Africa of MVA85A by 2006.” “These are promising results from the first recombinant tuberculosis vaccine to pass through phase I safety trials”, comments Mark Doherty (Statens Serum Institute, Copenhagen, Denmark), “but they are [only] phase I results so too much should not be read into them in terms of eventual effectiveness.” Many other candidate vaccines also are about to enter clinical trials, adds Doherty, “including our own Hybrid1 (DK) vaccine. All of these show promise in animals but whether that promise is fulfilled, only time will tell.” Jane Bradbury
Infectious Diseases Vol 4 December 2004
http://infection.thelancet.com
Rights were not granted to include this image in electronic media. Please refer to the printed journal. Reuters
The Sriracha tiger zoo in Chonburi, Thailand, has been under quarantine since the middle of October, because of an outbreak of avian influenza in captive tigers (Panthera tigris) there. Among 441 tigers at the zoo, authorities identified 102 cases of avian influenza; almost half of the sick tigers were dead by the end of October. The cases ranged in age from 8 months to 2 years. Clinical signs in the tigers included lethargy, respiratory distress, and fever. Avian influenza-infected chicken carcasses are suspected to be the source of infection. One broker, who bought chicken from multiple slaughterhouses, has been identified as supplying the animal feed to the zoo, according to the October 29, 2004 report (http://www.oie.int) to the World Organisation for Animal Health (OIE). The trace-back investigation is ongoing. Virginia Hinshaw (Provost and Executive Vice Chancellor, University of California, Davis), is not surprised that tigers can be infected and even die from these influenza viruses. “Chickens infected with the virulent H5N1 virus contain large amounts of virus because
Even big cats have not got the stomach for flu
their respiratory tract would be exposed to virus during that process and result in infection”, Hinshaw told TLID. Healthy animals include tiger cubs (under 6 months of age) that were fed with chicken meat and pork. Hinshaw notes that because there is less genetic diversity among zoo animals, the level of virus exposure might explain the
difference in susceptibility to infection among the zoo tigers. Juan Lubroth (Infectious Disease Group, Food and Agriculture Organization of the United Nations, Rome, Italy), points out bad practice in the animal feed source. “As a veterinarian, any sick animal that is visibly sick and has died is not fit for animal consumption and should not enter into the animal food chain. We are not surprised that when you feed a nontypical host great quantities of virus they will become infected”, he told TLID. Outbreak control measures included separating sick and healthy tigers in the zoo, and feeding tigers well-cooked chicken carcasses or pork and beef, as well as treatment with an antiviral agent, oseltamivir. According to the OIE report: “19 other tigers presented clinical signs after the antiviral drug was no longer administered, with two deaths on October 27, and a further three deaths on October 28”. To date, no clinical disease or deaths have been seen in other animals housed at the zoo. Mary Quirk
Recombinant tuberculosis booster vaccine looks promising Booster vaccination with a recombinant tuberculosis vaccine could provide a “practical and efficient strategy for enhancing and pro longing antimycobacterial immunity”, according to Helen McShane (University of Oxford, UK) and colleagues (Nat Med 2004; 10: 1240–244). Vaccination with the BCG vaccine, an attenuated Mycobacterium bovis, provides protection against childhood tuberculosis but only for about 10 years, and repeated doses of BCG do not boost immunity. With the emergence of drug-resistant tuberculosis and the increased incidence of tuberculosis in Asia and Africa as a result of HIV infection, improved vaccination strategies are urgently needed. Because M tuberculosis is an intracellular pathogen, explains McShane,
716
“we need to induce a cellular immune response with vaccination. Although there are several ways to do this, in animal models repeated vaccinations with the same vaccine do not increase cellular immunity, in part because of immunity to the vaccine vector itself”. To circumvent this problem, McShane and her co-workers are using a heterologous prime-boost vaccination strategy in which the same antigen is given in two different vaccines. They have developed a recombinant modified vaccinia virus Ankara (MVA) expressing antigen 85A, an immunodominant antigen present in all mycobacteria. In their phase I trial, MVA85A vaccine alone in BCG-naive healthy volunteers induced a strong cellular response to mycobacterial proteins. In volunteers who had been vaccinated up to 38
years previously with BCG, MVA85 induced a 5–30-times higher cellular response than that seen in naive volunteers given BCG alone. If all goes to plan, explains McShane, “we aim to move to an efficacy trial in South Africa of MVA85A by 2006.” “These are promising results from the first recombinant tuberculosis vaccine to pass through phase I safety trials”, comments Mark Doherty (Statens Serum Institute, Copenhagen, Denmark), “but they are [only] phase I results so too much should not be read into them in terms of eventual effectiveness.” Many other candidate vaccines also are about to enter clinical trials, adds Doherty, “including our own Hybrid1 (DK) vaccine. All of these show promise in animals but whether that promise is fulfilled, only time will tell.” Jane Bradbury
Infectious Diseases Vol 4 December 2004
http://infection.thelancet.com