Analysis of West Nile Virus in Franklin County, Pennsylvania

Transcription

1 Analysis of West Nile Virus in Franklin County, Pennsylvania Aaron Barkdoll May 10, 2007 This report examines the research of the 2006 West Nile Virus (WNV) Summer Program, Franklin County, PA. The program s research was focused on mosquito biology/ behavior patterns, detecting viral strands of WNV within the county, and applying control measures to decrease the mosquito populations that carry the virus. Positive viral collections were tabulated from human, avian, mosquito, sentinel chicken flocks, and veterinary samplings. Both environmental and human factors are examined to demonstrate the region s ability to constantly experience high frequencies of WNV during the summer seasons. Solutions for preventive infection procedures will be overviewed. 1

2 Introduction During the 2006 WNV Summer Program, Franklin County received the top ranking for viral positives in Pennsylvania. There were a total of 65 positive WNV samples collected in Franklin County between the months of April 2006 and October 2006 (DEPPA 2007). The amount of positive cases collected have sparked an interest with both state and county officials in determining why Franklin County is able to generate consistently high numbers of positives year after year. In examining this problem this report will focus on examining the biology/transmission of West Nile Virus, viral collection data, environmental/ human factors that promote viral presents in the county, and explore solutions to decrease human infection rates. Biological Information on West Nile Virus Biological Classification of West Nile Virus WNV is a mosquito-transmitted virus that causes cases of encephalitis (inflammation of the brain). People from the age range of 1-10 and 50+ are most susceptible to develop the severe/fatal cases of encephalitis (CDC 2004). Although most people may contract the virus, many do not experience the symptoms. These people unknowingly carry the virus and within a few days the body recovers. But for some people, symptoms experienced include fever, headache, tiredness, body aches, occasional skin rash, and swollen lymph glands (CDC 2004). While the illness can be as short as a few days, even healthy people have reported being sick for several weeks and then hospitalized. Since there is no cure or vaccine, people should consult their physicians for diagnosis to receive antibiotics to help control symptoms and kill off the virus to prevent the formation of encephalitis (CDC 2004). Transmission of West Nile Virus Figure 1: Transmission Cycle of WNV West Nile Virus is a disease that incorporates multiple pathways to both spread and develop within organism populations. The virus begins its cycle as an airborne pathogen that infects birds from Africa, Asia, and Europe (Helwig 2007). The infected birds then migrate into the Americas were it is then transmitted to local mosquito populations (vector spiecies) when the infected birds are bitten. Within a period of days the virus incubates inside the mosquito s saliva duct to form a viral strand that can infect mammals (Helwig 2007). Mosquitoes then bite a second host; being 2

3 people, other mammals, or other birds in order to extract blood to produce their offspring (Helwig 2007). At this stage the virus is transmitted to the mammalian host were it has the potential of developing into encephalitis. The virus can also be transmitted from female mosquito to offspring, which means that the new generations of larvae that survive to the adult stage already have the ability to infect new host (Helwig 2007). West Nile Viral Collection and Data Since the summer of 2000, The Department of Environmental Protection has preformed multiple collection operations in Pennsylvania and Franklin County. These collection efforts were created to detect the presents of WNV, within the area, over the course of a mosquito-breeding season (usually April-October) viral samples were collected and tabulated from mosquitoes samples, human cases, blood donors, dead bird samples, sentinel chicken flock samples, and veterinary samples. (PAWNVSP 2007) Surveillance Type Collected Tested Positives Humans N/A N/A 9 Blood Donors N/A N/A 1 Dead Birds Mosquito Sentinel testing may produce multiple positive results for an individual animal. Sentinel Veterinary N/A N/A 2 Figure 2: Total collection data for Pennsylvania Surveillance Type Collected Tested Positives Humans N/A N/A 1 Dead Birds Mosquito Sentinel testing may produce multiple positive results for an individual animal. Sentinel Veterinary N/A N/A 0 Figure 3: Total collection data for Franklin County, PA. 3

4 Factors Promoting WNV Presence in Franklin County Migration Patterns of Birds in Franklin County The United States is divided into 4 major migratory flyways (Bolen 2003). The flyway that PA is located in is the Atlantic Flyway. This flyway typically has birds migrating back to the U.S. from countries such as Africa and Asia (Bolen 2003). Africa and Asia are two of the three main counties were bird populations can first contract WNV. This pattern along with PA s geographical location is a good resting location for migratory bird populations. In turn, with more birds stopping within the state, WNV frequency increases within the area. This then can increases possibility that the migratory bird populations will transfer the virus to the mosquito populations (Helwig 2007). Agriculture in Franklin County Agriculture is Pennsylvania s number one industry with a total of 51,000 farms (PAHMC 2006). These farms may be important to the state, but they also play a large role in creating potential habitat for mosquito populations. Mosquitoes are apart of a family of insects that lay their eggs in temporary or stagnant pools of water (Davis 2007). This is a biological adaptation to increase survival rates of offspring because the water sources chosen contain adequate food supplies along with a decreased interaction with predatory organisms that generally exist in more permanent/cleaner water structures (Davis 2007). Dairy farms within the region can create perfect habitat for mosquito breeding. Manure lagoons and silage seepage areas create potential habitat for mosquito larvae (Helwig 2007). These two factors, however, are minor to the number one breeding stop created by these farms. Tires used by farm owners to brace tarps over silage bunkers create a problem because as rainwater enters the tire it becomes trapped and does not evaporate quickly. The water collected in the tires becomes heated during the summer, which allows for bacteria to grow, creating the primary food source for mosquito larvae (Helwig 2007). Figure 4: (Left) picture of a manure lagoon. (Right) picture of a silage bunker with tires piled over top of tarp. 4

