Georgia epidemiology report, Vol. 22, no. 04 (Apr. 2006)

April 2006

volume 22 number 04

Mosquito-Borne Viruses in Georgia, 2005

Human Arboviral Surveillance West Nile virus (WNV) is a mosquito-borne viral pathogen that was introduced into the United States during 1999. Within four years after its initial detection in New York, WNV was detected in states on the East and West coasts as well as in Mexico and Canada. In Georgia, the virus was first identified during 2001. WNV is now considered endemic in most parts of the U.S., including Georgia.
West Nile virus is maintained in birds. It occasionally infects humans who are bitten by mosquitoes that have been feeding on birds. Most people (approximately 80%) infected with WNV do not develop symptoms. About one in five infected persons experiences a mild illness, often termed "West Nile Fever" (WNF), characterized by fever, headache, muscle weakness or myalgia, arthralgia, and sometimes rash. Less than one percent of persons infected with WNV develop neurologic illness ("West Nile Neurologic Disease" or WNND) in the form of meningitis, encephalitis, or acute flaccid paralysis. Approximately three to fifteen percent of WNND cases are fatal. Risk of WNND is associated with increasing age and with the presence of underlying medical conditions.
Nationwide, 2,949 cases of WNV illness and 116 deaths were reported to CDC during 2005 (as of March 16, 2006). In Georgia, an acute arboviral infection is a reportable condition; however, the majority of cases of arboviral infection remain undetected when moderate or severe illness does not develop. In 2005, Georgia reported 24 verified cases of WNV infection, including 2 deaths (Table 1). Twelve (50%) of the 24 cases experienced WNND and 7 (29%) were diagnosed with WNF. One (4%) case was lost to follow up and symptoms were never recorded. Four (17%) cases were WNV positive viremic blood donors who were identified when donating blood. None of the blood donors subsequently reported symptoms of West Nile virus infection. The mean age of cases was 53 years (range 15-87). The mean age of those who experienced neurologic illness was 57 years (range 15-83). The ages of the fatal cases were 63 and 87. Eighteen (75%) of the 24 cases were male. The majority of cases were reported during September. Fulton County (part of metro Atlanta) reported the largest number of WNV cases (9), followed by DeKalb and Muscogee Counties (4 cases each).

Table 1. Human Arbovirus Cases, Georgia 2005

Arbovirus LAC EEE

Month of Onset July August

County of Residence Lowndes Tattnall

DENGUE DENGUE DENGUE DENGUE DENGUE

July September September November December

Fulton Fayette Cobb Fulton Brantley

WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV WNV

June June August August August September September September September September September September September September September September October October October November

Paulding Cobb Muscogee Fulton Tift Fulton Muscogee Fulton Fulton Fulton Fulton DeKalb Richmond Fulton DeKalb Fulton Muscogee Cobb Cobb DeKalb

WNV*

August

WNV*

August

WNV*

August

WNV*

September

*Positive Viremic Blood Donors

Fulton Muscogee Jones DeKalb

Clinical Syndrome Encephalitis Encephalitis
Fever Fever Fever Fever Fever
Guillain-Barre Syndrome Fever Fever Meningitis Unknown Altered Mental Status Fever Fever Encephalitis Encephalitis Meningitis Meningitis Fever Meningitis Fever Encephalitis Altered Mental Status Encephalitis Encephalitis Fever
Asymptomatic Asymptomatic Asymptomatic Asymptomatic

Fatal No No
No No No No No
No No No No No No No No No No No No No No No No Yes No No Yes
No No No No

Other Mosquito-Borne Viruses in Georgia West Nile virus is one of several mosquito-borne viruses, also called arboviruses (arthropod-borne viruses) that circulate in Georgia and can infect humans. Other identified arboviruses include Eastern Equine Encephalitis virus (EEE), LaCrosse virus (LAC), and rarely St. Louis Encephalitis virus (SLE), which is closely related to WNV. WNV is the most commonly reported arbovirus in Georgia, although LAC infection is probably under-recognized because it usually causes only mild clinical illness. EEE is the most severe arboviral infection, leading to death in 30-50% of symptomatic cases and often leaving survivors permanently disabled. During 2005 one human case each of LaCrosse Encephalitis and Eastern Equine Encephalitis were reported in Georgia. Five cases of internationally acquired Dengue fever were also reported during 2005. The cases had traveled to Thailand, Puerto Rico, Haiti and India (Figure 1).

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Reported Number of Cases # cases
5-year mean

% positive 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Dec Nov Oct Sept Aug July June May Apr Mar Feb Jan

HuHmuamn AarnboAvrirbaol vCiarsaelsCbaysMeosnbthy oMf oOnntsheto, Gf Oeonrgseiat,2005

Georgia 2005 13

12

11

10

9

Dengue

8

7

Eastern Equine Encephalitis

6

LaCrosse Encephalitis

5

West Nile Virus

4

3

2

1

0

Month of Onset
Figure 1: 2005 Human Case Surveillance, by Month of Onset. Most WNV cases had disease onset during September.

