Surfing Conditions Research Articles

EXPLORATION OF PHYSICAL PERFORMANCE CAPACITIES IN EMERGING ADOLESCENT SURFING TALENT

Open water surfing conditions are unpredictable and dynamic, requiring athletes to possess well-rounded physical attributes to compete successfully. Current research focuses on adolescent athletes in competitive pathways at state and national levels, however few studies have explored the emerging talent pathway where most athletes compete. Further, adolescent female surfers are underrepresented in surfing research. This study aimed to examine the physical performance capacities of emerging adolescent athletes within a state surfing talent pathway and explore how these athletic properties vary between different sex and age cohorts. Participants (age: 13.89 ± 1.29 years) were recruited from state-based competitions (female n=14, male n=20) during the 2022-2023 season. Athletes completed a testing battery inclusive of anthropometric measures, upper and lower body strength, and power outcomes (dynamic push-up, isometric push-up, counter-movement jump, and isometric mid-thigh pull). Findings revealed significant between sex differences for anthropometric measures, with females demonstrating greater height, body mass and body fat compared to males. However, there were no significant strength or power differences evidence between males and females. Age group comparisons highlighted under-16 female athletes demonstrated superior, but non-significant, upper body strength compared to under-14 females. Contrastingly, under-16 male athletes reported significantly greater lower body strength and power outcomes relative to their younger counterparts. In conclusion, this study provides coaches with greater insight into the development of strength and power in adolescent surfing athletes involved in emerging talent pathways.

INVESTIGATING DREDGE PLACEMENT OPTIMISATION TO BENEFIT SURF AMENITY

Dredge material removed from the Tweed River Entrance is deposited offshore from Gold Coast beaches to assist in mitigating erosion. Research was undertaken by the Queensland Government Hydraulics Laboratory (QGHL), in collaboration with Tweed Sand Bypassing (TSB), to investigate the potential of targeting dredge depositions to also improve surf amenity. A time-domain numerical wave model (SWASH) was developed as a design tool and calibrated using physical model data. Overall, SWASH reproduced wave heights over and in the lee of the mound with reasonable accuracy. However, tuning of the breaking parameters (α and β) is necessary to accurately simulate the onset and persistence of the breaking process. The results of both physical and numerical modelling highlight the importance of sand mound shape in disrupting the wave field, resulting in breakpoint variability in the mound's lee, which could potentially create more favorable surfing conditions.

Exploring the Climatic Potential of Somo’s Surf Spot for Tourist Destination Management

Surfing is one of the most popular activities in coastal tourism resorts. However, the sport depends strongly on the met-ocean weather conditions, particularly on the surface wind-generated waves that reach the coast. This study provides examples of how users’ needs and user perspectives are considered by climate data specialists to develop needed, highly useful information addressing human and social needs. In this vein, the climate analysis of such data can provide input on the expected length of a surfing season, according to the surfer’s level of expertise. In addition, other water sports, such as SUP Wave and windsurfing, among others, might be indicated when surfing conditions are not optimal. Finally, the safety of surfers and other tourists who venture into the sea is also dependent on those conditions. We collaborated with the surfing community to define a series of indices for quantifying surfing days (SD), surfing days stratified by surfers’ skills (SDS), alternate offers (AOs), and surfers’ and swimmers’ safety (SuS and SwS). These are of general applications but require wind and wave data at a very fine scale as the input. To illustrate the potential of our indices, we applied them to the Somo beach (Cantabria, Spain). We downscaled a global wave hindcast dataset covering a 30-year period to a spatial resolution of 100 m to obtain wave-surfing information at Somo’s surf spot. The results confirmed Somo’s status as a year-round surf spot, with SD values of 229.5 days/year and monthly values between 22 days/month and 16 days/month. SDS showed different seasonal peaks according to the surfers’ skills. Beginners’ conditions occurred more often in the summer (18.1 days/month in July), intermediate surfers’ conditions appeared in the transitional seasons (14.1 days/month in April), and advanced and big-wave riders in the winter (15.1 days/month in January and 0.7 days/month, respectively). The AO index identified the SUP wave values of 216 days/year. Wind water sports presented values of 141.6 days/year; conversely, SUP sports were possible on only 7.4 days/year. SuS and SwS identified different seasonal hazard values, decreasing from the winter, autumn, and spring to minimum values in the summer.

