Vectorborne Diseases
Vectorborne diseases in California having significant public health importance include infectious diseases whose pathogens are transmitted by, or in association with, mosquitoes, ticks, fleas, lice, and rodents. Pediculosis is a non-infectious disease that results directly from infestations of humans by lice, usually head lice.[HideMe]Mosquitoborne Diseases
Mosquitoes are primary vectors of serious infectious diseases in California. They transmit several arboviruses of public health importance, filarial worms causing dog heartworm, and sporadically and focally, human malarial parasites.
Photo credit Edman/McClelland collection
[HideMe]Arboviruses
Worldwide, there are several thousand recognized arboviruses. The term arbovirus was coined many years ago to include viruses that were transmitted to vertebrate animals by arthropods. Mosquitoes, ticks, and biting flies of various kinds are all vectors. In California, the most important viruses transmitted to humans and other vertebrates are mosquitoborne. Western equine encephalomyelitis virus (abbreviated WEE) is one of the important mosquitoborne viral diseases in California. For information on specific California mosquitoborne viruses, select the name of the virus from the menu at the right.
St. Louis Encephalitis Virus
St. Louis encephalitis virus (SLE), a member of the flavivirus family, was the most important mosquito-borne arbovirus in North America up until 1999, when West Nile virus (WNV) was introduced into the United States. Wild birds are the maintenance and amplifying hosts of SLE, which is transmitted among birds and to humans by primarily Culex mosquitoes. Human infection with SLE can result in mild to severe illness, with case-fatality rates ranging from 3%-30%.
SLE was first recognized in 1933 in St. Louis, Missouri, where it caused over 1000 human cases and 200 fatalities. The virus is found throughout the U.S., Canada, and nothern Mexico, and causes periodic epidemics of encephalitis, with outbreaks generally occuring between August and October. An average of 128 cases are reported annually in the U.S. The most recent outbreak occured in 1999, in New Orleans, Louisiana, with 20 reported cases.
SLE in California
Since 1945, 597 human cases of SLE have been reported in California. The most recent outbreaks occurred in 1984 and 1989 in the Los Angeles Basin (26 cases) and the southern San Joaquin Valley (29 cases), respectively. The last human case reported was in 1997, from Los Angeles County. SLE activity has not been detected in mosquito pools or sentinel chickens since 2003.
West Nile Virus
West Nile virus (WNV) belongs to the flavivirus family which includes, among others, the dengue, yellow fever, and Japanese encephalitis viruses. WNV can cause mild to severe illness in human, other mammal (eg. horses, squirrels), and avian hosts. The virus circulates and amplifies in birds, and is transmitted to humans primarily by Culex mosquitoes. Prior to 1999, WNV was known to occur only in Africa, Asia, and the Middle East. WNV was first detected in North America in New York in 1999, and has subsequently spread to 48 states, Canada, and Mexico.
History of WNV Activity in California
WNV first appeared in California in 2002 with the identification of one human case. In 2003, WNV activity was detected in six counties in southern California; three human WNV cases and one equine WNV case were reported and WNV activity was detected among dead birds, mosquito pools, and sentinel chickens. In 2004, 58 counties detected WNV activity and 779 human cases were reported, with 28 WNV-associated fatalities. In 2005, 880 human cases and 19 fatalities were reported, and non-human WNV activity was detected in 54 counties.
2006 Summary of WNV Activity in California
In 2006, 54 counties in California reported WNV activity. A total of 278 human cases were reported to the California Department of Health Services from 36 counties. Of the 278 cases, 190 (68%) were classified as West Nile fever, 83 (30%) were identified as neuroinvasive disease cases (i.e. encephalitis, meningitis, or acute flaccid paralysis), and five were of unknown clinical presentation. There were seven reported WNV-associated fatalities. Non-human WNV activity reported included the following: 58 horse cases were reported from 23 counties--24 died or were euthanized; 832 WNV positive mosquito pools were detected from 33 counties; 640 WNV positive sentinel chickens were reported from 29 counties; 1,446 positive dead birds were reported from 53 counties; and 32 WNV positive tree squirrels were reported from nine counties.