ArAbrobvoivriurusseessiinn HHorrsseess, ,GGeeorogrigai2a0200505

EEE

WNV/EEE

W NV

11

10

9

8

7

6

5

4

3

2

1

0 April May June July Aug Sept Oct

Month of Onset

Figure 2: Horse Surveillance, 2005. Detection of virus in horses indicates an increased risk of human disease locally.

90 Dead Bird SDueravdeiBllairndcSeufrovreWillaNnVc,eG2e0o0r1g-2ia0,025001 - 2005 60%

80 50%
70

mean submitted

60

mean WNV+

40%

% WNV+

50

30%

40

30

20%

20 10%
10

0

0%

Jan Feb March April May June July Aug Sept Oct Nov Dec week
Figure 3: Dead Bird Surveillance, 2001-2005. Detection of virus during dead bird surveillance determines when WNV is circulating through bird populations, and indicates a potential for increased risk of human disease.

Testing for WNV and other Arboviruses Commercial tests to detect WNV antibodies are readily available. Submitting specimens to the Georgia Public Health Laboratory (GPHL) is another testing option and all specimens submitted are tested for serologic evidence of infection with each of the arboviruses that circulate in Georgia. GPHL does not charge for WNV and arbovirus panel tests. Criteria for testing at GPHL were instituted in 2001 to conserve limited laboratory resources and were intended primarily to detect neurologic manifestations of arboviral infections. Table 2 displays the criteria for testing in 2006. Specimens will not be tested by GPHL unless they meet these criteria. Please call the Georgia Division of Public Health (GDPH 404-6572588) or the appropriate District Health Office before submitting specimens for arboviral testing to assure that the criteria are met for testing at GPHL. If needed, specimens positive for WNV or other arboviruses at commercial laboratories can be retested at GPHL to verify the results.
Table 2. GPHL Arboviral Testing Criteria for 2006
Adults: To qualify for testing at GPHL, persons must be 18 years or older and meet at least one of the following clinical criteria: Meningitis, OR Encephalitis, OR Acute onset of profound muscle weakness or acute flaccid paralysis
(including Guillian-Barre syndrome), OR Fever (greater than 100.4F) and at least 2 of the following:
Headache Malaise Arthralgia Fatigue Eye Pain Children: To qualify for testing at GPHL, persons must be 17 years or younger and meet at least one of the following criteria: Fever (greater than 100.4F) with ataxia or extrapyramidal signs, OR New onset seizures or increased seizure activity in children with preexisting seizure disorders, OR Encephalitis, OR Acute onset of profound muscle weakness or acute flaccid paralysis (including Guillian-Barre syndrome)
Note: Because meningitis due to other causes is rather frequent among children during arbovirus transmission season, children with meningitis will not be tested unless they meet additional criteria described above, or after other bacterial and viral causes have been ruled out.
Arbovirus Surveillance in Sentinel Species In Georgia, in addition to surveillance for human disease caused by arboviruses, GDPH and its partners conduct surveillance for arboviruses in horses, birds, and mosquitoes in an effort to determine local risk of human disease. Below is a summary of arbovirus surveillance results during 2005.
Horse Surveillance Like humans, horses are incidental hosts for WNV and other arboviral infections. Detection of arboviral infection in horses provides a valuable means to recognize areas of viral activity and increased risk of human disease. Reports of positive horses in an area indicate increased human risk because mammal-biting mosqui-

