Epidemiological risk factors for clinical malaria infection in the highlands of Western Kenya.

BackgroundUnderstanding the complex heterogeneity of risk factors that can contribute to an increased risk of malaria at the individual and household level will enable more effective use of control measures. The objective of this study was to understand individual and household factors that influence clinical malaria infection among individuals in the highlands of Western Kenya.MethodsThis was a matched case-control study undertaken in the Western Kenya highlands. Clinical malaria cases were recruited from health facilities and matched to asymptomatic individuals from the community who served as controls. Each participant was screened for malaria using microscopy. Follow-up surveys were conducted with individual households to collect socio-economic data. The houses were also checked using pyrethrum spray catches to collect mosquitoes.ResultsA total of 302 malaria cases were matched to 604 controls during the surveillance period. Mosquito densities were similar in the houses of both groups. A greater percentage of people in the control group (64.6%) used insecticide-treated bed nets (ITNs) compared to the families of malaria cases (48.3%). Use of ITNs was associated with lower level of clinical malaria episodes (odds ratio 0.51; 95% CI 0.39-0.68; P < 0.0001). Low income was the most important factor associated with higher malaria infections (adj. OR 4.70). Use of malaria prophylaxis was the most important factor associated with less malaria infections (adj OR 0.36). Mother's (not fathers) employment status (adj OR 0.48) and education level (adj OR 0.54) was important malaria risk factor. Houses with open eaves was an important malaria risk factor (adj OR 1.72).ConclusionThe identification of risk factors for clinical malaria infection provides information on the local malaria epidemiology and has the potential to lead to a more effective and targeted use of malaria control measures. These risk factors could be used to assess why some individuals acquire clinical malaria whilst others do not and to inform how intervention could be scaled at the local level

A cohort study of Plasmodium falciparum infection dynamics in Western Kenya Highlands

Abstract Background The Kenyan highlands were malaria-free before the 1910s, but a series of malaria epidemics have occurred in the highlands of western Kenya since the 1980s. Longitudinal studies of the genetic structure, complexity, infection dynamics, and duration of naturally acquired Plasmodium falciparum infections are needed to facilitate a comprehensive understanding of malaria epidemiology in the complex Kenyan highland eco-epidemiological systems where malaria recently expanded, as well as the evaluation of control measures. Methods We followed a cohort of 246 children residing in 3 villages at altitudes 1430 - 1580 m in western Kenya. Monthly parasitological surveys were undertaken for one year, yielding 866 P. falciparum isolates that were analyzed using 10 microsatellite markers. Results Infection complexity and genetic diversity were high (HE = 0.787-0.816), with ≥83% of infections harboring more than one parasite clone. Diversity remained high even during the low malaria transmission season. There was no significant difference between levels of genetic diversity and population structure between high and low transmission seasons. Infection turn-over rate was high, with the average infection duration of single parasite genotypes being 1.11 months, and the longest genotype persistence was 3 months. Conclusions These data demonstrate that despite the relatively recent spread of malaria to the highlands, parasite populations seem to have stabilized with no evidence of bottlenecks between seasons, while the ability of residents to clear or control infections indicates presence of effective anti-plasmodial immune mechanisms

Changing Patterns of Malaria Epidemiology between 2002 and 2010 in Western Kenya: The Fall and Rise of Malaria

The impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010.Longitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5-10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50-70% in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3%, 49.4% and 28.2% in 2010 in Iguhu, Kombewa, and Marani, respectively.The resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission

Acanthobothrium lentiginosum Vardo-Zalik & Campbell, 2011, sp. nov.

