Georgia epidemiology report, Vol. 21, no. 5 (May 2005)

May 2005

volume 21 number 05

Mosquito-Borne Viruses in Georgia 2004

Human Arboviral Illness Surveillance West Nile virus (WNV) is a mosquito-borne viral pathogen introduced into the United States (U.S.) in 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. The virus was first identified in Georgia in 2001. WNV is now considered endemic in most parts of the U.S., including Georgia.
West Nile virus is one of several mosquito-borne viruses, also called arboviruses (arthropod-borne viruses) that circulate in Georgia. Other identified arboviruses include Eastern Equine Encephalitis virus (EEE), LaCrosse virus (LAC), and 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.
West Nile virus 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 a 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 possibly 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, 2,470 cases of WNV illness and 88 deaths were reported to the Centers for Disease Control and Prevention (CDC) in 2004. In Georgia, an acute arboviral infection is a reportable condition; however, the majority of cases of arboviral infection likely remain unreported due to mild or asymptomatic illness. In 2004, the Georgia Division of Public Health (GDPH) reported 23 residents infected with WNV, one of who developed fatal illness. The first human case occurred in Clayton County in July. The last human case reported in Georgia during 2004 occurred in Gwinnett County in October. Fourteen (61%) cases were diagnosed with WNND while 7 (30%) developed WNF. One of the reported WNV infections did not develop any symptoms of illness. One case was also lost to follow-up so the course of the disease is unknown. The average age of cases was 53 years (range 1881 years). The average age of people who experienced neurologic illness was 56 years (range 1877 years). The age of the fatal case was 76 years. Seventeen (74%) of the 23 cases were male. The majority of cases had onsets in August. Table 1 displays the number of cases by month of onset, county of residence, clinical syndrome, and whether the case was fatal.

Other Mosquito-Borne Viruses in Georgia In 2004, there were no reported cases of EEE in Georgia. There were, however, five non-fatal reported cases of LAC infection. No cases of SLE infection were reported.
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 or 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 2005. Should submissions exceed the laboratory's capacity, the previous years' criteria will be reinstituted. For this reason, please call the Georgia Division of Public Health (GDPH) before submitting specimens for arboviral testing (404-657-2588). If needed, specimens positive for WNV or other arboviruses at commercial laboratories can be retested at GPHL to verify the results.
Arbovirus Surveillance in Sentinel Species In addition to surveillance for human disease caused by arboviruses in Georgia, GDPH and its partners conduct surveillance for arboviruses in birds, horses, and mosquitoes in an effort to determine local risk of human disease. Below is a summary of arbovirus surveillance results in 2004.
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 mosquitoes are transmitting virus. Public health contacts the owners of WNVpositive horses to educate them about their personal risk of disease and risk-reduction 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 decreased dramatically between 2003 and 2004, from 61 to 3 cases. Because we are still learning about trends from year to year, we cannot accurately predict what 2005 holds, 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 for use in the prevention of human disease.