ASSESSING THE EFFECT OF EARTHQUAKE-INDUCED UPLIFT AND ENGINEERING WORKS ON A SURF BREAK OF NATIONAL SIGNIFICANCE

In November 2016 a Mw7.8 earthquake struck the northeast coast of the New Zealand South Island triggering numerous large landslips which severed key infrastructure and caused parts of the coastline to be uplifted by up to 3 m. This affected a notable surf break at Mangamaunu, north of Kaikoura. The uplift of the seabed at this location caused changes in the wave breaking characteristics and, at the same time, infrastructure recovery efforts proposed construction of engineering works along the site shoreline. The potential impacts of these works on the surf break caused significant local, national and international concern. An extensive study was initiated to better understand the characteristics of the surf break, the effects of the earthquake-induced seabed uplift and the potential effects of the engineering works. This included collection of topographic and bathymetric data using a combination of LiDAR, multibeam and an innovative UAV-based collection method within the surf zone. This provided a seamless terrain model which could be adjusted to pre-earthquake levels based on observed uplift rates. Two fixed camera stations were established with ground control information to collect data on wave breaking position and GPS-watches were deployed and utilized by the local surfing community to collect similar data. Image processing algorithms were developed to extract wave breaking on a wave-by-wave basis and aggregate to obtain breaking exceedance contours, an improvement from threshold analysis on time-averaged imagery. Both physical and numerical modelling was undertaken to better understand the effect of the earthquake and of the proposed works on wave characteristics, particularly wave reflection. The non-hydrostatic wave-flow model SWASH (Smit et al., 2013) was used to evaluate changes in the breaking position, the incident and reflected wave energy gradients, and surf zone hydrodynamics during a range of typical and optimal surfing conditions for present day and future water levels. An innovative wave breaking position post-processing routine was developed to allow assessment of the impact of reflected waves on the surfability of incoming wave forms on a wave-by-wave basis. Results found that the breaking mechanics of the surf break is controlled not only by nearshore bathymetry around break point but also offshore features which cause focusing of wave energy. The uplift has caused significant changes to the breaking characteristics, with increased wave focusing, breaking and dissipation. The proposed engineering works were found to potentially cause increased wave reflection at the outer part of the surf break during high water levels, however the spatial and temporal characteristics of this reflection mean that direct impacts on surfability are likely to be limited.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/u6nLAp-gQxw

Impacts of a Multi-Purpose Artificial Reef on Hydrodynamics, Waves and Long-Term Beach Morphology

Vieira da Silva, G.; Hamilton, D.; Murray, T.; Strauss, D.; Shaeri, S.; Faivre, G.; Silva, A.P., and Tomlinson, R., 2020. Impacts of a multi-purpose artificial reef on hydrodynamics, waves and long-term beach morphology. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 706-710. Coconut Creek (Florida), ISSN 0749-0208.Multipurpose Artificial Reefs (MPARs) are structures placed in the nearshore to protect the coast, enhance surfing conditions and ecology. Narrowneck reef is the first MPAR aimed to protect the coast with secondary goal of enhance surfing. Since then, few other structures such as Narrowneck have been deployed and limited data is available in terms of their performance. This paper looks into the impacts the reef has on hydrodynamics, waves and morphologic changes. The results indicate that the reef acts as a hold point deflecting the longshore currents and changing the sediment pathway which resulted in morphological changes observed over longer term. Whilst expected during the design phase of the reef a long-term salient is not observed in the historical record. The primary reef impacts are observed underwater where an increase of sand volume updrift of the reef is clear. This highlights the importance of analysing the whole profile as opposed to the shoreline changes to assess long-term impact of such nearshore structures.

