Imported Plasmodium Falciparum Malaria in HIV Patients
Imported Plasmodium Falciparum Malaria in HIV Patients
Plasmodium falciparum parasitaemia is higher in HIV-infected patients, especially in those with a low CD4 cell count. In the first case, the patient had a parasitaemia of 7% in the blood smear at the time of diagnosis and a 650 CD4 T cell count/μl. A parasitaemia above 5% in non-immune travellers for malaria falls within the severity criteria according to WHO definition. Older age, European origin, travel to eastern Africa, absence of chemoprophylaxis, time to diagnosis of four to 12 days and diagnosis during the fall-winter season have been associated with severe imported P. falciparum malaria in non-immune travellers. Data about the impact of HIV-1 infection on the severity of imported P. falciparum malaria have been reported and the most frequent criterion of severity was hyperparasitaemia. There are few clinical trials on the co-administration of anti-retroviral therapy and anti-malarial drugs. Interactions between quinine and nevirapine or ritonavir, including ritonavir-boosted protease inhibitor regimens have been reported. The concurrent administration of nevirapine and quinine can lead to significant reductions in the efficacy of the quinine and increased toxicity. The co-administration of ritonavir and quinine can lead to elevations in plasma levels of quinine and suggest that quinine dosages should be shifted downward. Anti-retroviral drugs are the most therapeutically risky drugs for drug-drug interactions because of their potent inhibition and induction of cytochrome enzymes. This is particularly important during co-administration of lumefantrine (in combination with artemisinin derivates) and protease inhibitors or non-nucleoside reverse transcriptase inhibitor-based anti-retroviral regimens. The first patient received intravenous quinine and doxycycline with a successful therapeutic response. Quinine therapy was used because in Europe the available formulations of intravenous artesunate recommended as the first-line by WHO were not produced according to Good Manufacturing Practices (GMP). WHO recently pre-qualified intravenous artesunate manufactured by Guilin Pharmaceuticals in China and this may resolve problems in acquiring GMP artesunate in Spain.
In the second case, the patient was initially treated with atovaquone/proguanil. Atovaquone-proguanil has shown high efficacy against multi- drug-resistant P. falciparum with few side effects and a mode of action unrelated to that of other anti-malarial drugs, such as quinine, plus one of the three following: doxycycline, tetracycline or clindamycin and mefloquine. The patient developed an early treatment failure (within 72 hours) with an elevation of parasitaemia and a jump from 0.5% to 8% infected erythrocytes in the thick blood film. The malarial treatment failures can be attributed to recrudescence of P. falciparum due to suboptimal therapy or anti-malarial drug-resistant genotypes. Atovaquone is a low genetic barrier drug but proguanil synergizes with atovaquone in combination, reducing the selection of resistance mutations. Resistance to atovaquone and proguanil has been associated with sequence changes in cytochrome b (cytb) and dihydrofolate reductase (dhfr) gene respectively. Isolates of P. falciparum collected by the European Network on Imported Infectious Disease surveillance were analysed for single-point mutations of the cytb gene and the results showed a level < 1% of these mutations. Atovaquone inhibits electron transfer of the respiratory chain by binding to cytochrome b of plasmodial mitochondria. On the other side, proguanil, as its active form cycloguanil, is an inhibitor of the DHFR involved in pyrimidine biosysnthesis. However, in combination with atovaquone, by an unknown mechanism, it lowers the effective concentration at which the former collapses the mitochondrial membrane potential. In the second case, the analysis of mutations of the DHFR and cytochrome b genes showed the characteristic triple DHFR mutations associated with failure for the treatment of pyrimethamine, but not of proguanil. The cytb gene showed the mutation L283I. This mutation, associated with V284K, shows a 76-fold increase in IC50 of atovaquone compared to non-mutant strains, but this effect must be the direct responsibility of V284K, as I283 has been observed in atovaquone sensitive parasites. The presence of the L283I mutation by itself does not confer resistance to atovaquone. These data suggest that the early treatment failure in the second patient, could be more related to a suboptimal therapy than to a drug-resistant genotype. Atovaquone/proguanil is used in the treatment of uncomplicated multi- drug-resistant P. falciparum malaria, but we do not have an answer to this question: could the HIV-infected patients have also a higher rate of atovaquone/proguanil treatment failure? No data about this point have been reported in HIV-infected patients. This question must be approached with caution. An explanation could be a delayed parasite clearance due to a slowness of action by atovaquone/proguanil, but the parasitaemia increased from 0.5% to 8% on day 3. On the other hand, treatment failure could be attributed to poor bioavailability of the atovaquone, proguanil or its active metabolite, cycloguanil. The biotransformation of proguanil could have been reduced. A possible interaction between atovaquone/proguanil and IP-based regimens could be presented. However, it was not possible to measure drug concentrations at that time.
