Transovarial Transmission

Topics with information and discussion about published studies related to Lyme disease and other tick-borne diseases.
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Claudia
Posts: 1448
Joined: Wed 14 Nov 2007 1:19
Location: Connecticut, USA

Transovarial Transmission

Post by Claudia » Thu 29 Nov 2007 0:06

Transovarial transmission is considered an important mechanism for maintaining and distributing tick-borne protozoa, bacteria, and viruses in nature. Ticks can be hatched out of the egg already infected, and don't require a reservoir host meal during the larval stage, or at any other stage to acquire Bb or other diseases.

Transovarial and Transstadial Passage of Borrelia burgdorferi in the Western Black-Legged Tick, Ixodes pacificus (Acari: Ixodidae) (1987)

Robert S. Lane AND Willy Burgdorfer

Transovarial and transstadial passage of Borrelia burgdorferi was demonstrated for the first time in the western black-legged tick, Ixodes pacificus. One of three field-collected females with spirochetes in ovarial tissues produced 100% infected progeny that maintained the spirochetes transstadially and in 4 of 5 cases passed them via eggs to as many as 97% of F2 filial ticks. The progeny infected ovarially and by subsequent transstadial passage had generalized tissue infections that exhibited reduced immunofluorescence staining reactivity with a fluorescein isothiocyanate-labeled polyclonal antibody. Attempts to isolate the spirochete from ticks in BSK medium or various modifications of it were unsuccessful. Spirochetes in tissue smears of all three parasitic stages of the F1 generation were nonreactive with a monoclonal antibody (H5332) specific for B. burgdorferi, whereas those present in tissue smears of F2 larvae bound with it.

http://www.ajtmh.org/cgi/content/abstract/37/1/188

Claudia
Posts: 1448
Joined: Wed 14 Nov 2007 1:19
Location: Connecticut, USA

Re: Transovarial Transmission

Post by Claudia » Thu 29 Nov 2007 0:24

Tick Tock: Summary of Keynote Address by Dr. Willy Burgdorfer CME
Introduction

It seems that no successful tick-borne disease conference would be complete without a presentation from Dr. Willy Burgdorfer, the man for whom the Lyme disease spirochete (Borrelia burgdorferi) is named. It has been suggested that the discovery of B burgdorferi is one of the greatest findings of the 20th century. Dr. Burgdorfer delivered the keynote lecture on the second day of the 13th Lyme Disease Conference. He primarily spoke about transovarial transmission of tick-borne pathogens, although he included a few well-placed remarks regarding elementary acarology.

Know thy Enemy
During his introduction, Dr. Burgdorfer reminded us that ticks are classified as arthropods, a biological grouping of invertebrate animals with jointed legs, segmented bodies, and an external skeleton. About 850 species of ticks have been identified to date. Of these, 680 species belong to the family Ixodidae (hard ticks) and 170 to the family Argasidae (soft ticks). Biologically, hard ticks differ from soft ticks, which do not have a hard shell and appear leathery and wrinkled; they also differ in terms of feeding habits, environmental habitats, and climatic requirements.
Most hard ticks require 3 hosts to complete their life cycle, which consists of 4 stages: the egg, the 6-legged larva, the 8-legged nymph, and the 8-legged adult. The larvae, nymphs, and adults are parasitic and require a single blood meal before developing into the next stage. Soft ticks require multiple feedings as nymphs before they become adults; adult soft ticks are also capable of multiple feedings.

Even in ancient times, ticks were recognized as "disgusting" parasitic animals that adversely affect the well-being of humans and other animals. However, Dr. Burgdorfer said it was not until the 19th century that their roles as vectors and reservoirs of tick-borne pathogens were established. For half a century, scientists had struggled with the mysteries of Texas fever, associated with devastating disease outbreaks that killed thousands of cattle. Then, in the summer of 1886, Theobald Smith discovered the Texas fever agent, now known as Babesia bigemina, in the red blood cells of infected cattle. Subsequently, in 1889 and 1890, Smith and Frederick Kilborne showed that the larval stage of the cattle tick, Boophilus annulatus, was the vector. Once this tick acquires the parasite, it can pass it on, via its eggs, to the larval progeny. The larvae transmit the Babesia when they feed on a susceptible host.