“Para Hacer un Buen Reentry es Esencial que te Salga Bien el Bottom Primero” – The Presence of English in Portuguese and Spanish Surf Talk

Although modern surfing can be traced back to early 20th century Hawaii, only quite recently has surfing become a truly global phenomenon. The aim of this paper is to discuss how the arrival of such a new cultural phenomenon as surfing to the Spanish and Portuguese speaking world is managed linguistically, i.e. to account for how one goes about talking about surfing in Portuguese and Spanish. I propose to investigate how the existing surfing vocabulary in English affects surf talk in Portuguese and Spanish. On the one hand, I will determine which words are incorporated as such and which pieces are incorporated as semantic loans. On the other hand, I will describe what old, native vocabulary is adapted to fit the needs of surf talk. The results indicate that loans are used in roughly 65 per cent of the surfing terms in both Portuguese and Spanish. On a more detailed level, the surfing manoeuvres and conditions, for example, are mostly lexicalized using direct loans, as the terms rentry ‘re-entry’ and bottom ‘bottom turn’ used in the title indicate. Waves, on the other hand, are most often described by means of loan translations, i.e. using Portuguese and Spanish terms reflecting English uses. For example, the goal of any surfer is to ride a tube, tubo in both Portuguese and Spanish. The main difference between the two languages is found in the manoeuvre terms, where Portuguese has introduced several own expressions (e.g. cavada and rasgada) while Spanish relies almost uniquely on direct loans from English.

Broad-Spectrum Adaptive Antibiotic Resistance Associated with Pseudomonas aeruginosa Mucin-Dependent Surfing Motility.

Surfing motility is a novel form of surface adaptation exhibited by the nosocomial pathogen Pseudomonas aeruginosa in the presence of the glycoprotein mucin, which is found in high abundance at mucosal surfaces, especially those of the lungs of cystic fibrosis and bronchiectasis patients. Here, we investigated the adaptive antibiotic resistance of P. aeruginosa under conditions in which surfing occurs compared that in to cells undergoing swimming. P. aeruginosa surfing cells were significantly more resistant to several classes of antibiotics, including aminoglycosides, carbapenems, polymyxins, and fluoroquinolones. This was confirmed by incorporation of antibiotics into growth medium, which revealed a concentration-dependent inhibition of surfing motility that occurred at concentrations much higher than those needed to inhibit swimming. To investigate the basis of resistance, transcriptome sequencing (RNA-Seq) was performed and revealed that surfing influenced the expression of numerous genes. Included among genes dysregulated under surfing conditions were multiple genes from the Pseudomonas resistome; these genes are known to affect antibiotic resistance when mutated. Screening transposon mutants in these surfing-dysregulated resistome genes revealed that several of these mutants exhibited changes in susceptibility to one or more antibiotics under surfing conditions, consistent with a contribution to the observed adaptive resistance. In particular, several mutants in resistome genes, including armR, recG, atpB, clpS, nuoB, and certain hypothetical genes, such as PA5130, PA3576, and PA4292, showed contributions to broad-spectrum resistance under surfing conditions and could be complemented by their respective cloned genes. Therefore, we propose that surfing adaption led to extensive multidrug adaptive resistance as a result of the collective dysregulation of diverse genes.

Design of a TW-SLIM Module for Dual Polarity Confinement, Transport, and Reactions.

Here we describe instrumental approaches for performing dual polarity ion confinement, transport, ion mobility separations, and reactions in structures for lossless ion manipulations (SLIM). Previous means of ion confinement in SLIM, based upon rf-generated pseudopotentials and DC fields for lateral confinement, cannot trap ions of opposite polarity simultaneously. Here we explore alternative approaches to provide simultaneous lateral confinement of both ion polarities. Traveling wave ion mobility (IM) separations experienced in such SLIM cause ions of both polarities to migrate in the same directions and exhibit similar separations. The ion motion (and relative motion of the two polarities) under both surfing and IM separation conditions are discussed. In surfing conditions the two polarities are transported losslessly and non-reactively in their respective potential minima (higher absolute voltage regions confine negative polarities, and lower absolute potential regions are populated by positive polarities). In separation mode, where ions roll over an overtaking traveling wave, the two polarities can interact during the rollovers. Strategies to minimize overlap of the two ion populations to prevent reactive losses during separations are presented. A theoretical treatment of the time scales over which two populations (injected into a DC field-free region of the dual polarity SLIM device) interact is considered, and SLIM designs for allowing ion/ion interactions and other manipulations with dual polarities at 4Torr are presented. Graphical Abstract ᅟ.