Click here for information on current WNV activity in California.
WNV Reports and Presentations
CA Arbovirus Bulletins
Last 28 Days Positive Samples in California
As part of California's vector control efforts, samples from a variety of sources are regularly tested for the presence of West Nile virus, St. Louis encephalitis and Western equine encephalomyelitis. The map below is provided to illustrate the ongoing efforts to detect and control the these diseases. Use the layer checkboxes below the map to enable or disable the various layers.[wmap id="survCAMap"][width]100%[/width] [height]400px[/height] [center]37.16031654673677,-119.2236328125[/center] [scale]5[/scale] [align]center[/align] [togglesize]Large[/togglesize] [basetoggle]on[/basetoggle] [scaletoggle]on[/scaletoggle] [basetype]Map[/basetype] [drag]yes[/drag] [overlays toggle="true"] [markers id="mosqpool" name="Mosquito Pools" display="true"] [icon]dot_black_red_16[/icon] [file] [source]http://www.calsurv.org/sites/calsurv.org/files/etc/PositiveMosquitoPools.csv[/source] [display]agency,city,county,species,collection date,test date,positive for[/display] [latitude]latitude[/latitude] [longitude]longitude[/longitude] [/file] [/markers][markers id="sentinel" name="Sentinel Chickens" display="true"] [icon]dot_black_blue_16[/icon] [file] [source]http://www.calsurv.org/sites/calsurv.org/files/etc/PositiveSentinelChickens.csv[/source] [display]agency,city,county,collection date,test date,positive for[/display] [latitude]latitude[/latitude] [longitude]longitude[/longitude] [/file] [/markers][/overlays] [/wmap]
All map data are updated every 30 minutes. All data coordinates are randomized estimations within half a degree of the true collection site.
[HideMe]Malaria
Malaria is no longer endemic in California. However, the disease is diagnosed in California residents every year, primarily as a result of contracting the disease in malarious areas outside the USA, and rarely, because of small focal outbreaks occurring as a result of importation of a case into an area when and where anopheline mosquitoes are prevalent.
Terms to describe the methods of acquiring human malaria cases have been developed by the World Health Organization and adopted by the Malaria Branch of the Centers for Disease Control and Prevention. They can be studied by selecting this link: Malaria Terms.
A thorough discussion of malaria occurring in areas where it is no longer endemic can be found by visiting the CDC malaria website.
Over the past several decades, California has had more cases of locally-acquired malaria than any other US state. To read an article summarizing subject of locally-transmitted malaria in the USA, click this link: Locally-transmitted malaria.
Malaria Outbreaks in California Since 1945
Malaria is not endemic to California. But on occasion, imported malaria resulted in local outbreaks. The map below illustrates those transmissions where 10 or more cases resulted.[wmap id="poolCAMap"] [width]100%[/width] [height]400px[/height] [center]37.16031654673677,-119.2236328125[/center] [scale]5[/scale] [align]center[/align] [togglesize]Large[/togglesize] [basetoggle]on[/basetoggle] [scaletoggle]on[/scaletoggle] [basetype]Map[/basetype] [drag]yes[/drag] [overlays] [markers] [icon]blue[/icon] [file] [source]http://www.calsurv.org/sites/calsurv.org/files/etc/malaria_map.csv[/source] [display]location,nearest_city,county,probable_vector,first_case,last_case,number_of_cases,description,reference[/display] [latitude]latitude[/latitude] [longitude]longitude[/longitude] [/file] [/markers][/overlays] [/wmap]
For terms and definitions used when describing human malaria cases, please look at Terms Associated with Human Malaria Cases
[HideMe]Tickborne Diseases
Ticks are the vectors of a large number of disease-causing agents in California. While Lyme disease is by far the most common tickborne disease of people in the United States and California, ticks also transmit the organisms that cause tickborne relapsing fever, Rocky Mountain spotted fever, tularemia, anaplasmosis, human ehrlichiosis, and babesiosis. In addition, people and domestic animals can develop tick paralysis following a tick bite.
