Research Leads to Promising Malaria Drug Candidate

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A chemical that rid mice of malaria-causing parasites after a single oral dose may eventually become a new malaria drug if further tests in animals and people uphold the promise of early findings. The compound, NITD609, was developed by an international team of researchers including Elizabeth A. Winzeler, Ph.D., a grantee of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

“Although significant progress has been made in controlling malaria, the disease still kills nearly 1 million people every year, mostly infants and young children,” says NIAID Director Anthony S. Fauci, M.D. “It has been more than a decade since the last new class of antimalarials — artemisinins — began to be widely used throughout the world. The rise of drug-resistant malaria parasites further underscores the need for novel malaria therapies.”

Dr. Fauci adds, “The compound developed and tested by Dr. Winzeler and her colleagues appears to target a parasite protein not attacked by any existing malaria drug, and has several other desirable features. This research is also a notable example of successful collaboration between government-supported scientists and private sector researchers.”

The study, in the Sept. 3 issue of Science, was led by Thierry T. Diagana, Ph.D., of the Novartis Institute for Tropical Diseases (NITD), and Dr. Winzeler. Dr. Winzeler is affiliated with The Scripps Research Institute and the Genomic Institute of the Novartis Research Foundation, La Jolla, Calif.

Work on what eventually became NITD609 began in Dr. Winzeler’s lab in 2007. Scientists screened 12,000 chemicals using an ultra-high throughput robotic screening technique customized to detect compounds active against Plasmodium falciparum, the most deadly malaria parasite. The screen identified a chemical with good parasite-killing abilities and the potential to be modified into a drug. Medicinal chemists at the NITD then synthesized and evaluated about 200 versions of the original compound to arrive at NITD609, which could be formulated as a tablet and manufactured in large quantities. NITD609 is one of a new class of chemicals, the spiroindolones, which have been described in recently published research by Dr. Winzeler and colleagues as having potent effects against two kinds of malaria parasites.

“From the beginning, NITD609 stood out because it looked different, in terms of its structure and chemistry, from all other currently used antimalarials,” says Dr. Winzeler. “The ideal new malaria drug would not just be a modification of existing drugs, but would have entirely novel features and mechanism of action. NITD609 does.”

In the current study, the scientists detail attributes of NITD609 that suggest it could be a good malaria drug. For example

  • In test-tube experiments, NITD609 killed two species of parasites in their blood-stage form and also was effective against drug-resistant strains. In humans, malaria parasites spend part of their life cycle in the blood and part in the liver.
  • The compound worked faster than some older malaria drugs, although not as quickly as the best current malaria drug, artemisinin.
  • Other laboratory tests showed that NITD609 is not toxic to a variety of human cells.

When given orally to rodents, the compound stayed in circulation long enough to reach levels predicted to be effective against malaria parasites. According to Dr. Winzeler, if NITD609 behaves similarly in people, it might be possible to develop the compound into a drug that could be taken just once. Such a dosage regimen, she says, would be substantially better than the current standard treatment in much of the world in which uncomplicated malaria infections are treated for three to seven days with drugs that are taken between one and four times daily.

“We were excited by the potential NITD609 showed in the first series of test-tube experiments, ” says Dr. Winzeler. “We became even more enthusiastic when our co-investigators at the Swiss Tropical Institute in Basel tested NITD609 in a mouse model of malaria.”

Typically, she says, rodents infected with the mouse malaria parasite, Plasmodium berghei, die within a week. But a single large dose of NITD609 cured all five infected mice that received it, while half of six mice receiving a single smaller dose were cured of infection. Three doses of the smaller amount of NITD609 upped the cure rate to 90 percent.

The researchers also compared NITD609 with other malaria drugs in P. berghei-infected mice. “No other currently used malaria drug was as potent,” says Dr. Winzeler. NITD609’s effectiveness in relatively few doses is a key point in its favor, she adds. A novel malaria drug that works in as few doses as possible leaves less opportunity for parasites to develop drug resistance.