Recomendações de Gestão dos Recifes Artificiais para a Prática do Surfe

Os recifes artificiais são estruturas afundadas em ambiente marinho a fim de oferecer múltiplos usos e beneficiar um maior número de usuários. Entretanto, sua capacidade de propiciar melhores condições de surfe tem sido a principal característica atrativa para experiências já realizadas em alguns países do mundo. Neste contexto, esta pesquisa tem o objetivo de apresentar um conjunto de recomendações que possam contribuir com gestores públicos e privados que planejam incluir a implantação de recifes artificiais tendo como foco a melhoria nas condições de surfe em suas localidades. Para tanto, esta pesquisa qualitativa exploratória se desenvolve a partir de breve revisão teórica sobre o tema e de um estudo de casos múltiplos – Austrália, Estados Unidos, Nova Zelândia, India e Inglaterra - para sustentar o raciocínio. Os resultados incluem o caráter inovador deste tipo de estrutura demandando um aprimoramento nos métodos de construção e gestão, programas de monitoramento de longo prazo para avaliação de eficácia, desafios na integração de usuários, participação pública nas diferentes etapas do processo, gestão das expectativas dos mercados envolvidos. Uma vez que poucos estudos referentes ao tema foram desenvolvidos até o presente momento, as análises presentes neste trabalho podem contribuir com o preenchimento desta lacuna no conhecimento.

LONG TERM PERFORMANCE OF A SUBMERGED COASTAL CONTROL STRUCTURE: A CASE STUDY OF THE NARROWNECK MULTI-FUNCTIONAL ARTIFICIAL REEF

In response to the increasing occurrences of beach erosion along Surfers Paradise and Main Beaches - Gold Coast, Australia, the Northern Gold Coast Beach Protection Strategy [NGCBPS] was developed to widen the beach by 20-30m as well as improving surfing conditions as a secondary objective. The strategy, implemented in 1999- 2000, involved large-scale beach nourishment and construction of a submerged breakwater "reef† to act as a control point at Narrowneck. Construction of the reef involved innovative filling and placement methods using very large sand filled geotextile containers coupled with significant advances with regards to design of the geotextile material and containers. In the 11 years since construction, there has been substantial monitoring of the project since its completion in late 2000 including: - video imaging using webcams; hydrographic and beach surveys; aerial and oblique photography; surf and surf safety observations and GPS surfing track plots; and geotextile container condition and stability. This paper presents an update on the performance of the reef over the last four years. In particular, the response of the structure and the shoreline to a series of major storm events in 2009 has been examined. The results have shown that the erosion caused by these major events was accommodated within the wider beach created in 1999. Over the next 2 years there was a gradual recovery in the lee of the reef with a subtle groyne effect resulting in an even larger increase in the width of the updrift beach. A detailed underwater condition survey was also undertaken in 2011, to determine changes in the condition of the geotextile containers. This revealed a number of containers missing or damaged, and that seaward containers were covered by sand. The marine habitat which has been a feature of the reef has been impacted by the increased coverage of sand, but still shows high abundance and biodiversity.

