Friday, April 04, 2014

Minnesota: Rare Imported Case Of Lassa Fever


Credit CDC’s Lassa Information Page



# 8433


Although its lethality is nowhere in the same league as Ebola Zaire, Lassa fever is another Viral Hemorrhagic Fever (VHF) which is endemic in Western Africa. The Lassa virus is commonly found in multimammate rats, a local rodent that often likes to enter human dwellings.


Exposure is typically through the urine or dried feces of infected rodents, and roughly 80% who are infected only experience mild symptoms.  The overall mortality rate is believed to be in the 1%-2% range, although it runs much higher (15%-20%) among those sick enough to be hospitalized.


Like many other hemorrhagic fevers, person-to-person transmission may occur with exposure to the blood, tissue, secretions, or excretions of an individual. The CDC is quick to assure, however, that the risk to fellow travelers who may have had contact with this patient is extremely low:


Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus. 


This is the 7th known imported case of Lassa fever into the US, although most of the early cases were diagnosed abroad and the patients were then airlifted to the US for treatment.  Two previous cases (2004 in New Jersey (MMWR) & 2010 in Pennsylvania (EID Journal)) involved travelers who arrived in the US without knowing they had been infected.


Here is the CDC’s press release, after which I’ll return with a bit more:


Press Release

For Immediate Release: Friday, April 4, 2014
CDC Media Relations
(404) 639-3286

Lassa Fever Reported in U.S. Traveler Returning from West Africa

Contact investigation under way; risk to other travelers considered extremely low

The CDC and the Minnesota Department of Health (MDH) have confirmed a diagnosis of Lassa fever in a person returning to the United States from West Africa. The patient was admitted to a hospital in Minnesota on March 31 with symptoms of fever and confusion. Blood samples submitted to CDC tested positive for Lassa fever on April 3. The patient is recovering and is in stable condition.

“This imported case is a reminder that we are all connected by international travel. A disease anywhere can appear anywhere else in the world within hours,” said CDC Director Tom Frieden, M.D., M.P.H.

Lassa fever is a severe viral disease that is common in West Africa but rarely seen in the United States.  Seven other Lassa fever cases, all travel related, have been identified in the United States, with the last one reported in Pennsylvania in 2010. Although Lassa fever can produce hemorrhagic symptoms in infected persons, the disease is not related to Ebola hemorrhagic fever, which is responsible for the current outbreak in West Africa. 

In West Africa, Lassa virus is carried by rodents and transmitted to humans through contact with urine or droppings of infected rodents. In rare cases it can be transmitted from person to person through direct contact with a sick person’s blood or bodily fluids, through mucous membrane, or through sexual contact. The virus is not transmitted through casual contact. About 100,000 to 300,000 cases of Lassa fever, and 5,000 deaths related to Lassa fever, occur in West Africa each year.

CDC is working with public health officials and airlines to determine the patient’s travel route from West Africa and identify any passengers or others who may have had close contact with the infected person. Preliminary information indicates that the patient flew from West Africa to New York City and caught another flight to Minneapolis.

“Given what we know about how Lassa virus is spread to people, the risk to other travelers and members of the public is extremely low,” said Martin Cetron, M.D., M.P.H., director of CDC’s Division of Global Migration and Quarantine. 

“Casual contact is not a risk factor for getting Lassa fever,” said Barbara Knust, D.V.M., M.P.H., an epidemiologist in CDC’s Division of High-Consequence Pathogens and Pathology, which performed the laboratory testing.  “People will not get this infection just because they were on the same airplane or in the same airport.”

As part of its investigation, CDC is working with the airlines to gather contact information for passengers and crew who were seated near the infected individual. CDC will provide passenger contact information to state and local health departments where the passengers live to notify them about their possible exposure.

For additional information about Lassa fever see the CDC website at

For more information about airline contact investigations see

(Continue . . .)


While Lassa fever is a rarity, imported diseases such as measles, polio, dengue, malaria (and many others) remain a constant threat – even in places where they have been officially `eliminated’.  And emerging diseases, like Chikungunya, H5N1, H7N9, or MERS-CoV can easily expand to new geographic regions due to enhanced global travel and trade.


Photo Credit- CDC


As both the CDC and the World Health Organization reminded us a few weeks ago (see The Global Reach Of Infectious Disease), pathogens are excellent international travelers. A few recent blogs on other `imported’ disease threats includes:

Chikungunya Update & CDC Webinar Online
CDC Statement On 1st H5N1 Case In North America
Pathogens At the Gate