Changes in vector species composition and current vector biology and behaviour will favour malaria elimination in Santa Isabel Province, Solomon Islands

Hugo Bugoro 1 2 Charlie Iro'ofa 2 Donna O Mackenzie 0 Allen Apairamo 2 Watson Hevalao 2 Sarah Corcoran 0 Albino Bobogare 2 Nigel W Beebe 4 Tanya L Russell 3 Cheng-Chen Chen 1 Robert D Cooper 0 0 Australian Army Malaria Institute , Gallipoli Barracks, Enoggera, 4052 , Australia 1 Institute of Tropical Medicine, National Yang-Ming University , No. 155, Sec.2, Li-Nong Street, Taipei 112 , Taiwan 2 National Vector Borne Disease Control Programme, Ministry of Health , Honiara , Solomon Islands 3 The University of Queensland, School of Population Health, Australian Centre for Tropical and International Health, Pacific Malaria Initiative Support Centre , Herston, 4006 , Australia 4 School of Biological Sciences, University of Queensland , Goddard Building, St.Lucia, Qld 4068 , Australia Background: In 2009, Santa Isabel Province in the Solomon Islands embarked on a malaria elimination programme. However, very little is known in the Province about the anopheline fauna, which species are vectors, their bionomics and how they may respond to intensified intervention measures. The purpose of this study was to provide baseline data on the malaria vectors and to ascertain the possibility of successfully eliminating malaria using the existing conventional vector control measures, such as indoor residual spraying (IRS) and long-lasting insecticidal nets (LLIN). Methods: Entomological surveys were undertaken during October 2009. To determine species composition and distribution larval surveys were conducted across on the whole island. For malaria transmission studies, adult anophelines were sampled using human landing catches from two villages - one coastal and one inland. Results: Five Anopheles species were found on Santa Isabel: Anopheles farauti, Anopheles hinesorum, Anopheles lungae, Anopheles solomonis, and Anopheles nataliae. Anopheles hinesorum was the most widespread species. Anopheles farauti was abundant, but found only on the coast. Anopheles punctulatus and Anopheles koliensis were not found. Anopheles farauti was the only species found biting in the coastal village, it was incriminated as a vector in this study; it fed early in the night but equally so indoors and outdoors, and had a low survival rate. Anopheles solomonis was the main species biting humans in the inland village, it was extremely exophagic, with low survival rates, and readily fed on pigs. Conclusion: The disappearance of the two major vectors, An. punctulatus and An. koliensis, from Santa Isabel and the predominance of An. hinesorum, a non-vector species may facilitate malaria elimination measures. Anopheles farauti was identified as the main coastal vector with An. solomonis as a possible inland vector. The behaviour of An. solomonis is novel as it has not been previously found biting humans in any numbers. Both species appear to be short-lived, a characteristic that will limit their transmission potential. The early night feeding behaviour and a degree of outdoor biting seen in An. farauti and particularly in An. solomonis will require that their response to IRS and LLIN be closely monitored. In coastal villages, where large, favourable breeding sites allow for high numbers of An. farauti may require the addition of larval control to achieve elimination. - Background Recently, the international community has prioritized national and regional malaria elimination based on the strategy of shrinking the malaria map from the margins inwards [1]. The Solomon Islands is at the eastern edge of the distribution of malaria in the southwest Pacific, the disease is endemic throughout many parts of the country and up until the early 1990s was the leading public health problem [2]. The Solomon Islands has now entered the malaria pre-elimination stage together with 31 other countries [3]. To initiate this, the countrys National Vector Borne Disease Control Programme (NVBDCP) has selected Temotu and Santa Isabel Provinces in which to commence malaria elimination programmes. In the remaining six provinces intensified control will be implemented. Malaria eradication was attempted in Solomon Islands through a Malaria Eradication Programme (MEP) conducted during 1970 - 1975 [4]. On Santa Isabel, this programme was highly successful and elimination was nearly achieved with entry into the consolidation phase (cessation of DDT - IRS) planned for 1974 [4]. However similar success was not achieved in other parts of the country, most notably on the north coast of Guadalcanal [5]. The MEP was abandoned in 1975 and reduced to control measures and focal DDT indoor residual spraying (IRS) to contain outbreaks. The malaria rate rose during this period peaking in 1992 [2], in 1993 insecticide impregnated bed nets (ITN) were introduced [6] and in early 2000, DDT was replaced by lambdacyhalothrin (ICON) for IRS, also at this time ITNs were being replaced by long-lasting insecticidal nets (LLIN). Through these intervention methods Santa Isabel Province has maintained a continual attack on the vector for the last 40 years with the introduction of ITN and LLIN resulting in a continual fall in transmission rates from 44% in 1992 to 4.5% in 2008 [Source: SI NVBDCP data: unpublished]. The current malaria situation on Santa Isabel indicates a further reduction in malaria transmission. Passive case detection at the main hospital in the capital Buala recorded 81 cases over 33 months, January 2007 to September 2009. At least 11 of these cases were reported as being imported from other provinces - Guadalcanal and Malaita. The species composition was Plasmodium falciparum 47% and Plasmodium vivax 53%. A mass blood survey conducted on Santa Isabel in October 2009 screened 8552 of the local population. A total of 14 were found positive by microscopy (n = 1) and PCR (n = 13) giving a parasite prevalence rate of 0.16%; of these 92.9% were due to P. vivax and the remainder due to P. falciparum [7]. Several species of anophelines occur in the Solomon Islands, six members of the Anopheles punctulatus group: Anopheles farauti (formerly Anopheles farauti 1), Anopheles irenicus (formerly Anopheles farauti 7), Anopheles hinesorum (formerly Anopheles farauti 2), Anopheles punctulatus, Anopheles koliensis, and Anopheles rennellensis [8,9]; as well as three members of the Anopheles lungae complex: Anopheles lungae, Anopheles solomonis, and Anopheles nataliae [10]. Of these nine species, only An. farauti, An. punctulatus and An. koliensis are considered vectors of malaria [10]. With the latter two species the use of IRS and LLIN over the years appears to have eliminated An. koliensis and An. punctulatus is now uncommon with a patchy distribution [11,12]. The third species, An. farauti, did not respond well to IRS during the MEP and subsequent control programmes due to a change in behaviour to early evening, outdoor biting [12]. This species is now the primary vector in the Solomon Islands, being the most abundant and widespread species [13]. It is primari (...truncated)