Prevalence of dhfr-dhps sextuple mutants and gametocyte-harboring quintuple mutants resistant to sulfadoxine-pyrimethamine among pregnant women in Mozambique

A molecular analysis of 100 *Plasmodium falciparum* isolates from pregnant women in Mozambique revealed that while 7% of parasites carried sextuple mutations conferring sulfadoxine-pyrimethamine resistance, quintuple mutants were significantly associated with increased gametocyte carriage, highlighting the need for ongoing surveillance to guide malaria prevention strategies.

The Gist

The Big Picture: A Broken Shield and a Hidden Enemy

Imagine malaria as a relentless invader trying to break into a fortress (the pregnant woman's body). To protect the fortress, health workers use a specific shield called IPTp-SP (a combination of two drugs, Sulfadoxine and Pyrimethamine). This shield is supposed to be given monthly during pregnancy to stop the invader from causing harm to both the mother and the baby.

However, the invader (the malaria parasite) is smart. It has started wearing camouflage (genetic mutations) that makes the shield less effective. This study went to Mozambique to check how many invaders were wearing this camouflage and, more importantly, if they were still able to spread the infection to others.

The Cast of Characters

1. The Invaders (Parasites): Specifically, Plasmodium falciparum. They are the ones causing malaria.
2. The Camouflage (Mutations): The parasites changed their "uniforms" (genes) to ignore the drugs.
   • The "Quintuple" Camouflage: A five-piece disguise. This is the most common one. It makes the drug only partially effective.
   • The "Sextuple" Camouflage: A six-piece disguise (the five-piece plus one extra). This is the "super-camouflage" that makes the drug almost useless.
3. The Messengers (Gametocytes): These are the special "spores" the parasite creates to jump from a human to a mosquito. If a mosquito bites a person with these spores, the mosquito becomes infected and can spread malaria to the next person.

What the Researchers Found

The scientists looked at 100 pregnant women in Mozambique who had just given birth. They took blood samples to see what kind of parasites were hiding inside.

1. The Camouflage is Everywhere

• 54% of the women had parasites wearing the "Quintuple" camouflage. The drug could still fight them a little, but not very well.
• 7% had the "Sextuple" camouflage. The drug was basically useless against these.
• Only 2% had the "naked" (wild-type) parasites that the drug could easily kill.
• Analogy: Imagine a security guard (the drug) trying to stop a crowd. Most of the crowd (54%) is wearing raincoats that make the guard's water cannon slide off. A few (7%) are wearing full hazmat suits that the water cannon can't penetrate at all.

2. The Hidden Danger: The "Silent" Carriers

• Most of the women (73%) didn't even know they were sick. Their parasite levels were too low to be seen under a regular microscope, but the DNA tests found them.
• The Big Surprise: Among the women who were carrying the "Quintuple" camouflage parasites, 80% were also carrying the "Messengers" (gametocytes).
• Analogy: It's like a spy who is hiding in a building. Even though the security guard (the drug) hasn't kicked them out yet, the spy is already sending out secret messages (gametocytes) to the outside world to call for backup.

3. The Link Between Camouflage and Spreading
The study found a strong link: The more resistant the parasite was (the Quintuple type), the more likely the woman was to be a carrier of the "Messengers."

• Women with the resistant parasites were 7.5 times more likely to have gametocytes than women with non-resistant parasites.
• Analogy: The parasites that are good at dodging the drug seem to be the ones that are also best at packing their bags and getting ready to travel to new hosts.

4. Did the Drug Doses Matter?
The researchers checked if women who took more doses of the drug (3 or more) had different results than those who took fewer.

• Result: It didn't change the outcome much. Whether they took 1 dose or 3, the resistant parasites were still there, and they were still sending out "Messengers."
• Takeaway: Throwing more of the same shield at a smart invader isn't working. The invader has already learned how to dodge it.

Why Should We Care?

This study highlights a dangerous cycle:

1. The Drug Fails: Because of the camouflage, the drug can't clear the infection completely.
2. The Reservoir Grows: The pregnant women become "silent reservoirs." They aren't necessarily feeling sick, but they are full of resistant parasites.
3. Transmission Continues: These women pass the "Messengers" (gametocytes) to mosquitoes.
4. The Cycle Repeats: The mosquitoes bite other people, spreading the super-resistant malaria to the whole community.

The Bottom Line

The "shield" (IPTp-SP) is getting rusty in Mozambique. While it still helps prevent low birth weight (perhaps by reducing inflammation rather than killing the parasite), it is failing to stop the infection itself.

The most worrying finding is that the resistant parasites are the ones most likely to spread. Pregnant women are acting as a hidden factory, producing and releasing drug-resistant malaria into the community.

The Solution? We can't just keep using the same old shield. We need to:

• Keep a close watch (surveillance) on how the parasites are changing.
• Think about new strategies or different drugs to protect mothers and babies.
• Understand that if we don't act, the "super-camouflage" (Sextuple mutants) might become the new normal, making malaria much harder to control.

Technical Summary

1. Problem Statement

Malaria in pregnancy (MiP) remains a critical public health challenge in sub-Saharan Africa, causing significant maternal and perinatal morbidity. The primary preventive strategy is Intermittent Preventive Treatment in pregnancy with Sulfadoxine-Pyrimethamine (IPTp-SP). However, the efficacy of SP is increasingly compromised by the emergence and spread of Plasmodium falciparum strains carrying specific point mutations in the pfdhfr and pfdhps genes.

