You are currently browsing the monthly archive for August 2007.
South East Asian Quinine Artesunate Malaria Trial (Download article here.)
In my attempt to familiarize myself with the clinical management of malaria, I reviewed the SEAQUAMAT Study headed by Nick White’s group in Thailand. I’m reviewing the major points here, primarily so I can go back to it when needed:
Design: Multi-center, open-label, randomized controlled trial in Bangladesh, Myanmar, India, and Indonesia.
Inclusion criteria: Age > 2; Positive bloodstick for PfHRP2 Antigen; and severe malaria defined as:
1) malaria positive on blood smear
AND ONE OF THE FOLLOWING:
1) GCS less than 11/15 or Blantyre Coma Scale less than or equal to 3/5
2) Parasitemia greater than 10%
3) Glucose less than 2.2 mmol/L
4) HCT less than 20% and parasite load greater than 100,000/ul
5) Jaundice and parasite load greater than 100,000/ul
6) bicarb less than 17 mmol/L
7) BUN greater than 15 mmol/L (mnemonic 15+17=32)
9) evidence of shock determined by clinician (low BP, cool extremities)
Note that the study was done with intention to treat analysis. Initial treatment was made on clinical grounds. Per protocol analysis was done after severe malaria was confirmed.
Treatment arms: artesunate IV 2.4 mg/kg bolus at 0, 12, 24 h and a once daily bolus thereafter until PO meds can be taken
quinine IV, 20 mg/kg infusion loading over the first 4 hours, then 10 mg/kg infusion over 2-8 hours three
times daily
Adverse effects: artesunate: well-tolerated
quinine: narrow therapeutic range, hyperinsulinemic hypoglycemia, can cause hypotension if infused
rapidly, IM injections are painful, cause sterile abscesses, and predisposes to tetanus.
Primary outcome: mortality
Secondary outcome: neurological sequelae, combined death and neurological sequelae, recovery times from neurological
sequelae and development of severe complications
Results: Artesunate (15% mortality, n=730)
Quinine (22% mortality, n=731) P = 0.0002
Overall mortality: 19%
Overall mortality of those found to have severe malaria: 24%
Mortality in the 202 chidren < 15 yo analysed: Artesunate 5% vs. Quinine 11%, P = 0.15
Conclusion: Artesunate is superior and safer for severe malaria in this Southeast Asian adults.
Reference: Lancet. 2005 Aug 27-Sep 2;366(9487):717-25.
Here is a brief article highlighting the recent paradigm shift in malaria vaccine development.
Briefly:
Use a combination of transgenic parasites and mice to humanize a rodent infection. Meaning, make transgenic Plasmodium berghei parasites capable of expressing extracellular antigens from human Plasmodia species and use them to infect mice containing human Fc receptors and then passively transfer human antibodies raised against PfMSP-1. McIntosh et al. recently pioneered this technique (McIntosh RS et al. PLoS Pathog. 2007;3:e72)
Figure out which strains are clinically important to a region and focus on developing a vaccine that contain multiple strains. Thus, a P. falciparum vaccine would include FVO, 3D7, FUP, etc. For P. vivax, if could be the Sal-I, Belem, and Thai strains.
An effective malaria vaccine would not only have to account for multiple strains, but also multiple antigens that are expressed at the various stages of infection. On top of that, you’re likely going to have to cover P. vivax and P. falciparum.
Going through some of the antigens in each stage:
Pre-erythrocytic: CS, LSA1, TRAP
Erythrocytic: MSP1, MSP2, MSP3, RBLs, EBAs, GLURP,
Gametocyte: Pfs25, Pfs28
and you can see that a recombinant subunit or DNA vaccine must include a lot to cover it all–might as well create a non-virulent, artificial parasite from scratch. I’m being facetious but it’s not so far fetched when you think of Hoffman’s plan to produce GMP attenuated sporozoites on a massive scale.
Here’s the roadmap.