toes are transmitting virus. Public Health staff contacts the owners of arboviralpositive horses to educate them about their personal risk of disease and riskreduction measures they can take on their farm to prevent future cases.
Due to increased immunity, increased vaccination, and decreased interest in testing, the reported number of WNV cases in horses continued to decrease between 2004 and 2005, from 3 cases to 1 case. Because we are still learning about trends from year to year, we cannot accurately predict 2006 case counts, but it is likely that numbers of horse cases will continue to be low. Reduced disease reporting for horses makes this surveillance system less useful as a sentinel for determining increasing human disease risk. Horse surveillance has been especially useful in rural counties where bird and mosquito surveillance resources are few.
There were 20 cases of EEE in Georgia horses during 2005, 85% of which died or were euthanized (Figure 2). This represents an increase in cases from the 7 cases of EEE reported in horses during 2004, and indicates the possibility of an EEE epidemic during 2006 if weather conditions continue to be favorable for the vector mosquito, Culiseta melanura.
WNV and EEE in horses are preventable by vaccination. Horse owners should be encouraged to vaccinate their horses against WNV and EEE on schedule. However, even late vaccination can provide some protection. Studies show that even one dose of the vaccine helps prevent death if the horse becomes infected, and the few horses that become infected despite being properly vaccinated have a better chance of survival after infection.
Bird Surveillance Although the number of birds being submitted for testing has continued to decrease, bird mortality surveillance remains a sensitive tool to determine the geographic range and extent of WNV and other arbovirus activity in various parts of the state. In areas where no mosquito surveillance occurs, bird surveillance can be useful in predicting increased risk of human disease. During 2005, there were 310 birds submitted from 51 of 159 Georgia counties; a total of 23 WNV-positive birds were found in 10 of those counties. With fewer birds being submitted, the first positive bird in 2005 was not detected until 8/5/05 in Paulding County, nearly two months after the first human WNV case was reported, also in Paulding County. The last positive bird was submitted on 10/18/05 from metro Atlanta. A flock of quail from South Georgia tested positive for EEE infection during 2005.
It is likely that the number of dead birds submitted for testing will continue to decrease. As local populations of crows and jays continue to die out, birds less likely to die from WNV infection will become more important to the amplification cycle. In addition, WNV is currently perceived by the public to be less of a threat, leading to a decrease in reporting of dead birds. Decreased funding will also make it less likely that arboviral surveillance programs will be sustainable.
Surveillance indicates there is some level of WNV transmission occurring almost year-round (Figure 3). Based on currently available data, it is likely that there is detectable transmission occurring from April or May of one year until January or February of the next, depending on meteorologic conditions.
Mosquito Surveillance Mosquito surveillance is conducted to detect the presence of arboviruses in potential vectors and to help guide and evaluate mosquito control programs. Pools of vector species are submitted for testing starting in May. Mosquito pools are comprised of a single species of mosquito collected at a given site during a given

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WNV Index
52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

mean # mosquitoes/trap

90 85

CCuulleexx2qq0uu0ii1qqu-u2ee0ffa0as5sc,ci5aia-tYutuesasS,r uM5r-evYaeenilalar nMcee,an

240 230

220

80 mean # mosquitoes per trap night

210

75

W NV+ Index*

200

70

190

180

65

170

60

160

55

150

140

50

130

45

120

40

110

100

35

90

30

80

25

70

60

20

50

15

40

10

30

20

5

10

0

0

Jan Feb March A pril May June July A ug Sept Oct Nov Dec
we ek * the WNV Index is the number of inf ected mosquitoes per trap night
Figure 4: Culex quinquefasciatus Surveillance, 2001-2005. Detection of WNV in mosquitoes indicates an increased risk of human disease locally.

WNV+ None or limited survelliance

time period. For testing purposes, mosquito pools contain 20 or fewer mosquitoes.

Some level of mosquito surveillance was conducted in 59 of 159 Georgia counties during 2005. Intensive mosquito surveillance was conducted in fewer than 10 counties. Five counties reported WNV-positive mosquito pools. Positive mosquitoes were detected in South Georgia in May, with additional positives being detected throughout Georgia starting in July. The last positive pool was collected in Fulton County during mid-November, with peaks in numbers of positive pools occurring in August, September, and October. Ninety-six percent of the positive pools collected were comprised of Culex quinquefasciatus, the southern house mosquito. An additional 3% of the positive pools were Cx. restuans, and 1% were Cx. nigripalpus. In general, Culex spp. are bird-feeders involved in the amplification of the virus in bird populations, although most will also feed on mammals; Cx. nigripalpus is considered an important vector in Florida and may be involved in rural transmission in Georgia. Culex quinquefasciatus, our primary WNV vector in Georgia (Figure 4), is a container-breeding mosquito that flies only a short distance from its breeding site when searching for a blood meal.
EEE was isolated from 8 mosquito pools, collected during May, June, and July in Lowndes County and July in Chatham County. Two pools testing positive for EEE were comprised of Cx. quinquefasciatus; the other 6 positive pools contained Cs. melanura, a bird-biting species that maintains the EEE virus in birds. This increase in detection of EEE in mosquito pools, and the increased numbers of horse cases as well as the one human case reported during 2005, may indicate a build-up of virus in bird populations leading to a higher risk of disease in horses and humans during 2006.
Personal protection measures are ways in which the public can help reduce the risk of WNV for themselves and in their community. These include:
wearing repellent, dumping out standing water at least once a week,