In routine clinical practice, the PCR is performed on admission samples to confirm the results obtained by microscopy, as shown in this cases, and to avoid the limitations of the microscopy and RDT: misdiagnosis of mixed-species infections and low parasitaemia. The microscopic examination of Giemsa-stained thin and thick blood films remains the "gold standard" for the diagnosis of malaria and detects parasites at a density of 50 parasites/μl by an experienced microscopist. The RDT, using a protein rich in histidine (HRP-2) and aldolase or lactate dehydrogenase antigens, detects parasites quickly and cheaply, but it cannot provide data regarding drug resistance genotypes. RDT is accepted as an excellent tool in the diagnosis of P. falciparum malaria. However, it is not useful in the follow-up anti-malarial therapy, because it could positive HRP-2 antigen for three or four weeks after a successful therapy. The PCR-based methods are extremely sensitive with a detection limit of < 10 parasites/μl. Various authors have reported the development of a real-time PCR assay to detect P. falciparum, Plasmodium vivax and Plasmodium ovale in routine clinical diagnosis. The risks of contamination are minimal and the result can be obtained in only 2 h. In the cases presented, molecular methods were essential for rapid and accurate diagnosis and follow-up.
In conclusion, this are two cases of HIV-infected patients with imported P. falciparum malaria, high parasitaemia, both severe clinical episodes with > 350 CD4 cell count/μl, absence of chemoprophylaxis and successful response. Factors such as drug interactions and the possible implication of anti-malarial therapy bioavailability are all especially interesting in HIV-malaria co-infections.
Conclusions
Plasmodium falciparum parasitaemia is higher in HIV-infected patients, especially in those with a low CD4 cell count. In the first case, the patient had a parasitaemia of 7% in the blood smear at the time of diagnosis and a 650 CD4 T cell count/μl. A parasitaemia above 5% in non-immune travellers for malaria falls within the severity criteria according to WHO definition. Older age, European origin, travel to eastern Africa, absence of chemoprophylaxis, time to diagnosis of four to 12 days and diagnosis during the fall-winter season have been associated with severe imported P. falciparum malaria in non-immune travellers. Data about the impact of HIV-1 infection on the severity of imported P. falciparum malaria have been reported and the most frequent criterion of severity was hyperparasitaemia. There are few clinical trials on the co-administration of anti-retroviral therapy and anti-malarial drugs. Interactions between quinine and nevirapine or ritonavir, including ritonavir-boosted protease inhibitor regimens have been reported. The concurrent administration of nevirapine and quinine can lead to significant reductions in the efficacy of the quinine and increased toxicity. The co-administration of ritonavir and quinine can lead to elevations in plasma levels of quinine and suggest that quinine dosages should be shifted downward. Anti-retroviral drugs are the most therapeutically risky drugs for drug-drug interactions because of their potent inhibition and induction of cytochrome enzymes. This is particularly important during co-administration of lumefantrine (in combination with artemisinin derivates) and protease inhibitors or non-nucleoside reverse transcriptase inhibitor-based anti-retroviral regimens. The first patient received intravenous quinine and doxycycline with a successful therapeutic response. Quinine therapy was used because in Europe the available formulations of intravenous artesunate recommended as the first-line by WHO were not produced according to Good Manufacturing Practices (GMP). WHO recently pre-qualified intravenous artesunate manufactured by Guilin Pharmaceuticals in China and this may resolve problems in acquiring GMP artesunate in Spain.
