Malaria vector sibling species distribution in different endemic districts of Punjab, India.

BACKGROUND & OBJECTIVES: Malaria transmission in Punjab, India is mainly seasonal with variation in its endemicity that may be due to varying vector behaviour in different areas of the state, primarily attributed to the existence of sibling species complexes among the vector species. So far there is no report regarding the existence of malaria vectors sibling species in the state of Punjab, therefore, the present study was planned to investigate the status of sibling species of two main vectors of malaria viz. Anopheles culcifacies and Anopheles fluviatilis in different districts of Punjab. METHODS: Mosquito collections were made through hand catch in the morning hours. Malaria vector species An. culicifacies and An. fluviatilis were morphologically identified and man hour density was calculated. Both the vector species were subjected to molecular assays for sibling species identification through amplification of D3 domain of 28S ribosomal DNA by allele-specific PCR. RESULTS: Four sibling species of An. culicifacies, were identified viz. A, B, C and E. Species A was identified from Bhatinda district, species B, C and E from. S.A.S. Nagar and species C from Hoshiarpur. Two sibling species S and T of An. fluviatilis were identified from districts S.A.S. Nagar and Rupnagar. INTERPRETATION & CONCLUSION: Presence of four sibling species of An. culicifacies and two sibling species of An. fluviatilis in Punjab necessitates planning of longitudinal studies to ascertain their role in disease transmission so that appropriate interventions may be applied to achieve malaria elimination.

Impact of changing over of insecticide from synthetic pyrethroids to DDT for indoor residual spray in a malaria endemic area of Orissa, India.

BACKGROUND & OBJECTIVES: Development of insecticide resistance in malaria vectors has been a major problem for achieving effective vector control. Due to limited availability of insecticides, the only option is management of resistance by judiciously using the insecticides and rotating them to maintain their effectiveness. This study was carried out in a malaria endemic area of Sundergarh district in Orissa where synthetic pyrethroids (SP) were in use for the last couple of years. The change-over from SP to DDT was done in one arm of study, and the other two arms remained on SP and insecticide-treated nets (ITN). Entomological and parasitological monitoring was done to assess the impact. METHODS: The study design comprised of three arms (i) two rounds of indoor residual spraying (IRS) with DDT 1g/m(2) as a change-over insecticide in areas previously under synthetic pyrethroids; (ii) two rounds of IRS with synthetic pyrethroid (alphacypermethrin, ACM) @ 25 mg/m(2) ; and (iii) an unsprayed area under ITN/long lasting insecticide nets (LNs). Indoor residual spraying was undertaken under strict supervision to maintain quality and coverage. Contact bioassays were conducted to know the persistence of insecticide on sprayed surfaces and adult vector density was monitored in fixed and randomly selected houses. Malaria incidence was measured through fortnightly domiciliary surveillance under primary health care system in all the study villages. RESULTS: The insecticide susceptibility tests showed that An.culicifacies was resistant to DDT but susceptible to malathion and ACM. However, An. fluviatilis was susceptible to all the three insecticides. ACM was effective in killing An. culicifacies on mud and wooden sprayed surfaces and maintained effective bioefficacy ranging from 92 to 100 per cent up to five months, whereas DDT failed to achieve effective mortality in An.culicifacies. However, there was significant decline in the density of An.culicifacies in ACM and DDT areas in comparison to ITNs/LNs. There was 61 per cent reduction in the slide positivity rate in ACM area in comparison to 48 and 51 per cent in DDT and ITN/LNs areas, respectively. The adjusted incidence rate of malaria cases per 1000 population in three study areas also showed significant declines within each group. INTERPRETATION & CONCLUSIONS: The present findings show that the change-over of insecticide from synthetic pyrethroids to DDT brings about the same epidemiological impact as envisaged from continuing SP spray or distributing insecticide treated nets/long-lasting insecticidal nets provided there is a good quality spray and house coverage.

Wash-resistance and field evaluation of alphacypermethrin treated long-lasting insecticidal net (Interceptor) against malaria vectors Anopheles culicifacies and Anopheles fluviatilis in a tribal area of Orissa, India.

A field trial was conducted on the efficacy of Interceptor nets-a long-lasting insecticidal net (LLN) factory treated with alphacypermethrin 0.667% (w/w) corresponding to 200mg/m(2), against malaria vectors Anopheles culicifacies and Anopheles fluviatilis in one of the highly endemic areas of Orissa. The study area comprised 19 villages which were randomized into three clusters and designated as Interceptor net cluster, untreated net cluster, and no net cluster. Baseline studies showed that both the vector species An. culicifacies and An. fluviatilis were 100% susceptible to alphacypermethrin. Results of wash-resistance and bio-efficacy of Interceptor nets showed 100% mortality in An. culicifacies and An. fluviatilis even after 20 washings. Bioassays on the Interceptor nets while in use in the field conditions showed a knockdown effect on 70-90% mosquitoes during different months of intervention after 3 min of exposure and 100% mortality was recorded after 24h of recovery period. The median knockdown time for these species ranged between 4.10-5.25 min and 4.00-5.00 min respectively during intervention period. In Interceptor net study area, there was a significant reduction of 88.9, 96.3 and 90.6% in the entry rate of An. culicifacies, An. fluviatilis and other anopheline species respectively with an over all reduction of 87.5% in total mosquitoes. The overall feeding success rate of mosquitoes in the trial villages was only 12.8% in comparison to 35.0 and 78.8% in villages with untreated nets and no nets respectively. A significant reduction was also recorded in parity rate and human blood index of vector species in Interceptor net area. The results of the study showed that Interceptor nets are effective against the malaria vectors and may be used as a suitable intervention strategy in high-risk areas.

