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How common is West Nile Virus and when is it a threat to equines?
By Allison Griest
How common is West Nile Virus and when is it a threat to equines?
Horses are used both
professionally and
recreationally.
If West Nile Virus is a threat
to horses’ existence, humans
as the horse owners have a
responsibility to protect
horses from the virus, no
matter where they live.
This presentation is catered
toward horse owners in Texas
North East Independent School District.http://www.neisd.net/elmlang/images/j0189633.jpg.Viewed 02/21/10.
History of West Nile Virus•West Nile Virus (WNV) was first diagnosed in the United States
in 1999.
•West Nile Virus is transmitted through the bite of infected
mosquitoes.
•Mosquitoes become infected
when they feed on infected
birds.
•The virus multiplies in the
horse’s blood system, crosses
the blood-brain barrier,
and infects the brain.
History of West Nile Virus•The virus has been found in all 48 of the Continental
United States.
•The virus has also been found in Africa, western Asia,
the Middle East, and the Mediterranean regions of
Europe.
Mosquito-pictures.com. http://www.mosquito-pictures.com/mosquito_pictures.htm.02/24/10.
History of West Nile Virus•According to the Center for Disease Control, the virus
interferes with the normal central nervous system
functioning and causes inflammation of the brain.
Center for Disease Control.http://www.cdc.gov/ncidod/dvbid/westnile/qa/wnv_horses.htm.02/23/10.
About West Nile Virus• WNV has an incubation period of 3 to 15 days.
•Horse-to-horse transmission of the virus is unlikely because horses
do not have significant amounts of the virus circulating in their
blood.
•Clinical signs of a WNV infection include but are not limited to:
Muscle twitching
Tremors
Difficulty rising
Convulsions
Partial paralysis
A droopy lip
Teeth grinding
Frequency of West Nile Virus•The following maps illustrate the decrease in the number of WNV
infections from 2002 to 2009.
•Notice the deep red states on the 2002 maps. States colored deep
red have 800 or more reported cases of WNV.2009 2002
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/wnv_distribution_maps.htm.02/22/10.
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/wnv_distribution_maps.htm.02/22/10.
Frequency of West Nile Virus•The number of WNV infections has significantly decreased since
2002.
•However, when WNV appeared in New York in 1999, it didn’t
take long for it to quickly spread throughout the Continental
United States.
•The maps on the following slide illustrate the great increase in
WNV cases between 1999 and 2002.
Frequency of West Nile VirusIn 1999, New York was the only state to report WNV infections. There were 25 cases.
In 2002, there were 15,257 reported cases of WNV.Note that Texas had the most cases: 1,699.
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/wnv_distribution_maps.htm.02/22/10.
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/wnv_distribution_maps.htm.02/22/10.
Frequency of West Nile Virus
2009
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/wnv_distribution_maps.htm.02/22/10.
•In 2009 Texas only had 18 cases of
WNV.
•Washington had the most cases,
with 72. Horses are often traded
over the Canadian border. Another
data mining question might
investigate the reason why
Washington has so many WNV
cases.
Frequency of West Nile Virus
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://nsu.aphis.usda.gov/nahss_web/arbovirus_county_level.faces?STATE=TX.02/22/10.
•This chart from the United
States Department of
Agriculture – Animal and
Plant Health Inspection
Service shows the cumulative
number of equine cases in
the state of Texas in 2009.
•Note the second column in
the graph: West Nile Virus
Cases.
•The majority of the cases in
Texas appear to occur in the
fall months.
Equine WNV Cases in Texas in 2009
This Excel file shows the total of West Nile Virus cases reported in Texas in 2009 and includes the month of earliest detection of the virus.
Equine WNV Cases in Texas in 2009
March6%
August22%
September22%
October50%
West Nile Virus Cases Per Month
January February March April May JuneJuly August September October November December
•This pie chart was
generated from the
Excel file shown on the
previous slide.
•50% of WNV cases
occurred in the month of
October.
•94% of WNV cases
occurred in the fall
months of August,
September, and October.
•As shown in the chart
on the previous slide,
there were a total of 18
WNV cases documented
in Texas in 2009.
Equine WNV Cases in Texas in 2009•By analyzing the data from the current year, one can say that
October is the month equines in Texas are at the most risk of being
bitten by an infected mosquito and getting West Nile Virus.
•However, many horses travel across several states for breeding,
showing, and trading purposes, so it is also important to know the
months that an equine is at the most risk of being bitten by an
infected mosquito throughout the Continental United States.
•The following slides explain the data mining used to create an
Excel spreadsheet that shows the number of WNV cases reported
each month for all states.
WNV Data Mining
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://nsu.aphis.usda.gov/nahss_web/arbovirus_county_level.faces?STATE=TX.02/22/10.
•I referenced the United States
Department of Agriculture –
Animal and Plant Health
Inspection Service’s website to
find out how many cases of WNV
are reported each month in the
Continental United States.
