Home

About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

CPT Codes 2016

Quizzes

Review Tests

FAQ

Information Tables

Organism Index (A-Z)

Presentation of Quiz #72

A 49-year-old traveler from the United States presented with a low grade fever, headache, and overall malaise 13 days after visiting friends and relatives in sub-Saharan Africa.  While in Africa, the patient was well with no symptoms of malaria.  On presentation to the Emergency Room at 10:30 PM, blood was collected and a rapid BinaxNOW rapid malaria test was performed.  Results of the test are seen below.  Based on this result the test was interpreted as negative.  This was the patient’s first trip outside of the U.S.
quiz72_slide2quiz72_slide3quiz72_slide4 

  • Can this negative result be accepted as correct?  Why or why not?
  • What additional tests should be performed?  Why or why not?
  • If additional tests are recommended, can they be performed the following morning?  Why or why not?

Scroll Down for Answer and Discussion

 

 Answer and Discussion of Quiz #72

Remember that all requests for malaria diagnosis are considered STAT requests, and specimens should be ordered, collected, processed, examined, and reported accordingly.  If patients are tested using one of the rapid malarial tests, it is mandatory that thick and thin blood films be examined STAT if the rapid test is negative.  Therefore the “negative” test report for this patient is unacceptable as a final report.  Thick and thin blood films should be examined STAT prior to sending out the final report.  Waiting to perform these blood films is NOT ACCEPTABLE.  They need to be prepared and examined immediately.

It is well known that malaria causes significant morbidity and mortality worldwide, including in countries where imported cases are seen. In many developing countries where malaria is highly endemic, diagnostic testing is often inadequate or unavailable due to a lack of trained personnel or funds or both. Although microscopic examination of stained thick and thin blood films remains the standard of practice, this approach is time-consuming, is based on the need for a great deal of expertise in microscopic morphology, and requires the purchase and maintenance of expensive equipment. Rapid diagnostic tests (RDTs) offer great potential to improve the diagnosis of malaria, particularly in remote areas.

Additional patient testing
Since the BinaxNOW rapid test was reported as negative, thick and thin blood films were immediately prepared and examined.  The following images were seen in the microbiology laboratory.  How should these films be interpreted?

  quiz72_slide5  quiz73_slide6

Although the thin blood film appears to be negative, the thick film reveals two Plasmodium ring forms.  This patient has a very low parasitemia; thus the rapid test was negative, while the thick blood film was positive.

Discussion
From the time of the original mosquito bite until a week or more later, the patient remains asymptomatic. During this time, the organisms are undergoing multiplication (preerythrocytic cycle) in the liver. When the liver merozoites invade the RBCs, several broods begin to develop; however, one will eventually dominate and suppress the others, thus beginning the process of periodicity; this periodicity is very rarely seen in an immunologically naïve patient early in the infection.  Therefore, these patients with no prior exposure to malaria tend to be symptomatic early with a very low parasitemia and most often do not present as a possible malaria patient. Once the cycle is synchronized, the simultaneous rupture of a large number of RBCs and liberation of metabolic waste by-products into the bloodstream precipitate the paroxysms of malaria.

This patient has never been exposed to malaria before; thus he is immunologically naïve and has no residual antibody.  These patients (often travelers) tend to become symptomatic very early and present with a very low parasitemia (may be as low as 0.001% to 0.0001%) (Table 72.1).  The BinaxNOW is most sensitive at 0.1% parasitemia, a much higher parasite load than seen in these travelers.  THEREFORE, IF THE RAPID TEST IS NEGATIVE, THICK AND THIN BLOOD FILMS MUST BE EXAMINED IMMEDIATELY.

If the rapid malaria tests are not being used, blood films should be prepared on admission of the patient (ordering, collection, processing, examination, reporting on a STAT basis). A fever pattern may not be apparent early in the course of the infection (immunologically naïve patient – travelers); symptoms may be completely random and may mimic any other condition with vague complaints.

It is important for both physicians and laboratorians within areas where malaria is not endemic to be aware of the difficulties related to malaria diagnosis and the fact that symptoms are often nonspecific and may mimic other problems. It is important for physicians to recognize that travelers are susceptible to malarial infection when they return to a country where malaria is endemic, and they should receive prophylactic medication. It is also important to remember that 80% of the P. falciparum cases acquired by American civilians are contracted in sub-Saharan Africa; currently there are 40 cities in Africa with over 1 million inhabitants, and by 2025 over 800 million people will live in urban areas. Malaria has always been a rural disease in Africa; however, it appears that the urban poor are at a much higher risk of contracting malaria than was previously recognized. These changes also have the potential to affect travelers to Africa.