Figure 5: Map of counties with WNV-positive birds, mosquito pools, horses, and/or human cases during 2001-2005. However, there has been little to no surveillance in counties showing no WNV activity.
applying larvicide to areas of standing water that can not be dumped out or drained,
keeping gutters clear of debris, removing saucers from under outdoor potted plants, keeping window screens repaired, and picking up all containers that may hold water The short time we have been conducting surveillance for WNV in Georgia, along with the lack of historical mosquito data, make it difficult to predict human risk of disease. It is likely that WNV is now endemic throughout Georgia (Figure 5). Based on current data, it seems likely that Cx. quinquefasciatus is our primary vector for WNV. Continued monitoring of mosquitoes and targeting control and education towards changing vector populations is our best course of action for continuing to reduce the incidence of arboviral diseases in Georgia.
For more information regarding arbovirus activity in Georgia, please visit http://health.state.ga.us/epi/vbd/mosquito.asp or call 404-657-2588.
Authors: Marianne Vello; Meghan Weems, M.P.H.; Laurel E. Garrison, M.P.H.; Rosmarie Kelly, Ph.D., M.P.H.; Dana Cole, DVM, Ph.D., Dipl. ACVIM

Division of Public Health http://health.state.ga.us
Stuart T. Brown, M.D. Director
State Health Officer

Epidemiology Branch http://health.state.ga.us/epi
Susan Lance, D.V.M., Ph.D. Director
State Epidemiologist

Georgia Epidemiology Report Editorial Board
Carol A. Hoban, M.S., M.P.H. Editor Kathryn E. Arnold, M.D.
Cherie Drenzek, D.V.M., M.S. Susan Lance, D.V.M., Ph.D.
Stuart T. Brown, M.D. Angela Alexander - Mailing List Jimmy Clanton, Jr. - Graphic Designer
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Two Peachtree St., N.W. Atlanta, GA 30303-3186 Phone: (404) 657-2588
Fax: (404) 657-7517

Georgia Department of Human Resources
Division of Public Health

Please send comments to: Gaepinfo@dhr.state.ga.us

The Georgia Epidemiology Report Epidemiology Branch Two Peachtree St., NW Atlanta, GA 30303-3186

PRESORTED STANDARD U.S. POSTAGE
PAID ATLANTA, GA PERMIT NO. 4528

April 2006

Volume 22 Number 04

Reported Cases of Selected Notifiable Diseases in Georgia Profile* for January 2006

Selected Notifiable Diseases
Campylobacteriosis Chlamydia trachomatis Cryptosporidiosis E. coli O157:H7 Giardiasis Gonorrhea Haemophilus influenzae (invasive) Hepatitis A (acute) Hepatitis B (acute) Legionellosis Lyme Disease Meningococcal Disease (invasive) Mumps Pertussis Rubella Salmonellosis Shigellosis Syphilis - Primary Syphilis - Secondary Syphilis - Early Latent Syphilis - Other** Syphilis - Congenital Tuberculosis

Total Reported for January 2006
2006 30
3043 13 1 23
1350 10 3 5 1 0 0 0 2 0 99 56 4 18 13 37 0 18

Previous 3 Months Total

Ending in January

2004

2005 2006

98

121

97

7803

7942

8328

40

21

42

3

7

2

181

209

163

3831

3933

3609

28

42

22

124

41

10

129

115

19

2

7

9

2

0

0

14

8

3

0

0

1

7

16

6

0

0

0

376

335

352

158

128

194

36

34

19

111

134

82

129

66

65

185

210

127

1

1

0

123

134

111

Previous 12 Months Total

Ending in January

2004 2005

2006

614

581

585

35356

34357

33382

129

170

162

27

25

28

830

898

744

17383

16020

15457

88

126

96

762

289

106

599

460

140

32

45

38

11

10

6

37

17

12

3

2

2

33

35

43

0

1

0

2044

1933

2007

1053

629

701

131

120

118

472

495

474

715

376

362

883

858

827

9

6

2

520

534

493

* The cumulative numbers in the above table reflect the date the disease was first diagnosed rather than the date the report was received at the state office, and therefore are subject to change over time due to late reporting. The 3 month delay in the disease profile for a given month is designed to minimize any changes that may occur. This method of summarizing data is expected to provide a better overall measure of disease trends and patterns in Georgia.

** Other syphilis includes latent (unknown duration), late latent, late with symptomatic manifestations, and neurosyphilis.

Report Period
Latest 12 Months: 04/05-03/06 Five Years Ago: 04/01-03/02 Cumulative: 07/81-03/06

Total Cases Reported* <13yrs >=13yrs Total

2

1,843 1,845

1

1,708 1,709

226

29,687 29,913

Percent Female

AIDS Profile Update
Risk Group Distribution (%) MSM IDU MSM&IDU HS Blood Unknown

25.6

32.2

5.7

2.0

9.1

1.1

49.8

25.6

36.1

8.8

2.9

17.9

2.0

32.4

19.6

45.0

15.6

4.9

14.1

1.8

18.6

Race Distribution (%) White Black Other

23.1 74.9

2.0

18.7 76.6

4.7

31.6 65.9

2.5

MSM - Men having sex with men

IDU - Injection drug users

HS - Heterosexual

* Case totals are accumulated by date of report to the Epidemiology Section

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