Pneumonic plague outbreaks are relatively infrequent in modern times but in the early part of the 20th century, they were commonplace including several well-documented epidemics responsible for the deaths of thousands. The transmissibility of this disease seems to be discontinuous since in some outbreaks few transmissions occur, while in others, the progression of the epidemic is explosive. Modern epidemiological studies explain that transmissibility within populations is heterogenous with relatively few subjects likely to be responsible for most transmissions and that ‘super spreading events’, particularly at the start of an outbreak, can lead to a rapid expansion of cases. These findings concur with outbreaks observed in real-world situations. It is often reported that pneumonic plague is rare and not easily transmitted but this view could lead to unnecessary complacency since future risks such as the spontaneous incidence of anti-microbial strains, climate change leading to a disruption of natural cycles within plague foci and use of plague as a bioweapon cannot be discounted. Carers and first responders are vulnerable, particularly in poorer countries where access to medicines may be limited, out-breaks occur in inaccessible areas or where there is a lack of surveillance due to a paucity of funds.

The plague caused by the Yersinia pestis bacterium is primarily a flea-transmitted zoonosis of rodents that can also be conveyed to humans and other mammals. In this work, we analyzed the spatial and temporal distribution of rodents’ populations during active and quiescent periods of the plague in the municipality of Exu, northeastern Brazil. The geospatial analyses had shown that all rodent species occurred through the whole territory of the municipality with different hotspots for the risk of occurrence of the different species. Important fluctuation in the rodent populations was observed with a reduction in the wild rodent fauna following the end of a plague epidemic period, mostly represented by Necromys lasiurus and increase of the commensally species Rattus rattus. A higher abundance of rats might lead to an increased exposure of humans populations, favoring spillovers of plague and other rodent-borne diseases. Our analysis contributed to further highlight the role of the wild rodent species as the amplifier hosts and of the commensally rats (Rattus rattus) as the preserver hosts on the quiescent period on that transmission infection area.

The crayfish plague is a devastating disease of European freshwater crayfish and is caused by the oomycete Aphanomyces astaci (Ap. astaci), which was introduced to Europe around 1860. All European species of freshwater crayfish are susceptible to the disease, including the white-clawed crayfish Austropotamobius pallipes. The aquatic mould is primarily spread by North American crayfish species and can also disperse rapidly through contaminated wet gear moved between water bodies. This spread, coupled with competition from non-indigenous crayfish, has drastically reduced and fragmented native crayfish populations across Europe. Remarkably, the island of Ireland remained free from the crayfish plague pathogen for over 100 years, providing a refuge for A. pallipes. However, this changed in 1987 when a mass mortality event was linked to the pathogen marking the pathogen's introduction to the region. Fortunately, the plague did not establish and was not detected again in Ireland until 2015 when a molecular analysis linked a mass mortality event in the Erne catchment to Ap. astaci. Since then, the pathogen has appeared across the island. Between 2015 and 2023, Ap. astaci was detected in 18 Irish water catchments, revealing multiple genotypes. Intriguingly, the pathogen in Ireland exists without its natural host species. The uneven distribution of various genetic lineages strongly suggests human-mediated transport of zoospores via contaminated water equipment as a primary cause of spread. This review details the timeline of these events, Ap. astaci’s introductions into Ireland, its rapid spread, the genotypes documented, the issue of non-indigenous crayfish species in Ireland and management efforts.

To develop a modern plague vaccine, we used hypo-endotoxic Yersinia pestis bacterial ghosts (BGs) with combinations of genes encoding the bacteriophage ɸX174 lysis-mediating protein E and/or holin-endolysin systems from λ or L-413C phages. Expression of the protein E gene resulted in the BGs that retained the shape of the original bacterium. Co-expression of this gene with genes coding for holin-endolysin system of the phage L-413C caused formation of structures resembling collapsed sacs. Such structures, which have lost their rigidity, were also formed as a result of the expression of only the L-413C holin-endolysin genes. Similar holin-endolysin system from phage λ containing mutated holin gene S and intact genes R-Rz coding for the endolysins caused generation of mixtures of BGs that had (i) practically preserved and (ii) completely lost their original rigidity. The addition of protein E to the work of this system shifted the equilibrium in the mixture towards the collapsed sacs. The collapse of the structure of BGs can be explained by endolysis of peptidoglycan sacculi. Immunizations of laboratory animals with the variants of BGs followed by infection with a wild-type Y. pestis strain showed that bacterial envelopes protected only cavies. BGs with peptidoglycan maximally hydrolyzed had a greater protectivity compared to BGs with preserved peptidoglycan skeleton.