Acanthobothrium lentiginosum sp. nov. (Figs. 9–13) Specimens deposited: holotype (USNPC 103815); paratypes (USNPC 103816–103819). Host: Rhinobatos lentiginosus Garman, 1880; Atlantic guitarfish; Rajiformes: Rhinobatidae. Type Locality: Gulf of Mexico at 26 16.11 ’N, 97 8.05 ’W at 9 fathoms 15.x. 94, coll. R. A. Campbell. Site of Infection: spiral intestine. Prevalence: 1 of 1 individual examined. Etymology: This species is named after its host, Rhinobatos lentiginosus. Description: Based upon measurements of 5 whole mounted specimens and 2 with SEM. Small worms 2–3.1 mm (3, n= 5) long composed of 5–7 (6, n= 5) segments; strobila acraspedote, euapolytic. Scolex proper 288–474 (347, n= 5) long by 168–304 (227, n= 5) wide, composed of 4 triloculate bothridia. Bothridia, 272–474 (347, n= 8) long by 85–140 (111, n= 8) wide; mean (BL: BW) 2.7: 1. Each of 4 bothridia free at posterior end, acuminate, covered with spinitriches over proximal surfaces and divided into three loculi by muscular septa. Anterior loculus 100– 235 (168, n= 11) long, middle loculus 45–90 (58, n= 11) long, posterior loculus 45–95 (65, n= 11) long; (A: M: P) 1: 0.35: 0.39. Apical pad 30–50 (40, n= 6) long by 65–120 (88, n= 6) wide, bearing a single accessory sucker, 10–20 (14, n= 8) long by 20–40 (29, n= 8) wide. Cephalic peduncle 288–456 (373, n= 5) long by 52–80 (65, n= 5) wide covered with spinitriches; (BL: CPL) 1: 1.2–1.6. Hook dimensions: Hooks of similar shape; handle and prongs about equal in length. Lateral hook (n= 6): A = 35–40 (38); B= 60–100 (82); C= 80–110 (88); D= 90–135 (114); E= 110–150 (125); W= 30–40 (38). Medial hook (n= 6): A’= 30–40 (33); B’= 75–110 (87); C’= 65–100 (88); D’= 100–140 (118); E’= 95–140 (123); W’= 40–60 (45). (THL: BL) 1: 2.7 to 1: 2.8. Strobila: Immature segments, 2–6 (4, n= 5) per worm wider than long becoming longer than wide with maturity. Mature segments, 350–570 (483, n= 3) long by 135–200 (165, n= 3) wide, 1 (1, n= 4) per worm. Genital pore opening on lateral margin, 59–69 % (63, n= 3) from posterior end of the segment; genital atrium shallow. Cirrus sac near middle of segment, subspherical in mature segments, 60–164 (142, n= 5) long by 50–108 (85, n= 5) wide, containing coiled cirrus; cirrus armed with microtriches. Testes arranged in two, single layered columns extending between ovarian lobes near ovarian isthmus to near anterior extremity of segment. Testes 22–29 (26, n= 3) in number, 5–7 (6, n= 3) preporal, 10–13 (12, n= 3) aporal, 4–6 (5, n= 3) postporal; subspherical 30–50 (37, n= 10) long by 25–40 (33, n= 10) wide. Vas deferens anteromedian, sinuous, enters cirrus sac at adnate pole. Ovary posterior, inverted -A shaped in frontal view (Fig. 12), 192–418 (272, n= 3) long, by 104–152 (132, n= 3) wide, bilobed in cross-section, lobes approximately equal in length, extending c. 75 % distance to cirrus sac from posterior end of segment; ovarian isthmus well posterior. Mehlis’ gland and ootype small, elongated, c. 15–27 long by 10–23 wide, located immediately posterior to ovarian isthmus. Vagina thick-walled, ascends along midline as sinuous tube from ootype to cirrus sac, then laterally along anterior border of cirrus sac to enter genital atrium; seminal receptacle, c. 15 in diameter, at level of ovarian isthmus; vaginal sphincter absent. Vitellarium in 2 lateral follicular columns, each column 1–2 follicles deep, extending from just posterior to ovarian isthmus to level of the most anterior testes; interrupted by cirrus sac and vagina on poral side. Uterus median, tubular, extending from ootype to near anterior extremity of segment. Excretory ducts lateral. Remarks: Acanthobothrium lentiginosum from R. lentiginosus is a category 1 species (SFFS) and possesses ovarian lobes of approximately equal length that reach about 75 % of the distance from the posterior end of the segment to the level of the cirrus sac (Goshroy & Caira 2001). This is the first species of Acanthobothrium described from a guitarfish (Rhinobatidae) in the Atlantic Ocean and only the fifth species of Acanthobothrium reported from the genus Rhinobatos worldwide. Fyler and Caira (2004) reported finding Acanthobothrium in two species of guitarfish