The waiter looked expectantly to take more drinks orders….
“I’m sure she said a mango lassie, I’ll get her one …yes… one mango lassie please and five cobra beers and another taka dahl, thanks”. The waiter scuttled off.
“I ordered you the mango lassie” said the (tipsy off duty) Microbiologist
“Why did you get me a lassie?” asked the oncall Microbiologist.
“You said mango lassie while on the phone… when we were ordering more drinks… didn’t you!?!”
“No… that was the Med Reg from the Royal Free, saying they thought one of contacts of the Dutch Lassa fever cases might be transferred to us for follow up and thought we’d like to be aware, as it was in the news and may cause us a call or two if the local media get to know!”… continuing… [and huffing] “Really… its 10:30 on Friday night, I do not need to know this oncall, but everyone wants their minute of fluster and fame!!” … “Mango lassie…?! You lot need a hearing test or less Cobra beer!” said the oncall Microbiologist.
“5 Cobras and a mango lassie…” said the waiter with impeccable timing!
The Microbiologists crumpled in laughter and thanked the waiter who just looked puzzled and said he’d bring over the dahl.
There have been no confirmed cases in the Brits arriving home BUT I thought it would be a good idea to revise Lassa fever so that if anyone did start asking (daft?) questions I would be up-to-date with my knowledge. In my experience knowledge is the best way to prevent rumours spreading or panic setting in…
So what is Lassa fever?
Lassa fever is one of a group of infections known as the viral haemorrhagic fevers (VHF) that includes viral infections like Ebola, Marburg and Crimean-Congo haemorrhagic fever. Lassa Virus is a member of the arenavirus family. It is named after Lassa in North-Eastern Nigeria (not Lhasa in Tibet, as I thought when I first heard about it!) It was first identified there in 1969, although the disease was suspected since the early 1950s.
Lassa fever is common in West Africa, there are approximately 300,000 cases every year (1 in 1,300 population), with about 5,000 deaths.
The normal host for Lassa Virus is the multi-mammate rat (Mastomys natalensis); humans normally become infected after exposure to rat urine or faeces either from contaminated surfaces or food. Lassa Virus is endemic in West Africa, especially Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo and Nigeria. In some rural parts of Sierra Leone and Guinea over half the population show serological evidence of past exposure to Lassa Virus. In these countries Lassa fever is responsible for about 15% of all admissions to hospital and 30% of all deaths.
Approximately 80% of people infected with Lassa Virus are asymptomatic.
The incubation period for Lassa fever is 1 to 3 weeks. Infection starts as a low grade fever, headache and general malaise. In severe infection this progresses to cough, sore throat, nausea, vomiting, diarrhoea, chest pain, back pain and abdominal pain. Later facial and pulmonary oedema occurs followed by bleeding from the nose, mouth, gastrointestinal and genital tract. In the late stages shock, seizures and coma occur.
1 in 5 infections result in severe disease. Lassa fever is associated with necrosis of the liver, spleen and adrenal glands as well as inflammation of the heart, lung tissue and kidneys. Haemorrhage occurs as the endothelial surfaces start to leak. It is a multi-system disease. The mortality in severe Lassa fever is 15-30% even with expert treatment. If patients with severe disease are going to survive then they start to show improvement after 8-10 days of illness.
The most common long term sequela of Lassa fever is actually deafness which occurs in about 30% of survivors of severe disease, and is permanent in about 20%.
How is Lassa fever diagnosed?
Lassa Virus is an Advisory Committee on Dangerous Pathogens (ACDP) Hazard Group 4 organism, this means that it poses a serious risk to the safety of the laboratory personnel processing samples containing this virus and they should only be handled in a Category 4 laboratory (in the UK this is at the Rare and Imported Pathogens Laboratory at Porton Down). It is therefore imperative that Lassa fever is considered in anybody who has been to an endemic country who presents with a fever so that samples are not processed using the wrong biological safety levels.
In the UK, the Infectious Diseases Physician or Microbiologist will discuss VHF testing with the National Imported Fever Service based at Porton Down on 0844 7788990. Ward staff should not call this service directly.
Sample requirements include ALL of the below:
- 4.5ml* serum in red or yellow vacutainer tube
- 4.5ml* whole blood in purple EDTA vacutainer tube
- 20-25ml urine in a sterile universal
Note: *For children a minimum of 1ml can be sent however it will not have an extended imported fever screen in the event the VHF test is negative and the diagnosis is still unclear. Send >1ml if possible.
Urgent results are usually available within 4-6 hours of arrival in the testing laboratory. A positive malaria test DOES NOT exclude the diagnosis of VHF; dual infection can occur.
If a patient tests positive for VHF then they should be transferred to an High Level Isolation Unit (HLIU); in the UK this is located at the Royal Free London NHS Foundation Trust, contact the oncall Infectious Diseases Consultant on 0207 7940500. IMPORTANT No further tests should be carried out locally unless they would be immediately life-saving.
How is Lassa fever treated?
In the UK Lassa fever should be treated in an HLIU by doctors experienced in the treatment of VHF. IV Ribavirin should be started as soon as a patient is suspected to have Lassa fever. It is most effective when started within 6 days of the onset of fever. Other priorities include good supportive care with fluids, transfusions and ventilation as necessary.
Diagnosis and prompt treatment are essential. Among patients who are hospitalized with severe clinical presentation of Lassa fever, case-fatality is approximately 15-30%. Early supportive care with rehydration and symptomatic treatment improves survival.
Lassa Virus is normally transmitted via the nasopharyngeal route, with inhalation being the most common route of acquisition. Lassa fever can be transmitted from person-to-person although this is not quite as likely as with other VHFs such as Ebola and Marburg. All body fluids from symptomatic patients are potentially infectious, including blood, urine, faeces and saliva. Urine can remain infectious for up to 9 weeks after recovery and sexual transmission occur during this time.
Remember: there is always the slight possibility of a patient being admitted to a UK hospital having been abroad in one of the Lassa fever endemic countries of West Africa. It is therefore important to consider Lassa fever as part of the differential diagnosis in this situation and act quickly to instigate infection control procedures, test the patient safely for the virus and start treatment as soon as possible.