5 Residential Construction in Franklin County Over the past two decades the number of new residential housing complexes has increased in the Franklin County area. Franklin County is the third fastest growing community in Pennsylvania (PAHMC 2006). With the increase in construction, potential habitat for mosquitoes is also increasing. Construction forms retention ponds that temporarily drain and collect water away from the building sites (Eckhart 2007). These ponds form habitat for mosquitoes to breed. Also, after construction the retention ponds are usually allowed to remain in the residential complex. This allows for a sustainable habitat for mosquitoes. Another problem with the new residential complexes is that catch basins are implemented into the construction plans. Catch basins are structures that collect storm water and drain the water into the sewer system (Eckhart 2007). The design the catch basins are problematic because there is an area in the structure that collects sediment that could travel into the sewer. This area also can contain excess water that can create another form of potential breeding site for mosquito populations (Eckhart 2007). Figure 5: (Left) a retention pond in a residential setting. (Right) diagram of a common catch basin installed in a residential setting. Preventative Ways to Protect Against WNV Personal Protection According to Jennifer Davis, DEPPA entomologist, there are some simple practices people can use to protect themselves from becoming infected with WNV. If you go outside you should apply a bug repellent that contains a product known as DEET. It is the best commercial product that repels both mosquitoes and ticks. Also, wear lighter colored clothing because darker colored clothes absorb more heat. 5 Figure 6: Consumer product containing DEET.

6 Mosquitoes, along with other insets, are attracted to heat. When outside at night the use of citronella candles and bug zappers are good ways to keep bugs off you. Citronella deters insects because the chemical aroma and vapor irritates the sensory organs of insects. Also, be aware that mosquitoes are active during the day, but they are mainly active during dusk and dawn, so if you are outside when it is dark there is a greater risks that you will be bitten. Preventative Procedures Around the House According to Franklin County s WNV Coordinator, Ray Eckhart, there are some things around your house that you can fix to reduce both the number of mosquitoes and potential mosquito habitat. If you occasionally clean out your gutters obstructions can be removed to prevent water build up. Birdbaths should be cleaned every one to two weeks with fresh water. Pools, garden ponds, and catch basins around your home should be treated with chemicals (chlorine) or larvaecides that are specially designed for mosquito larvae and are water activated. Check for items around the house that could collect water such as tires, cans, bottles, pots, buckets, toys, lawn equipment, etc. By fixing some of these problems you can help to reduce the potential habitat for Figure 7: Potential problem areas around the house. mosquitoes, which in turn, will reduce mosquito numbers and decrease your chances of being infected with WNV. Conclusion In examining this report it evident that West Nile Virus is becoming an increasing problem for Pennsylvania. The information presented shows why Franklin County, Pennsylvania is a prominent breeding ground for both the vector species (mosquitoes) and the virus. This information also expresses the importance of why more people should be educated and how they can protect themselves from potential contracting the virus. By using this report people can have a better understanding of what WNV is and how it can be spread through the population. From there were approx. over 9,000 cases of WNV in PA. Over the next few years the number of birds, mammals, and mosquitoes positives could continue to increase. But as more of the population becomes educated on WNV, people can begin making simple changes to help control the virus and maybe even stop it from becoming a future epidemic. 6

7 Works Cited: Bolen, Eric G., and William L. Robinson. Animal Behavior and Wildlife Management. Wildlife Ecology and Management. Ed. 5 th. New Jersey: Pearson Education, Inc., pp: [CDC] West Nile Virus: Overview of West Nile Virus. 26 Apr Center for Disease Control and Prevention. < Davis, Jennifer (DEPPA Entomologist). Personal interview. 1 May Eckhart, Ray (Franklin County WNV Coordinator). Personal interview. 30 Apr Helwig, Matt (DEPPA WNV Program Coordinator). Personal interview. 29 Apr [PAHMC] PA History: Agriculture in Pennsylvania. Pennsylvania Historical and Museum Commission. < agriculture/ page1.asp?secid=31>. [PAWNVSP] Surveillance/Maps: 2006 Surveillance Results. Pennsylvania s West Nile Surveillance Program. Program. 14 Nov < surv.htm.>. 7