Differentials
Malaria infection
SIGNS / SYMPTOMS
Residence in/travel from malaria-endemic region.
Inadequate or absence of malaria chemoprophylaxis.
Difficult to distinguish from Rift Valley fever virus (RVFV) infection without diagnostic testing.
INVESTIGATIONS
Giemsa-stained blood film: positive for Plasmodium species.
Rapid diagnostic tests: positive for Plasmodium species.
West Nile virus
SIGNS / SYMPTOMS
Residence in/travel from West Nile virus-endemic region.
Visual disturbances are common.
Rarely causes neuroinvasive disease (e.g., encephalitis, meningitis, flaccid paralysis syndrome).
Difficult to distinguish from RVFV infection without diagnostic testing.
INVESTIGATIONS
West Nile virus-specific IgM in serum or cerebrospinal fluid: positive.
Crimean-Congo haemorrhagic fever
SIGNS / SYMPTOMS
Residence in/travel from Crimean-Congo haemorrhagic fever-endemic regions.
Contact with ticks, infested animals, infected animals, or fomites.
Difficult to distinguish from RVFV infection without diagnostic testing.
INVESTIGATIONS
Reverse transcriptase-polymerase chain reaction detection of Crimean-Congo haemorrhagic fever virus RNA.
Positive detection of IgM for Crimean-Congo haemorrhagic fever virus with negative IgM for RVFV. Cross-reactivity may occur.
Presence of tick bites or infestation.
Hantavirus cardiopulmonary syndrome
SIGNS / SYMPTOMS
Residence in/travel from hantavirus-endemic regions.
Residence in/travel to densely forested areas with large rodent populations.
Exposure to rodent faeces, urine, or carcasses, or rodent bite.
Difficult to distinguish from RVFV infection without diagnostic testing.
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of hantavirus RNA.
Onset of severe pulmonary distress.
Dengue fever
SIGNS / SYMPTOMS
Residence in/travel from dengue-endemic regions.
Difficult to distinguish from RVFV infection without diagnostic testing.
Infection may present as asymptomatic, acute febrile illness, or severe disease.
Often presents with rash.
Transmission not associated with direct contact with livestock.
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of dengue virus RNA during initial onset of illness.
Positive detection of IgG against dengue virus may be indicative of previous exposure to a different serotype. IgM detection can be used to determine current infection without overlapping detection of previous exposure.
Ebola virus infection
SIGNS / SYMPTOMS
Residence in/travel from regions currently experiencing an Ebola virus outbreak.
Difficult to distinguish from RVFV infection without diagnostic testing in early stages of illness.
Not spread by mosquitoes or contact with livestock.
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of Ebola virus RNA.
Enzyme-linked immunosorbent assay detection of IgG or IgM against Ebola virus.
Lassa fever
SIGNS / SYMPTOMS
Residence in/travel from West Africa, where Lassa fever is endemic.
Residence in/travel from areas with large Mastomys rodent population.
Not spread by mosquitoes.
Characteristic symptom includes loss of hearing or deafness.
Symptom onset after much longer incubation period (1-3 weeks).
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of Lassa virus RNA.
Enzyme-linked immunosorbent assay detection of IgG or IgM against Lassa virus.
Chikungunya virus infection
SIGNS / SYMPTOMS
Residence in/travel from chikungunya-endemic regions.
Infection may present as asymptomatic, acute febrile illness, or severe disease with chronic sequelae.
Characteristic maculopapular rash and severe, debilitating arthralgia.
Transmission not associated with direct contact with livestock.
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of chikungunya virus RNA during initial onset of illness.
Enzyme-linked immunosorbent assay detection of IgG or IgM against chikungunya virus.
Japanese encephalitis
SIGNS / SYMPTOMS
Residence in/travel from Japanese encephalitis-endemic regions.
May be difficult to distinguish from RVFV infection without diagnostic testing.
INVESTIGATIONS
Reverse transcription polymerase chain reaction detection of Japanese encephalitis virus RNA during initial onset of illness.
Enzyme-linked immunosorbent assay detection of IgG or IgM against Japanese encephalitis virus.
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
Residence in/travel to a country/area or territory with local transmission, or close contact with a confirmed or probable case of COVID-19, in the 14 days prior to symptom onset.
The situation is evolving rapidly; see our COVID-19 topic for further information.
INVESTIGATIONS
Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA.
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