from Senegal but did not describe them. The Atlantic guitarfish, R. lentiginosus, is found along the east coast of North America and the Gulf of Mexico in coastal waters and in Cuba (Robins & Ray 1986; Froese & Pauly 2010). Other species of Acanthobothrium described from rhinobatids are: Acanthobothrium olseni Dailey & Mudrey, 1968, Acanthobothrium rhinobati Alexander, 1953 and Acanthobothrium robustum Alexander, 1953 all from Rhinobatos productus (Ayres); Acanthobothrium satyanarayanaroi Sarada, Lakshmi & Rao, 1993 in Glaucostegus granulatus (Cuvier); and Acanthobothrium southwelli Subhapradha, 1955 in Rhinobatos schlegelii Müller & Henle. Acanthobothrium lentiginosum can be differentiated from all of these species using the original descriptions and categorical system of Ghoshroy & Caira (2001) as follows: A. olseni belongs to category 2 in having an asymmetrical ovary, and A. lentiginosum possesses fewer testes (22–29 vs. 26–39) and a shorter cephalic peduncle (288–456 vs. 667); A. rhinobati fits categories 9 (5) due to the variable number of segments and a symmetrical ovary and is different from A. lentiginosum by larger overall size (32mm. vs. 2–3 mm) and greater numbers of segments (50 vs. 5–7) and testes (51–62 vs. 22–29); A. robustum is designated a category 4 species by possessing a symmetrical ovary, and differs in possession of 2 accessory suckers per bothridium and an accessory spur on each outer hook prong; A. satyanarayanaroi is a much larger worm (9–15 cm vs. 2–3 mm) with many segments and testes (80–90 vs. 22–29); and finally, A. lentiginosum differs from A. southwelli in the absence of postovarian testes, total number of testes (22–29 vs. 34) and number of postporal testes (4–6 vs. 13). Acanthobothrium lentiginosum differs from other category 1 species in the western Atlantic in the following ways: from Acanthobothrium fogeli Goldstein, 1964 by the presence of postporal testes and fewer testes in total (22–29 vs. 36–54); it differs from Acanthobothrium himanturi Brooks, 1977 by its smaller size (2–3mm vs.> 3.8 mm long), fewer segments (5–7 vs. 17–26) and fewer testes (22–29 vs. 38–57); A. lentiginosum lacks a vaginal sphincter and has a more anterior genital pore (59–69 % vs. 50 %) than A. lineatum; it differs from A. lintoni in possessing fewer segments (5–7 vs. ave. 23), and fewer total testes (22–29 vs. 30–46); it possesses fewer aporal testes (10–13 vs. 17–34) and shorter ovarian lobes (192–418 vs. 620–676) than A. paulum; and A. lentiginosum is smaller (2–3 mm vs. 4.79–8.44 mm) and has fewer segments (5–7 vs. 18–30) than A. marplatense Ivanov & Campbell, 1998. In the eastern North Atlantic and Mediterranean Sea A. lentiginosum closely resembles A. minus Tazerouti, Kechemir-Issad & Euzet, 2009 from Raja asterias Delaroche from Algeria and Acanthobothrium mathiasi Euzet, 1959 in Mustelus mustelus (Linnaeus) and M. canis from the Mediterranean Sea. Acanthobothrium lentiginosum differs from A. minu s in numerous characters including the distribution of testes (preovarian testes vs. between ovarian lobes), ovarian symmetry and extent of ovarian lobes (75 % of distance to cirrus sac vs. beyond level of cirrus sac). It differs from A. mathiasi in possessing a shorter total hook length (100–140 vs. 155–200) and fewer testes per segment (22–29 vs. 26–43). Other small species of Acanthobothrium from the eastern North Atlantic that have been reported from various hosts including rhinobatids and are <5mm total length, have similar scolex morphology and hook form and have <30 testes are: Acanthobothrium dujardinii van Beneden, 1849, Acanthobothrium edwardsi Williams, 1969 from Raja (Leucoraja) fullonica Linnaeus, Acanthobothrium quadripartitum Williams, 1968 from Raja naevus Montagu and Acanthobothrium tripartitum Williams, 1969. Despite the numerous hosts and disparate localities reported for A. dujardinii discussed by Williams (1969) it is distinct from A. lentiginosum in the possession of marginal lappets on the bothridia, as is A. edwardsi (see illustrations of Williams (1969); Figs. 21, 39,47), which also differs in having ovarian lobes that extend to the cirrus sac. Acanthobothrium lentiginosum differs from