Wave hydrodynamics around a multi-functional artificial reef at Leirosa

This paper describes an application of the Boussinesq-type COULWAVE model to study the wave hydrodynamics in the vicinity of a multi-functional artificial reef (MFAR). This reef is under investigation and consists of a supplementary protection solution for the Leirosa sand dune system located at South of Figueira da Foz, on the Portuguese West coast. Such installation near the coastline is expected to contribute to enhance the surfing conditions in the area, protect the sand dune system in the surroundings of Leirosa beach, and increase its environmental value. Numerical calculations with the COULWAVE model were performed for four test cases, considering two reef geometries (differing in the reef angle) and two incident wave conditions (storm condition and a common wave condition). Comparisons between the results obtained, in terms of wave heights and breaking line positions allow us to assess the influence of the reef on the hydrodynamics near the beach and around the reef. Moreover, the reef performance was analysed in terms of surfability and coastal protection. The surfability parameters (breaker height, Iribarren number and peel angle) were calculated for each test case using the numerical wave heights, wave directions and wave breaking positions. Comparisons of parameters allow characterizing the most appropriate configuration of the reef to improve the surfing conditions in the study area. A methodology based on numerical free surface elevations and horizontal velocity components was developed to calculate wave directions, since this is not a direct output of the COULWAVE model. Concerning coastal protection, analyses of the mean currents around the reef were used together with observations of the velocity cells near the shoreline as an indication of the sediment transport.

ASSESSMENT OF ALTERNATIVE BEACH PLACEMENT ON SURFING RESOURCES

The beach fill was constructed using an innovative feeder beach design, rather than a standard linear fill template. The feeder beach design was adopted to address the concerns of local surfing groups by initially burying fewer structures, and by potentially creating additional surfing opportunities through enhanced bar formation during the equilibration process. Nine months of monitoring results show that roughly 84% of the placed material can be accounted for within the project area and on the downdrift beaches. The immediate impact of the fill on the local surfing conditions was negative within the project area as steep slopes, violent plunging breakers, and narrow surfzones limited the use of the feeder beach area; however traditional surf spots to the north and south were unaffected by the nourishment due to the concentrated nature of its placement. More recently, as the post-nourishment slopes have begun to equilibrate, surfing conditions have improved markedly within the project area, while the up drift and down drift beaches remain relatively unaffected.

Enhancing submerged coastal constructions by incorporating multifunctional purposes

Surfing has becoming more and more attractive in the past few decades, constituting nowadays an important source of revenue for many countries with extensive coastlines. For this purpose and also for environmental reasons, the conventional ways of protecting a coastline appear to entail some disadvantages. An innovative and interesting way of improving surfing capacities and contributing to protect a local coastal zone is by means of multifunctional artificial reefs. A multifunctional artificial reef (MFAR) is a submerged structure that serves several purposes; in particular, it may enhance the surfing possibilities and the environmental value of the local area. This structure has some promising new aspects, too: first, it provides an unimpaired visual amenity; second, it offers tourist and economic benefits by improving the surfing conditions; third, it can enhance the environmental value of the area where it is built, and fourth, if designed properly, the down drift erosion can be minimal. An appropriate reef design in terms of ‘surfability’, i.e. the possibility to surf a wave, for the Leirosa beach, located to the south of Figueira da Foz, midway along Portugal’s West Atlantic coast, has been investigated. In order to achieve the best design several steps were conducted. First, the performance of the Boussinesq-type COULWAVE model is tested with experimental data. Next, this numerical model is used to define the best values for three design parameters: reef angle; geometry of the reef (without or with a platform), and horizontal dimensions for the appropriate geometry. A preliminary design was achieved step by step, making use of the theory and of the state of the art of multifunctional reefs. This reef geometry is used in the numerical study. In terms of ‘surfability’ and for the conditions of the local coastline of Leirosa, the following values were found for the main parameters: a reef angle of 66°; a structure height of 3.20 m; a reef geometry composed of a delta without a platform; a reef submergence of 1.50 m, and a structure seaward slope of 1:10.