Patient Outcome
The patient was treated for malaria; post-treatment review revealed no parasitemia.  Based on the travel history, the assumption was the patient had been infected with Plasmodium falciparum.  The patient remained healthy with no additional problems.

References:

1.Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.

2.   National Committee for Clinical Laboratory Standards. 2000. Laboratory Diagnosis of Blood-Borne Parasitic Diseases. Approved guideline M15-A. NCCLS, Wayne, Pa.

3.  Garcia, L.S. (ed.). 2010. Clinical Microbiology Procedures Handbook, 3rd ed. ASM Press, Washington, D.C.

4.   De Monbrison F., P. Gerome, J. F. Chaulet, M. Wallon, S. Picot, and F. Peyron. 2004. Comparative diagnostic performance of two commercial rapid tests for malaria in a non-endemic area. Eur. J. Clin. Microbiol. Infect. Dis. 10:784–786.

5.   Forney, J. R., C. Wongsrichanalai, A. J. Magill, L. G. Craig, J. Sirichaisinthop, C. T. Bautista, R. S. Miller, C. F. Ockenhouse, K. E. Kester, N. E. Aronson, E. M. Andersen, H. A. Quino-Ascurra, C. Vidal, K. A. Moran, C. K. Murray, C. C. DeWitt, D. G. Heppner, K. C. Kain, W. R. Ballou, and R. A. Gasser, Jr. 2003. Devices for rapid diagnosis of malaria: evaluation of prototype assays that detect Plasmodium falciparum histidine-rich protein 2 and a Plasmodium vivax-specific antigen. J. Clin. Microbiol. 41:2358–2366.

6.   Grobusch, M. P., T. Hanscheid, K. Gobels, H. Slevogt, T. Zoller, G. Rogler, and D. Teichmann. 2003. Comparison of three antigen detection tests for diagnosis and follow-up of falciparum malaria in travelers returning to Berlin, Germany. Parasitol. Res. 89:354–357.

7.   Calderaro, A, G Piccolo, C Gorrini, S Rossi, S Montecchini, ML Dell’Anna, F De Conto, MC Medici, C Chezzi, MC Arcangeletti. 2013.  Accurate identification of the six human Plasmodium spp. causing imported malaria, including Plasmodium ovale wallikeri and Plasmodium knowlesi.  Malar J 12:321     

8.   Hanscheid, T. 1999. Diagnosis of malaria: a review of alternatives to conventional microscopy. Clin. Lab. Haematol. 21:235–245.

9.   Moody, A. 2002. Rapid diagnostic tests for malaria parasites. Clin. Microbiol. Rev. 15:66-78.

10. World Health Organization. 2012.  Malaria rapid diagnostic test performance (Summary results of WHO product testing of malaria RDTs:  Round 1-4 (2008-2012) (http://apps.who.int/iris/bitstream/10665/77748/1/9789241504720_eng.pdf?ua=1  

11. Garcia, LS, 2010. Malaria. Clin Lab Med 30:93-129.


.

 

Table 72.1 Parasitemia determined from conventional light microscopy: clinical correlation*a

Parasitemia (%)

No. of parasites/µl

Clinical correlation*b

0.0001 – 0.0004

5 – 20

Number of organisms that are required for a positive TBF (sensitivity)
Note (TBF): Examination of 100 TBF fields (0.25 µl) may miss up to 20% of infections (sensitivity, 80–90%); at least 300 TBF fields should be examined before reporting a negative result
Note (THBF): Examination of 100 THBF fields (0.005 µl); at least 300 THBF fields should be examined before reporting a negative result; both TBF and THBF should be examined for every specimen submitted for a suspect malaria case. One set (TBF + THBF) of negative blood films does not rule out a malaria infection.

0.002

100

Naïve patients may be symptomatic below this level; remember emergency room patients - travelers

0.1

     5,000

BinaxNOW (maximum sensitivity); patients with low parasitemias will often have a false negative rapid test; if negative, then STAT thick and thin films are required.

0.2

10,000

Level above which immune patients will exhibit symptoms

2

100,000

Maximum parasitemia of P. vivax and P. ovale (infect young RBCs only) (rarely may exceed 2%)

2 – 5

100,000 – 250,000

Hyperparasitemia, severe malaria, increased mortality

10

500,000

Exchange transfusion may be considered, high mortality

*a Adapted from references 1 and 11
*b TBF, thick blood film; THBF, thin blood film.