This phenomenon of passing organisms via eggs to the progeny of infected female ticks became known as transovarial transmission. It is considered an important mechanism for maintaining and distributing tick-borne protozoa, bacteria, and viruses in nature.

Ricketts and Spotted Fever
Dr. Burgdorfer went on to tell us that at the beginning of the 20th century, Howard Taylor Ricketts was credited for demonstrating that the wood tick, Dermacentor andersoni, transmits the agent of Rocky Mountain spotted fever (RMSF). Ricketts also showed that the RMSF agent - which was unknown to him - was passed via eggs to the offspring of both naturally and experimentally infected ticks. Ricketts' findings were confirmed by many investigators, including Dr. Burgdorfer himself. The efficiency of transovarial transmission was found to depend on the concentration of organisms ingested. Ticks feeding on animals with a low level of infection developed mild systemic infections, whereas ticks ingesting large concentrations of organisms developed massive infections in all tissues, including the ovary.

Historical Thesis: Salivary Glands or Coxal Fluid? Dr. Burgdorfer said that in 1951, he submitted a thesis entitled "Analysis of Infection in Ornithodoros moubata and the Natural Transmission of Spirochaeta duttoni". Dr. Burgdorfer found that during this soft tick's feeding period (10-30 minutes), it ingests spirochetes into the midgut. Within hours, these spirochetes accumulate in the tick's gut epithelium and subsequently enter the body cavity, where they begin multiplying by binary fission. From there, the spirochetes invade various other tissues. Only in nymphal ticks does the salivary gland become heavily infected.

Once a tick reaches the adult stage, the salivary glands are free of spirochetes or are only mildly infected. Thus, nymphs can transmit spirochetes by bite (via saliva) or excretion of coxal fluid shortly before feeding ends. Adult ticks, on the other hand, transmit spirochetes through infected coxal fluid and only rarely via saliva. The invasion of spirochetes into germinal cells leads to transovarial transmission, with filial infection rates as high as 90%. The percentage of infected female ticks passing spirochetes via eggs (transovarial transmission rates) varies greatly, depending on the extent of the spirochetal infection in the ovarian tissues. Spirochetal development similar to that described in Dr. Burgdorfer's thesis has been reported for at least 9 other Ornithodoros tick species, except that in 3 of the 9 species, transovarial transmission does not occur.

Hard Ticks
With the exception of Borrelia theileri, the causative agent of bovine borreliosis in South Africa, spirochetes were not associated with hard ticks until 1981, the year Dr. Burgdorfer discovered B burgdorferi in deer ticks (Ixodes scapularis) and European sheep ticks (Ixodes ricinus). B burgdorferi - unlike the spirochetes associated with Ornithodoros ticks, which leave the midgut of their vectors within a few days of being ingested - usually remains and multiplies in the tick midgut. Nevertheless, detection of B burgdorferi in field-collected, unfed deer ticks suggests that transovarial transmission does occasionally occur. However, according to Dr. Burgdorfer, since this is a rare occurrence, transovarial transmission plays only a very minor role in maintaining and distributing B burgdorferi in nature.

Transovarial Transmission of Ehrlichiae
Finally, Dr. Burgdorfer discussed the possibility of transovarial transmission of ehrlichiae. He said that early on, French researchers postulated that Ehrlichia canis, an agent of canine ehrlichiosis, is maintained transstadially and transovarially in the brown dog tick, Rhipicephalus sanguineus. Although transstadial transmission in the brown dog tick is now well established, transovarial transmission has not been confirmed. Moreover, other tick species are now known to transmit Ehrlichia species. Amblyomma americanum, the lone star tick transmits Ehrlichia chaffeensis; I scapularis transmits the HGE agent; and Ixodes pacificus, the black-legged tick found in the western United States, transmits Ehrlichia equi. Dr. Burgdorfer concluded by suggesting that current tick research will undoubtedly reveal the processes whereby Ehrlichia sp and their vectors interact in nature. All the while, he said, our "struggle with ticks will continue."