• The Quintuple Mutant: Combinations of mutations in pfdhfr (N51I, C59R, S108N) and pfdhps (A437G, K540E) confer mid-level resistance, leading to reduced prophylactic efficacy.
• The Sextuple Mutant: The addition of the pfdhps A581G mutation to the quintuple background confers high-level resistance, potentially rendering IPTp-SP ineffective for preventing infection.
• Transmission Risk: SP has limited gametocytocidal activity. There is concern that drug pressure may select for resistant strains that persist asymptomatically and harbor gametocytes (the sexual stage transmissible to mosquitoes), thereby acting as a reservoir for transmission.

The study aims to assess the prevalence of these resistance markers (specifically quintuple and sextuple mutants) and their association with gametocyte carriage among pregnant women in a high-transmission setting in Mozambique.

2. Methodology

Study Design and Population:

• Location: Chókwè district, Gaza province, Southern Mozambique (perennial malaria transmission).
• Population: 100 pregnant women with confirmed P. falciparum infection at the time of delivery (collected between 2014–2015).
• Data Collection: Venous blood samples were collected immediately post-delivery. Placental tissues were also examined histologically.

Laboratory Techniques:

• Diagnosis: Molecular detection of P. falciparum via qPCR targeting the varATS gene (limit of detection: 0.04 parasites/µL).
• Genotyping: PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) was used to detect mutations in pfdhfr (N51I, C59R, S108N, I164L) and pfdhps (S436F, A437G, K540E, A581G, A613S). Mixed infections were defined as mutant.
• Multiplicity of Infection (MOI): Determined via PCR and capillary electrophoresis of pfmsp1 and pfmsp2 loci.
• Gametocyte Detection:
  • RT-qPCR: Targeting female gametocyte-specific Pfs25 transcripts (limit of detection: 0.1 gametocytes/µL).
  • Light Microscopy (LM): Standard peripheral blood smear examination.
• Statistical Analysis: Univariate and multivariate logistic regression (for carriage) and linear regression (for density) were used to assess associations between mutant haplotypes, IPTp-SP uptake, and gametocyte carriage/density.

3. Key Contributions

• First Report of Sextuple Mutants in Gaza Province: The study identifies the presence of the pfdhps A581G mutation (sextuple mutant) in a region where it was previously undetected or rare, suggesting evolving selection pressure.
• Link Between Resistance and Transmission: It provides evidence that quintuple mutant infections are significantly associated with higher odds of gametocyte carriage, highlighting a potential mechanism for the spread of drug-resistant malaria.
• Submicroscopic Reservoir: The study quantifies the burden of submicroscopic infections and gametocyte carriage at delivery, emphasizing the role of asymptomatic pregnant women as a reservoir for transmission.

4. Key Results

Resistance Prevalence:

• Mutations: 92% of isolates carried pfdhfr mutations; 91% carried pfdhps mutations.
• Haplotypes:
  • Quintuple Mutant (IRN-GE): 54% (54/100) of isolates.
  • Sextuple Mutant (IRN-GEG): 7% (7/100) of isolates.
  • Wild-type: Only 2% (2/100).
  • Additional Mutations: pfdhps A581G was found in 14% of samples; pfdhfr I164L was found in 2% (a novel finding for this region).

Risk Factors for Resistance:

• Women receiving ≥3 doses of IPTp-SP had significantly higher odds of carrying quintuple mutants (AOR = 3.7, p = 0.004).
• No significant association was found between IPTp-SP dose and sextuple mutant carriage (likely due to low sample size for sextuple mutants).
• No significant association was found between mutant carriage and adverse pregnancy outcomes (Low Birth Weight, Placental Malaria, Pre-term delivery).

Gametocyte Carriage:

• Prevalence: 34% (34/100) of women were gametocyte carriers by RT-qPCR, whereas only 2% were positive by Light Microscopy.
• Association with Mutants: Gametocyte carriage was strongly associated with quintuple mutant infections (AOR = 7.5, p = 0.001).
  • 80% of all gametocyte carriers harbored quintuple mutants.
  • 50% of quintuple mutant infections carried gametocytes.
• Densities: Median gametocyte densities were low and did not differ significantly between haplotype groups or IPTp-SP dose groups.

5. Significance and Implications

• Evolving Resistance Landscape: The detection of the sextuple mutant (A581G) in Gaza province signals a critical shift in the resistance profile of P. falciparum in Mozambique. While quintuple mutants are now dominant, the emergence of sextuple mutants threatens the complete failure of IPTp-SP for infection prevention.
• Transmission Dynamics: The strong link between quintuple mutants and gametocyte carriage suggests that drug-resistant parasites are not only surviving treatment but are also more likely to be transmitted to mosquitoes. This creates a feedback loop where resistant strains are amplified in the community.
• Policy Recommendations:
  • Surveillance: Continuous molecular surveillance of pfdhps A581G and pfdhfr I164L is urgent in Mozambique.
  • Alternative Strategies: The findings support the need to evaluate alternative IPTp regimens (e.g., using different drugs like Azithromycin or Doxycycline, though safety in pregnancy must be considered) or increased frequency of SP dosing in areas with high sextuple mutant prevalence.
  • Reservoir Management: Interventions must address the asymptomatic, submicroscopic reservoir in pregnant women to prevent the spread of resistant strains.

Conclusion:
The study confirms that SP resistance is widespread in pregnant women in Southern Mozambique, with a significant proportion carrying high-risk quintuple mutants that are strongly linked to gametocyte carriage. The emergence of the sextuple mutant underscores the urgency for monitoring and potentially transitioning to alternative malaria prevention strategies to protect maternal and fetal health and curb the transmission of resistant malaria.