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There were 7 cases of EEE in Georgia horses during 2004, 6 of which died or were euthanized. This is in sharp contrast to the 81 cases in 2003, an epidemic year for EEE.
Poisson probability analysis for equine cases of WNV and EEE for 2001-2004 shows that cases were not randomly distributed across the state, but were clustered within a small number of counties. The clustering is in accord with past experience of mosquito problems being localized, and supports focusing surveillance and control strategies at the local level. No county with significantly high incidence of equine WNV in one year had a significantly high incidence of equine WNV in subsequent years; this may be due to natural immunity and vaccination. In all, there were 21 county-years with a significantly high incidence of equine WNV (in 2001, 2002, and 2003, but not in 2004) and eight county-years with a significantly high incidence of equine EEE (all in 2003). During 2001-2003, equine surveillance was useful in rural counties where bird and mosquito surveillance resources were few.
WNV and EEE 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 Bird mortality surveillance in Georgia remains a sensitive tool to determine the geographic range and extent of WNV and other arbovirus activity in various parts of the state and to predict risk of human disease. In 2004, there were 581 birds submitted from 71 of 159 Georgia counties; a total of 105 WNV-positive birds were found in 24 of those counties. The first positive bird in 2004 was submitted for testing on 1/22/04 from Ware County, but the second WNV-positive bird, from Henry County, was not submitted until 6/28/04. The last positive bird was submitted on 11/17/04 from metro Atlanta. Approximately 75 species of birds were submitted for testing, with blue jays, American crows, and fish crows making up 30% of the birds submitted. Fifty-five percent of the fish crows, 38% of the American crows, and 49% of the blue jays submitted were positive for WNV. No birds tested positive for EEE in 2004.
Surveillance indicates there is some level of WNV transmission occurring almost year-round (Figure 1). Based on currently available data, it is likely that there is detectable transmission occurring from April or May of one year until Jan or Feb of the next, depending on meteorological conditions.
Mosquito Surveillance Mosquito surveillance is conducted to detect the presence of arboviruses in potential vectors and to help guide mosquito control programs. Some level of mosquito surveillance was conducted in 60 of 159 Georgia counties in 2004. In addition, the U.S. Army Center for Health Promotion and Preventive Medicine South (USA-CHPPM) conducted mosquito surveillance on military bases in Georgia, sharing those data with GDPH. Intensive mosquito surveillance was conducted in fewer than 10 counties. Seven counties reported WNV-positive mosquito pools. Positive mosquitoes were detected in metro Atlanta as

Table 1. Human Arbovirus Cases, Georgia 2004

Arbovirus Month of County of Clinical Syndrome Onset Residence

Fatal

LAC* March

Brantley Meningitis

No

LAC

July

Rabun

Encephalitis

No

LAC

September Rabun

Meningitis

No

LAC

September Oconee

Meningoencephalitis

No

LAC

October Cherokee Meningoencephalitis

No

WNV** July

Fulton

Encephalitis

No

WNV July

Clayton Encephalitis

No

WNV August

Fulton

Fever

No

WNV August

Fulton

Encephalitis

No

WNV August

Chatham Meningitis

No

WNV August

Fulton

Fever

No

WNV August

Fulton

Encephalitis

No

WNV August

Fulton

Unknown

No

WNV August

Gwinnett Asymptomatic

No

WNV August

Clayton Fever

No

WNV August

DeKalb

Fever

No

WNV August

Fulton

Meningitis

No

WNV August

Muscogee Fever

No

WNV August

Richmond Meningitis

No

WNV August

Fulton

Acute Flaccid Paralysis No

WNV September Muscogee Meningitis

No

WNV September Fulton

Encephalitis

No

WNV September Cobb

Fever

No

WNV September Cobb

Meningoencephalitis

No

WNV September Clayton Encephalitis

No

WNV September Richmond Encephalitis

Yes

WNV October Lowndes Encephalitis

No

WNV October Gwinnett Fever

No

* LAC- LaCrosse Encephalitis ** WNV- West Nile Virus

Table 2. GPHL Arboviral Testing criteria for 2005
Adults: To qualify for testing at GPHL, persons must be 18 years or older and meet at least one of the following criteria:
Meningitis, OR
Encephalitis, OR
Acute onset of profound muscle weakness or acute flaccid
paralysis (including Guillain-Barr syndrome), OR
Fever (greater than 100.4F) and at least 2 of the following:
o Headache o Malaise o Arthralgia o Fatigue o 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
pre-existing seizure disorders, OR
Encephalitis, OR
Acute onset of profound muscle weakness or acute flaccid
paralysis (including Guillain-Barr 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.
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early as mid-June. The last positive pool was collected in Newton County in mid-October, with a peak in number of positive pools occurring at mid-August. Mosquito pools are comprised of a single species of mosquitoes collected at a given site during a given time period. For testing purposes, mosquito pools contain 20 or fewer mosquitoes.
Ninety-six percent of the positive pools collected were comprised of Culex quinquefasciatus, the southern house mosquito, which is a primary WNV vector in Georgia (Figure 2). An additional 3.5% were unspecified Culex, most of which were likely to be Culex quinquefasciatus, based on time of year and location. Culex quinquefasciatus is a container-breeding mosquito that flies only a short distance from its breeding site when searching for a blood meal. Personal protection measures which include dumping out standing water at least once a week, applying larvicide to areas of standing water that can not be dumped or drained, keeping gutters clear of debris, removing saucers from under outdoor potted plants, and picking up all containers that may hold water are ways in which the public can help reduce the risk of WNV in their community.
EEE was isolated from 2 mosquito pools, both collected in August in Lowndes County. One pool testing positive for EEE was comprised of Culex nigripalpus, a bird and mammal feeder; the other positive mosquitoes were Culiseta melanura, a birdbiting species that maintains the EEE virus in birds.
For more information regarding arbovirus activity in Georgia, please visit http://health.state.ga.us/ epi/vbd/mosquito.shtml or call 404-657-2588.
Authors: Meghan Weems, M.P.H.; Laurel E. Garrison, M.P.H.; Marianne Schady; Rosmarie Kelly, Ph.D., M.P.H.

