Page 368 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com
mebooksfree.com
mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com the Rocky Mountains. There are approximately 100 to 300 357 mebooksfree.com
CHAPTER 42 Arboviruses
usually ranges between 5 and 20 per year, and the fatality
cases per year in the United States.
rate is roughly 2%.
The virus is transmitted primarily by Culex mosquitoes
The disease occurs primarily in people hiking or camp-
ing in the Rocky Mountains and is characterized by fever,
among the wild bird population of the western states, espe-
cially in areas with irrigated farmland.
headache, retro-orbital pain, and severe myalgia. The diag-
The clinical picture of WEE virus infection is similar but
by detecting a rise in antibody titer. No antiviral therapy or
less severe than that caused by EEE virus. Sequelae are less
common. The diagnosis is made by isolating the virus or
vaccine is available. Prevention involves wearing protective
observing a rise in antibody titer. There is no antiviral ther- nosis is made either by isolating the virus from the blood or
clothing and inspecting the skin for ticks.
apy. There is a killed vaccine for horses but not for humans.
mebooksfree.com mebooksfree.com mebooksfree.com West Nile virus (WNV) is the most common cause of mebooksfree.com
mebooksfree.com
mebooksfree.com
West Nile Virus
St. Louis Encephalitis Virus
St. Louis encephalitis (SLE) virus causes disease over a wider
neuroinvasive (encephalitis, meningitis) arboviral dis-
geographic area than do EEE and WEE viruses. It is found in
ease in the United States. WNV caused an outbreak of
the southern, central, and western states and causes 10 to
encephalitis in New York City and environs in July, August,
30 cases of encephalitis per year in the United States.
and September 1999. This is the first time WNV caused
The virus is transmitted by several species of Culex
disease in the United States. In this outbreak, there were 27
mosquitoes that vary depending on location. Again, small
confirmed cases and 23 probable cases, including 5 deaths.
wild birds, especially English sparrows, are the reservoir,
and humans are dead-end hosts. Although EEE and WEE
occurred after area-wide spraying of mosquito-control
viruses are predominantly rural, SLE virus occurs in urban
compounds and the onset of cooler weather.
areas because these mosquitoes prefer to breed in stagnant Many birds, especially crows, died as well. No human cases
In the summer of the year 2000, there were 18 cases and
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com Florida) and as far west as Louisiana. In 2002, there was a mebooksfree.com
mebooksfree.com
wastewater.
1 death, and by July 2001, the virus had spread to many
SLE virus causes moderately severe encephalitis with a
states along the East Coast (from New Hampshire to
fatality rate that approaches 10%. Most infections are inap-
parent. Sequelae are uncommon.
marked increase in the number of cases. There were more
The diagnosis is usually made serologically, because the
than 4000 cases, 274 people died, and the virus had spread
virus is difficult to isolate. No antiviral therapy or vaccine
as far west as Colorado. In 2003, there were 7700 cases, of
is available.
whom 166 died, and the virus had spread to California. In
2012, there were 3142 reported cases and 134 deaths. Each
California Encephalitis Virus
year, WNV causes the highest number of deaths due to a
mosquito-borne encephalitis in the United States. It is not
California encephalitis (CE) virus was first isolated from
known how WNV entered the United States, but either an
mosquitoes in California in 1952, but its name is something
infected traveler or an infected mosquito brought by an
of a misnomer because most human disease occurs in the
north-central states. The strain of CE virus that causes
and roughly 80% of infections are asymptomatic. mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com airplane seems likely to be involved. mebooksfree.com
mebooksfree.com
WNV is a flavivirus that is classified in the same anti-
encephalitis most frequently is called La Crosse for the city
genic group as SLE virus. It is endemic in Africa but has
in Wisconsin where it was isolated. CE virus is the only one
caused encephalitis in areas of Europe and Asia as well.
of the four major encephalitis viruses in the United States
Wild birds are the main reservoir of this virus, which is
that is a member of the bunyavirus family.
transmitted by mosquitoes, especially Culex species.
La Crosse virus is transmitted by the mosquito Aedes
Humans are dead-end hosts. Transmission of the virus via
triseriatus among forest rodents. The virus is passed trans-
solid organ transplants has also occurred.
ovarially in mosquitoes and thus survives the winter when
The most important clinical picture is encephalitis with
mosquitoes are not active. The clinical picture can be mild,
or without signs of meningitis, typically in a person over
resembling enteroviral meningitis, or severe, resembling
60 years of age. Encephalitis occurs in about 1% of infections,
herpes encephalitis. Death rarely occurs. Diagnosis is usu-
fever and headache without encephalitis occur in about 20%,
ally made serologically rather than by isolation of the virus.
No antiviral therapy or vaccine is available.
The laboratory diagnosis can be made by either isola-
mebooksfree.com
tion of the virus from brain tissue, blood, or spinal fluid or
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com able. No antiviral therapy or vaccine is available. In an mebooksfree.com
Colorado Tick Fever Virus
by detection of antibodies in spinal fluid or blood. Poly-
Of the five diseases described in Table 42–2, Colorado tick
merase chain reaction (PCR)–based assays are also avail-
fever (CTF) is the most easily distinguished from the oth-
attempt to prevent blood-borne transmission, blood banks
ers, both biologically and clinically. CTF virus is a reovirus
transmitted by the wood tick Dermacentor andersoni
screen donated blood for the presence of WNV using
nucleic acid probes specific for the virus.
among the small rodents (e.g., chipmunks and squirrels) of
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com