Since 1996, the incidence of rickettsiosis has been increasing in Yucatán, Mexico, but recent prevalence data are lacking. This study aimed to determine exposure to the Spotted Fever Group (SFG) and Typhus Group (TG) in human serum samples suspected of tick-borne diseases (TBD) between 2015 and 2022. A total of 620 samples were analysed using indirect immunofluorescence assay (IFA) to detect IgG antibodies against SFG (Rickettsia rickettsii) and TG (Rickettsia typhi), considering a titer of ≥64 as positive. Results showed that 103 samples (17%) were positive for R. rickettsii and 145 (24%) for R. typhi, while 256 (41%) and 229 (37%) were negative, respectively. There was a cross-reaction in 244 samples (39%). Individuals with contact with vectors, such as ticks, showed significant exposure to fleas (p = 0.0010). The study suggests a high prevalence of rickettsiosis and recommends prospective studies to assess the disease burden and strengthen surveillance and prevention in Yucatán, considering factors like temperature and ecological changes.

Paul-Louis Simond’s 1898 experiment demonstrating fleas as the vector of plague is today recognised as one of the breakthrough moments in modern epidemiology, as it established the insect-borne transmission of plague. Providing the first exhaustive examination of primary sources from the Institut Pasteur’s 1897–98 ‘India Mission’, including Simond’s notebooks, experiment carnets and correspondence, and cross-examining this material with colonial medical sources from the first years of the third plague pandemic in British India, the article demonstrates that Simond’s engagement with the question of the propagation of plague was much more complex and ambiguous than the teleological story reproduced in established historical works suggests. On the one hand, the article reveals that the famous 1898 experiment was botched, and that Simond’s misreported its ambiguous findings for the Annales de l’Institut Pasteur. On the other hand, the article shows that, in the course of his ‘India Mission’, Simond framed rats as involved in the propagation of plague irreducibly in their relation to other potential sources of infection and not simply in terms of a parasitological mechanism. The article illuminates Simond’s complex epidemiological reasoning about plague transmission, situating it within its proper colonial and epistemological context, and argues for a new historical gaze on the rat as an ‘epidemiological dividual’, which highlights the relational and contingent nature of epidemiological framings of the animal during the third plague pandemic.

Environmental fluctuations are expected to require special adaptations only if they are associated with a decrease in fitness. We compared reproductive performance between fleas fed on alternating (preferred and non-preferred) hosts and fleas fed solely on either a preferred or a non-preferred host to determine whether (1) host alternation incurs an immediate negative effect, and, if yes, then (2) whether this effect is greater in a host specialist (Parapulex chephrenis) than in host generalists (Xenopsylla conformis and Synosternus cleopatrae). We also compared flea performance under alternating host regimes with different host order (initial feeding on either a preferred or a non-preferred host). An immediate negative effect of alternating hosts on reproductive performance was found in P. chephrenis only. These fleas produced 44·3% less eggs that were 3·6% smaller when they fed on alternating hosts as compared with a preferred host. In contrast, X. conformis and S. cleopatrae appeared to be able to adapt their reproductive strategy to host alternation by producing higher quality offspring (on average, 3·1% faster development and 2·1% larger size) without compromising offspring number. However, the former produced eggs that were slightly, albeit significantly, smaller when it fed on alternating hosts as compared with a preferred host. Moreover, host order affected reproductive performance in host generalists (e.g. 2·8% larger eggs when the first feeding was performed on a non-preferred host), but not in a host specialist. We conclude that immediate effects of environmental fluctuation on parasite fitness depend on the degree of host specialization.

To investigate larval development of Acanthocheilonema reconditum in the cat flea Ctenocephalides felis, fleas were fed through an artificial feeding system with dog blood containing different concentrations of microfilariae (i.e. low, group L = 250; medium, group M = 500; high, group H = 1500 microfilariae per mL) or no microfilariae (group C). Fleas were sampled at 12 different time-points throughout the study period (D1–D28) and A. reconditum was detected by dissection, PCR and histology. Of 2105 fleas fed with infected dog blood, 891 (38·7%) died during the study before being sampled whilst the remaining (n = 1214) were examined for A. reconditum. Upon dissection, first-stage larvae (L1) were identified after 2 days post infection (D2), second-stage (L2) at D13 and infective third-stage larvae (L3) at D15. Eighteen (30%) of 60 pools of fleas molecularly examined tested positive. Histologically, L2 were detected at D13 in the sub-cuticle region embedded in the back muscle of one female flea. This study provides original data on larval development of A. reconditum in C. felis and reports on the usefulness of the artificial feeding system.

Habitat fragmentation can adversely impact biodiversity, although where remnant fragments of natural vegetation provide favourable conditions the negative effects of fragmentation may be mitigated. Host-parasite systems in fragmented areas have only recently been examined, with parasites generally showing higher prevalence and richness in fragments, mediated by changes in host density. However, the effect of fragmentation on parasite body size and fecundity remains poorly investigated. Thus, here we compared the body size and condition of a generalist rodent host, Rhabdomys pumilio and the body size of 2 common flea species between pristine natural areas and remnant fragments within agriculture areas. Host body length, weight and body condition values were significantly larger in fragments than in pristine natural vegetation. Listropsylla agrippinae fleas showed the same pattern, being significantly larger in fragments, while Chiastopsylla rossi fleas did not differ in size between fragments and natural areas. The differential response of the 2 flea species may reflect the strength of association between the host and parasite, with the former spending a greater proportion of its lifespan on the host. Therefore, in this study agriculture fragments provide better conditions for both an opportunistic rodent and a closely associated flea species.

Phylogenetic and geographical overlaps in host distributions influence the compositional similarity of ectoparasite fauna in a host–parasite system. In these systems, hosts that are more closely related (phylogenetically) are expected to share more parasitic species than more distantly related hosts. Similarly, hosts sharing a larger geographical distribution overlap are expected to have similar ectoparasites. This study investigated the influence of phylogeny (divergence time) and geographical overlap of some neotropical sigmodontine rodent species on the similarities among their ectoparasite fauna (Mesostigmata and Siphonaptera), using a partial Mantel test. Divergence time was the only significant factor that influenced the similarity among the ectoparasites, when mites and fleas were analysed together. Host species that had diverged more recently displayed ectoparasite fauna that were similar. The similarities of the flea species showed similar results in both separate and joint analyses, but neither phylogenetic nor geographical overlap influenced the similarity in mite species. Fleas were shown to be more host-specific than were mesostigmate mites, probably because of the increased influence of host phylogeny.

Wild-caught Xenopsylla brasiliensis from Kibwawa village, Chunya District, in south-west Tanzania were colonised in the laboratory and their offsprings used for determining the baseline susceptibility levels of the strain to DDT. A total of 120 fleas were tested with each concentration of DDT, using the techniques described by the WHO Expert Committee on Insecticides (1970).

Several filial generations were selectively raised, using DDT as a selection pressure. They were tested with various concentrations of the insecticide and their dosage–mortality regression lines compared with that of their parents.

About 5% of the parental generation (normal population) survived 1 hr exposure to 4% DDT. The LC50 of this population was 0.79% DDT. The mortality rates of the successive filial generations decreased gradually; their dosage–mortality regression lines moved to the right; and the slopes of these lines decreased. LC50s of F1, F2 and F3 were 1.6, 1.9 and 3.1% DDT, respectively. The highest DDT concentration (4%) killed 21.1 and 18.3%, of F4 and F5, respectively.

It was generally concluded that DDT resistance was present in the population, and that the selection pressure (DDT) was responsible for increasing the level of this resistance in the laboratory.