Photo credit Edman/McClelland Collection
[HideMe]Lyme disease
Lyme disease is a tickborne disease caused by the bacteria Borrelia burgdorferi. It was first identified in California in 1978 from a Sonoma County hiker. While incidence of Lyme disease (number of cases adjusted per population) is highest in the northwestern part of the state, human cases have been reported from many regions of California.
In California, the western black-legged tick, Ixodes pacificus, is the only tick that transmits Lyme disease to people. This tick has three life stages, a larval, nymphal and adult stage. People become infected with Lyme disease via the bite of an adult female or a nymphal western-black legged tick. Infection prevalences of B. burgdorferi in the western black-legged tick are approximately 1-2% in adults, 2-15% in nymphs, and 0% in larvae. People are at highest risk of acquiring Lyme disease from nymphal ticks due to their small size and higher infection prevalence. Lyme disease is most commonly reported in spring and early summer in California, when nymphal ticks are most abundant. Adult western black-legged ticks are most active in fall and winter.
For more information on Lyme disease, please visit the California Department of Public Health website at: http://www.cdph.ca.gov/healthinfo/discond/Pages/LymeDisease.aspx
Anaplasmosis
Human granulocytic anaplasmosis (HGA) is an infection caused by the bacteria Anaplasma phagocytophilum. HGA bacteria infect the whte blood cells of their hosts, specifically a group of cells called granulocytes. People acquire HGA in California, when they are bitten with a western black-legged tick (Ixodes pacificus) infected with HGA bacteria.
For more information on Anaplasmosis, please visit the California Department of Public Health http://www.cdph.ca.gov/healthinfo/discond/Pages/Anaplasmosis.aspx
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is a serious disease caused by Rickettsia rickettsii bacteria and transmitted to people by ticks, principally the Rocky Mountain wood tick, Dermacentor andersoni and the American dog tick Dermacentor variabilis. In California, RMSF is a rare disease, with only 1 to 3 cases reported per year; most cases are reported from the south Atlantic region of the United States.
Additional information on RMSF can be found at the Center for Disease Control and Prevention website:
http://www.cdc.gov/ncidod/dvrd/rmsf/index.htm
as well as at the California Department of Public Health website: http://www.cdph.ca.gov/healthinfo/discond/Pages/RockyMountainSpottedFever.aspx
Tickborne Relapsing Fever
Tickborne relapsing fever (TBRF) is a bacterial disease transmitted to people by soft ticks in the genus Ornithodors. TBRF is a rare disease in California with between 1 and 8 cases reported per year, generally during the summer months. People are at risk of contracting TBRF when they sleep in rustic mountain cabins that are infested with wild rodents. The soft ticks that transmit TBRF feed rapidly; most people who contract TBRF have no recollection of a tick bite.
For more information on Tickborne relapsing fever, please visit the California Department of Public Health website: http://www.cdph.ca.gov/healthinfo/discond/Pages/Tick-BorneRelapsingFever.aspx
[HideMe]Fleaborne Diseases
In California, there are several fleaborne diseases associated with fleas. Probably the most important is plague. Active plague surveillance has been underway in the state for many years by the California Department of Health Services.
