Differentials
Japanese encephalitis (JeV)
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
History of mosquito bite (although lack of recognised bites does not exclude JeV).
JeV infection does not require contact with animals or sick patients.
INVESTIGATIONS
Cerebrospinal fluid/serum serology: positive for JeV.
Herpes simplex encephalitis
SIGNS / SYMPTOMS
Lack of respiratory signs or symptoms.
May not have a travel history to endemic area.
INVESTIGATIONS
Cerebrospinal fluid polymerase chain reaction: positive for herpes simplex virus.
Bacterial meningitis
SIGNS / SYMPTOMS
Severe neck stiffness and photophobia seen in bacterial meningitis are less common in henipavirus infection.
May not have a travel history to endemic area.
INVESTIGATIONS
Cerebrospinal fluid (CSF) analysis: shows predominantly polymorphs with low glucose.
CSF culture: positive.
Malaria
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
No differentiating signs or symptoms.
Malaria patients more likely to present with rigors and severe thrombocytopenia.
INVESTIGATIONS
Thick and thin blood film: positive for Plasmodium.
Rapid diagnostic tests: positive for Plasmodium.
Leptospirosis
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
No differentiating signs or symptoms.
INVESTIGATIONS
Serology: positive for leptospirosis.
Polymerase chain reaction assay: positive for leptospirosis.
West Nile virus
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
No differentiating signs or symptoms.
INVESTIGATIONS
Serum/cerebrospinal fluid: West Nile virus-specific IgM.
Plaque-reduction neutralisation test: positive.
Dengue fever
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
Much less likely to cause encephalitis.
INVESTIGATIONS
Dengue-specific serology and polymerase chain reaction: positive.
Zika virus infection
SIGNS / SYMPTOMS
Residence in/travel history to endemic area.
Characteristic maculopapular (sometimes morbilliform) rash with or without intense pruritus.
Arthralgia, particularly in the small joints of hands and feet.
Non-purulent conjunctivitis or conjunctival hyperaemia.
INVESTIGATIONS
Polymerase chain reaction/serology: positive for Zika virus RNA or antibodies.
Varicella
SIGNS / SYMPTOMS
Often characteristic rash or other features.
Exposure history.
INVESTIGATIONS
Polymerase chain reaction/serology: positive for DNA virus/IgG for varicella.
Measles
SIGNS / SYMPTOMS
Often characteristic rash or other features.
Exposure history.
INVESTIGATIONS
Measles-specific IgM and IgG serology: positive.
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