Additional tests in animals are under way and NITD609 could enter early-stage safety testing in humans later this year, says Dr. Winzeler. But, she adds, many drug candidates fail in clinical trials and thus it will be important for the community to continue to work on developing other potential antimalarial compounds.

To learn how parasites might develop resistance to this potential drug, the researchers also exposed parasites to sublethal levels of NITD609 continuously for several months until drug-resistant strains emerged. Then they analyzed those strains and determined that resistance results from a single change in one of the parasite’s genes. The gene contains the code to make a protein called PfATP4, which allows substances to cross cell membranes. No other anti-malaria drugs act on the PfATP4 protein, notes Dr. Winzeler. Having information in hand about the genetic basis for NITD609 resistance at this early stage of the compound’s development is advantageous, she adds, because it will allow scientists to rapidly detect drug-resistant strains in clinical settings if the compound is eventually approved as a drug for human use.

Source: NIH

Anopheles Mosquitoes

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Anopheles Mosquitoes

Diagram of Adult Female MosquitoDiagram of Adult Female Mosquito
 

Malaria is transmitted among humans by female mosquitoes of the genus Anopheles. Female mosquitoes take blood meals to carry out egg production, and such blood meals are the link between the human and the mosquito hosts in the parasite life cycle. The successful development of the malaria parasite in the mosquito (from the “gametocyte” stage to the “sporozoite” stage) depends on several factors. The most important is ambient temperature and humidity (higher temperatures accelerate the parasite growth in the mosquito) and whether the Anopheles survives long enough to allow the parasite to complete its cycle in the mosquito host (“sporogonic” or “extrinsic” cycle, duration 10 to 18 days). Differently from the human host, the mosquito host does not suffer noticeably from the presence of the parasites.

Thumbnail of the mosquito distribution map.Map of the world showing the distribution of predominant malaria vectors 

General Information

There are approximately 3,500 species of mosquitoes grouped into 41 genera. Human malaria is transmitted only by females of the genus Anopheles. Of the approximately 430 Anopheles species, only 30-40 transmit malaria (i.e., are “vectors”) in nature.

Geographic Distribution

Anophelines are found worldwide except Antarctica. Malaria is transmitted by different Anopheles species, depending on the region and the environment.

Anophelines that can transmit malaria are found not only in malaria-endemic areas, but also in areas where malaria has been eliminated. The latter areas are thus constantly at risk of re-introduction of the disease.

Anopheles freeborni mosquito pumping bloodAnopheles freeborni mosquito pumping blood

 

Powerpoint slide of Anopheles freeborni mosquito pumping blood

Life Stages

Like all mosquitoes, anophelines go through four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are aquatic and last 5-14 days, depending on the species and the ambient temperature. The adult stage is when the female Anopheles mosquito acts as malaria vector. The adult females can live up to a month (or more in captivity) but most probably do not live more than 1-2 weeks in nature.

Eggs

Adult females lay 50-200 eggs per oviposition. Eggs are laid singly directly on water and are unique in having floats on either side. Eggs are not resistant to drying and hatch within 2-3 days, although hatching may take up to 2-3 weeks in colder climates.

Larvae

Mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax, and a segmented abdomen. They have no legs. In contrast to other mosquitoes, Anopheles larvae lack a respiratory siphon and for this reason position themselves so that their body is parallel to the surface of the water.

Larvae breathe through spiracles located on the 8th abdominal segment and therefore must come to the surface frequently.

Top: Anopheles Egg; note the lateral floats. Bottom: Anopheles eggs are laid singlyTop: Anopheles Egg; note the lateral floats.
Bottom: Anopheles eggs are laid singly. 

Image of a Anopheles larva, floating parallel to water surfaceAnopheles Larva. Note the position, parallel to the water surface. 

The larvae spend most of their time feeding on algae, bacteria, and other microorganisms in the surface microlayer. They dive below the surface only when disturbed. Larvae swim either by jerky movements of the entire body or through propulsion with the mouth brushes.