Photo credit Edman/McClelland collection
[HideMe]Plague
California plague surveillance
Plague testing 2004
The California Department of Public Health routinely tests various types of animals for evidence of infection by plague bacilli. The map displays data for 2004 for tests on carnivores, rodents, and pets.[wmap id="Plague_positives_2004"]
[width]100%[/width]
[height]400px[/height]
[center]37.16031654673677,-119.2236328125[/center]
[scale]5[/scale]
[align]center[/align]
[togglesize]Large[/togglesize]
[basetoggle]on[/basetoggle]
[scaletoggle]on[/scaletoggle]
[basetype]Map[/basetype]
[drag]yes[/drag]
[overlays toggle="true"]
[markers id="blue" name="Carnivore"]
[icon]blue[/icon]
[file]
[source]http://www.calsurv.org/sites/calsurv.org/files/u7/plague_data_2004.csv[/source]
[display]specimen,group[/display]
[latitude]latitude[/latitude]
[longitude]longitude[/longitude]
[filter]group=Carnivore[/filter]
[/file]
[/markers]
[markers id="orange" name="Rodent"]
[icon]orange[/icon]
[file]
[source]http://www.calsurv.org/sites/calsurv.org/files/u7/plague_data_2004.csv[/source]
[display]specimen,group[/display]
[latitude]latitude[/latitude]
[longitude]longitude[/longitude]
[filter]group=Rodent[/filter]
[/file]
[/markers]
[markers id="green" name="Pet"]
[icon]green[/icon]
[file]
[source]http://www.calsurv.org/sites/calsurv.org/files/u7/plague_data_2004.csv[/source]
[display]specimen,group[/display]
[latitude]latitude[/latitude]
[longitude]longitude[/longitude]
[filter]group=Pet[/filter]
[/file]
[/markers]
[/overlays]
[/wmap]
[HideMe]Louseborne Diseases
Body lice can transmit infectious diseases to humans (epidemic typhus, louseborne relapsing fever, trench fever). Head lice also create serious public health problems by infesting humans (pediculosis).
Photo credit California Department of Public Health
[HideMe]Pediculosis
Resources:
"A Parent's Guide to Head Lice 2008" brochure and "Guidelines for the Control and Prevention of Head Lice in Child Care Facilities" published by the California Department of Public Health.
Test your knowledge of Head Lice. This crossword is based upon the brochure: A Parent's Guide to Head Lice
Body lice
 |
BODY LICE | |
What are human body lice?
Body lice are small insects that live on the body and in the clothing or bedding of humans. They feed only on human blood. Currently in the United States, body lice infestations are found occasionally on homeless persons who do not have access to a clean change of clothes or facilities for bathing.
How do body lice differ from head and pubic lice?
Body (Pediculus humanus humanus) and head lice (P. humanus capitis) are morphologically indistinguishable, although head lice are smaller than body lice. Body lice are most reliably differentiated from head lice by their presence on the clothing or on parts of the body other than the head. These lice prefer to spend most of their time on the clothing of an infested person, visiting the body up to five times a day to feed. The eggs (called nits) of body lice are cemented to clothing fibers and seams or, occasionally, to body hairs. Head lice live in people’s hair and glue their eggs directly to hair near the scalp. Pubic lice (Phthirus pubis) are easily distinguished from head and body lice by their round shape and crab-like appearance. Pubic lice are usually found in pubic hair, but may occasionally be found on other coarse body hair such as underarm and facial hair.
What do body lice look like?
The body louse has three life stages: the egg (nit), the nymph, and the adult. The eggs are small (less than 1 mm long), oval, and yellow to white in color. They are generally easy to see in the seams of clothing, particularly around the waistline, neckline, and under the armpits. The immature stage of the body louse is called a nymph. It looks like the adult louse and feeds on human blood, but is smaller. The adult body louse is grayish-white, reddish, or cream in color, has six legs, and is about 2-4 mm long.
What are the signs and symptoms of body lice infestation?
The most common signs of body lice infestation are intense itching and a red rash located on the trunk. The bites from body lice are initially seen as small red dots that develop into wheal
like areas of inflammation (light red elevation of the skin with a white center). Long-term body lice infestations may lead to thickening and discoloration of the skin, particularly around the waist, groin, and upper thighs. Secondary skin infections can result from scratching.
Can body lice transmit disease?
Yes, epidemics of trench fever (Bartonella quintana), typhus (Rickettsia prowazekii), and louse-borne relapsing fever (Borrelia recurrentis) have been caused by the human body louse. Epidemic typhus and louse-borne relapsing fever do not occur in the United States. Infections with Bartonella quintana, including trench fever, are occasionally diagnosed in the United States. Homeless individuals with chronic alcoholism and body lice infestation have been found to be at higher risk for Bartonella quintana infection than the general population.