# birds submitted for testing

% WNV-positive
51 49 47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 1

Dead Bird Surveillance, 2002-2004

110

60%

100

90

50%

80

3-year mean

WNV+ 70
% WNV+

60

50

40% 30%

40 20%
30

20

10%

10

0

0%

week
Figure 1: Dead Bird Surveillance, 2002-2004. 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.

average # pools

150 140

Culex quinquefasciatus Surveillance, 2002-2004

17 16

130

15

120

Average # pools

14

110

Average # WNV+

13 12

100

11

90

10

80

9

70

8

60

7

50

6

40

5 4

30

3

20

2

10

1

0

0

average # positive pools
51 49 47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 1

week

Figure 2: Culex quinquefasciatus Surveillance, 2002-2004. Detection of WNV in mosquitoes indicates an increased risk of human disease locally.

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

Epidemiology Branch http://health.state.ga.us/epi
Paul A. Blake, M.D., M.P.H. Director
State Epidemiologist
Mel Ralston Public Health Advisor

Georgia Epidemiology Report Editorial Board
Carol A. Hoban, M.S., M.P.H. Editor
Kathryn E. Arnold, M.D. Paul A. Blake, M.D., M.P.H. 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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Division of Public Health Two Peachtree St., N.W. Atlanta, GA 30303-3186 Phone: (404) 657-2588 Fax: (404) 657-7517

Georgia Department of Human Resources

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

May 2005

Volume 21 Number 05

Reported Cases of Selected Notifiable Diseases in Georgia Profile* for February 2005

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 February 2005
2005 20 914 9 1 41 327 9 7 19 1 0 1 0 1 0 52 24 1 3 3 5 0 7

Previous 3 Months Total

Ending February

2003 10

2004 5

2005 59

7143

6394

5015

5

13

15

0

0

5

59

46

115

3051

2514

2023

1

1

29

0

0

21

14

17

73

0

0

2

0

0

0

0

0

7

0

0

0

0

0

6

0

0

0

24

28

147

21

13

64

10

7

9

37

55

33

48

33

11

42

22

36

0

0

0

14

5

26

Previous 12 Months Total

Ending in February

2003 26

2004 27

2005 94

28096

28242

25431

20

25

45

0

0

5

261

225

331

12900

11773

9784

2

1

41

1

2

25

63

99

151

0

0

2

0

0

0

0

0

7

0

0

0

0

0

7

0

0

0

131

163

330

121

60

138

24

24

25

121

196

176

156

186

64

123

120

161

0

0

0

56

39

74

* 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.

AIDS Profile Update

Report Period
Latest 12 Months: 05/04-04/05 Five Years Ago: 05/00-04/01 Cumulative: 07/81-04/05

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

8

1,436 1,444

9

1,189 1,198

224

28,346 28,570

Percent Female
26.2
27.4
19.2

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

32.2

7.0

2.0

11.4

1.7

45.6

31.9

11.2

2.4

17.6

1.9

35.1

45.5

16.0

4.9

14.3

1.9

17.3

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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Race Distribution (%) White Black Other

22.0 75.7

2.3

19.9 76.0

4.2

32.0 65.4

2.6