Larvae develop through 4 stages, or instars, after which they metamorphose into pupae. At the end of each instar, the larvae molt, shedding their exoskeleton, or skin, to allow for further growth.

Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Tire tracks habitat.
Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Rice fields habitat
Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Irrigation water habitat.

Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in diverse habitats. Three habitats are shown from left to right: tire tracks, rice fields, and irrigation water.

 

The larvae occur in a wide range of habitats but most species prefer clean, unpolluted water. Larvae of Anopheles mosquitoes have been found in fresh- or salt-water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools. Many species prefer habitats with vegetation. Others prefer habitats that have none. Some breed in open, sun-lit pools while others are found only in shaded breeding sites in forests. A few species breed in tree holes or the leaf axils of some plants.

Graph of pupa of Anopheles, illustrating coma shapeAnopheles Pupa 

Pupae

The pupa is comma-shaped when viewed from the side. The head and thorax are merged into a cephalothorax with the abdomen curving around underneath. As with the larvae, pupae must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on the cephalothorax. After a few days as a pupa, the dorsal surface of the cephalothorax splits and the adult mosquito emerges.

The duration from egg to adult varies considerably among species and is strongly influenced by ambient temperature. Mosquitoes can develop from egg to adult in as little as 5 days but usually take 10-14 days in tropical conditions.

Schema of adult Anopheles seen from above, and from the side to show typical resting position) Anopheles Adults. Note (bottom row) the typical resting position. 

Adults

Like all mosquitoes, adult anophelines have slender bodies with 3 sections: head, thorax and abdomen.

The head is specialized for acquiring sensory information and for feeding. The head contains the eyes and a pair of long, many-segmented antennae. The antennae are important for detecting host odors as well as odors of breeding sites where females lay eggs. The head also has an elongate, forward-projecting proboscis used for feeding, and two sensory palps.

The thorax is specialized for locomotion. Three pairs of legs and a pair of wings are attached to the thorax.

The abdomen is specialized for food digestion and egg development. This segmented body part expands considerably when a female takes a blood meal. The blood is digested over time serving as a source of protein for the production of eggs, which gradually fill the abdomen.

Anopheles mosquitoes can be distinguished from other mosquitoes by the palps, which are as long as the proboscis, and by the presence of discrete blocks of black and white scales on the wings. Adult Anopheles can also be identified by their typical resting position: males and females rest with their abdomens sticking up in the air rather than parallel to the surface on which they are resting.

Adult mosquitoes usually mate within a few days after emerging from the pupal stage. In most species, the males form large swarms, usually around dusk, and the females fly into the swarms to mate.

Female Anopheles dirus FeedingFemale Anopheles dirus feeding 

Males live for about a week, feeding on nectar and other sources of sugar. Females will also feed on sugar sources for energy but usually require a blood meal for the development of eggs. After obtaining a full blood meal, the female will rest for a few days while the blood is digested and eggs are developed. This process depends on the temperature but usually takes 2-3 days in tropical conditions. Once the eggs are fully developed, the female lays them and resumes host seeking.

The cycle repeats itself until the female dies. Females can survive up to a month (or longer in captivity) but most probably do not live longer than 1-2 weeks in nature. Their chances of survival depend on temperature and humidity, but also their ability to successfully obtain a blood meal while avoiding host defenses.

Factors Involved in Malaria Transmission and Malaria Control

Understanding the biology and behavior of Anopheles mosquitoes can help understand how malaria is transmitted and can aid in designing appropriate control strategies. Factors that affect a mosquito’s ability to transmit malaria include its innate susceptibility to Plasmodium, its host choice, and its longevity. Factors that should be taken into consideration when designing a control program include the susceptibility of malaria vectors to insecticides and the preferred feeding and resting location of adult mosquitoes.

