Even More on Mosquitoes:Final Words on Malaria, Filariasis

and Yellow Fever

Announcements

No Quiz Today – Next Tuesday

About Nov. 12 …

Talking today: Sarah and Natalie

On Deck: Charity

Malaria Eradication in the US

• Prior to WWII, malaria had been on the decline in the US– Improved mosquito

control– Improved availability of

antimalarial drugs– Improved health care,

water sources, etc.

Malaria Decline in the US

Malaria Eradication in the US

• After WWII, spraying base housing at Ft. Campbell eliminated malaria from the base

• National Malaria Eradication Program began July 1, 1947

• Based on DDT application to the interior surfaces of rural homes in malaria locales

• Nearly 5 million homes treated in first 2 years• Program ended in 1952

World Malaria Eradication

• Following success in NA, eradication was achieved in Australia & W. Europe in the 1950’s

• July, 2008: 10 Countries on verge of elimination (Algeria, Argentina, Armenia, Egypt, El Salvador, Iraq, Paraguay, Republic of Korea, Saudi Arabia and Turkmenistan)

• 19 other countries are approaching elimination (<1 person/1000 at risk)

World Malaria Eradication

• Main effort now is the “Roll Back Malaria” Global Malaria Action Plan

• Objectives are to – eliminate malaria as a global health threat by

2015– eliminate malaria from another 8 – 10

countries by then– Move toward eventual global eradication

• More on this program here

It could happen in our lifetimes

Dengue

• Dengue Fever and breakbone fever• Flavivirus transmitted by Aedes (esp. Ae.

aegypti but Ae. albopictus is an efficient vector too).

• At least as prevalent in urban areas as rural (unlike malaria).

• Mosquito transmits virus via saliva. Once infected, remains infective for life.

• Humans are the amplifying host.

Dengue Symptoms

• sudden onset of severe headache, muscle and joint pains (myalgias and arthralgias resp).

• Characteristic rash (“red sea and islands”).

• gastritis common• fever that lasts 6 – 7

days

Accute Symptoms

• Dengue Hemorrhagic Fever (DHF)– widespread hemorrhage– thrombocytopenia (few platelets in blood)– haemoconcentration via plasma reduction– hepatocellular carcinoma and cirrhosis common 1 – 3

years post-DHF

• Dengue Shock Syndrome (case mortality 20%): All of the above PLUS– Weak rapid pulse, – Narrow pulse pressure (less than 20 mm Hg) – Cold, clammy skin and restlessness.

All three types of Dengue Fever caused by one of four viral

serotypes• DEN-1, DEN-2, DEN-3, DEN-4• Relationship between these, the vector, and the disease

is not clear.• In an epidemic, usually only one is dominant. The

dominant serotype varies by location and year.• If you catch one and survive, you are immune to it. But

…• Prior immunity to one increases susceptibility to others

(and the probability of DHF or DSS reaction).• This has complicated the development of a vaccine.

Current Epidemic: 2008

Epidemic Dengue in red, Ae. aegypti distribution in blue

> 100 million people being infected yearly at present

Current Epidemic

• Significant new cases in Australia March, 2009• Rio de Janiero: >55,000 cases 2008-2009 season• Major outbreak in Northern Provinces of Argentina (incl.

Buenos Aires), April 2009, >10,000 cases• Numerous S. Pacific islands report Dengue outbreaks in

2009• Bolivia, March 2009: >30,000 new cases• WHO estimates that current case load in S. America, C.

America & Caribbean is 10 fold the historic normal.• Insignificant number of cases in the US but that could

change. Was once found as far north as Boston. >500,000 cases in Texas in 1922.

Lymphatic Filariasis

• Caused by nematodes (same family as onchocerciasis) transmitted by mosquitoes (all major genera and many spp.)

• Affects 120 million people world wide• Note: There are other forms of filariasis not vectored by

mosquitoes (e.g. loa loa).• About 128 million infected world wide• 3 main nematode species

– Wuchereria bancrofti: most common, bancroftian filariasis, 115 million people

– Brugia malayi, SE Asia, Malayan filariasis, 15 million people– Brugia timori, Timori Islands, Timorian filariasis.

Bizarre Clinical Presentations are the Norm with this Disease

Distribution

• > 80 Countries• Mostly an endemic disease because requires

many bites.• Was common in Charleston, SC until mid

1800’s

Treatment

• Similar to oncherciasis– Ivermectin for microfilarae– Recent work suggests doxycycline will help

against adult worms• Kills the Wolbachia symbiont• Adults die• Symptoms partially or totally reverse• Not effective in all patients• Low cost ($0.10 to $2/patient/year)• Helps with other vectored diseases

Yellow Fever

• Historically second only to malaria but now lags dengue.• Potential for catastrophic outbreaks persists.• Like Dengue, a Flavivirus• Called “Yellow Fever” because of the jaundice that it

often creates• First arbovirus (arthropod borne virus) associated with

human disease.– Carlos Finlay, Cuban physician, first suggested the connection

between mosquitoes and yellow fever– Walter Reed conducted human experiments with US soldier

volunteers to confirm the connection.– Reed’s discovery enabled the US to complete the Panama

Canal where the French could not.