RitaA
Posts: 2768
Joined: Thu 1 Jul 2010 8:33

Re: Transovarial Transmission

Post by RitaA » Sat 6 Oct 2012 22:24

I have much more to add, however I'll start with the most recent reference to possible transovarial transmission that I just came across. I'll add the older abstracts and other references later.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3214628/
Infect Genet Evol. Author manuscript; available in PMC 2012 October 1.
Published in final edited form as:
Infect Genet Evol. 2011 October; 11(7): 1545–1563.
Published online 2011 August 5. doi: 10.1016/j.meegid.2011.07.022
PMCID: PMC3214628
NIHMSID: NIHMS321670

Population genetics, taxonomy, phylogeny and evolution of Borrelia burgdorferi sensu lato

Gabriele Margos,1,* Stephanie A. Vollmer,1 Nicholas H. Ogden,2 and Durland Fish 3

1 Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
2 Zoonoses Division, Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, Public Health Agency of Canada, Ottawa, Canada
3 Yale School of Public Health, New Haven, CT 06520
* corresponding author: Department of Biology and Biochemistry 3 South University of Bath Claverton Down Bath BA2 7AY U.K.

Abstract

In order to understand the population structure and dynamics of bacterial microorganisms, typing systems that accurately reflect the phylogenetic and evolutionary relationship of the agents are required. Over the past 15 years multilocus sequence typing schemes have replaced single locus approaches, giving novel insights into phylogenetic and evolutionary relationships of many bacterial species and facilitating taxonomy. Since 2004, several schemes using multiple loci have been developed to better understand the taxonomy, phylogeny and evolution of Lyme borreliosis spirochetes and in this paper we have reviewed and summarized the progress that has been made for this important group of vector-borne zoonotic bacteria.
2. Ecology of LB group of spirochetes

Due to the obligate parasitic lifestyle of LB spirochetes, their biology is intimately linked to that of their invertebrate and vertebrate hosts which also broadely defines their ecological niches (Kurtenbach et al., 2002b). The ecological niche diversity of different species varies in the degree of specialization (from generalist to specialised strategies) in terms of host and vector adaptation and this influences the geographic distribution at species and population levels. There are several excellent recent reviews regarding the ecology of LB spirochetes, describing in detail host and vector interactions (Gern, 2008; Gern and Humair, 2002; Kurtenbach et al., 2006; Masuzawa, 2004; Piesman and Gern, 2004; Tsao, 2009). Here we will only briefly describe the general ecology of LB spirochetes.

The life cycle of the LB group of spirochetes is a dynamic interplay between bacteria, reservoir hosts and vectors which is confounded by landscape and climatic factors impacting host and vector ecology (Figure 1, (Kurtenbach et al., 2006)). All known vectors of LB spirochetes belong to the genus Ixodes and these ticks are three host ticks, i.e. they have three feeding stages (larvae, nymphs and adult females) each utilizing a different individual host, although not necessarily a different host species. Except in the case of nidicolous (nest-living) tick vectors, adult female ticks prefer large animals, such as deer, as hosts which are considered not susceptible to Borrelia infection (Telford et al., 1988). The preference of both immature stages for small to medium sized vertebrates (mammals, birds or lizards) is essential for maintaining the bacteria in its natural transmission cycles. The bacteria are taken up during a bloodmeal from an infected and infectious host, are maintained transstadially during the moulting process and are then transmitted to other hosts during the subsequent bloodmeal during the next life stage (Gern and Humair, 2002). Other means of transmission are co-feeding transmission (between neighbouring ticks feeding on a susceptible or non-susceptible host) (Ogden et al., 1997) and transovarial transmission ((Gern and Humair, 2002) and references therein), although the latter may depend on the tick species as it has not been experimentally demonstrated for I. scapularis and I. persulcatus (Nefedova et al., 2004; Patrican, 1997). However, relapsing-fever like spirochetes (e.g. B. miyamotoi) are transmitted transovarially in Ixodes ticks and occur sympatrically with LB group spirochetes, which may explain some or perhaps all observations of transovarial transmission (Piesman, 2002; Scoles et al., 2001).