Preferred Sources for Blood Meals

One important behavioral factor is the degree to which an Anopheles species prefers to feed on humans (anthropophily) or animals such as cattle (zoophily). Anthrophilic Anopheles are more likely to transmit the malaria parasites from one person to another. Most Anopheles mosquitoes are not exclusively anthropophilic or zoophilic. However, the primary malaria vectors in Africa, An. gambiae and An. funestus, are strongly anthropophilic and, consequently, are two of the most efficient malaria vectors in the world.

Life Span

Once ingested by a mosquito, malaria parasites must undergo development within the mosquito before they are infectious to humans. The time required for development in the mosquito (the extrinsic incubation period) ranges from 10 to 21 days, depending on the parasite species and the temperature. If a mosquito does not survive longer than the extrinsic incubation period, then she will not be able to transmit any malaria parasites.

It is not possible to measure directly the life span of mosquitoes in nature. But indirect estimates of daily survivorship have been made for several Anopheles species. Estimates of daily survivorship of An. gambiae in Tanzania ranged from 0.77 to 0.84 meaning that at the end of one day between 77% and 84% will have survived. (Charlwood et al., 1997, Survival And Infection Probabilities of Anthropophagic Anophelines From An Area of High Prevalence of Plasmodium falciparum in Humans, Bulletin of Entomological Research, 87, 445-453).

Assuming this is constant through the adult life of a mosquito, less than 10% of female An. gambiae would survive longer than a 14-day extrinsic incubation period. If daily survivorship increased to 0.9, over 20% of mosquitoes would survive longer than a 14-day extrinsic incubation period. Control measures that rely on insecticides (e.g., indoor residual spraying) may actually impact malaria transmission more through their effect on adult longevity than through their effect on the population of adult mosquitoes.

Patterns of Feeding and Resting

Most Anopheles mosquitoes are crepuscular (active at dusk or dawn) or nocturnal (active at night). Some Anopheles mosquitoes feed indoors (endophagic) while others feed outdoors (exophagic). After blood feeding, some Anopheles mosquitoes prefer to rest indoors (endophilic) while others prefer to rest outdoors (exophilic). Biting by nocturnal, endophagic Anopheles mosquitoes can be markedly reduced through the use of insecticide-treated bed nets (ITNs) or through improved housing construction to prevent mosquito entry (e.g., window screens). Endophilic mosquitoes are readily controlled by indoor spraying of residual insecticides. In contrast, exophagic/exophilic vectors are best controlled through source reduction (destruction of the breeding sites).

Insecticide Resistance

Insecticide-based control measures (e.g., indoor spraying with insecticides, ITNs) are the principal way to kill mosquitoes that bite indoors. However, after prolonged exposure to an insecticide over several generations, mosquitoes, like other insects, may develop resistance, a capacity to survive contact with an insecticide. Since mosquitoes can have many generations per year, high levels of resistance can arise very quickly. Resistance of mosquitoes to some insecticides has been documented just within a few years after the insecticides were introduced. There are over 125 mosquito species with documented resistance to one or more insecticides. The development of resistance to insecticides used for indoor residual spraying was a major impediment during the Global Malaria Eradication Campaign. Judicious use of insecticides for mosquito control can limit the development and spread of resistance. However, use of insecticides in agriculture has often been implicated as contributing to resistance in mosquito populations. It is possible to detect developing resistance in mosquitoes and control programs are well advised to conduct surveillance for this potential problem.

Source: CDC

NITD609 Compound May Be Promising Malaria Drug Candidate, Say Researchers

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A chemical that rid mice of malaria-causing parasites after a single oral dose may eventually become a new malaria drug if further tests in animals and people uphold the promise of early findings. The compound, NITD609, was developed by an international team of researchers.

“Although significant progress has been made in controlling malaria, the disease still kills nearly 1 million people every year, mostly infants and young children,” says NIAID Director Anthony S. Fauci, M.D. “It has been more than a decade since the last new class of antimalarials—artemisinins—began to be widely used throughout the world. The rise of drug-resistant malaria parasites further underscores the need for novel malaria therapies.”