Designing a multifunctional artificial reef: studies on the influence of parameters with most influence in the vertical plane

Multifunctional artificial reefs are submerged breakwaters that serve several purposes. As well as protecting the local coastline, they enhance surfing possibilities and/or increase the environmental value of the area where they are situated. Multifunctional artificial reefs (MFARs) have some promising new aspects, too: first, they provide an unimpaired visual amenity, and second, they can offer tourist and economic benefits by improving the surfing conditions. Regarding the functionality of an MFAR, much research has been carried out on surfability, i.e. whether a wave is good for surfers. However, no research has yet been done on the influence of the submergence and the length of the reef slope on the breaker type, even though this is important for the design of the reef in terms of surfability. A preliminary design was achieved step by step, making use of the theory and state of the art of multifunctional artificial reefs (Voorde et al. 2009a, 2009b). This reef geometry was then used as an initial design in physical and numerical tests. These were performed to ascertain the capacity of a multifunctional reef to serve as a submerged breakwater and so protect the local coastline of Leirosa, Portugal, and improve the local surfing possibilities. This paper describes the numerical study conducted to analyze the influences of the main relevant parameters in the vertical plane, namely: the height, the submergence, and the length and slope of the reef. The investigation was conducted using the COBRAS-UC numerical model in the vertical plane and the main results and conclusions are described and presented; a brief discussion and some recommendations for future work are also included.

Wave and Flow Response to an Artificial Surf Reef: Laboratory Measurements

Waves and currents are essential elements in the design of an artificial surfing reef (ASR). ASRs are primarily designed to optimize the surfing conditions (i.e., increase the surfability of the incoming waves) possibly in combination with the shoreline protection from erosion. The currents generated by waves breaking on the ASR play an important role in the surfability through the wave-current interaction (WCI). Depending on the design, the WCI may negatively affect the surfability by causing the waves to break prematurely due to the current-induced wave steepening. In addition, wave breaking tends to become more irregular due to the temporal variability of the underlying currents. To mitigate the negative effects of wave breaking induced currents on the surfability, three ASR layouts are examined through detailed laboratory experiments. The layouts differ in the alongshore separation distance between two symmetrical reef sides. The ensuing flow circulations are examined in detail with both in situ current meters and video observations of surface drifters. This is done for regular incident waves, bichromatic incident waves, and irregular incident waves, all with equal energy. A data analysis shows that for a given layout the mean flow patterns for regular, bichromatic, and irregular waves are qualitatively similar, with oblique rip currents exiting at either side of the reef and strong flow circulations onshore of the gap in between the two reef sides. Increasing the separation distance leads to a significant reduction of the obliquely exiting rip currents at the outer sides of the reef, but an increase in the flow circulation onshore of the gap. This has a positive effect on the surfability by reducing the negative effects associated with the WCI on the wave breaking, thus, providing longer rides.

Designing a Preliminary Multifunctional Artificial Reef to Protect the Portuguese Coast

Abstract Portugal is one of many countries in the world that suffers from coastal erosion. Conventional ways of protecting a coastline appear to entail some disadvantages. An innovative and interesting way of protecting a local coastal zone by means of multifunctional artificial reefs avoids some of them. A multifunctional artificial reef is a submerged breakwater which, besides helping to protect the local coastline, can have other purposes; in particular it may enhance the surfing possibilities and the environmental value of the local area. The structure has several positive side effects: first, it provides an unimpaired visual amenity; second, it offers tourist and economic benefits by improving the surfing conditions. A preliminary design, achieved step-by-step, is proposed for a multifunctional artificial reef making use of the theory and state of the art multifunctional artificial reef design, a preliminary design, achieved step-by-step, a priliminary design is proposed. The proposed reef geometry, ...