A. quadripartitum in number of testes (22–29 vs. 18), locular ratio and total hook length (90–140 vs. 80–90) and from A. tripartitum in testis number (22–29 vs. 13–16) and ovarian symmetry and form where the lobes do not reach or exceed the level of the cirrus sac as they do in A. tripartitum. Acanthobothrium lentiginosum can be differentiated from category 1 species from the eastern Pacific as follows: it has a smaller anterior loculus (100–235 vs. 272–310), and shorter medial and lateral total hook lengths (100 –140, 90– 135 vs. 163–166, 193 – 195) than Acanthobothrium atahualpai Marques, Brooks & Barriga, 1997; it possesses fewer testes than Acanthobothrium dollyae Caira & Burge, 2001 (22–29 vs. 42–55); it possesses more testes (22–29 vs. 6–10) and has a more anterior genital pore (58–69 % vs. 10–37 %) than Acanthobothrium minisculum Marques, Brooks & Barriga, 1997; it is shorter than Acanthobothrium monski Marques, Brooks & Barriga, 1997 (2–3 vs. 3.4–7.6 mm) and possesses fewer segments (5–7 vs. 24–48); A. lentiginosum has fewer segments (5–7 v. 13 –19) and lacks the vaginal sphincter and protruding genital pore of A. nicoyaense; and it has fewer segments than Acanthobothrium royi Caira & Burge, 2001 (5–7 vs. 19–26). In the Indo-Pacific region A. lentiginosum can be differentiated from five category 1 species by the absence of postovarian testes (Acanthobothrium foulki Reyda& Caira, 2006; Acanthobothrium marymichaelorum Twohig, Caira & Fyler, 2008; Acanthobothrium larsoni Reyda &Caira, 2006; Acanthobothrium saliki Fyler & Caira, 2006; and A. southwelli). It lacks the weak horizontal band of musculature running across the posterior loculi of Acanthobothrium asnihae Fyler & Caira, 2006 and Acanthobothrium gnomus Reyda & Caira, 2006 and it has fewer testes (22–29 vs. 44–45) than Acanthobothrium guptai Shinde & Bhagwan, 2002. Acanthobothrium lentiginosum has fewer segments than A. zainali Fyler & Caira, 2006 (5–7 vs. 19–26) In the waters of Australia, numerous species belonging to category 1 have been described by Campbell and Beveridge (2002), Fyler & Caira (2006) and Fyler et al. (2009). A canthobothrium lentiginosum differs from each of these as follows: from Acanthobothrium bartonae Campbell & Beveridge, 2002 by bothridial shape (acuminate vs. rounded), and longer abaxial prongs (65–100 / 80–100 vs. 54–67 / 61– 65); it possesses fewer testes than Acanthobothrium clarkae Campbell & Beveridge, 2002, Acanthobothrium laurenbrownae Campbell & Beveridge, 2002, Acanthobothrium urolophi Schmidt, 1973, and Acanthobothrium pearsoni Williams, 1962 (22–29 vs. 45 –52, 31– 46, 34–41, 56– 60 respectively) but has more testes than Acanthobothrium martini Campbell & Beveridge, 2002, Acanthobothrium stevensi Campbell and Beveridge, 2002 and Acanthobothrium thomasae Campbell and Beveridge, 2002 (22–29 vs. 8 –11, 14–18, 12– 18 respectively); it lacks the vaginal sphincter and short cephalic peduncle (288–456 vs. 25–150) of Acanthobothrium mooreae Campbell & Beveridge, 2002; it lacks the very long microtriches on the cephalic peduncle and has fewer postporal testes (4–6 vs. 7–12) than Acanthobothrium odonoghuei Campbell &Beveridge, 2002; it possesses longer bothridia (240–430 vs. 170–228) and longer medial hook prongs (50–75 vs. 34–59) than Acanthobothrium rohdei Campbell & Beveridge, 2002; it has more postporal testes (4–6 vs. 0–2), fewer segments (5–7 vs. 16–23) and longer lateral abaxial hook lengths (80–110 vs. 65–75) than Acanthobothrium romanowi Fyler, Caira & Jensen, 2009; it has fewer segments (5–7 vs. 9–13) and smaller suckers (10–20 vs. 35–53) than Acanthobothrium oceanharvestae Fyler, Caira & Jensen, 2009; and it is distinct from Acanthobothrium zimmeri Fyler, Caira & Jensen, 2009 in having more postporal testes (4–6 vs. 1–2) and in lacking testes posterior to the ovarian isthmus (0 vs. 2–6).Published as part of Vardo-Zalik, Anne M. & Campbell, Ronald A., 2011, Five new species of Acanthobothrium van Beneden, 1849 (Cestoda: Tetraphyllidea) in elasmobranchs from the northwest Atlantic and Gulf of Mexico with first records from smooth-hound sharks and guitarfish, pp. 41-64 in Zootaxa 2838 on pages 48-51, DOI: 10.5281/zenodo.20600