We have all known that vector control and reducing mosquito bites theoretically prevent malaria, and one way to achieve this is to put a physical barrier between the skeeters and babies by way of a net impregnated with a pesticide (long-lasting insecticide treated nets to use scientific parlance). The debate has been on whether or not this was practical or doable. Some excuses: Oh, we can give them nets, but people won’t use them, I’ve seen it myself. The nets make people hot at night–they’re so uncomfortable. If you give them away, the people won’t value them and will end up using them for other purposes. The parents will end up using them for themselves, leaving the kids on the outside. Let’s sell them really cheap–like dollar store prices–this will encourage distribution and the consumers will value them much more.
Well, the WHO just released some data that dispel any myths about freebie nets not being effective:
“In Kenya, from 2004 to 2006, a near ten-fold increase in the number of young children sleeping under insecticide-treated mosquito nets was observed in targeted districts, resulting in 44% fewer deaths than among children not protected by nets, according to preliminary data from the Government of Kenya. This is the first demonstration of the impact of large-scale distribution of insecticide treated mosquito nets under programme conditions, rather than in research settings, where, in different parts of Africa, reduction observed in overall mortality has ranged from 14 % up to 60 %.
“These achievements can be attributed to three principal ingredients, which all need to be present for malaria control efforts to succeed – high political commitment from the government, strong technical assistance from WHO, and adequate funding from bilateral and multilateral donors.”
The success has been a result of a well thought out strategy for malaria control developed by the Kenyan Government and implemented with generous aid from the Global Fund to Fight AIDS, Tuberculous, and Malaria (US $17M) and the United Kingdome Department for International Development (GBP $6M).
You can read the full press release here.
We can expect a landmark paper in one of the leading clinical journals as soon as all the data is analyzed. I suspect it may be Lancet, but JAMA did surprise me with a special malaria issue in May. JAMA also published this insecticide treated net study done in Kenya by Lindblade et al. that provided good evidence that protecting young kids with bednets did not increase their mortality in later years (presumably from not acquiring necessary immunity during infancy and toddlerdom).
Now that I’m spending every third night in the MICU, I thought it might be appropriate to review a paper with some physiology. I’ve learned quite a bit about lactic acidosis, as we had one patient with severe lactic acidosis (22 mmol/L) presumably due to hepatic shock.
This paper by Sasi and colleagues at KEMRI examines the determinants of acidosis in Kenyan children with severe malaria, defined as malaria with a base deficit >18 mmol/L; refractory base deficit; coma after correction for hypoglycemia; and hemoglobin less than 5 and compared them to relatively well controls who were returning for 4 week follow-up for non-severe malaria. They measured the pH, blood glucose, MCV, MCHC, base deficit, lactate, beta-hydroxybutyrate, salicylate, BPG, temperature and pCO2 as well as the patient’s age and fever duration.The P50 was calculated from the pH, MCHC, base deficit, BPG, and temperature.
Multiple stepwise logistic regression revealed lactate and BPG as the only independent determinants of acidosis. As expected (given the inclusion criteria), cases were more acidotic than controls (mean venous pH 7.26 vs. 7.42) as reflected by higher lactate, beta-OH-butyrate, base deficit and P50. Cases were also more anemic than the controls, although the controls had some baseline anemia (mean Hb of 9.86). Salicylates were not detected in any child, excluding salicylate as the cause of anion gap metabolic acidosis. Interestingly, mean blood glucose were the similar between cases and controls, but it must be noted that those with severe coma due to hypoglycemia were corrected before samples for the study were drawn. Mean BPG was surprisingly similar in both groups—BPG is usually elevated in low oxygen states (such as hypoperfusion) to promote dissociation of oxygen—“possibly because of opposing effects of acidosis and anemia on its synthesis.” This doesn’t make too much sense to me since through my readings, I’ve learned that acidosis generally decreases BPG levels via inhibition of glycolysis in erythrocytes, thus preventing its overproduction since BPG itself causes acidosis. (Protons also inhibit 2,3 BPG synthase, by the way.) Intuitively, anemia would also decrease BPG by reducing the only cells that produce this metabolite. It is more likely that the authors meant hypoxia as counterbalancing the negative effects of acidosis and anemia on BPG, resulting in levels no different than controls. The authors suggest that the rise in lactate may be due to inhibition of liver gluconeogenesis from lactate by acidosis. (Note, if this were true, would they not see lower blood glucose in the cases?) Although this might be true, the lactate itself is probably the primary cause of the acidosis. It would be nice if the authors published the mean anion gaps of the cases to give a better idea of the contribution of lactic acid to the acidosis (there may be an additional non-gap acidosis) as well as the rest of the BMPs and the blood pressures.
