Credit CDC’s Lassa Information Page
A recurring theme in public health is just how easily that `exotic’ diseases can cross vast oceans or borders, propelled by our modern air travel industry and our penchant for international travel (see The Global Reach Of Infectious Disease).
Every week scores of viremic travelers arrive on our shores, carrying everything from measles to dengue to Chikungunya. For some of these diseases – like measles - the risk of them spreading here is quite real.
For others, while plausible, the risks of their spreading are far lower.
Last night it was announced that a traveler – recently returned from Liberia – had died after being isolated last week when suspected of having a hemorrhagic fever. While he tested negative for Ebola, yesterday his tests confirmed Lassa fever.
The CDC believes that the risk to others is extremely low.
Lassa is endemic in Western Africa and is commonly found in local rodents that often like to enter human dwellings. Exposure is typically through their urine or dried feces. 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.
You may recall a similar importation last year (see Minnesota: Rare Imported Case Of Lassa Fever), along with a couple of earlier cases (2004 in New Jersey (MMWR) & 2010 in Pennsylvania (EID Journal)) – none of which resulted in a secondary transmission of the virus.
While the risks are considered quite low, contact tracing and monitoring will be conducted by health authorities to ensure that any possible spread is quickly detected and contained.
This from the CDC’s media center:
Risk to others considered extremely low
For Immediate Release: Monday, May 25, 2015
Contact: Media Relations
The CDC and the New Jersey Department of Health have confirmed a death from Lassa fever which was diagnosed earlier today in a person returning to the United States from Liberia. The patient traveled from Liberia to Morocco to JFK International Airport on May 17th. The patient did not have a fever on departure from Liberia, did not report symptoms such as diarrhea, vomiting, or bleeding during the flight, and his temperature was taken on arrival in the U.S. and he did not have a fever at that time. On May 18th, the patient went to a hospital in New Jersey with symptoms of a sore throat, fever and tiredness. According to the hospital, he was asked on the 18th about his travel history and he did not indicate travel to West Africa. The patient was sent home the same day and on May 21st returned to the hospital when symptoms worsened. The patient was transferred to a treatment center prepared to treat viral hemorrhagic fevers. Samples submitted to CDC tested positive for Lassa fever early this morning. Tests for Ebola and other viral hemorrhagic fevers were negative. The patient was in appropriate isolation when he died there this evening.
Lassa fever is a viral disease common in West Africa but rarely seen in the United States. There has never been person-to-person transmission of Lassa fever documented in the United States. The New Jersey case is the sixth known occurrence of Lassa fever in travelers returning to the United States since 1969, not including convalescent patients. The last case was reported in Minnesota in 2014. Although Lassa fever can produce hemorrhagic symptoms in infected people, the disease is different from Ebola, which is responsible for the current outbreak in West Africa. In general, Lassa fever is less likely to be fatal than Ebola (approximately 1% case fatality rate for Lassa vs approximately 70% case fatality rate for Ebola without treatment) and less likely to be spread from person to person. However, some Lassa patients develop severe disease, as the patient in New Jersey did.
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, and patients are not believed to be infectious before the onset of symptoms. 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 to generate a list of people who had contact with the patient. Those identified as close contacts of the patient will be monitored for 21 days to see if symptoms occur.
Updates will be provided as the investigation continues.