Shoreline response to submerged structures: A review

Submerged coastal structures are widely perceived to be capable of providing beach protection, without the adverse impacts (including loss of beach amenity and aesthetic considerations) often associated with more conventional structures such as revetments and groynes. In addition, there is growing interest in the concept that the layout and cross-section of submerged coastal protection structures can be optimised to also enhance local surfing conditions. However, as submerged structures have only rarely been adopted for beach protection, the shoreline response to these structures is not well understood at present. Therefore, this review of the available published literature was undertaken with the aim of investigating the environmental and structural parameters governing shoreline response to submerged structures, gleaned from the results of field, laboratory and numerical studies undertaken to date. The review reveals that, contrary to expectations, a majority of the submerged structures constructed to date have resulted in shoreline erosion in their lee. Furthermore, the key environmental and structural parameters governing the mode (i.e. erosion or accretion) and the magnitude (i.e. size of salient) of shoreline response to submerged structures are yet to be identified. Although submerged coastal structures offer the potential for low aesthetic impact incorporating multi-function design, until the response of the adjacent shoreline to submerged structures is better resolved, their use is likely to remain relatively limited.

Artificial reef in Newquay, UK

A proposal to build an artificial reef has been put together for Newquay in Cornwall. The aim is to enhance surfing conditions for local surfers, to attract visiting surfers and to provide a spectacle for other tourists, particularly during the autumn, winter and spring months. The message nowadays is that engineers should play a wider role in meeting the needs of society, that they must become key practitioners of sustainable development and that they should gain greater recognition for the role they play. It is considered that this proposal goes some way to delivering these goals. This paper discusses the project in the context of sustainable development.

Artificial reef in Newquay, UK

A proposal to build an artificial reef has been put together for Newquay in Cornwall. The aim is to enhance surfing conditions for local surfers, to attract visiting surfers and to provide a spectacle for other tourists, particularly during the autumn, winter and spring months. The message nowadays is that engineers should play a wider role in meeting the needs of society, that they must become key practitioners of sustainable development and that they should gain greater recognition for the role they play. It is considered that this proposal goes some way to delivering these goals. This paper discusses the project in the context of sustainable development.

The drug sensitivity and transmission dynamics of human malaria on Nias Island, North Sumatra, Indonesia.

Nias Island, off the north-western coast of Sumatra, Indonesia, was one of the first locations in which chloroquine-resistant Plasmodium vivax malaria was reported. This resistance is of particular concern because its ancient megalithic culture and the outstanding surfing conditions make the island a popular tourist destination. International travel to and from the island could rapidly spread chloroquine-resistant strains of P. vivax across the planet. The threat posed by such strains, locally and internationally, has led to the routine and periodic re-assessment of the efficacy of antimalarial drugs and transmission potential on the island. Active case detection identified malaria in 124 (17%) of 710 local residents whereas passive case detection, at the central health clinic, confirmed malaria in 77 (44%) of 173 cases of presumed 'clinical malaria'. Informed consenting volunteers who had malarial parasitaemias were treated, according to the Indonesian Ministry of Health's recommendations, with sulfadoxine-pyrimethamine (SP) on day 0 (for P. falciparum) or with chloroquine (CQ) on days 0, 1 and 2 (for P. vivax). Each volunteer was then monitored for clinical and parasite response until day 28. Recurrent parasitaemia by day 28 treatment was seen in 29 (83%) of the 35 P. falciparum cases given SP (14, 11 and four cases showing RI, RII and RIII resistance, respectively). Recurrent parasitaemia was also observed, between day 11 and day 21, in six (21%) of the 28 P. vivax cases given CQ. Although the results of quantitative analysis confirmed only low prevalences of CQ-resistant P. vivax malaria, the prevalence of SP resistance among the P. falciparum cases was among the highest seen in Indonesia. When the parasites present in the volunteers with P. falciparum infections were genotyped, mutations associated with pyrimethamine resistance were found at high frequency in the dhfr gene but there was no evidence of selection for sulfadoxine resistance in the dhps gene. Night-biting mosquitoes were surveyed by human landing collections and tested for sporozoite infection. Among the five species of human-biting anophelines collected, Anopheles sundaicus was dominant (68%) and the only species found to be infective--two (1.2%) of 167 females being found carrying P. vivax sporozoites. The risk of malarial infection for humans on Nias was considered high because of the abundance of asymptomatic carriers, the reduced effectiveness of the available antimalarial drugs, and the biting and infection 'rates' of the local An. sundaicus.