Sorting Out the Plague

This chapter explores the complex interactions among mammal hosts, insect vectors, bacteria and even amoebae implicated in the movement of the plague around the world. As it shows, trying to find the cause for the three plague pandemics is similar to the way a television detective solves a murder mystery. While the third pandemic established the roles of rats, rat fleas, and bacteria, that explanation has been incorrectly applied to explain the first two pandemics. The chapter shows how bacterial DNA collected from the teeth of 6th-Century plague victims, exhumed 1,400 years later, established greater understanding of the rate and geographic extent of the plague's spread. It goes on to relate how the age-old conclusions that brown rats were disease reservoirs and their fleas were vectors have been reconsidered, assigning rats and fleas specific roles and recognizing that humans and human lice as host and vector are more consistent with the plague’s rapid spread. Using clues from hosts and vectors to solve the mystery requires investigators to be like detectives.

Detection of asymptomatic Leishmania infection in Bangladesh by novel antigen and antibody diagnostic tools shows strong association with PKDL patients

BackgroundAsymptomatic Leishmania infections outnumber clinical infections on the Indian sub-continent (ISC) where disease reservoirs are anthroponotic. Diagnostics which detect active asymptomatic infection, which are suitable for monitoring and surveillance, may be of benefit to the visceral leishmaniasis (VL) elimination campaign on the ISC.Methodology/Principal FindingsQuantitative polymerase chain reaction (qPCR), loop mediated isothermal amplification (LAMP), the direct agglutination test (DAT), and the Leishmania antigen ELISA were carried out on blood and urine samples collected from 720 household and neighbouring contacts of 276 VL and post kala-azar dermal leishmaniasis (PKDL) index cases, with no symptoms or history of VL and PKDL, in endemic regions of Bangladesh between September 2016 and March 2018. Of the 720 contacts of index cases, asymptomatic infection was detected in 69 (9.6%) participants by a combination of qPCR (1.0%), LAMP (2.1%), DAT (3.9%), and Leishmania antigen ELISA (3.3%). Only 1 (0.1%) participant was detected positive by all 4 diagnostic tests. Poor agreement between tests was calculated using Cohen’s kappa (k) statistics, however the Leishmania antigen ELISA and DAT in combination capture all participants positive by more than one test. We find strong evidence for association between the index case being a PKDL case (OR 1.94, p = 0.009), specifically macular PKDL (OR 2.12, p = 0.004) and being positive for at least one of the four tests.Conclusions/SignificanceLeishmania antigen ELISA detects active asymptomatic infection, requires a non-invasive sample, and therefore may be of benefit for monitoring transmission and surveillance in an elimination setting in combination with serology. Development of an antigen detection test in RDT format would be of benefit to the elimination campaign.Author summaryInfection with the parasite Leishmania donovani can lead to an asymptomatic infection with only around 5% of asymptomatics converting to visceral leishmaniasis the clinical manifestation of the infection. Serological assays detect anti-Leishmania antibodies and therefore cannot distinguish between past and active infection. Molecular assays and those which detect Leishmania antigens detect active infection. Since the signing of a memorandum of understanding in 2005, visceral leishmaniasis has been targeted for elimination in India, Nepal and Bangladesh. In an elimination setting such as Bangladesh, where disease reservoirs are anthroponotic, a relatively simple test such as the Leishmania antigen ELISA which requires a non-invasive urine sample, may be of benefit in combination with serology for surveillance and monitoring of Leishmania transmission. Development of an antigen test into a field compatible rapid diagnostic test would be of further benefit to the elimination campaign.

A SOME ECOLOGICAL CHARACTERISTICS OF EBOLA VIRUS IN NATURAL FOCIES

Ebola virus that composed Ebolavirus genus of Filoviridae Family causes severe hemorrhagic fever in humans with high case-fatality rates (up to 90%). The Ebolavirus genus includes Ebola-Zaire, Ebola-Sudan, Ebola-Reston, Ebola-Tai Forest and Ebola-Bundibugyo viruses. The date about epidemic outbreaks of disease, reservoirs of infection, accidental hosts of Ebola virus are presented in this review. The date about natural reservoirs of infection are accessed only for Ebola-Zaire and Ebola-Reston viruses. For Ebola-Sudan, Ebola-Tai Forest and Ebola-Bundibugyo viruses such information is absence. The bats are natural reservoirs for Ebola-Zaire and Ebola-Reston viruses. The formation of natural reservoirs of filoviruses assumes possibilities of existence of several hosts. The interrelation of Ebola virus and their hosts, dynamics of infection are the classical «susceptible-infected-immune» (recovered) cycle. The likely schemes of rises of epidemic outbreaks, caused by Ebola-Zaire virus are suggested.