•The site was most recently
updated December 9, 2009.
http://nsu.aphis.usda.gov/nahss_w
eb/arbovirus_summary.faces
•Only 36 states have reported
data.
WNV Data Mining•Each state has a chart showing
the number of reported cases of
WNV.
•For reference, here is a screen
shot of the cumulative number
of equine cases for Alabama.
As noted previously in this
presentation, the second
column is of interest.
•Each chart lists the date of
earliest detection of WNV in a
county.United States Department of Agriculture – Animal and Plant Health Inspection Service.http://nsu.aphis.usda.gov/nahss_web/arbovirus_county_level.faces?STATE=TX.02/22/10.
WNV Data Mining•I logged the total number of cases
per month in an Excel
spreadsheet.
•The chart does not give a total
per month, so first I had to log the
data by visiting each state’s
spreadsheet.
•Because of the chance of human
error, I could total the number of
cases I had logged in the monthly
columns and compare it to the
chart showing all state
information. That chart includes a
total number of cases per state for
the selected year.
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://nsu.aphis.usda.gov/nahss_web/arbovirus_county_level.faces?STATE=TX.02/22/10.
WNV Data Mining•Continuing to use Alabama as an example, the previous chart
shows that Alabama had 11 reported cases of WNV in 2009.
•I took the information shown in the chart for Alabama and placed
it in an Excel spreadsheet to show how many cases were reported
each month.
United States Department of Agriculture – Animal and Plant Health Inspection Service.http://nsu.aphis.usda.gov/nahss_web/arbovirus_county_level.faces?STATE=TX.02/22/10.
WNV Data Mining•A note about the charts from the United States Department of
Agriculture – Animal and Plant Health Inspection Service:
The additional columns show the number of Eastern Equine
Encephalitis (EEE) cases and Western Equine Encephalitis
(WEE) cases.
There are common equine vaccinations for both of these
viruses, but the vaccines and viruses are unrelated to West
Nile Virus. Vaccinations against EEE and WEE provide no
protection against West Nile Virus.
The states that are listed in my Excel spreadsheet that have
zero reported cases of WNV are listed in the state list
because there have been cases of EEE or WEE reported in
one of the state’s counties.
WNV Data Mining•This Excel file
shows the number
of reported cases
per month of WNV
in 36 states.
•The source of
information was
the United States
Department of
Agriculture –
Animal and Plant
Health Inspection
Service.
WNV Data MiningMarch; 1
July; 78
August; 89
September; 44
October; 26
November; 3
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
•This pie chart illustrates
the number of cases of WNV
in the 36 states per month.
•There were a total of 241
reported cases of WNV in
2009. This total was not on
the website but was instead
discovered through data
mining.
•The small Excel file is the
file used to create this pie
chart. The data was
extracted from the main
Excel file shown on the
previous slide.
WNV Data MiningMarch; 1
July; 78
August; 89
September; 44
October; 26
November; 3
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
•There was one case of
WNV reported in Texas
in March. The remaining
240 cases occurred
between July and
November.
•The majority of cases
were reported in August.
August’s 89 cases
account for 37% of WNV
cases in 2009.
•July had the second
highest number of cases,
78, accounting for about
32% of the WNV cases in
2009.
U.S. Department of Agriculture- Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/ada_wnv_2007.pdf.Viewed 2/24/10.
How to protect equines from WNV•The image to the right illustrates the
West Nile Virus transmission cycle.
•It can be difficult to isolate your horse
from mosquitoes, but there are
protective measures.
•The best ways to keep horses from
getting WNV is to:
Reduce the source (eliminate
mosquitoes)
Avoid the source (mosquitoes)
Vaccinate against the virus
How to protect equines from WNV•The best way to limit a horse’s exposure to infected mosquitoes is
to limit mosquito breeding sites.
Remove any potential sources of standing water
Clean water troughs
Clean clogged roof gutters
Turn over wheel barrows that are not in use
Manage property with landscaping to eliminate low spots
where standing water might collect.
Polyjumps.com.http://www.polyjumps.com/acatalog/TWtop.jpg.02/26/10
Vaccinating against WNV
U.S. Department of Agriculture – Animal and Plant Health Inspection Service.http://www.aphis.usda.gov/vs/nahss/equine/wnv/ada_wnv_2007.pdf.Viewed 2/24/10.
•The American Association of Equine
Practitioners (AAEP) recommends that all
horses in North America be immunized
against West Nile Virus.
•The risk of exposure to an infected
mosquito and the fact that mosquitoes
carry the virus make it difficult to predict
what regions of the country are most likely
to have infected mosquitoes.
•The AAEP recommends annual
revaccination in the spring, prior to the
peak WNV season.
•This supports my finding that the fall
months are the months with the most WNV
cases, meaning horses are at the most risk
for WNV infection during these months.
Is WNV under control?•The Texas Department of
State Health Services
provides annual statistics for
West Nile Virus in Texas.
