Guidance for Malaria Diagnosis in Patients with Suspected Orthoebolavirus or Orthomarburgvirus Infection in the United States

Patients suspected of having an orthoebolavirus or orthomarburgvirus after travel to an area experiencing an Ebola or Marburg outbreak should be evaluated urgently for malaria infection as the symptoms of malaria infection are very similar to those of Ebola and Marburg. The gold standard diagnostic test for malaria is microscopic examination of thick and thin blood smears adhering to OSHA’s bloodborne pathogens standard. Thick blood smears are more sensitive in detecting malaria parasites because the blood is more concentrated allowing for a greater volume of blood to be examined. Thin smears are necessary for parasite species identification and quantification of parasites. Blood films should be prepared, processed (stained), and read immediately. If on-site smear microscopy is not feasible, contact your local or state public health lab which may be able to assist with performing and reading urgent blood films. If timely microscopy is still not available, a malaria rapid diagnostic test can be used to make a preliminary diagnosis, which subsequently can be confirmed by microscopy or PCR. Laboratory staff can safely perform testing by adhering to the OSHA bloodborne pathogens standard including wearing appropriate PPE to prevent exposures to all bloodborne pathogens and manipulating the specimen in a Biosafety Cabinet. 

The standard protocols for preparing and staining thick and thin smears do not sufficiently inactivate orthoebolaviruses and orthomarburgviruses. A modified thick smear procedure that inactivates orthoebolaviruses and orthomarburgviruses is being investigated and this page will be updated when it is available. For thin smears, extending the fixation time in 100% MeOH to 15-30 minutes inactivates up to 7.9×10⁶ TCID₅₀/mL of orthoebolaviruses in whole blood (Cutts et al, J Clin Microbio, 2016, 54:1157–1159 and CDC unpublished data). Orthomarburgviruses are in the same genetic viral family as orthoebolaviruses, therefore inactivation data for orthoebolaviruses is applicable to orthomarburgviruses. 

Modified thin smear protocol to inactivate orthoebolaviruses and orthomarburgviruses: 

1. Fix thin smears for 15 to 30 minutes in 100% methanol. Allow to dry.
2. Prepare 40 ml of working Giemsa stain. Add 2 drops of 5% Triton X-100 and mix.  Stain thin smears for 45 minutes.
3. Measure 40ml of working Giemsa buffer for rinsing. Add 2 drops of 5% Triton X-100.  Rinse thin smears for a few seconds with agitation to remove excess stain.
4. Allow smears to air-dry (do not use a hair dryer or fan) before examination.

Both thick and thin blood smears should be air dried as fan drying may aerosolize the blood specimen and infectious agents. As an added precaution, laboratories may choose to apply coverslips to stained slides. For optimal results the thinnest coverslip available should be used with rapid drying mounting medium to expedite processing. 

Additional diagnostic information is available at Clinical Guidance: Malaria Diagnosis & Treatment in the U.S. Healthcare providers needing assistance with diagnosis or management of suspected cases of malaria should 

• Call the CDC Malaria Hotline: 770-488-7788 or (toll free) 855-856-4713 M–F, 9am–5pm ET 

• Emergency consultation after hours: call 770-488-7100 and request to speak with a CDC Malaria Branch clinician, or 

• Email: malaria@cdc.gov