Dr. Fauci adds that the compound “appears to target a parasite protein not attacked by any existing malaria drug, and has several other desirable features. This research is also a notable example of successful collaboration between government-supported scientists and private sector researchers.”

The study, in the Sept. 3, 2010 issue of Science, was led by Thierry T. Diagana, Ph.D., of the Novartis Institute for Tropical Diseases (NITD), and Dr. Winzeler. Dr. Winzeler is affiliated with The Scripps Research Institute and the Genomic Institute of the Novartis Research Foundation, La Jolla, Calif.

Work on what eventually became NITD609 began in Dr. Winzeler’s lab in 2007. Scientists screened 12,000 chemicals using an ultra-high throughput robotic screening technique customized to detect compounds active against Plasmodium falciparum, the most deadly malaria parasite. The screen identified a chemical with good parasite-killing abilities and the potential to be modified into a drug. Medicinal chemists at the NITD then synthesized and evaluated about 200 versions of the original compound to arrive at NITD609, which could be formulated as a tablet and manufactured in large quantities. NITD609 is one of a new class of chemicals, the spiroindolones, which have been described in recently published research by Dr. Winzeler and colleagues as having potent effects against two kinds of malaria parasites.

“From the beginning, NITD609 stood out because it looked different, in terms of its structure and chemistry, from all other currently used antimalarials,” says Dr. Winzeler. “The ideal new malaria drug would not just be a modification of existing drugs, but would have entirely novel features and mechanism of action. NITD609 does.”

Source: NIH

Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Malaria

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Partial mosquito-proofing of houses with screens and ceilings has the potential to reduce indoor densities of malaria mosquitoes. We wish to measure whether it will also reduce indoor densities of vectors of neglected tropical diseases.

Methodology: The main house entry points preferred by anopheline and culicine vectors were determined through controlled experiments using specially designed experimental huts and village houses in Lupiro village, southern Tanzania. The benefit of screening different entry points (eaves, windows and doors) using PVC-coated fibre glass netting material in terms of reduced indoor densities of mosquitoes was evaluated compared to the control.

Findings: 23,027 mosquitoes were caught with CDC light traps; 77.9% (17,929) were Anopheles gambiae sensu lato, of which 66.2% were An. arabiensis and 33.8% An. gambiae sensu stricto. The remainder comprised 0.2% (50) An. funestus, 10.2% (2359) Culex spp. and 11.6% (2664) Mansonia spp. Screening eaves reduced densities of Anopheles gambiae s. l. (Relative ratio (RR) = 0.91; 95% CI = 0.84, 0.98; P = 0.01); Mansonia africana (RR = 0.43; 95% CI = 0.26, 0.76; P<0.001) and Mansonia uniformis (RR = 0.37; 95% CI = 0.25, 0.56; P<0.001) but not Culex quinquefasciatus, Cx. univittatus or Cx. theileri. Numbers of these species were reduced by screening windows and doors but this was not significant.

Significance: This study confirms that across Africa, screening eaves protects households against important mosquito vectors of filariasis, Rift Valley Fever and O’Nyong nyong as well as malaria. While full house screening is required to exclude Culex species mosquitoes, screening of eaves alone or fitting ceilings has considerable potential for integrated control of other vectors of filariasis, arbovirus and malaria.

Author Summary: Mosquito vectors that transmit filariasis and several arboviruses such as Rift Valley Fever, Chikungunya and O’Nyong nyong as well as malaria co-occur across tropical Africa. These diseases are co-endemic in most rural African countries where they are transmitted by the same mosquito vectors. The only control measure currently in widespread use is mass drug administration for filariasis. In this study, we used controlled experiments to evaluate the benefit of screening the main mosquito entry points into houses, namely, eaves, windows and doors.