•http://www.dshs.state.tx.us/
idcu/disease/arboviral/
westnile/statistics//annual/
default.asp
The annual summaries
include the number of
cases and counties related
to bird, human (virus and
fever), mosquito, horse,
and other West Nile Virus
infections.
Texas Department of State Health Services.http://www.dshs.state.tx.us/idcu/disease/arboviral/westnile/statistics//annual/default.asp.02/25/10.
Is WNV under control?•The Texas Department of State Health Service’s website has
Annual Summaries from 2009 to 2002. (2010 is available but has
zero cases.)
•The maps of the United States shown at the beginning of this
presentation showed that the number of WNV cases in equines
has decreased. However, mosquitoes are the main factor in
equine WNV cases.
•Therefore, the information on the Texas Department of State
Health Service’s website will allow me to see if WNV has
decreased among mosquitoes.
•I will take the chart information on cases of mosquitoes and
horses and compile it in an Excel spreadsheet.
Is WNV under control?•This Excel spreadsheet shows the number of cases of WNV in
mosquitoes and horses from 2002 through 2009.
Is WNV under control?
2009 2008 2007 2006 2005 2004 2003 20020
200
400
600
800
1000
1200
1400
1600
1800
MosquitoHorse
•The graph shows that
cases of mosquitoes
with WNV and horses
with WNV have
decreased.
•Please note that the
dates decrease in order
along the x-axis. (The
graph starts at 2009,
the most recent year.)
•I would like the site to
have included
information about how
they complied research
relating to the number
of mosquitoes carrying
WNV.
Is WNV under control?
2009 2008 2007 2006 2005 2004 2003 20020
200
400
600
800
1000
1200
1400
1600
1800
MosquitoHorse
•It is interesting to note
that the number of
mosquitoes cases of
WNV decreased from
2007 to 2008 but then
increased again in 2009.
•The number of horse
cases of WNV only
increased slightly
between 2008 and 2009,
suggesting that
vaccinations are
effective even when
WNV is being carried by
large numbers of
mosquitoes.
Is WNV under control?•It is also interesting to look at the number of mosquito
and horse cases in a line graph form. Please note that this
time, the dates are sequential (from 2002 to 2009).
•Below is the Excel sheet used to create
the line graph.
Is WNV under control?
2002 2003 2004 2005 2006 2007 2008 20090
200
400
600
800
1000
1200
1400
1600
1800
MosquitoHorse
•The line graph really illustrates the decrease in WNV infections from
2002 to 2009.
•It will be interesting to see if the number of mosquito cases continues
to increase in 2010.
•Hopefully horse and mosquito cases will decrease in the future years.
Answering the Question•The question asked at the beginning of this presentation was,
“How common is West Nile Virus and when is it a threat to
equines?”
•This question has two sections.
How common is West Nile Virus?
West Nile Virus is common enough that the American
Association of Equine Practitioners recommends that all
horses in North America receive an annual vaccination.
According to the American Association of Equine
Practitioners, WNV is considered to be endemic in all areas
of North America. The results of data mining shown in this
PowerPoint confirm this point.
Answering the Question When is West Nile Virus a threat to equines?
West Nile Virus is definitely a threat to
equines.
The American Association of Equine
Practitioners states that the mortality rate for
horses with signs of a West Nile Virus
infection is 33%.
The data shown in my graphs shows that
West Nile Virus is most frequent in the fall
months, so it is extremely important that
horses are vaccinated prior to those months,
ideally in the spring.
The line graph shows a decrease in WNV
cases in horses over the past 7 years.
However, WNV is still present, so it is still a
threat.
ReferencesAmerican Association of Equine Practitioners (2010). Retrieved February 25,
2010, from http://www.aaep.org/pdfs/AAEP_WNV_Guidelines_2005.pdf.
Center for Disease Control (2010). Retrieved February 23, 2010, from
http://www.cdc.gov/ncidod/dvbid/westnile/qa/wnv_horses.htm.
North East Independent School District (n.d.). Retrieved February 21, 2010, from
http://www.neisd.net/elmlang/images/j0189633.jpg.
Polyjumps.com (n.d.). Retrieved February 26, 2010, from http://www.polyjumps.com/acatalog/TWtop.jpg.
Texas Department of State Health Services (n.d.). Retrieved February 25, 2010, from
http://www.dshs.state.tx.us/idcu/disease/arboviral/westnile/statistics//annual/default.asp.
ReferencesUnited States Department of Agriculture – Animal and Plant Health Inspection
Service (n.d.). Retrieved February 22, 2010, from http://www.aphis.usda.gov/vs/nahss/equine/wnv/
wnv_distribution_maps.htm.
United States Department of Agriculture – Animal and Plant Health Inspection
Service (n.d.). Retrieved February 24, 2010, from
http://www.aphis.usda.gov/vs/nahss/equine/wnv/ada_wnv_2007.pdf.