Updates-By Carol A. Kemper, MD, FACP
Updates-By Carol A. Kemper, MD, FACP
Are Seals a Reservoir for Influenza B?
Source: Osterhaus AD, et al. Science 2000;288:1051-1053.
While birds are a well-recognized reservoir for influenza A, and influenza C has been isolated from pigs, no known animal host or non-human reservoir of infection has heretofore been identified for influenza B virus. While investigating the causes of respiratory illness in 12 juvenile harbor seals stranded on the Dutch Coast in 1999, the Seal Rehabilitation and Research Center in the Netherlands found evidence that at least two of the animals were infected with influenza B virus (B/Seal/Netherlands/1/99). Al-though both animals were suffering from respiratory illness at the time, a number of other pulmonary infections (e.g., lungworm) were also identified in the seals, obscuring the relationship of influenza B infection to illness. However, researchers demonstrated that the virus could be successfully propagated in seal kidney cell cultures.
Studies demonstrated that B/Seal/ Netherlands/1/99 was similar to the strain of influenza B virus that had circulated in the human population in 1995—about 4-5 years earlier. Studies on stored sera demonstrated that eight of 391 seals (2%) cared for at the center after 1995 but none of 580 seals cared for before 1995 had evidence of influenza B infection. Thus, these data suggest the transmission of this or a related virus from the human population to seals in or around 1995, with subsequent persistence of low-level infection.
Harbor seals may therefore represent a previously unrecognized reservoir of influenza B infection for humans. These are the same seals tourists in San Francisco love to watch cavorting off of Pier 39, although presumably closer contact would be necessary for transmission of influenza. Such reservoirs are important for two reasons: they have the potential to allow for mutation of virus in a non-human host, and could serve as a point source for later introduction of virus into the human population.
Michigan White-tailed Deer Spreading TB
Source: ProMED-mail postings, April 26 and May 15, 2000; www.promed-mail.org.
An outbreak of bovine tuberculosis (TB) due to Mycobacterium bovis has recently escalated in the white-tailed deer population in the northeastern section of Michigan’s lower peninsula, potentially threatening domestic cattle in the area and in nearby Indiana. TB first appeared in the deer population in the mid-1990s, with reports of bagged deer with pulmonary and thoracic lesions. While 58 infected deer were identified in 1999, screening thus far this year has identified 282 positive deer of 27,175 tested (~1%). Most of the infected deer appear to be limited to Osceola, Antrim, and Mecosta counties, although three deer tested positive outside these areas. TB has also been identified in at least five herds of cattle in the lower peninsula—and authorities in both Michigan and Indiana are concerned about the potential for migrating deer to affect the vital cattle industry in both states. Indiana officials have even threatened to "fence in" their state to prevent deer migration across the state border.
Although pasteurization sterilizes milk products sold to the public, persons in contact with infected cattle, especially their respiratory secretions and mucous, would be at risk for infection. This reminds me of the outbreak of TB in circus elephants in 1996—the elephants with runny noses (runny trunks?) were highly contagious, especially if the animals sneezed (Kemper CA. Infect Dis Alert 1998;17:133-134). We often forget that other warm-blooded animals—domestic or wild—are potential TB carriers. Dogs in contact with infected humans have been known to "catch" TB, and their distant cousins, coyotes, are another increasing source of infection in the wild.
Rabies Devastating Cattle Herds in Chiapas
Source: ProMED-mail post, April 7, 2000; www.promedmail.org.
An outbreak of rabies transmitted by vampire bats preying on cattle in Chiapas, Mexico, is threatening the local population and economic base. And at least 2300 cattle have died from rabies infection in the first three months of this year—90% of which have been confirmed on necropsy. At least 92 ranches, most of which are small in size, have been affected. One rancher alone has lost 50 bulls, cows, and calves thus far this year. In addition, 27 people have been bitten by bats, all of whom are receiving therapy.
Rabies was first detected in Chiapas in 1987, but bat migration has resulted in spread of disease throughout the region. Ranchers are faulting the local government which they claim has been slow to respond to the endemic. Government officials claim that ranchers ignored the problem for too long, failing to adequately vaccinate their herds. Rabies vaccine is being made available to ranchers for an approximate cost of $0.11 per dose, but too few vaccines are being administered. Whichever group has been less responsive to date is irrelevant. Government officials would do better by initiating an area-wide vaccine program for all cattle at no charge to ranchers, less they face a public health disaster. Human rabies immune globulin is both costly and in short supply.
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