Standby Emergency Treatment of Malaria in Travelers

Experience to Date and New Developments

Patricia Schlagenhauf; Eskild Petersen

Disclosures

Expert Rev Anti Infect Ther. 2012;10(5):537-546. 

In This Article

Use of Malaria Rapid Tests for & by Travelers

After rapid tests based on detection of circulating antigen became available in 1995,[37] it was proposed that this might be a useful adjunct for travelers carrying an SBET because the main problem with the strategy is the correct diagnosis of malaria.[38]

Rapid tests that show a 100% sensitivity down to a parasite density level of 200 parasites per microliter equivalent to a parasitemia of approximately 0.004% are available.[105] Compared with this, a good microscopist can detect down to five parasites per microliter[39] and molecular diagnosis by PCR can detect parasites down to a density of 0.5 parasites per microliter.[40]

Rapid tests are increasingly used in medical centers with limited access to experienced microscopists and they are an option for travelers without access to qualified healthcare. However, a rapid test cannot determine the parasite density, and rapid tests may be difficult to perform and interpret by untrained persons. One study found that the test interpretation for medically untrained individuals particularly in distress might be too complicated even after proper instruction,[41,42] the pros and cons are summarized in Box 1. An evaluation of self-diagnosis and treatment in oil service employees showed that provision of a malaria kit with diagnostic tests and treatments was useful in expatriates.[43] Self-diagnosis led to decreased incorrect treatment use – however, follow-up on negative tests and post-treatment medical checks were poor.

Rapid tests have limitations. False-negative tests in patients with very high parasite densities have been described, probably due to the so-called 'pro-zone' phenomena known from other diagnostic tests.[44,45] The problems seem to be limited to tests based on detection of the histidine-rich protein 2 (HRP2) and not tests based on detection of LDH.[42] Mutations in the HRP2 gene may result is false-negative tests.[46,47] Assays are available, which find P. falciparum, P. vivax, P. ovale and P. malariae, and P. knowlesii will be found with tests based on the detection of pan-malarial aldolase antigen aldolase and LDH antigens.[48]P. ovale can be divided into variant and classic P. ovale, and variant P. ovale is not picked up in rapid diagnostic tests.[49–51] Thus travelers using rapid tests should be instructed that no test so far is 100% reliable. To reduce the risk of false-negative tests, testing should be performed at least twice with 24 h in between. However, this does not exclude false-negative tests due to the pro-zone phenomenon.[51] The latest results of the WHO multicenter evaluation of different rapid diagnostic tests show that the best performance was found in tests based on a combination of the HRP2 and plasmodium LDH proteins.[105]

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