This study aims to illustrate the potential of screening specific house openings with the intention of preventing endophagic mosquitoes from entering houses and thus reducing contact between humans and vectors of neglected tropical diseases. This study confirms that while full house screening is effective for reducing indoor densities of Culex spp. mosquitoes, screening of eaves alone has a great potential for integrated control of neglected tropical diseases and malaria.

Citation: Ogoma SB, Lweitoijera DW, Ngonyani H, Furer B, Russell TL, et al. (2010) Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors. PLoS Negl Trop Dis 4(8): e773. doi:10.1371/journal.pntd.0000773

Editor: Neal D. E. Alexander, London School of Hygiene and Tropical Medicine, United Kingdom

Funding: SBO was supported by a scholarship kindly provided by Valent Bioscience Corporation. This study was also supported by the Centers for Disease Control and Prevention and the United States Agency for International Development through the U.S. President’s Malaria Initiative (Award Number 621-A-00-08-0007-00), the Addessium Foundation (Reenwijk, The Netherlands) and a Research Career Development Fellowship (076806) provided to GFK by the Wellcome Trust. The funders of this study had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Copyright: © 2010 Ogoma et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

More information: Full text: Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors (PDF)

The Effects of Maternal Helminth and Malaria Infections on Mother-to-Child HIV Transmission

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Objective: To investigate the effect of helminth and/or malaria infection on the risk of HIV infection in pregnant women and its transmission to their offspring.

Design: A retrospective cohort study of pregnant Kenyan women and their offspring from term, uncomplicated vaginal deliveries (n = 936) with a nested case-control study.

Methods: We determined the presence of HIV, malaria, schistosomiasis, lymphatic filariasis, and intestinal helminthes in mothers and tested for HIV antibodies in 12-24 month-old offspring of HIV-positive women. We related these findings to the presence of cord blood lymphocyte activation and cytokine production in response to helminth antigens.

Results: HIV-positive women (n = 83, 8.9% of all women tested) were 2-fold more likely to have peripheral blood and/or placental malaria (P < 0.025) and a 2.1-fold greater likelihood of lymphatic filariasis infection (P < 0.001) compared to location-and-parity matched HIV-negative women. Women with HIV and malaria tended to show an increased risk for mother-to-child-transmission (MTCT) of HIV, although this difference was not significant. MTCT of HIV, however, was significantly higher in women co-infected with one or more helminthes (48%) verses women without helminth infections (10%, P < 0.01; adjusted odds ratio, 7.3; 95% confidence interval, 2.4-33.7). This increased risk for MTCT of HIV correlated with cord blood lymphocytes production of interleukin-5/interleukin-13 in response to helminth antigens (P < 0.001).

Conclusion: Helminth co-infection is associated with increased risk for MTCT of HIV, possibly by a mechanism in which parasite antigens activates lymphocytes in utero. Treatment of helminthic infections during pregnancy may reduce the risk of MTCT of HIV.

Author Information

Gallagher, Maureena; Malhotra, Indua; Mungai, Peter La,b; Wamachi, Alex Nc; Kioko, John Mb; Ouma, John Hd; Muchiri, Ericb; King, Christopher La,e

From the aCenter for Global Health and Diseases and Center for AIDS Research, Case Western Reserve University, Cleveland, OH, USA

bDivision of Vector Borne Diseases, Nairobi, Kenya

cKenyan Medical Research Institute, Kenya

dMaseno University, Maseno, Kenya

eDepartment of Veteran’s Affairs Medical Center, Cleveland, OH, USA.

Correspondence to C. L. King, Center for Global Health and Diseases, Case Western Reserve University, 2103 Cornell Rd, WRB Rm 4132, Cleveland, OH 44106-7286, USA. Tel: +1 216 368 4817; fax: +1 216 368 4825; e-mail: christopher.king@case.edu

Citation: AIDS: Official Journal of the International AIDS Society, Nov. 4, 2005, – Volume 19 – Issue 16 – p 1849-1855

More information: Full text – The Effects of Maternal Helminth and Malaria Infections on Mother-to-Child HIV Transmission (PDF)