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

M. Harimalala et al. Am. J. Trop. Med. Hyg., 110(2), 2024, pp. 311–319. doi:10.4269/ajtmh.23-0363.

Abstract. 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 5 SWIO seaports as well as Yersinia pestis detection: 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.

Note: This study describes a high X. cheopis flea index among mammals collected at SWOI port areas. With increasing global trade from a variety of sources and routes, it would seem MVCAC agencies that include port areas should be aware of this continuing threat to the public health and the importance of the proper use of rodent guards on ship mooring lines.