Biological and pathological characterisation of novel plasmid-carrying avian Chlamydia abortus strain 84/2334
Lead Research Organisation:
Moredun Research Institute
Department Name: Vaccines and Diagnostics
Abstract
Many infectious diseases affect livestock, impacting not only on the health and welfare of the animals but also on the economic sustainability of the agricultural sector and future food security. Ovine enzootic abortion (OEA) is an economically important endemic disease of worldwide significance in small ruminant species, caused by the Gram-negative bacterium Chlamydia abortus. In the UK it is the most common cause of infectious abortion in sheep, resulting in foetal death in the last 2-3 weeks of pregnancy or the delivery of weak offspring and causing losses in a flock of up to around 30%. Losses in the UK have been estimated to be around £25M per annum. The organism can also infect humans causing spontaneous abortion, and in whom infections can be life-threatening.
Vaccination is currently considered the most effective way of controlling disease and vaccines based on inactivated or live whole-organisms are commercially available for use in small ruminants. However, live vaccines have been reported to cause infection and disease in some animals and inactivated vaccines have been found to have much lower effectiveness in protecting animals from infections. Thus, there is a need to develop safer, more effective vaccines for use in livestock. Reducing infection and disease burden in animals will also reduce the risk of infections in humans.
In recent years, research has progressed into developing methods for manipulating the genomes of human chlamydial species, making use of an endogenous plasmid (DNA that is extra to that present on the chromosome) that many of the strains possess. These plasmids are also present in avian chlamydial species (Chlamydia psittaci) from which C. abortus evolved. However, no plasmid has been found to date in C. abortus strains. Recently, we have characterised the genome of a novel strain, designated 84/2334, which has been reclassified from C. psittaci to C. abortus and carries a plasmid. Therefore, this strain could potentially be used to develop a new C. abortus vaccine for controlling OEA. However, before doing this, we need to know how biologically similar the strain is to C. abortus and determine whether the strain causes infection and disease similar to that caused by C. abortus.
In this project we will compare the growth dynamics of the 84/2334 strain in relation to both C. abortus and C. psittaci, investigate its growth cycle in the target host cell, identify the key molecules involved in causing pathogenesis, and determine its potential to cause infection and abortion. These studies will identify whether the strain is more similar to classical C. abortus than to C. psittaci and determine its suitability for use in future vaccine development studies.
Vaccination is currently considered the most effective way of controlling disease and vaccines based on inactivated or live whole-organisms are commercially available for use in small ruminants. However, live vaccines have been reported to cause infection and disease in some animals and inactivated vaccines have been found to have much lower effectiveness in protecting animals from infections. Thus, there is a need to develop safer, more effective vaccines for use in livestock. Reducing infection and disease burden in animals will also reduce the risk of infections in humans.
In recent years, research has progressed into developing methods for manipulating the genomes of human chlamydial species, making use of an endogenous plasmid (DNA that is extra to that present on the chromosome) that many of the strains possess. These plasmids are also present in avian chlamydial species (Chlamydia psittaci) from which C. abortus evolved. However, no plasmid has been found to date in C. abortus strains. Recently, we have characterised the genome of a novel strain, designated 84/2334, which has been reclassified from C. psittaci to C. abortus and carries a plasmid. Therefore, this strain could potentially be used to develop a new C. abortus vaccine for controlling OEA. However, before doing this, we need to know how biologically similar the strain is to C. abortus and determine whether the strain causes infection and disease similar to that caused by C. abortus.
In this project we will compare the growth dynamics of the 84/2334 strain in relation to both C. abortus and C. psittaci, investigate its growth cycle in the target host cell, identify the key molecules involved in causing pathogenesis, and determine its potential to cause infection and abortion. These studies will identify whether the strain is more similar to classical C. abortus than to C. psittaci and determine its suitability for use in future vaccine development studies.
Technical Summary
Recently we have characterised the genome of a novel chlamydial strain, named 84/2334, which is evolutionary related to mammalian Chlamydia abortus species, which has evolved from avian chlamydial species Chlamydia psittaci. The strain possesses an extrachromosomal plasmid, similar to that found in most C. psittaci but not in C. abortus. Current commercial vaccines against C. abortus have some limitations: inactivated vaccines having lower efficacy and live vaccines that can cause infection and disease. The ability to transform and manipulate the genomes of human chlamydial species via their plasmids, means it may be possible to do the same for this 84/2334 strain and thereby develop a novel vaccine to protect animals from C. abortus infection and disease (ovine enzootic abortion or OEA). Before attempting to develop a novel mutant strain, it is important to establish whether 84/2334 is biologically and pathologically similar to mammalian C. abortus strains, thus suitable for vaccine development studies.
To do this we will compare the infection dynamics of the 84/2334 strain in vitro with representative strains of C. abortus and C. psittaci in their target host cell and a common mammalian epithelial cell line used for growing chlamydial species. We will specifically investigate the maturation of the developing chlamydial inclusion by electron microscopy. This will identify whether the strain has a short (like C. psittaci) or longer (like C. abortus) developmental cycle. We will compare RNAseq profiles of 84/2334 and C. abortus strains at different time points in the cycle to identify similarities and differences in key expressed genes (pathogen and host) that are linked to pathogenesis. Then we will determine the pathogenic potential of strain 84/2334 in an established C. abortus pregnant sheep challenge model to see if the strain results in infection and disease indistinguishable from typical OEA.
To do this we will compare the infection dynamics of the 84/2334 strain in vitro with representative strains of C. abortus and C. psittaci in their target host cell and a common mammalian epithelial cell line used for growing chlamydial species. We will specifically investigate the maturation of the developing chlamydial inclusion by electron microscopy. This will identify whether the strain has a short (like C. psittaci) or longer (like C. abortus) developmental cycle. We will compare RNAseq profiles of 84/2334 and C. abortus strains at different time points in the cycle to identify similarities and differences in key expressed genes (pathogen and host) that are linked to pathogenesis. Then we will determine the pathogenic potential of strain 84/2334 in an established C. abortus pregnant sheep challenge model to see if the strain results in infection and disease indistinguishable from typical OEA.
