Mosquito & Tick Borne Disease Control

 Vectorborne Diseases that Present a Public Health Risk


The medical community should be aware that diseases such as West Nile virus and Lyme disease are much more likely to be observed in urban residents than one would reasonably expect.
(click here to read a copy of a supporting article from the 2007 San Mateo County Times)
(click here to read a copy of a more current supporting article from the 2014 San Jose Mercury News)
There are tangible reasons we face an increased risk for vectorborne diseases and knowledge of the source of these vectors and the diseases they transmit can help us to prevent disease as well as identify these diseases more readily when people become ill.


The control of mosquitoes and ticks, vectors that can carry West Nile virus and Lyme disease (also ehrlichiosis, Rocky Mountain spotted fever and babesiosis), is under the purview of your local Mosquito Abatement District (MAD).   A representative of San Mateo County Mosquito Abatement District (SMCMAD) was asked the following question:  wetland restorations being implemented in our County are creating breeding grounds for mosquitoes…why isn’t the public made aware of that negative consequence? She answered, “we don’t feel the need to inform the public because we can control the mosquitoes”.  When asked if the MAD could control the ticks, she responded simply “No”. 


In 2007, California declared an "emergency" situation with outbreaks of the West Nile virus statewide. In 2008, the cases of West Nile Virus in California continued to mount. We have yet to see how severe the West Nile Virus will be in 2009, but it appears the ability of our government to “control” the mosquitoes is questionable at best.  The news coverage talks about abandoned swimming pools but does not discuss the larger issue of wetlands, natural and manmade, and the significant hazard they represent.  (Click here to see an article about Gov. Arnold Schwarzenegger's Executive Order for spraying of State wildlife wetlands exclusively as a measure to check the spread of West Nile virus).


In addition, Park Managers in Federal, State, County and local parks have been and still are creating environmental features to foster native plants and enhance wildlife, that also are breeding grounds for mosquitoes, and enhancing the proliferation of ticks and their movement into our neighborhoods. A perfect example would be the Mori Point ponds created by the National Park Service and the current proposal by San Francisco to turn a popular, functioning golf course into wetlands. 

2007 West Nile Virus Activity in the United States
(Reported to CDC for the entire year of 2007)
2008 West Nile Virus Activity in the United States
(Reported to CDC for the entire year of 2008)


West Nile encephalitis and West Nile meningitis are forms of severe disease that affect a person’s nervous system. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord. Symptoms of severe disease include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, muscle weakness, vision loss, numbness, and paralysis. These are illnesses that usually require hospitalization. Neurological effects can be life-altering and permanent. Transplant recipients and immunocompromised individuals are at increased risk of severe West Nile virus disease.


West Nile fever refers to typically less severe cases that show no evidence of neuroinvasion. WN fever is considered a notifiable disease, however the number of cases reported (as with all diseases) may be limited by whether persons affected seek care, whether laboratory diagnosis is ordered and the extent to which cases are reported to health authorities by the diagnosing physician. Symptoms include fever, headache, body aches, nausea, vomiting., and sometimes a skin rash on the chest, stomach, and back.


Other Clinical includes persons with clinical manifestations other than WN fever, WN encephalitis or WN meningitis, such as acute flaccid paralysis.

Unspecified cases are those for which sufficient clinical information was not provided.


There is no specific treatment for WNV disease. Human vaccines for WNV are still in the early stages of development.

West Nile Virus Survivors Video

Several patients discuss their health problems associated with West Nile virus

It is still early in the mosquito season, yet in the San Francisco  Bay Area we already have evidence of West Nile virus in humans as well as animals and mosquitoes.  Depending upon variable weather patterns, the skill and budgets of our respective Mosquito Abatement Districts, and public awareness, the incidence of West Nile virus in 2009 could skyrocket. 

The National Park Service has completed the process of building ponds/wetlands at Mori Point in Pacifica, directly adjacent to the backyards of residents.  We note there was no mention of West Nile Virus in the Park Service's environmental review for the proposed changes at Mori Point. Please click on the following video to see photos of the project in progress, as well as brush piles and intentional standing water features to attract damselflies.


The environmental features the NPS has created are precisely the environmental features the CDC instructs you to remove to protect you, your family and your community from mosquitoes and ticks.

Mosquito & Tick Breeding Ground
Mori Point, Pacifica, CA (September, 2007)

Acknowledging the fact that these are breeding grounds for mosquitoes, MAD has been out to spray to control mosquitoes even during construction, however, the neighbors have not been personally notified of the risk of mosquitoes or the intermittent risk the spraying may create.