How are body lice spread?
Body lice can spread in crowded conditions where hygiene is poor and when clothing and/or bedding are shared. Infestations are more common in cooler climates and seasons when heavier clothes are worn. Lice rely on body heat to hatch eggs and to mature. The life cycle of the body louse is completed in an average of 18-21 days. Eggs can remain viable on clothing for up to 30 days when away from a host.
How are body lice infestations diagnosed?
Body lice infestation may be suspected in homeless individuals with itching and rash on the body, with or without secondary skin infections. Infestations are diagnosed by looking closely in the seams of clothing and on the body for eggs and for crawling lice. Body lice are usually found on clothing that is close to the skin and will be seen on other layers only when there is a heavy infestation.
How are body lice infestations treated?
Body louse infestations should be treated by washing infested clothing and bedding in hot water (130o F). Items should then be placed in a clothes dryer on the hot cycle. The infested person should shower; individuals with extensive body hair may apply a one percent permethrin or pyrethrin shampoo or lotion (pediculicide) to the body.
How can body lice infestations be prevented?
Avoid sharing clothing or bedding. When practical, discard infested clothing. Remove and wash clothing frequently (at least once per week). Regular bathing can reduce pruritis and chance of secondary bacterial infections.
Three Stages of Body Lice*
Egg Nymph Adult
*Illustrations enlarged to show detail
[HideMe]Trench Fever
Belgian soldiers digging trenches in World War I. Photo from firstworldwar.com
Trench fever is caused by a bacterium, Bartonella quintana, and may also be known as five-day fever and wolhynia. It is transmitted by the human body louse from person to person. People who are infected with trench fever have nonspecific symptoms such as head ache, muscle ache, nausea, and fever. Relapses may occur several times during the course of disease and sometimes years later.
[HideMe]Rodentborne Diseases
The most important rodentborne diseases in California are those caused by various strains of hantaviruses. Although plague and some other diseases are often associated with rodents, they have arthropod vectors and are usually classified accordingly.
Photo credit Purdue University
[HideMe]Hantaviruses
Hantavirus pulmonary syndrome (HPS) is a deadly disease from rodents. Humans can contract the disease when they come into contact with infected rodents or their urine and droppings. HPS was first recognized in 1993 and has since been identified throughout the United States. Although rare, HPS is potentially deadly. Rodent control in and around the home remains the primary strategy for preventing hantavirus infection.
Information and photo from US Centers for Disease Control and Prevention
Hantavirus in California 2005
Hantavirus diseases are under active surveillance by the California Department of Health Services. Click here to read the hantavirus section of the 2005 Annual Report of the Vector-Borne Disease Section of CDHS.
Hantavirus in California 2006-2007
2006 Summary:
Four cases of hantavirus pulmonary syndrome* (HPS) were diagnosed in
California residents in 2006. Three of these were fatalities.
Surveillance for hantavirus in California rodents
In 2006, 2498 rodents were collected and serologically tested for SNV antibody,
representing at least 17 species from 8 genera. At least one seroreactive rodent
was detected in 11 of 14 California counties in which surveillance was conducted in 2006. Of 2274 Peromyscus spp. collected, 224 (9.9 %) had serologic evidence of infection with SNV. Seroprevalence was highest in Peromyscus maniculatus at
15.7 percent.
2007 Activity:
No cases of hantavirus pulmonary syndrome have been detected in California
residents in 2007 to date.
Two Peromyscus maniculatus and one Reithrodontomys megalotis from Riverside
county have tested positive for SNV antibodies from January through March, 2007.
Vector-borne Disease Bulletin
|
Click one of the following for the Vector-borne Disease Bulletins from the Vector-borne Disease Section, California Department of Public Health.
|
|
|
|
2008
|
