Eventually the Microbiologist was located and the GP was able to put the story to them and get their advice.
What is Japanese Encephalitis Virus?
The Japanese Encephalitis (JE) Virus is from the Flavivirus family which also includes viruses such as Yellow Fever Virus, Dengue Virus, West Nile Virus and Zika Virus amongst others.
JE Virus is found throughout Asia and parts of the Western Pacific. It is estimated that there are up to about 70,000 cases a year in these countries. The number of cases increases during the wet season (June – July) during which time there can be large outbreaks. Whilst travellers to endemic countries are potentially at risk of JE the incidence is approximately 1 in 1 million travellers, so it’s really pretty rare to see it present in returned travellers, especial out of season.
The normal animal hosts for JE Virus are pigs, not macaque monkeys! (Poor macaques they’re blamed for everything). Infection is transmitted from pigs to human by the bite of infected Culex mosquitos (whereas mosquitos serve no purpose but to cause disease and irritation!!). These mosquitos bite in the evening and at night. They breed in shallow pools of water such as rice fields, marches and puddles, hence the link to outbreaks during the wet season.
Humans are an accidental and dead end host for JE Virus as we have insufficient viraemia (the presence of viruses in the blood) to infect further biting mosquitos. Pigs are usually asymptomatic but other animals such as horses, who are also dead-end hosts for the virus, can suffer fatal encephalitis. Person-to-person transmission doesn’t occur except theoretically from direct inoculation of large volumes of blood e.g. contaminate blood transfusion or needle stick injuries in the same way as other Flaviviruses.
How does JE Virus infection present?
The majority of patients with JE are asymptomatic; less than 1% of patients actually develop symptoms. The most common symptomatic presentation, following an incubation period of 5-15 days, is encephalitis with fever, headache, diarrhoea and vomiting followed by neurological features which can include some of the following:
- Confusion, abnormal behaviour or acute psychosis
- Focal neurological deficits such as cranial nerve palsies
- Movement disorders
- Parkinsonian features e.g. flat, mask-like face, tremor, cogwheel rigidity and choreoathetoid movements due to extrapyramidal brain involvement
- Poliomyelitis-like illness with flaccid paralysis
How is JE diagnosed?
By the time most patients are symptomatic with JE it is impossible to detect virus in blood or CSF by PCR. The main diagnostic strategy is to detect the immune response to the virus in either CSF or blood taken within 10 days of onset of illness (acute) and compared to a repeat sample taken 2-3 weeks later (convalescent). The presence of IgM against Flaviviruses in the acute serum suggests acute infection whereas a four-fold rise in IgG between acute and convalescent suggests recent infection. A positive IgG that doesn’t change between acute and convalescent suggests past infection.
The main drawback to this way of diagnosing JE is that there is considerable cross reactivity between the different Flaviviruses and therefore the reference laboratories who perform these tests need to get detailed travel and vaccination histories from these patients to be aware of potential cross reaction so they can then perform further tests to try and find which specific Flavivirus is reacting.
How is JE Virus infection treated?
There is no specific treatment for JE Virus infection. Supportive care, control of intracranial pressure and seizures are important aspects of the patient’s management.
What is the prognosis of JE?
Most common viral encephalitis’ in the UK (HSV, VZV and Enterovirus) are self-limiting and resolve completely. The mortality of JE however is 20-30%, with 30-50% of survivors having long-term neurological sequelae.
How is JE Virus infection prevented?
The most effective method for preventing JE virus infection is through the use of vaccines. There are a number of different JE Virus vaccines available and these are part of routine vaccination strategies in many endemic countries in Asia.
Travellers to endemic countries are also often offered the JE vaccine as part of the travel advise but in my experience this rarely takes in to account the exact details of the trip; what season the person is going in, what they will be doing and how long they will be going for. Someone who will be spending many months in a rural area during the wet season is at much higher risk than someone on a 2 week ski trip in snow season or on the beach for a week during the dry season. Both the dry and wet season traveller should be advised to cover up with long sleeves and trousers in the evening and to use insect repellents and mosquito nets for sleeping but in snow season in the mountains, there will be no mosquitoes; even the macaques are too cold and need to take a bath in the hot springs.
So the Microbiologist had to chuckle a little, as the GP divulged about the “slight” overreaction of the patient, but now armed with some extra facts the GP explained to the patient just how rare JE Virus infection was in travellers and that spending 2 weeks in Shiga Kogen skiing was definitely not a risk for the virus. Eventually the patient was sufficiently reassured and was able to leave… the Microbiologist however, put a reminder into his diary to make an appointment to see his Practice Nurse to discuss travel vaccines for his next holiday… Costa Rica…