San Francisco’s “Natural Areas Program” advocates the construction of water features which are again mosquito breeding grounds in San Francisco and Pacifica recreational areas.  In fact, San Francisco Recreation and Park Department acknowledges the mosquito problem in their “System Wide Management Actions and Practices” document pertaining to significant natural areas.  Section 5, page 22 of that document states:

First detected in the United States in 1999, West Nile virus (WNV) is a mosquito-borne disease that is common in Africa, west Asia and the Middle East. In 2004, there were a total of 829 WNV human infections, from 23 counties in California. West Nile virus activity has been detected in all counties, but there have been no cases reported from San Francisco (DHS 2005). Although it can be fatal to birds (and even humans), most of the people infected with WNV do not exhibit any symptoms. The San Francisco Health Department currently participates in the statewide IPM program targeting WNV. In Natural Areas, two types of BMPs [Best Management Practices] are recommended:


1. Staff should be provided education regarding the most effective way to avoid contracting WNV, which is to not get bitten by mosquitoes. Clothing such as long pants, long-sleeved shirts, and application of a mosquito repellent may all be helpful in this regard. Volunteers and site stewards working with the program should also be informed. Editor’s note:  how about informing the public?


2. Some Natural Areas contain small water features such as abandoned tires and other refuse that holds water. These features could provide breeding habitat for mosquitoes. At times it may be feasible to remove the water from these areas or to treat the features with BT (Bacillus thuringiensis israeliensis), a safe and ready to use biocontrol treatment for mosquitoes. In other cases, removal of water cannot occur without damaging a sensitive resource.Editor’s note:  aren’t humans a more “sensitive resource”?


Purchased by Peninsula Open Space Trust and now under the stewardship of the Don Edward San Francisco Bay Wildlife Refuge, Bair Island is being restored to tidal marsh, and will support wildlife including migrating waterfowl, shorebirds, and at least two endangered species, the clapper rail, and salt marsh harvest mouse.


"In 2004, changes in the landscape on Outer Bair resulted in the development of large populations of summer salt marsh mosquitoes for the first time in over 20 years. Adult mosquioes inundated neighboring cities and had to be brought under control by truck-mounted fogging. Since that time, these summer mosquitoes have been controlled in their larval stages and have not reached the population levels seen in 2004."

(Excerpted from SMCMAD Entomology Report, May, 2007 )


The question must be asked, “Is public health of primary concern when decisions are made to pursue projects such as this?”


"Environmentalists have condemned attempts to control the transmitting mosquitos by spraying pesticide, saying that the detrimental health effects of spraying outweigh the relatively few lives which may be saved, and that there are more environmentally friendly ways of controlling mosquitoes."  (from News-Medical.Net: 

CDC Reported Cases of Lyme Disease by Year, U.S., 1992-2007
In 2005, 23,305 cases of Lyme disease were reported yielding a national average of 7.9 cases for every 100,000 persons. In the ten states where Lyme disease is most common, the average was 31.6 cases for every 100,000 persons.
In 2007, 27,444 cases of Lyme disease were reported yielding a national average of 9.1 cases per 100,000 persons. In the ten states where Lyme disease is most common, the average was 34.7 cases per 100,000 persons.

The CDC reports that Lyme disease is the most common vectorborne disease in the United States.  Since Lyme disease became nationally notifiable in 1991, the annual number of reported cases has more than doubled.


Locally, urban residents are also noting for the first time ticks which can transmit Lyme and other diseases upon their own person, even if they have not been outside of their immediate neighborhood.  They have also noted a dramatic increase in the number of the same ticks found on their dogs as compared to previous years.  Experts, such as Dr. Robert Lane at UC Berkeley, have traditionally advised that if we did not have deer in our immediate environment, we must have acquired the ticks elsewhere.  We usually look to open space and recreational areas where people might hike with or without a dog.  Unfortunately, the paradigm has changed.  Ticks that are vectors of Lyme disease are also being found in urban neighborhoods, often in vegetation adjacent to a curb, or in the yards of homeowners, even when deer do not frequent the area.


"The District was contacted from residents of Belmont (near Water Dog Lake) and Pacifica with concerns about ticks in their neighborhoods. In Pacifica, questing ticks can be found in the open spaces between homes. In Belmont, western black-legged ticks were found inside a home adjoining the open space around Water Dog Lake, presumably brought in by the family cat. These instances illustrate the need to watch out for ticks even if one does not engage in outdoor activities at this time of year."

(Excerpted from SMCMAD Entomology Report, January, 2007)


A study conducted at the Institute of Ecosystem Studies in New York and published in 2006, concludes that the risk of Lyme disease is correlated positively with the prevalence of small mammal hosts and the abundance of their food supply, not the number of deer or fluctuations in climate.  (Click here to see the study abstract).  The small mammal hosts carry the ticks into residential neighborhoods when they search for food and/or shelter.


Another study concluded the spatial arrangement of landcovers is a critical consideration when analyzing the links between the environment and the transmission risk of Lyme disease.  Forested areas correlated with a higher risk, while areas with predominantly ornamental vegetation had the lowest risk.  (Dister et al, 1993).


