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An impossible journey? The development of Plasmodium falciparum NF54 in Culex quinquefasciatus.

Knöckel J, Molina-Cruz A, Fischer E, Muratova O, Haile A, Barillas-Mury C, Miller LH - PLoS ONE (2013)

Bottom Line: Our results reveal that ookinetes develop in the midgut lumen of C. quinquefasciatus in slightly lower numbers than in Anopheles gambiae G3.Eight days after the mosquito's blood meal, no oocysts can be found in C. quinquefasciatus.Our results suggest that the mosquito immune system could be involved in parasite killing early in development after ookinetes have crossed the midgut epithelium and come in contact with the mosquito hemolymph.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America. julia.knoeckel@gmail.com

ABSTRACT
Although Anopheles mosquitoes are the vectors for human Plasmodium spp., there are also other mosquito species-among them culicines (Culex spp., Aedes spp.)-present in malaria-endemic areas. Culicine mosquitoes transmit arboviruses and filarial worms to humans and are vectors for avian Plasmodium spp., but have never been observed to transmit human Plasmodium spp. When ingested by a culicine mosquito, parasites could either face an environment that does not allow development due to biologic incompatibility or be actively killed by the mosquito's immune system. In the latter case, the molecular mechanism of killing must be sufficiently powerful that Plasmodium is not able to overcome it. To investigate how human malaria parasites develop in culicine mosquitoes, we infected Culex quinquefasciatus with Plasmodium falciparum NF54 and monitored development of parasites in the blood bolus and midgut epithelium at different time points. Our results reveal that ookinetes develop in the midgut lumen of C. quinquefasciatus in slightly lower numbers than in Anopheles gambiae G3. After 30 hours, parasites have invaded the midgut and can be observed on the basal side of the midgut epithelium by confocal and transmission electron microscopy. Very few of the parasites in C. quinquefasciatus are alive, most of them are lysed. Eight days after the mosquito's blood meal, no oocysts can be found in C. quinquefasciatus. Our results suggest that the mosquito immune system could be involved in parasite killing early in development after ookinetes have crossed the midgut epithelium and come in contact with the mosquito hemolymph.

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Transmission electron microscopy of infected midguts 24 hours post feed on Plasmodium falciparum NF54-infected blood.Shown are overviews including the entire midgut epithelial layer (left) and magnifications of the parasite (right). (A) Parasite in the midgut epithelium of Anopheles gambiae G3, which is located on the basal side of the midgut epithelium underneath the basal lamina. (B) P. falciparum NF54 in the midgut of Culex quinquefasciatus. Parasites are located on the basal side of the midgut epithelium (overview left panel) outside the midgut cells. Parasite 1 (top) is located underneath the basal lamina outside the midgut cell, as it is surrounded by two membranes, one belonging to a midgut cell (arrow, M) and one of parasite origin (arrow, P) (see insets in right panel). The organelles inside the parasite are less pronounced than in An. gambiae (A), indicating lysis of the parasite (right panel). Parasite 2 (bottom) is located between two adjacent midgut cells toward the basal side of the epithelium. Two membranes can be seen (right panel inset, arrows M, P), showing an extracellular location of the parasite. Note here that one midgut epithelial cell (asterisk) is not connected to the basal lamina and lacks microvilli and most organelles, indicating apoptosis. MV: microvilli; BL: Basal lamina.
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pone-0063387-g004: Transmission electron microscopy of infected midguts 24 hours post feed on Plasmodium falciparum NF54-infected blood.Shown are overviews including the entire midgut epithelial layer (left) and magnifications of the parasite (right). (A) Parasite in the midgut epithelium of Anopheles gambiae G3, which is located on the basal side of the midgut epithelium underneath the basal lamina. (B) P. falciparum NF54 in the midgut of Culex quinquefasciatus. Parasites are located on the basal side of the midgut epithelium (overview left panel) outside the midgut cells. Parasite 1 (top) is located underneath the basal lamina outside the midgut cell, as it is surrounded by two membranes, one belonging to a midgut cell (arrow, M) and one of parasite origin (arrow, P) (see insets in right panel). The organelles inside the parasite are less pronounced than in An. gambiae (A), indicating lysis of the parasite (right panel). Parasite 2 (bottom) is located between two adjacent midgut cells toward the basal side of the epithelium. Two membranes can be seen (right panel inset, arrows M, P), showing an extracellular location of the parasite. Note here that one midgut epithelial cell (asterisk) is not connected to the basal lamina and lacks microvilli and most organelles, indicating apoptosis. MV: microvilli; BL: Basal lamina.

Mentions: Transmission electron microscopy (TEM) of parasites in the midgut epithelium was performed 24 hours after the mosquito blood meal to visualize more precisely the subcellular localization of the parasites in the midgut epithelium. Figure 4A shows a parasite in the midgut epithelium of An. gambiae. The parasite is located in the space between the basal membrane of the midgut epithelial cells and the basal lamina (Figure 4A, inset, BL), which seems to be detached from the cells. The parasite crossed the midgut cells and reached the basal side, the place where parasites develop into oocysts.


