Surveillance of Fleas and Their Small Mammal Hosts for Plague Risks in Some Main Seaports of the Islands of the Southwestern Indian Ocean.

Since ancient times, seaports have been the hot spots for plague introduction into free countries. Infected ship rats reached new areas, and epizootics occurred prior to human infection via flea bites. Beginning in the 1920s/1930s, rodent and flea surveillance was carried out as part of plague hazard management in seaports of the world. Nowadays, such activity is not done regularly. In the southwestern Indian Ocean (SWIO) region, plague surveillance is of great importance given plague endemicity in Madagascar and thus the incurred risk for neighboring islands. This study reports animal-based surveillance aimed at identifying fleas and their small mammal hosts in SWIO seaports as well as Yersinia pestis detection. Small mammal trappings were performed in five main seaports of Madagascar (Toamasina and Mahajanga), Mauritius (Port Louis), and the Union of Comoros (Moroni and Mutsamudu). Mammals were euthanized and their fleas collected and morphologically identified before Y. pestis detection. In total, 145 mammals were trapped: the brown rat Rattus norvegicus (76.5%), the black rat Rattus rattus (8.3%), and the Asian house shrew Suncus murinus (15.2%). Fur brushing allowed collection of 1,596 fleas exclusively identified as Xenopsylla cheopis. All tested fleas were negative for Y. pestis DNA. This study shows that both well-known plague mammal hosts and flea vectors occur in SWIO seaports. It also highlights the necessity of carrying out regular animal-based surveillance for plague hazard management in this region.

Knockdown resistance mutations are common and widely distributed in Xenopsylla cheopis fleas that transmit plague in Madagascar.

BACKGROUND: Plague, caused by the bacterium Yersinia pestis, remains an important disease in Madagascar, where the oriental rat flea, Xenopsylla cheopis, is a primary vector. To control fleas, synthetic pyrethroids (SPs) have been used for >20 years, resulting in resistance in many X. cheopis populations. The most common mechanisms of SP resistance are target site mutations in the voltage-gated sodium channel (VGSC) gene. METHODOLOGY/PRINCIPAL FINDINGS: We obtained 25 collections of X. cheopis from 22 locations across Madagascar and performed phenotypic tests to determine resistance to deltamethrin, permethrin, and/or dichlorodiphenyltrichloroethane (DDT). Most populations were resistant to all these insecticides. We sequenced a 535 bp segment of the VGSC gene and identified two different mutations encoding distinct substitutions at amino acid position 1014, which is associated with knockdown resistance (kdr) to SPs in insects. Kdr mutation L1014F occurred in all 25 collections; a rarer mutation, L1014H, was found in 12 collections. There was a significant positive relationship between the frequency of kdr alleles and the proportion of individuals surviving exposure to deltamethrin. Phylogenetic comparisons of 12 VGSC alleles in Madagascar suggested resistant alleles arose from susceptible lineages at least three times. Because genotype can reasonably predict resistance phenotype, we developed a TaqMan PCR assay for the rapid detection of kdr resistance alleles. CONCLUSIONS/SIGNIFICANCE: Our study provides new insights into VGSC mutations in Malagasy populations of X. cheopis and is the first to report a positive correlation between VGSC genotypes and SP resistance phenotypes in fleas. Widespread occurrence of these two SP resistance mutations in X. cheopis populations in Madagascar reduces the viability of these insecticides for flea control. However, the TaqMan assay described here facilitates rapid detection of kdr mutations to inform when use of these insecticides is still warranted to reduce transmission of plague.

Illustrated Morphological Keys for Fleas (Siphonaptera) in Madagascar.

Madagascar has an important diversity of fleas (Siphonaptera), which almost species do not exist elsewhere. Scientists have provided huge efforts to improve knowledge on Malagasy fleas since the middle of 1900s particularly by investigating topics such as taxonomy, systematics, biogeography, and flea vector role. Since then, new species discovery has increased and currently, 48 species are recorded which the majority is endemic. Therefore, it becomes necessary to have updated keys to identify species membership. This paper presents morphological-based keys to identify at genus and species levels adult fleas reported as occurring in Madagascar. Illustrations are proposed to make easier the observation of morphological criteria, which may be tricky for sibling species.