Category Archives: Plasmodium/Parasite

What to Observe on October 12th? Malaria’s Arrival in the Americas

Controversy exists about what historical event should be observed in the USA on 12th October. Ernest Faust explained many years ago that, “there is neither direct nor indirect evidence that the malaria parasites existed on this continent prior to the advent of the European conquerors,” while at the same time in the 16th through 18th Centuries, malaria was common in England, Spain, France, Portugal and other European nations that arrived in the “New World.” Initially, with the first voyage of Columbus the European explorers and settlers brought the disease, primarily Plasmodium vivax, while the slave trade brought P. falciparum.

National Geographic in its May 2007 issue provided the story “Jamestown, The Real Story.” This article reported that, “Colonists carried the plasmodium parasite to Virginia in their blood. Mosquitoes along the Chesapeake were ‘infected’ by the settlers and spread the parasite to other humans.” Thus malaria became one of many imported diseases that decimated the indigenous population. The spread of P. vivax in Jamestown was not surprising since the settlement was “located on marshy ground where mosquitoes flourished during the summer.”

Recent research has shown that the “Analysis of genetic material extracted showed that the American P. falciparum parasite is a close cousin of its African counterpart.” This research has documented two genetic groups in Latin America, related to two distinct slave routes run by the Spanish empire in the North, West Indies, Mexico and Colombia and the Portuguese empire to Brazil. Indigenous and remote rural populations of Bolivia, Colombia, Ecuador, Peru, Venezuela and Brazil remain at risk today.

In the South American continent the  native American population might have brought Melanesian strains of P. vivax before the Europeans arrived, but colonizers brought new strains from both Europe and Africa, as well as P. falciparum. Clearly, human migration has played an important role in malaria parasite dissemination through the Americas.

But back to the North American Continent where the USA is observing the historical implications of 12th October, Mark Blackmore reminds us that, “Anthropological and archeological data provide no indication of mosquito-borne diseases among the indigenous people of North America prior to contact with Europeans and Africans beginning in the fifteenth century” (Wing Beats Volume 25 Winter 2015). The spread of malaria by European colonizers is certainly not something to celebrate today.

Tropical Health Update 2019-07-28: Ebola and Malaria Crises

This posting focuses on Malaria and Ebola, both of which have been the recent focus of some disturbing news. The malaria community has been disturbed by the clear documentation of resistance to drugs in Southeast Asia. Those working to contain Ebola in the northeast of the Democratic Republic of Congo saw a change in political leadership even in light of continued violence and potential cross-border spread.

Malaria Drug Resistance

Several sources reported on studies in the Lancet Infectious Diseases concerning the spread of Multidrug-Resistant Malaria in Southeast Asia. Reuters explained that by sing genomic surveillance, researchers concurred that “strains of malaria resistant to two key anti-malarial medicines are becoming more dominant” and “spread aggressively, replacing local malaria parasites,” becoming the dominant strains in Vietnam, Laos and northeastern Thailand.”

The focus was on “the first-line treatment for malaria in many parts of Asia in the last decade has been a combination of dihydroartemisinin and piperaquine, also known as DHA-PPQ,” and resistance had begun to spread in Cambodia between 2007 and 2013. Authors of the study noted that while, “”Other drugs may be effective at the moment, but the situation is extremely fragile, and this study highlights that urgent action is needed.” They further warned of an 9impending Global Health Emergency.

NPR notes that “Malaria drugs are failing at an “alarming” rate in Southeast Asia” and provided some historical context about malaria drug resistance arising in this region since the middle of the 20th century. “Somehow antimalarial drug resistance always starts in that part of the world,” says Arjen Dondorp, who leads malaria research at the Mahidol Oxford Tropical Medicine Research Unit in Bangkok and who was a lead author of the report about the randomized trial. Ironically, “one reason could have something to do with the relatively low levels of malaria there. When resistant parasites emerge, they are not competing against a dominant nonresistant strain of malaria and are possibly able to spread easier.

When we are talking about monitoring resistance in low resource and logistically and politically challenging areas, we need to think of appropriate diagnostic tools at the molecular level. Researchers in Guinea-Bissau conducted a proof of concept study and used malaria rapid diagnostic tests applied for parallel sequencing for surveillance of molecular markers. While they noted that, “Factors such as RDT storage prior to DNA extraction and parasitaemia of the infection are likely to have an effect on whether or not parasite DNA can be successfully analysed … obtaining the necessary data from used RDTs, despite suboptimal output, becomes a feasible, affordable and hence a justifiable method.”