This is consistent with the CDC recommendations to use landscaping techniques to create a tick-safe zone around homes, parks, and recreational areas:

  • Removal leaf litter, brushpiles and woodpiles.
  • Clear tall grasses and brush.
  • Place wood chips or gravel between lawns and wooded areas to restrict migration to recreational areas.

Plans for “habitat restorations” already implemented and proposed for Sharp Park confirm the objective of enhancing habitat for small mammals and creating “wildlife corridors” which bring these mammals into close proximity to residential neighborhoods.  Excerpts  from San Francisco’s “Natural Areas Program” (NAP) state:

“Issue:  Important elements within natural habitats for the survival of small mammals as well as reptiles and amphibians include underbrush, fallen logs…debris such as lumber, brush piles…piles of abandoned lumber may be aesthetically unpleasing but provide important refuge habitat for many species…

Recommendation: The natural or biodegradable (branches trees and logs) elements shall be preserved during vegetation management activities or replaced with brush piles.” (Editor’s note-the phrase “vegetation management activities” refers in part to their plan to cut down 15,000 eucalyptus trees merely because they are non-native.  They don’t intend to remove the resultant lumber or leaf litter, and the remaining stumps will become mosquito-breeding sites as well). (Click here to see the NAP plan for Sharp Park specifically.)


The National Park Service in 1984 noted the following at Sweeney Ridge:  “The grassland areas of this site have been grazed by horses for many years, promoting a habitat for wildflowers and giving a mowed appearance.  Grazing has also prevented the encroachment of scrub species into the grassland…no evidence of overgrazing…grazing has reduced the habitat value of the grasslands for this species (San Francisco garter snake).”  NPS management activities at Sweeney Ridge removed the grazing horses, and the grass has been allowed to grow long and scrub encouraged to proliferate; facilitating habitat for the SF garter snake as well as small mammals. (Click here to see the NPS planning document for Sweeney Ridge).


The environmental features the CDC instructs you to remove to protect you, your family and your community from ticks are precisely the environmental features these Park managers are implementing.   

2006 San Mateo County MAD Tick Survey

Further, in City and County parks where the MAD knows we have a tick problem in large part due to park management activities, there are no warnings posted for the public on websites for those parks.  We all know that protecting ourselves from mosquito and tick bites includes dressing appropriately; this information should be on web sites for these problematic park facilities if public health was the major concern.  We have asked that the County post warnings on the web site for San Pedro County Park which is the worst park for ticks in San Mateo County, yet no web site cautions have been posted (click here to link to that web site).   There are no signs warning of the presence of ticks at the entrance to this park, no signs at the information center, none at the picnic sites or trails-except for just one sign on a single trailhead that was added due to our complaints. 


We asked that the public be advised ticks can and will be found in our neighborhoods so that parents understand that they should perhaps check their children after they walk to and from school.  SMCMAD has not yet implemented a comprehensive plan to do so. These ticks can be found everywhere and the public must be notified and alerted to the risks they present. SMCMAD excuses their failure to educate the public by explaining that they are just too busy.  The fact that MAD can find the time to assist the National Park Service (NPS) by spraying for mosquitoes as the NPS constructs a mosquito-breeding habitat leads us to believe MAD needs to re-evaluate their priorities.  Why is MAD not pressing our San Mateo County Department of Public Health to oppose these projects in the first place?


The Bio-Integral Resource Center is a non-profit organization here in the Bay Area dedicated to “Integrated Pest Management” as a means to suppress the pest population below the level that causes economic, aesthetic or medical injury.  Their international network of advisors design strategies that minimize effect to human health and the environment.  They state:  “To stop vectorborne diseases, we should apply our knowledge of pest biology and ecology.  We should manipulate ecological factors to discourage transmission.  What we should not do is indiscriminately apply massive amounts of insecticides through aerial spraying.  Such an act of desperation will not provide a long-term solution, will kill important beneficial insects, and needlessly expose the population to toxic agents”.  (click here to see their guidelines on the control of vectorborne diseases).


It should be pointed out that our government entities all publicly ascribe to the “Precautionary Principle”. 


"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. In this context the proponent of an activity, rather than the public, should bear the burden of proof. The process of applying the Precautionary Principle must be open, informed and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action." —1998 Wingspread Statement on the Precautionary Principle


This situation is a wholesale abandonment of this promise.  (cllck here to view a White paper on the "Precautionary Principle".)



The purpose of this web site is threefold: first, publicizing the problem of vector-borne diseases for the public benefit.  Second, informing the medical community so that physicians generally include WNV, Lyme disease and other tickborne diseases (ehrlichiosis, Rocky Mountain spotted fever and babesiosis) in their differential diagnoses, and third, to explain to the medical community why it should use its influence to halt these intentional environmental modifications/projects that are putting the public health at risk. 

Dr. Suzanne Valente discusses West Nile Virus
at Laguna Salada/Sharp Park

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