An impossible journey? The development of Plasmodium falciparum NF54 in Culex quinquefasciatus.

Knöckel J, Molina-Cruz A, Fischer E, Muratova O, Haile A, Barillas-Mury C, Miller LH - PLoS ONE (2013)

Transmission electron microscopy of infected midguts 24 hours post feed on Plasmodium falciparum NF54-infected blood.Shown are overviews including the entire midgut epithelial layer (left) and magnifications of the parasite (right). (A) Parasite in the midgut epithelium of Anopheles gambiae G3, which is located on the basal side of the midgut epithelium underneath the basal lamina. (B) P. falciparum NF54 in the midgut of Culex quinquefasciatus. Parasites are located on the basal side of the midgut epithelium (overview left panel) outside the midgut cells. Parasite 1 (top) is located underneath the basal lamina outside the midgut cell, as it is surrounded by two membranes, one belonging to a midgut cell (arrow, M) and one of parasite origin (arrow, P) (see insets in right panel). The organelles inside the parasite are less pronounced than in An. gambiae (A), indicating lysis of the parasite (right panel). Parasite 2 (bottom) is located between two adjacent midgut cells toward the basal side of the epithelium. Two membranes can be seen (right panel inset, arrows M, P), showing an extracellular location of the parasite. Note here that one midgut epithelial cell (asterisk) is not connected to the basal lamina and lacks microvilli and most organelles, indicating apoptosis. MV: microvilli; BL: Basal lamina.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3643899&req=5

pone-0063387-g004: Transmission electron microscopy of infected midguts 24 hours post feed on Plasmodium falciparum NF54-infected blood.Shown are overviews including the entire midgut epithelial layer (left) and magnifications of the parasite (right). (A) Parasite in the midgut epithelium of Anopheles gambiae G3, which is located on the basal side of the midgut epithelium underneath the basal lamina. (B) P. falciparum NF54 in the midgut of Culex quinquefasciatus. Parasites are located on the basal side of the midgut epithelium (overview left panel) outside the midgut cells. Parasite 1 (top) is located underneath the basal lamina outside the midgut cell, as it is surrounded by two membranes, one belonging to a midgut cell (arrow, M) and one of parasite origin (arrow, P) (see insets in right panel). The organelles inside the parasite are less pronounced than in An. gambiae (A), indicating lysis of the parasite (right panel). Parasite 2 (bottom) is located between two adjacent midgut cells toward the basal side of the epithelium. Two membranes can be seen (right panel inset, arrows M, P), showing an extracellular location of the parasite. Note here that one midgut epithelial cell (asterisk) is not connected to the basal lamina and lacks microvilli and most organelles, indicating apoptosis. MV: microvilli; BL: Basal lamina.
Mentions: Transmission electron microscopy (TEM) of parasites in the midgut epithelium was performed 24 hours after the mosquito blood meal to visualize more precisely the subcellular localization of the parasites in the midgut epithelium. Figure 4A shows a parasite in the midgut epithelium of An. gambiae. The parasite is located in the space between the basal membrane of the midgut epithelial cells and the basal lamina (Figure 4A, inset, BL), which seems to be detached from the cells. The parasite crossed the midgut cells and reached the basal side, the place where parasites develop into oocysts.

Bottom Line: Our results reveal that ookinetes develop in the midgut lumen of C. quinquefasciatus in slightly lower numbers than in Anopheles gambiae G3.Eight days after the mosquito's blood meal, no oocysts can be found in C. quinquefasciatus.Our results suggest that the mosquito immune system could be involved in parasite killing early in development after ookinetes have crossed the midgut epithelium and come in contact with the mosquito hemolymph.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America. julia.knoeckel@gmail.com

ABSTRACT
Although Anopheles mosquitoes are the vectors for human Plasmodium spp., there are also other mosquito species-among them culicines (Culex spp., Aedes spp.)-present in malaria-endemic areas. Culicine mosquitoes transmit arboviruses and filarial worms to humans and are vectors for avian Plasmodium spp., but have never been observed to transmit human Plasmodium spp. When ingested by a culicine mosquito, parasites could either face an environment that does not allow development due to biologic incompatibility or be actively killed by the mosquito's immune system. In the latter case, the molecular mechanism of killing must be sufficiently powerful that Plasmodium is not able to overcome it. To investigate how human malaria parasites develop in culicine mosquitoes, we infected Culex quinquefasciatus with Plasmodium falciparum NF54 and monitored development of parasites in the blood bolus and midgut epithelium at different time points. Our results reveal that ookinetes develop in the midgut lumen of C. quinquefasciatus in slightly lower numbers than in Anopheles gambiae G3. After 30 hours, parasites have invaded the midgut and can be observed on the basal side of the midgut epithelium by confocal and transmission electron microscopy. Very few of the parasites in C. quinquefasciatus are alive, most of them are lysed. Eight days after the mosquito's blood meal, no oocysts can be found in C. quinquefasciatus. Our results suggest that the mosquito immune system could be involved in parasite killing early in development after ookinetes have crossed the midgut epithelium and come in contact with the mosquito hemolymph.

Show MeSH
Related in: MedlinePlus