Thursday, August 07, 2014

Updating West Nile, CHKV & Dengue



# 8926


While Ebola dominates the daily news cycle, there are plenty of other public health concerns out there that are far more likely to threaten the average North American than imported cases of hemorrhagic fever.  Among those are mosquito-borne diseases like WNV, dengue, EEE, and Chikungunya.


Yesterday, the California Department of Public Health  announced two recent deaths from West Nile Virus, adding to a handful of deaths already reported this year in Arizona, Louisiana & Missouri.


CDPH Reports First Human West Nile Virus Fatalities This Summer

Date: 8/6/2014

Number: 14-069

Contact: Anita Gore - (916) 440-7259


The first two deaths this summer due to West Nile virus infection have been confirmed by the California Department of Public Health (CDPH) it was announced today by Dr. Ron Chapman, CDPH Director and state public health officer. The first was a senior citizen from Sacramento County. The second was an adult from Shasta County.

“These unfortunate deaths remind us that we must protect ourselves from mosquito bites to prevent West Nile virus and other mosquito born infections,” said Chapman. “West Nile virus activity is greatest during the summertime.”

West Nile virus is transmitted to humans and animals by the bite of an infected mosquito. The risk of serious illness to most people is low. However, some individuals – less than one percent – can develop a serious neurologic illness such as encephalitis or meningitis. People 50 years of age and older have a higher chance of getting sick and are more likely to develop complications. Recent data also indicate that those with diabetes and/or hypertension are at greatest risk for serious illness.

To date in 2014, West Nile virus has been detected in 36 California counties.

(Continue . . . )



The least severe form of the disease – West Nile Fever - probably infects more than 100,000 Americans every year, although most are so mildly affected they have no idea the are infected.


Neuroinvasive cases (which present with meningitis, encephalitis, or flaccid Paralysis), while less common, are severe enough that they nearly always result in hospitalization and diagnosis, and so they are considered the best indicator of the scope of each year’s epidemic. 


Right now, California and Arizona lead the nation in reporting neuroinvasive cases of WNV, with a combined total of 24.


The amount of WNV activity varies considerable from year-to-year, and this year (so far, anyway) we haven’t seen a huge number of cases.  Surveillance and reporting, however, often lags several weeks behind actual events, and so we may still see a substantial number of cases this year.


This year we are also monitoring the arrival of locally transmitted Chikungunya in the United States, and while only 4 cases have been reported (all in Florida), we continue to see large numbers of imported cases being reported across the nation. 

Each imported case provides an opportunity for local mosquitoes to pick up, and transmit, the disease.


Florida and New York lead the nation with the number of imported CHKV cases, but as Chikungunya is not a nationally notifiable disease, surveillance is likely to under report cases. 


Chikungunya – while rarely fatal - can cause prolonged fever and polyarthralgias (joint pain), which in some cases can lead to permanent disability. 


With PAHO reporting more than 500,000 CHKV cases across the Caribbean over the past 7 months, it isn’t surprising that we are beginning to see locally transmitted cases in both Puerto Rico and the U.S. Virgin Islands.



Despite its rapid spread across the islands of the Caribbean, and into Central and South America, there are reasons to hope that CHKV won’t spread as rapidly as WNV has in the United States.


Unlike WNV, which resides in birds, CHKV doesn’t have an animal host other than humans which can aid in its spread (see WNV vs CHIKV: A Host Of Differences).  And studies have suggested that lifestyle and economic factors (ie. air conditioning, window screens, mosquito control programs) may further reduce transmission. 


Thus far, we haven’t seen much reporting on locally acquired Dengue this summer, with only one case reported in the Miami-Dade region of south Florida (see Florida: Miami Reports 1st Locally Acquired Dengue Case Of 2014). 


While now the most common mosquito-borne virus in the world (causing up to 100 million infections a year), Dengue has managed to do little more than spark a few limited outbreaks in North America, despite an abundance of the right mosquito vectors.


Whether our relative good luck will continue to hold with Dengue, and CHKV, remains to be seen. 


While the overall risk of contracting a mosquito-borne illness anywhere in the United States remains very small, with no vaccines available, and scattered cases of Dengue, West Nile Virus, EEE, SLEV, and the recent arrival of Chikungunya  - Florida’s Health departments urge people to always follow the `5 D’s’:


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