A Look at Insecticide Treated Nets

On a positive note, Voice of America provides more details on the insecticide treated net (ITN) monitoring tool developed called “SmartNet” by Dr Krezanoski in collaboration with the Consortium for Affordable Medical Technologies in Uganda. The net uses strips of conductive fabric to detect when it’s in use. Dr. Krezanoski was happy to find that people given the net used it no differently that if they were not being observed. The test nets made it clear who what using and not using this valuable health investment and when it was in use. Such fine tuning will be deployed to design interventions to educate net users based on their real-life use patterns.

Another important net issue is local beliefs that may influence use. We can find out when people use nets, but we also need to determine why. In Tanzania, researchers found that people think mosquitoes that bite in the early evening when people are outside relaxing are harmless. As one community member said, “I only fear those that bite after midnight. We’ve always been told that malaria is spread by mosquitoes that bite after midnight.”

Even if people do use their ITNs correctly, we still need to worry about insecticide resistance. A study in Afghanistan reported that, “Resistance to different groups of insecticides in the field populations of An. stephensi from Kunar, Laghman and Nangarhar Provinces of Afghanistan is caused by a range of metabolic and site insensitivity mechanisms.” The authors conclude that vector control programs need to be better prepared to implement insecticide resistance management strategies.

Ebola Crisis Becomes (More) Political

Headlines such as “Congo health minister resigns over response to Ebola crisis” confronted the global health community this week. this happened after the DRC’s relatively new president took control of the response. The President set up a new government office to oversee the response to an outbreak outside of the Ministry of Health which was managing the current outbreak and the previous ones. The new board was set up without the knowledge of the Minister who was traveling to the effected provinces at the time.

The former Minister, Dr Oly Ilunga stated on Twitter that, “Suite à la décision de la @Presidence_RDC.  de gérer à son niveau l’épidémie d’#Ebola, j’ai remis ma démission en tant que Ministre de la Santé ce lundi. Ce fut un honneur de pouvoir mettre mon expertise au service de notre Nation pendant ces 2 années importantes de notre Histoire. (Following the decision of the @Presidence_RDC to manage the # Ebola outbreak, I resigned as Minister of Health on Monday. It was an honor to be able to put my expertise at the service of our Nation during these two important years of our History.)

The former Minister also warned that the “Multisectoral Ebola Response Committee would interfere with the ongoing activities of national and international health workers on the ground in North Kivu and Ituri provinces.” Part of the issue may likely have been “pressure to approve a new vaccine in addition to one that has already been used to protect more than 171,000 people.” People had warned about the potential confusion to the public as well as ethical issues if a second vaccine was used, especially one that did not have the strong accumulated evidence from both the current outbreak as well as the previous one in West Africa.

One might have thought that this would be a time when stability was needed since “The WHO earlier this month declared the outbreak a Public Health Emergency of International Concern, a rare step meant to highlight the urgency of the moment that has been used only four times before.” In addition, “the World Bank said it would release $300 million from a special fund set aside for crises like viral outbreaks to help cover the cost of the response.”

Unfortunately one of the msain impediments to successful Ebola control, violence in the region, continues. CIDRAP stated that. “the Allied Democratic Forces (ADF), a rebel group, attacked two villages near Beni, killing 12 people who live in the heart of the Democratic Republic of the Congo’s (DRC’s) ongoing Ebola outbreak. The terrorists killed nine in Eringeti and three in Oicha, according to Reuters. ADF has not publicly pledged allegiance to the Islamic state (ISIL), but that hasn’t stopped ISIL from claiming responsibility for the attacks.” It will take more than a change of structure in Kinshasa to deal with the realities on the ground.

CIDRAP also observed that since the resignation of the Health Minister, “DRC officials have provided no update on the outbreak, including statistics on the number of deaths, health workers infected, or suspected cases.” The last was seen on 21 July 2019.

ReliefWeb reports that, “Adding to the peril, the Ebola-affected provinces share borders with Rwanda and Uganda, with frequent cross-border movement for personal travel and trade, increasing the chance that the virus could spread beyond the DRC. There have already been isolated cases of Ebola reported outside of the outbreak zone.”

These are troubling times when parasites and mosquitoes are becoming more resistant to our interventions and when governments and communities are resistant to a clear and stable path to disease containment and control.

The Weekly Tropical Health News 2019-07-06: Eliminating Malaria in Low Transmission Settings

This week started with articles that drew attention to the challenges of malaria in low transmission areas and with low density infections. Malaria Journal has provided several insightful articles toward this end.