Efficacy of permethrin treated long-lasting insecticidal nets on malaria transmission and observations on the perceived side effects, collateral benefits and human safety in a hyperendemic tribal area of Orissa, India.

Studies were conducted on the efficacy of Olyset nets-a long-lasting insecticidal net (LLIN) factory treated with 2% (w/w) permethrin on malaria transmission in an area under the influence of pyrethroid susceptible vector species Anopheles culicifacies and A. fluviatilis in Sundargarh District, Orissa, India. The study area comprised 22 villages that were randomized into three clusters and designated as Olyset net, untreated net, and no net area. Malaria incidence in the study population was measured through longitudinal active surveillance at fortnightly intervals. There was a reduction of 65-70% in malaria incidence in Olyset net area as compared to the control areas. The attack rate of Plasmodium falciparum or number of episodes per person per year in different age groups also showed significant reduction in Olyset net area as compared to untreated net and no net areas. Cross-sectional point prevalence surveys showed 45.7% reduction of malaria prevalence in Olyset net users, whereas there was an increase of 33.3% and 51% in untreated net and no net villages respectively. The compliance rate of Olyset net usage in the study population was 80-98% during different months, whereas it was between 70% and 90% for untreated nets. There were minimal complains of skin irritation (4%), itching (8%) and eye irritation (1.2%). However, these effects were only transitory in nature lasting for few hours of the first usage. Olyset nets also provided collateral benefits in terms of relief not only from mosquitoes and malaria but also from other household pests such as head lice, bed bugs, cockroaches, ants and houseflies. The Olyset nets were found to be safe to humans as no adverse event was recorded in the net users that can be attributed to the use of net. The study showed that Olyset nets are effective personal protection tool that can be used in a community based intervention programme.

Building small dams can decrease malaria: a comparative study from Sundargarh District, Orissa, India.

The adverse health effect of environmental changes brought about with the construction of large and small dams has often been reported. Here, we present results of a 5-year (2001-2005) study documenting the positive effect of such developmental projects in reducing malaria in an area where malaria transmission is mainly due to the highly efficient anthropophagic vector Anopheles fluviatilis with some contribution from Anopheles culicifacies. The former breeds exclusively in the slow-flowing streams and the latter breeds in a variety of habitats. The study was conducted in San Dulakudar village and comparisons were made with two control villages situated near the stream with similar topography and malaria transmission pattern. Epidemiological data was collected through longitudinal weekly surveillance and cross-sectional surveys in all the study villages. The mean annual malaria incidence rates due to Plasmodium falciparum in children of 1-5 years age group during 2001 before construction of dam was 1304.3 and 785.7 cases/1000 population in dam site village and control villages, respectively. However, after construction of dam, there was gradual reduction in the malaria cases in dam site village and during 2005 the incidence was significantly reduced to 181.8 (P<0.01) whereas it was increased to 1000 in control villages without any significant change in comparison to baseline year (P>0.05). A significant reduction in malaria incidence and parasite rate was also recorded in all the age groups in dam site village without registering any significant change in control villages. The construction of a small dam in the study village altered the water flow above and below the dam thereby making it unfavourable for the breeding of A. fluviatilis which in turn brought about significant impact on malaria transmission.

Epidemiology of malaria transmission in forest and plain ecotype villages in Sundargarh District, Orissa, India.

A study of the epidemiology of malaria transmission was undertaken in 13 tribal villages located in forest and plain areas of Sundargarh District of Orissa state, India, from January 2001 to December 2003. In forest areas, intense transmission of malaria is attributed to the highly anthropophagic vector Anopheles fluviatilis sibling species S and is complemented by A. culicifacies sibling species C. In plain areas, A. culicifacies sibling species C is responsible for malaria transmission. The entomological inoculation rate in the forest and plain areas was 0.311 and 0.014 infective bites/person/night, respectively, during 2003. Malaria transmission is perennial both in forest and plain areas but is markedly low in the plain area compared with the forest area. Plasmodium falciparum accounted for 85.0% of the total malaria cases during the study period. In forest and plain areas, the number of P. falciparum cases per 1000 population per year was 284.1 and 31.2, respectively, whereas the parasite rate was 14.0% and 1.7%, respectively. In forest areas, clinical malaria occurs more frequently in children aged 0-5 years and declines gradually with increasing age. The study showed that villages in forest and plain areas separated by short geographical distances have distinct epidemiology of malaria transmission.