Alterations in Plasmodium falciparum Genetic Structure Two Years after Increased Malaria Control Efforts in Western Kenya

The impact of malaria intervention measures (insecticide-treated net use and artemisinin combination therapy) on malaria genetics was investigated at two sites in western Kenya: an endemic lowland and an epidemic highland. The genetic structure of the parasite population was assessed by using microsatellites, and the prevalence of drug-resistant mutations was examined by using the polymerase chain reaction-restriction fragment length polymorphism method. Two years after intervention, genetic diversity remained high in both populations. A significant decrease in the prevalence of quintuple mutations conferring resistance to sulfadoxine-pyrimethamine was detected in both populations, but the mutation prevalence at codon 1246 of the Plasmodium falciparum multidrug resistance 1 gene had increased in the highland population. The decrease in sulfadoxine-pyrimethamine-resistant mutants is encouraging, but the increase in P. falciparum multidrug resistance 1 gene mutations is worrisome because these mutations are linked to resistance to other antimalarial drugs. In addition, the high level of genetic diversity observed after intervention suggests transmission is still high in each population

A cohort study of Plasmodium falciparum infection dynamics in Western Kenya Highlands

BackgroundThe Kenyan highlands were malaria-free before the 1910s, but a series of malaria epidemics have occurred in the highlands of western Kenya since the 1980s. Longitudinal studies of the genetic structure, complexity, infection dynamics, and duration of naturally acquired Plasmodium falciparum infections are needed to facilitate a comprehensive understanding of malaria epidemiology in the complex Kenyan highland eco-epidemiological systems where malaria recently expanded, as well as the evaluation of control measures.MethodsWe followed a cohort of 246 children residing in 3 villages at altitudes 1430 - 1580 m in western Kenya. Monthly parasitological surveys were undertaken for one year, yielding 866 P. falciparum isolates that were analyzed using 10 microsatellite markers.ResultsInfection complexity and genetic diversity were high (HE = 0.787-0.816), with ≥83% of infections harboring more than one parasite clone. Diversity remained high even during the low malaria transmission season. There was no significant difference between levels of genetic diversity and population structure between high and low transmission seasons. Infection turn-over rate was high, with the average infection duration of single parasite genotypes being 1.11 months, and the longest genotype persistence was 3 months.ConclusionsThese data demonstrate that despite the relatively recent spread of malaria to the highlands, parasite populations seem to have stabilized with no evidence of bottlenecks between seasons, while the ability of residents to clear or control infections indicates presence of effective anti-plasmodial immune mechanisms

Epidemiological risk factors for clinical malaria infection in the highlands of Western Kenya.

BackgroundUnderstanding the complex heterogeneity of risk factors that can contribute to an increased risk of malaria at the individual and household level will enable more effective use of control measures. The objective of this study was to understand individual and household factors that influence clinical malaria infection among individuals in the highlands of Western Kenya.MethodsThis was a matched case-control study undertaken in the Western Kenya highlands. Clinical malaria cases were recruited from health facilities and matched to asymptomatic individuals from the community who served as controls. Each participant was screened for malaria using microscopy. Follow-up surveys were conducted with individual households to collect socio-economic data. The houses were also checked using pyrethrum spray catches to collect mosquitoes.ResultsA total of 302 malaria cases were matched to 604 controls during the surveillance period. Mosquito densities were similar in the houses of both groups. A greater percentage of people in the control group (64.6%) used insecticide-treated bed nets (ITNs) compared to the families of malaria cases (48.3%). Use of ITNs was associated with lower level of clinical malaria episodes (odds ratio 0.51; 95% CI 0.39-0.68; P &lt; 0.0001). Low income was the most important factor associated with higher malaria infections (adj. OR 4.70). Use of malaria prophylaxis was the most important factor associated with less malaria infections (adj OR 0.36). Mother's (not fathers) employment status (adj OR 0.48) and education level (adj OR 0.54) was important malaria risk factor. Houses with open eaves was an important malaria risk factor (adj OR 1.72).ConclusionThe identification of risk factors for clinical malaria infection provides information on the local malaria epidemiology and has the potential to lead to a more effective and targeted use of malaria control measures. These risk factors could be used to assess why some individuals acquire clinical malaria whilst others do not and to inform how intervention could be scaled at the local level