Being an island has certainly helped Zanzibar make progress toward malaria elimination as witness the fact that malaria prevalence has remained below 1% for the past decade. Not only does Zanzibar still face threats of infection from the mainland, it may also experience an upsurge locally if residual transmission and the role of human behavior and community actions are not well understood. April Monroe et al. conducted in-depth interviews with community members and local leaders across six sites on Unguja, Zanzibar as well as semi-structured community observations of night-time activities and special events to learn more.

While there was high reported ITN use, there were also times when people were exposed t mosquitoes while being outdoors during biting times. This could be around the house, or at special night events like such as weddings, funerals, and religious ceremonies. Men spent more time outdoors than women. Clearly appropriate interventions and needed and should be promoted in culturally appropriate ways in order to further reduce and eventually eliminate transmission.

Angela Early and colleagues presented findings on a diagnostic process of deep sequencing for understanding the dynamics and complexity of Plasmodium infections, but stress that knowing the lower limit of detection is challenging. They present “a new amplicon analysis tool, the Parallel Amplicon Sequencing Error Correction (PASEC) pipeline, is used to evaluate the performance of amplicon sequencing on low-density Plasmodium DNA samples.”

The authors learned that, “four state-of-the-art tools resolved known haplotype mixtures with similar sensitivity and precision.” They also cautioned that, “Samples with very low parasitemia and very low read count have higher false positive rates and call for read count thresholds that are higher than current default recommendations.” Better understanding of the genetic mix of plasmodium infections as countries move toward low transmission and elimination is crucial for selecting appropriate interventions and evaluating their outcomes.

Hannah Edwards and co-researchers examined conditions for malaria transmission along the Thailand-Myanmar border in areas approaching malaria elimination. While prevalence may be less than 1%, residual transmission still occurs. Transmission occurs not only around residences but in the forests where people work. The researchers therefore looked at the behavior of both humans and insects. Overall, they found that, “Community members frequently stayed overnight at subsistence farm huts or in the forest. Entomological collections showed higher biting rates of primary vectors in forested farm hut sites and in a more forested village setting compared to a village with clustered housing and better infrastructure.”

While mosquitoes preferred to bite inside huts, their threat was magnified by those who did not use long lasting insecticide-treated nets (LLINs). While out in the farms and forests, people tended to wake early and increase their likelihood of being bitten. The authors discuss the challenges of dual residences in terms of LLIN ownership and even concerning the potential access to indoor residual spraying. The definition for universal net coverage needs to expand from one net per two people to include adequate nets wherever people are located.

The Amazonian area of Brazil is another area working toward malaria elimination, in particular, Plasmodium vivax. Felipe Leão Gomes Murta et al. also looked at the human side of the equation and identified misperceptions by both community members and health workers that could inhibit elimination efforts. They found, “many myths regarding malaria transmission and treatment that may hinder the sensitization of the population of this region in relation to the use of current control tools and elimination strategies, such as mass drug administration (MDA),” and LLINs.

Problematic perceptions included mention by both groups that the use of insecticide-treated nets, may cause skin irritations and allergies. Both community members and health professionals said malaria is “an impossible disease to eliminate because it is intrinsically associated with forest landscapes.” They concluded that such perceptions can be a barrier to control and elimination.

Efforts to eliminate malaria from low transmission settings are an essential to the overall global goals. These four articles tell us that close attention to and better understanding of humans, parasites and mosquitoes is still needed to achieve these goals.

Sunday Symposium #176 at TropMed2013 Malaria: Biology and Pathogenesis – Human Responses to falciparum

AnnualMeetinggraphicOn this final day of the American Society of Tropical Medicine and Hygiene’s 62nd Annual Conference, there is a featured symposium on Malaria: Biology and Pathogenesis – Human Responses to falciparum. Presentations are listed below with links to the abstracts online.

Demonstration of enhanced strain-specific Plasmodium falciparum multifunctional T cell cytokine expression among Malian children immunized with the FMP2.1/AS02A vaccine by Shawna F. Graves et al.

The Study suggests that AMA1 vaccination induced an AMA1-specific CD4+ response; however, recognition of the vaccine antigen is not dependent upon c1L alone. In summary, AMA1-specific T cell cytokine expression was notably increased in children vaccinated with an AMA1-based vaccine compared to rabies. The possible role of CD4+ TNF-?+IL-2+-expressing T cells in vaccine-induced strain-specific protection against clinical malaria requires further exploration.