In the second case, the patient was initially treated with atovaquone/proguanil. Atovaquone-proguanil has shown high efficacy against multi- drug-resistant P. falciparum with few side effects and a mode of action unrelated to that of other anti-malarial drugs, such as quinine, plus one of the three following: doxycycline, tetracycline or clindamycin and mefloquine. The patient developed an early treatment failure (within 72 hours) with an elevation of parasitaemia and a jump from 0.5% to 8% infected erythrocytes in the thick blood film. The malarial treatment failures can be attributed to recrudescence of P. falciparum due to suboptimal therapy or anti-malarial drug-resistant genotypes. Atovaquone is a low genetic barrier drug but proguanil synergizes with atovaquone in combination, reducing the selection of resistance mutations. Resistance to atovaquone and proguanil has been associated with sequence changes in cytochrome b (cytb) and dihydrofolate reductase (dhfr) gene respectively. Isolates of P. falciparum collected by the European Network on Imported Infectious Disease surveillance were analysed for single-point mutations of the cytb gene and the results showed a level < 1% of these mutations. Atovaquone inhibits electron transfer of the respiratory chain by binding to cytochrome b of plasmodial mitochondria. On the other side, proguanil, as its active form cycloguanil, is an inhibitor of the DHFR involved in pyrimidine biosysnthesis. However, in combination with atovaquone, by an unknown mechanism, it lowers the effective concentration at which the former collapses the mitochondrial membrane potential. In the second case, the analysis of mutations of the DHFR and cytochrome b genes showed the characteristic triple DHFR mutations associated with failure for the treatment of pyrimethamine, but not of proguanil. The cytb gene showed the mutation L283I. This mutation, associated with V284K, shows a 76-fold increase in IC50 of atovaquone compared to non-mutant strains, but this effect must be the direct responsibility of V284K, as I283 has been observed in atovaquone sensitive parasites. The presence of the L283I mutation by itself does not confer resistance to atovaquone. These data suggest that the early treatment failure in the second patient, could be more related to a suboptimal therapy than to a drug-resistant genotype. Atovaquone/proguanil is used in the treatment of uncomplicated multi- drug-resistant P. falciparum malaria, but we do not have an answer to this question: could the HIV-infected patients have also a higher rate of atovaquone/proguanil treatment failure? No data about this point have been reported in HIV-infected patients. This question must be approached with caution. An explanation could be a delayed parasite clearance due to a slowness of action by atovaquone/proguanil, but the parasitaemia increased from 0.5% to 8% on day 3. On the other hand, treatment failure could be attributed to poor bioavailability of the atovaquone, proguanil or its active metabolite, cycloguanil. The biotransformation of proguanil could have been reduced. A possible interaction between atovaquone/proguanil and IP-based regimens could be presented. However, it was not possible to measure drug concentrations at that time.
In routine clinical practice, the PCR is performed on admission samples to confirm the results obtained by microscopy, as shown in this cases, and to avoid the limitations of the microscopy and RDT: misdiagnosis of mixed-species infections and low parasitaemia. The microscopic examination of Giemsa-stained thin and thick blood films remains the "gold standard" for the diagnosis of malaria and detects parasites at a density of 50 parasites/μl by an experienced microscopist. The RDT, using a protein rich in histidine (HRP-2) and aldolase or lactate dehydrogenase antigens, detects parasites quickly and cheaply, but it cannot provide data regarding drug resistance genotypes. RDT is accepted as an excellent tool in the diagnosis of P. falciparum malaria. However, it is not useful in the follow-up anti-malarial therapy, because it could positive HRP-2 antigen for three or four weeks after a successful therapy. The PCR-based methods are extremely sensitive with a detection limit of < 10 parasites/μl. Various authors have reported the development of a real-time PCR assay to detect P. falciparum, Plasmodium vivax and Plasmodium ovale in routine clinical diagnosis. The risks of contamination are minimal and the result can be obtained in only 2 h. In the cases presented, molecular methods were essential for rapid and accurate diagnosis and follow-up.
In conclusion, this are two cases of HIV-infected patients with imported P. falciparum malaria, high parasitaemia, both severe clinical episodes with > 350 CD4 cell count/μl, absence of chemoprophylaxis and successful response. Factors such as drug interactions and the possible implication of anti-malarial therapy bioavailability are all especially interesting in HIV-malaria co-infections.
