Health And Vectors In Ecology-traducido
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Ecologic Studies of Rodent Reservoirs:
Their Relevance for Human Health
James N. Mills and James E. Childs
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Address for correspondence: James N. Mills, Centers for
Disease Control and Prevention, 1600 Clifton Road, Mail Stop
G14, Atlanta, GA 30333, USA; fax: 404-639-4436; e-mail:
jum0@cdc.gov.
Within the past few years, the number of “new” human diseases associated with
small-mammal reservoirs has increased dramatically, stimulating renewed interest in
reservoir ecology research. A consistent, integrative approach to such research allows
direct comparisons between studies, contributes to the efficient use of resources and
data, and increases investigator safety. We outline steps directed toward understanding
vertebrate host ecology as it relates to human disease and illustrate the relevance of
each step by using examples from studies of hosts associated with rodent-borne
hemorrhagic fever viruses.
The practical importance of understanding
host and vector ecology has been recognized at
least since the early 1900s. Knowledge of the
container-breeding habits of Aedes aegypti
enabled early successes in the control of yellow
fever virus transmission and, ultimately, the
completion of the Panama Canal in 1914 (1).
Diverse applications of vector/reservoir ecologybased
measures to prevent zoonotic disease
include the prediction of Lyme disease risk by
monitoring acorn mast production and its impact
on the vertebrate hosts of the tick vectors (2),
control of vector populations for Borrelia
burgdorferi and Yersinia pestis through the
application of acaricides and insecticides to
rodents and deer at feeding stations (3,4),
dissemination of bait containing vaccines to
control rabies in foxes (5), and use of satellite
imagery to predict the activity of Rift Valley
fever in East Africa (6,7).
The rodent-borne hemorrhagic fevers, among
the most dramatic of recently emerging
infectious diseases, are caused by two distinct
groups of negative-stranded RNA viruses: the
arenaviruses (family Arenaviridae) and the
hantaviruses (genus Hantavirus, family
Bunyaviridae). With few exceptions, each virus
in these two groups is primarily associated with
a single species of rodent host of the family
Muridae. In the specific host, the virus
establishes a prolonged infection, which rarely
causes disease in the animal. The infected host
sheds virus into the environment (in urine, feces,
and saliva) for extended periods (8-10). These
characteristics are key to the transmission of the
viruses to humans (by the inhalation of
aerosolized virus) and to other rodents (by
horizontal and sometimes vertical mechanisms).
Arenaviruses cause the South American
hemorrhagic fevers, which produce hundreds of
cases annually, with a case-fatality ratio as high
as 33%. The best studied of these agents is Junín
virus, which is carried by the corn mouse
(Calomys musculinus) and causes Argentine
hemorrhagic fever (AHF). AHF was first
recognized in 1955 on the central pampas of
Argentina (11), where before the deployment of a
new vaccine in 1992, hundreds of cases occurred
each year. Although arenaviral diseases of
humans (other than lymphocytic choriomeningitis
associated with the introduced Old World
rodent Mus musculus) have not been recognized
in North America, Tamiami virus has been
recognized in association with cotton rats
(Sigmodon hispidus) since 1969 (12), and
Whitewater Arroyo virus was identified from
wood rats (Neotoma species) in the southwestern
United States in 1995 (13). The potential of
Whitewater Arroyo virus for causing human
disease is under investigation.
Hantaviruses cause hundreds of thousands
of cases of hemorrhagic fever with renal
syndrome (HFRS) in Europe and Asia each year.
Hantaviral disease was thought to be rare or
Ecologic Studies of Rodent Reservoirs:
Their Relevance for Human Health
James N. Mills and James E. Childs
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Address for correspondence: James N. Mills, Centers for
Disease Control and Prevention, 1600 Clifton Road, Mail Stop
G14, Atlanta, GA 30333, USA; fax: 404-639-4436; e-mail:
jum0@cdc.gov.
Within the past few years, the number of “new” human diseases associated with
small-mammal reservoirs has increased dramatically, stimulating renewed interest in
reservoir ecology research. A consistent, integrative approach to such research allows
direct comparisons between studies, contributes to the efficient use of resources and
data, and increases investigator safety. We outline steps directed toward understanding
vertebrate host ecology as it relates to human disease and illustrate the relevance of
each step by using examples from studies of hosts associated with rodent-borne
hemorrhagic fever viruses.
Emerging Infectious Diseases 530 Vol. 4, No. 4, OctoberDecember 1998
Perspectives
absent in the United States, although three cases
of mild HFRS associated with rat-borne Seoul
virus had been described (14). In 1993, the
discovery of hantavirus pulmonary syndrome
(HPS), which rapidly kills approximately half of
those infected, surprised public health officials
and virologists in the United States. The
causative agent, Sin Nombre virus (SNV), is
hosted by the deer mouse, Peromyscus
maniculatus, and the disease syndrome markedly
differs from HFRS. Since 1993, at least 20
additional hantaviruses have been isolated from
rodents throughout the Americas; about half are
known human pathogens (Figure 1).
Recognition of new rodent-borne diseases
has renewed interest in reservoir host ecology in
the United States, and recognition of HPS in
South America has prompted field studies in
Paraguay, Argentina, Chile, and Brazil. In 1997,
representatives from 13 American countries,
meeting in Lima, identified surveillance in
humans and rodents as a priority for combating
emerging hantaviral disease. Reservoir
...