Fatal Pediatric Cerebral Malaria is Associated with Intravascular Inflammation and Coagulation that is Exacerbated by HIV-1 Co-infection by Sarah Hochman and colleagues.

We hypothesize that the intravascular inflammation and coagulation seen in CM autopsies contribute to the pathogenesis of pediatric CM and that dysregulation of these processes in HIV infection contribute to CM mortality.

Immune responses of rhesus monkeys to a self-assembling protein nanoparticle (SAPN) vaccine displaying Plasmodium falciparum CSP B- and T-cell epitopes by David E. Lanar and co-researchers.

We have previously studied in mice the immune responses induced against Plasmodium falciparum circumsporozoite protein (PfCSP) epitopes using a self-assembling protein nanoparticle (SAPN) platform. In conclusion, a PfCSP-KMY-SAPN vaccine for malaria was safe and immunogenic in rhesus monkeys. Immune responses to the vaccine were greatly enhanced if the nanoparticle was formulated with the adjuvant GLA-SE.

Non-invasive Pulse Oximetry to Predict Mortality in African Children with Malaria by Andrea L. Conroy et al.

The mortality rate for children admitted with malaria was 3.1%. We evaluated whether non-invasive pulse oximetry would predict disease outcome in malaria and compared the findings to venous lactate, an established prognostic marker in malaria. These data suggest that pulse oximetry alongside assessment of venous lactate may be useful in the triage and treatment of children with severe malaria. Additional advantages in pulse oximetry are low operating costs and real-time patient monitoring.

Placental malaria induces excessive vasculogenesis by  Tara C. Bracken and colleagues.

Placental malaria (PM) results from sequestration of Plasmdium falciparum-infected erythrocytes and the resulting inflammatory responses in the maternal placental blood space. PM induces maternal anemia, preterm birth, low birth weight, or stillbirth, especially in primigravidae. The active/active chronic group had a significantly higher percentage of excessive vasculogenesis.

Retinal microvascular dysfunction in pediatric cerebral malaria is associated with death and neurological sequelae by Ian J. MacCormick and co-authors.

Our results suggest that central nervous system ischemia and leakage across blood-tissue barriers may be important contributors to the severity of pediatric Cerebral Malaria.

Ghanaian school children harbour antibody responses to antigens on the surface of Plasmodium falciparum gametocyte-infected erythrocytes

Bismarck Dinko of the School of Basic and Biomedical Sciences, University of Health and Allied Sciences, Ho, Ghana and his colleagues Teun Bousema and Colin Sutherland from the Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, UK. Presented their research findings at the just concluded Multilateral Initiative for Malaria 6th Pan African Malaria Conference in Durban. Bismark Dinko can be contacted as bismcck@gmail.com, bdinko@uhas.edu.gh for more information.

Malaria transmission-reducing interventions are key to malaria control and possibly elimination.1 Therefore, the development of new tools targeting malaria transmission reduction would mean a major leap forward in malaria control efforts. However, little is known about the immune responses directed at circulating P. falciparum gametocytes in the human host, knowledge of which will be useful in developing transmission reducing interventions targeting gametocytes.

Studies in the Gambia showed P. falciparum gametocytes carry antigens (GSA) which were recognized by malaria patients’ antibodies. These anti-GSA antibodies were found to be associated with lower duration of gametocyte carriage in these patients2,3.  Thus, we aimed to determine the presence of anti-GSA antibodies in an asymptomatic population and their relevance to gametocytaemia.

The study was conducted in Ahafo Ano South District, Ashanti Region, Ghana. 274 asymptomatic children aged 6-17yrs were screened by microscopy for malaria, 66% were asymptomatic parasite positive. 155 were treated with DHA-piperaquine upon second visit and enrolled. Enrolled children were followed-up for finger-prick blood donation weekly for 1 month.

1 Dinko 1a

Developing stages of P. falciparum gametocytes in culture

Gametocytaemia were determined by Microscopy and QT-NASBA.Gametocytes were produced according to established protocols.3   Mature stage V gametocytes were magnet-purified and tested with plasma samples for antibody recognition by flow cytometry as described elsewhere3 and we present here a summary of the findings.