Malaria causes a septic-like picture similar to bacteremia via release of inflammatory TNFa, IL-1, and IFNg, cytokines that are known to be associated with more severe malaria. In addition to sepsis, it is possible that the cases were hypoperfusing (probably pre-renal etiology due to insensible losses plus vomiting) leading to increased lactate production. The authors speculate that there is some other source of lactate in addition to plain old circulatory insufficiency but give no evidence. Again, it also seems that the authors believe there is an acidosis independent of that caused by lactic acid. They suggest that in addition to anti-malarials and a supportive therapy (fluids, pRBCs, and glucose) that cautious bicarbonate may also work. It may work, but only if salicylate (or another organic anion that is better excreted by alkanizing the urine) is the cause of acidosis or the acidosis is severe (pH < 7). As I have learned, giving a bicarb infusion to a patient with lactic acidosis may correct the pH in the short term, but 24 hours later, you will be dealing with hypervolemia, rebound metabolic alkalosis (the excess lactic acid is converted to bicarbonate—this on top of the bicarb that you gave), hypernatremia, and compensatory respiratory acidosis with hypercarbia (decreased respiratory rate to correct the alkalosis). I personally would not try this on a child except in cases of severe acidosis. What I would like find is something of a limited early, goal-directed therapy (like the Rivers study) in cases of severe malaria applied in a resource-poor setting. Keeping a defined MAP goal with pressors and obtaining ScvO2 may not be possible, but providing IVF to achieve BP goals, keeping up the UOP, correction of hypoglycemia , and transfusing pRBCs at appropriate thresholds (the authors transfused pRBCs at Hb <5 mg/dL in this study) would probably reduce the lactic acidosis and result in reduced mortality. This study has likely been done, just need to find it…
Reference: Am. J. Trop. Med. Hyg., 77(2), 2007, pp. 256-260
tmt
I am starting to look at the recent work of the malaria researchers at Johns Hopkins in anticipation of the inevitable return to basic science. A recent paper by Marcelo Jacobs-Lorena’s group at Bloomberg SPH caught my attention. They are investigating non-traditional transmission blocking vaccines (TBVs). Previous TBVs have targeted proteins on the parasite’s sexual stages (gametocytes) like Pfs25 and Pfs28, but this group focuses on the mosquito mid-gut proteins that are involved in parasite attachment and development. Dinglasan and colleagues knew that jacalin inhibited parasite binding to the mosquito gut epithelium and used jacalin affinity chromatography to select a candidate glycoprotein from a Anopheles gambiae midgut microvilli suspension. MASCOT analysis revealed A. gambiae aminopeptidase N (AgAPN1) as the predominant protein from the eluate. Based on the protein structure, the authors pursued this glycoprotein and were able to provide evidence that the protein is expressed in the midgut and is localized to the microvilli of midgut epithelial cells. They were able to detect a 125 kDa similar in size to AgAPN1 by immunoblot in Anopheles stephensi, Anopheles arabiensis, and Anopheles freeborni as well, suggesting that AgAPN1 is conserved among Anopheles spp. Polyclonal Abs raised against AgAPN1 were able to block development of P. berghei and P. falciparum in two different vectors, A. gambiae and A. stephensi. The transmission-blocking effect was incomplete at 67%-87% however, unless the 12 aa peptide SM1 (a peptide that has been previously shown to block P. berghei development in A. stephensi at a 60-70% clip) was added, resulting in a robust 95% inhibition. The authors concluded that this was possibly an additive effect, with AgAPN1 and the SM1 target being distinct epitopes but having overlapping transmission-blocking activities. Their data suggests that murine and human malaria parasite species differ in midgut adhesion strategies as evidenced by the failure of SM1 to block P. falciparum. The authors also mention some unpublished findings that suggest P. berghei ookinetes can also use AgAPN1 independent pathways—the implication being that future TBV development must target multiple antigens in order to achieve complete efficacy. Boy does this sound familiar…
Reference: PNAS 2007 Aug 2
tmt
