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) is a member of the family Flaviviridae, which includes, among others, St. Louis encephalitis, dengue, yellow fever, and Japanese encephalitis viruses.  WNV can cause mild to severe illness in human, other mammal (e.g., 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. The following table shows the primary surveillance indicator results for WNY from 2003-2008:

 

Surveillance indicator	2003	2004	2005	2006	2007	2008
Human cases (fatal)	3(0)	779(29)	880(19)	278(7)	380(21)	438(15)
Horse cases	1	540	456	58	28	32
Dead bird positives	96	3,232	3,046	1,446	1,395	2,530
Mosquito pool positives	32	1,136	1,242	832	1,007	2,001
Sentinel chicken positives	70	809	1,053	640	510	584
Squirrel positives	--	49	48	32	26	32

 

2008 Summary of WNV Activity in California 

In 2008, 49 counties in California reported WNV activity.  A total of 438 human cases were reported to the California Department of Public Health  from 27 counties. Of the 438 cases, 15 (3.4%) were fatal. During the previous year, 21 deaths resulted from WNV infections. Non-human WNV activity reported included the following: 32 horse cases were reported from 14 counties; 2,001 WNV-positive mosquito pools were detected from 26 counties; 584 WNV-positive sentinel chickens were reported from 27 counties; 2,530 positive dead birds were reported from 46 counties; and 32 WNV positive tree squirrels were reported from 7 counties.

Click here for information on current WNV activity in California.

 

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.

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All map data are updated every 30 minutes. All data coordinates are randomized estimations within half a degree of the true collection site.

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

Ixodes pacificus ticks tested for evidence of Borrelia species, California, 2008.

The following table contains the results of tests for evidence of Borrelia infection in ticks collected in California in 2008. The tests were conducted by the California Department of Public Health, Vector-Borne Disease Section (CDPH-VBDS), and by the United States Army Center for Health Promotion and Preventive Medicine - West (US Army).

 

County	Location	Ticks tested	Pools tested	Number Pools Positive
				DFA	PCR**		Laboratory
				Borrelia spp.	Borrelia spp.	Borrelia burgdorferi
Alameda	Indian Joe Trail	25	25	0			CDPH-VBDS
	Little Yosemite Area	4	4	0			CDPH-VBDS
Amador	Grinding Rock SP	31	4		1		US Army
Calveras	Natural Bridge	103	11				US Army
	Water Treatment Site	13	4		40		US Army
Contra Costa	Tilden Regional Park	115 (170*)	115 (170*)	1 (4*)			CDPH-VBDS
Lake	Mendocino NF	190 (2*)	19 (1*)		4	3	US Army
	Middletown	5 (3*)	5 (3*)	0			CDPH-VBDS
Los Angeles	Angeles NF	17	17	0			CDPH-VBDS
	Charmlee Wilderness	117	117	0			CDPH-VBDS
	Malibu	100	10		0		US Army
Madera	Chepo Saddle	2 (1*)	1 (1*)		0		US Army
Marin	Point Reyes NS	5	5	0			CDPH-VBDS
	Marin Headlands	67	67	3			CDPH-VBDS
Mariposa	Sierra NF	20	2		0		US Army
Mendocino	Manchester SB	26	26	0			CDPH-VBDS
Nevada	Nevada City	17 (8*)	11 (2*)		0		US Army
Riverside	San Bernardino NF	26 (1*)	26 (1*)	0			CDPH-VBDS
San Bernardino	San Bernardino NF	6	2		0		US Army
San Diego	Cleveland NF	24	3		0		US Army
	Cleveland NF	23	23	0			CDPH-VBDS
San Joaquin	Carnigie SP	22	8		0		US Army
Santa Clara	Henry Coe SP	100 (11*)	10 (1*)		2 (1*)	2 (1*)	US Army
Shasta	Anderson River Park	38	4		0		US Army
	Baily Cove CG	18	2		0		US Army
	Anderson	51	5		0		US Army
	Redding	70	7		0		US Army
Stanislaus	Patterson	3	2		0		US Army
Total ticks tested		1,238 (196*)	535 (179*)
Total pools positive				4 (4*)	11 (1*)	5 (1*)

 

* Nymphs; ** PCR primer sets were specific for B. burgdorferi;

Tests: DFA, Direct Fluorescent Antibody; PCR, Polymerase Chain Reaction;

CG, Campground; NF, National Forest; NS, National Seashore; SB, State Beach; SP, State Park;

California plague surveillance

Plague positives 2007

Plague positives 2006

Plague positives 2005

Plague positives 2004

Mammals tested for plague in California, 2007

In 2007, 482 blood samples were collected from wild carnivores and 914 blood samples from wild rodents in connection with the statewide plague surveillance program conducted by the Vector-borne Disease Section of the California Department of Public Health. Veterinarians submitted 5 samples from domestic pets. Plague was confirmed in one domestic cat from Kern County. Plague antibodies were detected in 37 of 335 coyotes, 12 of 47 black bears, and one of 4 gray foxes. Among wild rodents, antibodies were detected in 23 of 432 California ground squirrels, and one of 237 chipmunks. Additionally, samples from 124 feral pigs were negative. All data from 2007 Annual Report, Vector-Borne Disease Section, California Department of Public Health.

 

A summary of the blood samples tested are shown in the following table:

 

County	Rodents			Carnivores
	Tested	Positive	Species	Tested	Positive	Species
Alameda	4	0		4	0
Butte	6	0
El Dorado	29	0
Fresno	23	0
Imperial				25	0
Inyo	153	18	California ground squirrel
		1	Chipmunk
Kern	7	0		144	2	Coyote
					1	Domestic cat
Lassen	1	0
Los Angeles	5	0		24	0
Madera	24	0
Mariposa	4	0		34	2	Black bear
Mendocino				12	0
Modoc				43	16	Coyote
Mono	202	0
Monterey				24
Napa	30	0
Nevada	4	0
Orange	4	0		1	0
Placer				5	0
Plumas	1	0		63	8	Black bear
					13	Coyote
					1	Gray fox
Riverside	119	0
San Benito				6	0
San Bernardino	189	3	California ground squirrel
San Diego	21	2	California ground squirrel	8	0
San Francisco				2	0
San Joaquin				6	0
San Luis Obispo	12	0		34	0
Santa Barbara	1	0		13	0
Shasta	1	0
Sierra	2	0		22	2	Black bear
					6	Coyote
Siskiyou	16	0		4	0
Tuolumne	26	0		2	0
Ventura	30	0		3	0
Yuba				3	0
Totals	914	24		482	51

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.

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[display]specimen,group[/display]
[latitude]latitude[/latitude]
[longitude]longitude[/longitude]
[filter]group=Carnivore[/filter]
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[display]specimen,group[/display]
[latitude]latitude[/latitude]
[longitude]longitude[/longitude]
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[longitude]longitude[/longitude]
[filter]group=Pet[/filter]
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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 (130^o 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

 

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.