Prevalence of asexual parasites and gametocytes in malaria asymptomatics

Prevalence of asexual parasites and gametocytes in malaria asymptomatics

From a cohort of 113 children, all the children harboured plasma antibody responses that recognized GSA on a proportion of mature gametocyte-infected RBCs of 3D7 by flow cytometry. However, 56% of the children exhibited strong antibody responses to GSA (immune response above the median within the cohort per sampling time) by both the proportion of mature gametocytes bound to antibodies and the intensity of the antibody binding to GSA. Longitudinal data provided an additional 10% developing strong GSA responses during the 1 month follow-up.

Plasma antibodies recognised mature gametocyte-infected RBCs Serum from asymptomatic individuals were incubated with mature stage V gametocytes (or trophozoites) and analysed by flow cytometry. Parasites were dual labelled with Alexflour conjugate directly recognizing human IgG and EB staining nuclear DNA. Antibody binding was estimated from the percentage of cells with both EB and Alexaflour, and quadrant settings is based on the single staining controls for EB and Alexaflour.

Plasma antibodies recognised mature gametocyte-infected RBCs. Serum from asymptomatic individuals were incubated with mature stage V gametocytes (or trophozoites) and analysed by flow cytometry. Parasites were dual labelled with Alexflour conjugate directly recognizing human IgG and EB staining nuclear DNA. Antibody binding was estimated from the percentage of cells with both EB and Alexaflour, and quadrant settings is based on the single staining controls for EB and Alexaflour.

There were some children with antibody responses fluctuating around the median immune response within the cohort. Children with GSA antibodies present at enrolment were less likely to develop new gametocytaemia at subsequent visits (odds ratio = 0.29, 95% CI 0.06 – 1.05; P = 0.034).

Plasma antibodies from Ghana recognised mature gametocyte-infected RBCs from recent patient isolate from Kenya (HL1204)

Plasma antibodies from Ghana recognised mature gametocyte-infected RBCs from recent patient isolate from Kenya (HL1204)

3D7 is a laboratory adapted parasite line, so a selection of positive plasma samples was tested against mature gametocyte preparations from HL1204, and strong plasma antibody binding was again shown. No binding to the surface of RBCs infected with immature gametocytes of HL1204 was detected.

In conclusion, a proportion of malaria-infected children carry antibodies that recognized cultured stage V P. falciparum gametocytes from 3D7 and clinical isolates. Strong plasma antibody responses may contribute to gametocytaemia control in vivo. Further work is currently being carried out to identify GSA in collaboration with colleagues at Johns Hopkins School of Public Health, Baltimore, USA.

Antibody recognition to the surface of gametocyte-infected RBCs is distinct from the surface of trophozoite-infected RBCs in some children

Antibody recognition to the surface of gametocyte-infected RBCs is distinct from the surface of trophozoite-infected RBCs in some children

References

  1. Alonson et al., 2011. PLoS Med, 8, e1000406.
  2. Sutherland, 2009, Mol Biochem Parasitol, 166, 93-8.
  3. Saeed et al., 2008, PLoS One, 3, e2280.

Note that Bismarck Dinko was supported by a MIM travel award.

Mosquitoes also do not want to be infected

When the small copepod or cyclops swallows a guinea worm larva, seeing it as food, several things may happen as the larva develops – either someone swallows the cyclops when drinking the pond water, continuing the guinea worm cycle, or the larva grows so large that the cyclops is destroyed. Control measures have included putting temephos in ponds to kill the cyclops. All of these mean death for the cyclops. None of these alternatives bode well for the cyclops.

dscn0333-sm.jpgIt is not surprising to learn, as reported in PLoS Biology that disease vectors or intermediate hosts themselves are not very ‘happy’ to get infected with disease organizms that are later passed to humans. In essence Anophleles gambiae mosquitoes have genes that encode ‘essential components of the mosquito immune defense against malaria parasites.’

Furthermore, these genes are not static. Rottschaefer and colleagues report that, “Our data indicate that functionally variable APL1 alleles are evolutionarily maintained to combat diverse pathogens, perhaps including but probably not restricted to Plasmodium species.”

Most malaria control measures to date that involve the vector are aimed at killing, repelling or sterilizing.  These range from the newest, a toxic sugar bait, to the widely used instecticide treated bednets. There is exploration into a human vaccine that would prevent the parasite from developing in the mosquito.

While mosquitoes are certainly a nuissance in their own right, they are not necessarily the main enemy in the fight against malaria. We should certainly continue using bednets and indoor spraying and in appropriate cases larviciding, as major gains have been made from these. It would be hard though to completely eliminate the vectors.  Therefore continued research is needed on vaccines and genetic modifications that make mosquitoes a hostile host to plasmodium species.