Coinfection of tick cell lines has variable effects on replication of intracellular bacterial and viral pathogens

Anna Moniuszko,Claudia Rückert,M Pilar Alberdi,Gerald Barry,Brian Stevenson,John K Fazakerley,Alain Kohl,Lesley Bell-Sakyi

doi:10.1016/j.ttbdis.2014.01.010

Abstract

Ticks transmit various human and animal microbial pathogens and may harbour more than one pathogen simultaneously. Both viruses and bacteria can trigger, and may subsequently suppress, vertebrate host and arthropod vector anti-microbial responses. Microbial coinfection of ticks could lead to an advantage or disadvantage for one or more of the microorganisms. In this preliminary study, cell lines derived from the ticks Ixodes scapularis and Ixodes ricinus were infected sequentially with 2 arthropod-borne pathogens, Borrelia burgdorferi s.s., Ehrlichia ruminantium, or Semliki Forest virus (SFV), and the effect of coinfection on the replication of these pathogens was measured. Prior infection of tick cell cultures with the spirochaete B. burgdorferi enhanced subsequent replication of the rickettsial pathogen E. ruminantium whereas addition of spirochaetes to cells infected with E. ruminantium had no effect on growth of the latter. Both prior and subsequent presence of B. burgdorferi also had a positive effect on SFV replication. Presence of E. ruminantium or SFV had no measurable effect on B. burgdorferi growth. In tick cells infected first with E. ruminantium and then with SFV, virus replication was significantly higher across all time points measured (24, 48, 72h post infection), while presence of the virus had no detectable effect on bacterial growth. When cells were infected first with SFV and then with E. ruminantium, there was no effect on replication of either pathogen. The results of this preliminary study indicate that interplay does occur between different pathogens during infection of tick cells. Further study is needed to determine if this results from direct pathogen–pathogen interaction or from effects on host cell defences, and to determine if these observations also apply in vivo in ticks. If presence of one pathogen in the tick vector results in increased replication of another, this could have implications for disease transmission and incidence.

Highlights

Tick-borne viral and bacterial pathogens are major threats to human and animal health worldwide (Jongejan and Uilenberg, 2004)
When E. ruminantium was added to tick cell cultures previously inoculated with B. burgdorferi s.s., the amount of E. ruminantium DNA was consistently greater over the following 3 days compared to cultures without spirochaetes
Semliki Forest virus (SFV) replication in tick cells was enhanced following addition of extracellular B. burgdorferi or when the cells were already infected with intracellular E. ruminantium at the time of virus infection, but not vice versa

Summary

Introduction

Tick-borne viral and bacterial pathogens are major threats to human and animal health worldwide (Jongejan and Uilenberg, 2004). A. Moniuszko et al / Ticks and Tick-borne Diseases 5 (2014) 415–422 hosts and transmits the flavivirus tick-borne encephalitis virus (TBEV), the spirochaete Borrelia burgdorferi sensu lato (s.l.), the obligate intracellular rickettsiae Anaplasma phagocytophilum, Candidatus Neoehrlichia mikurensis, and Rickettsia helvetica, and the protozoa Babesia divergens and Babesia microti. Moniuszko et al / Ticks and Tick-borne Diseases 5 (2014) 415–422 hosts and transmits the flavivirus tick-borne encephalitis virus (TBEV), the spirochaete Borrelia burgdorferi sensu lato (s.l.), the obligate intracellular rickettsiae Anaplasma phagocytophilum, Candidatus Neoehrlichia mikurensis, and Rickettsia helvetica, and the protozoa Babesia divergens and Babesia microti Of these zoonotic pathogens, TBEV and B. burgdorferi s.l. are increasingly recognised as causing serious disease in significant numbers of human patients in areas of high I. ricinus prevalence (Fulop and Poggensee, 2008; Sumilo et al, 2007; Czupryna et al, 2011). In the closely related tick species Ixodes persulcatus, Alekseev et al (2003) found a high incidence of multiple pathogen infections and suggested that B. microti can only survive in these ticks in the presence of coinfecting Borrelia spp. Popov et al (2007) detected over 40% of unfed adult I. persulcatus ticks coinfected with multiple pathogens by PCR; transmission electron microscopic examination revealed cytopathic changes in salivary gland cells infected with Ehrlichia muris or a flavivirus, coinfection of the same cell or organ was not observed

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