3.2 Introduction
Fleas (Siphonaptera) are hematophagous insects and obligatory ectoparasites of vertebrates that have colonized variety of habitats from wet tropical forests to semi-arid and desert areas ( Zając et al ., 2020; Zhang et al ., 2022). They have an obligate parasitic life with a wide range of potential hosts, primarily small mammals and less often birds (Eads et al ., 2020). Fleas exhibit a holometabolous type of lifecycle and complete their life cycle in 14 days to 140 days, depending mainly on temperature and humidity (Krämer and Mencke, 2012; Ashwini et al ., 2017; Gram and Short, 2020).
Fleas contribute significantly in the circulation of pathogens hence receiving considerable attention mostly because they are vector of many zoonotic diseases (Eads et al ., 2020). They play role in spreading plague disease as well as other emerging pathogens that causes zoonoses such as bartonelloses, tularemia and rickettsioses (flea-borne spotted fever, Q fever and murine typhus), fleas also maintains and transmits pathogens of myxomatosis and trypanosomiasis and can act as intermediate hosts of some helminthes (Zając et al ., 2020; Cófreces et al ., 2021). However, the most known flea borne zoonotic disease is plague caused by bacteria known as Yersinia pestis ; a zoonotic bacteria renowned for killing millions of humans during the Black Death in Europe in 14 century (Ditchburn and Hodgkins, 2019; Barbieri et al ., 2021; Izdebski et al ., 2022). Plague is still threatening the public health in some parts of the world, especially in African countries (Ditchburn and Hodgkins, 2019). By doing surveillance studies on flea assemblage on rodent community in plague endemic areas we can understand factors that influence flea abundance and infestation potential on rodents and being aware of significant factors that may endanger the public health and therefore we can be in a good position to suggest effective intervention strategies to control their spread.
Plague persistence in plague endemic areas is characterized by coexistence of interactions among rodent communities and flea species, whereby some species of rodents and fleas are better at maintaining, amplifying and transmitting Yersinia pestis (Gage and Kosoy, 2006; Antolin et al ., 2010). Some of frequently reported fleas and rodents species involved in plague maintenance and transmission areXenopsylla cheopis, Xenopsylla brasiliensis andDinopsyllus lypusus and rodent species Lophuromys spp ,Praomys delectorum , Graphiurus murinus , Lemniscomys striatus, Mastomys natalensis , and Rattus rattus (Kilonzoet al ., 2006; Makundi et al ., 2008; Eisen and Gage, 2009). A study done by Ziwa et al. (2013) has reported the concurrence of host-vector interaction to be responsible for transmission of plague disease. Also Makundi et al. (2015) has reported the presence of multiple associations between domestic and peridomestic rodent species infested with fleas to be among major contributing factors for persistence and spread of plague in plague endemic areas. Moreover, the roles of hosts and fleas, for instance in plague maintenance or amplification, is mostly affected with change of space and time (Kosoyet al ., 2017).
The distributions and community structure of fleas are influenced by numerous biotic and abiotic factors, that include, host species diversity, sex, age, body size, immune status, host population abundance, habitat diversity and seasonal variation of temperature and precipitation (López-Pérez et al ., 2017, 2022). Host diversity is a relevant factor to consider since it involves variation in flea species richness (Fantozzi et al ., 2022), yet it is not a fixed rule, fleas can infest hosts phylogenetically close, switching between coexisting species within guilds (Cófreces et al ., 2021).
Noting this uncertainty plague management in plague foci is mostly efficient when encompassing rodents and their flea parasites. As described by Garcia-Longoria et al. (2019) host communities can influence parasitism. Community organization of parasites is considered to be determined mainly by their hosts because host present a habitat for parasites, providing them with place for living, feeding and mating (Fellin and Schulte, 2022). Thus, a host can be reflected as a biological shelter for parasites. Unlike endoparasites, ectoparasites are influenced not only by host characteristics, but also by characteristics of the host environment (Krasnov et al ., 1997). Therefore, a habitat of the ectoparasite should not be just a particular host, but a particular host in a particular habitat. If so, an important determinant of parasite community structure should be a complex host-habitat relationship. Quantifying variation of ectoparasites load among host species and comparing these variation with other ecological factors which are known to shape host communities is the good approach for understanding dual nature of host-parasite interaction (Merrillet al ., 2020; Veitch et al ., 2020).
Concisely, the aim of this study was to examine rodent’s flea load and their associated factors in plague endemic area of Karatu district by i) quantifying and assessing the variation of flea’s parasitological indices (specific flea index, total flea index and flea infestation prevalence on rodents), ii) assessing the association of abundance of species of fleas with rodent species, plague and non-plague foci villages, season (wet and dry season), habitat type and rodent sex, iii) investigating flea biased parasitism on rodent’s weight and sex (male and female rodents) and lastly, iv) assessing the influence of host characteristics (rodent species, sex and weight), habitat type, season and plague locations on abundance of fleas. Result of this study will help to create awareness to the public health sectors and vector control programs by providing valuable information that will help in decision making process regarding flea control in plague endemic area of Karatu district, northern Tanzania.