RitaA
Posts: 2768
Joined: Thu 1 Jul 2010 8:33

Re: Transovarial Transmission

Post by RitaA » Sun 7 Oct 2012 0:03

Here are more references regarding the possibility of transovarial transmission -- from oldest to newest, with a few that are undated:

http://www.tickencounter.org/tick_notes ... _miyamotoi (undated)
[snip]

But there are certain pathogens that CAN be passed on from an infected female tick through the egg stage and into the next generation of ticks, a process called transovarial (t/o) transmission. Pathogens capable of t/o transmission infect at least a portion of the new larval cohort, and conceptually, can be transmitted by the larvae when they bite.

Borrelia miyamotoi is a t/o transmitted bacterium in ticks. First reported in 1995 (1) infecting Ixodes persulcatus ticks in Japan, strains of this microbe also have been recovered in other Ixodes tick species, including Ixodes ricinus ticks in Europe as well as deer ticks and western blacklegged ticks in the United States.


Previously, 1.9 - 2.5% of host-seeking nymphal deer ticks collected in RI, CT, NY & NJ were shown to be infected with B. miyamotoi (2). In a preliminary study, TERC researchers recently found that 9% of egg-laying female deer ticks collected in Rhode Island passed B. miyamotoi infection to their offspring (larvae), and this study and other estimates suggest that 6 - 73% of larvae hatching from eggs laid by B. miyamotoi-infected females may be infected. It's still unknown how efficient these t/o infected larvae are in transmitting infection to humans.

In fact, until recently there was no evidence that Borrelia miyamotoi caused human infection. However, a study reported in the journal Emerging Infectious Disease in 2011 (3) reported on 46 human cases of influenza-like illness with high fever, all associated with Borrelia miyamotoi infection in Yekaterinburg City, Russia.

The study was clear that these cases WERE NOT Lyme disease. In some of the cases, a relapsing fever syndrome was observed. Other strains of Borrelia in the U.S. and elsewhere are known to cause relapsing fever.

The geographic extent of relapsing fever disease caused by Borrelia miyamotoi remains to be determined. But given the comparable tick infection rates between the Yekaterinburg region in Russia and other places where this pathogen has been detected, including here in the U.S., human infection likely does occurs outside of Russia.
http://www.vetmed.wisc.edu/pbs/zoonoses ... trans.html (undated)
Lyme Disease

Tick transmission of Borrelia burgdorferi

B. burgdorferi is transmitted by the Ixodes ("deer tick") family of "3 host" ticks. These ticks require 2 years to complete their life cycle and must feed on 3 independent hosts during this cycle. (Click here for a photo of the larvae, nymph and adult Ixodes scapularis ticks)

There is minimal transovarial transmission of B. burgdorferi in ticks, so each new generation of ticks must be infected de novo by feeding on an infected host. The organism can, however, be transmitted transstadially from larvae to nymph to adult.

In general, the tick larvae first become infected by feeding on rodents that are competent hosts for B. burgdorferi (i.e., these rodent hosts replicate B. burgdorferi to a sufficient level to be infectious for subsequently feeding ticks).

Robins have also been shown to be competent hosts for B. burgdorferi.

In the southeastern and western U.S., reptiles may also serve as competent hosts, although, conversely, some lizards contain a borreliacidal substance in their blood that eliminates Borrelia from feeding ticks.
The tick nymphs and especially adults obtain their blood meals by feeding on larger mammals. Deer are the preferred enzootic feeding hosts- dogs, horses, cows, people etc. are accidental victims of a hungry tick!

Deer are not competent hosts for B. burgdorferi - their role is to maintain the ticks, not the Borrelia.
Nymphs are the life stage most commonly involved in transmitting B. burgdorferi to dogs and humans.
http://www.ncbi.nlm.nih.gov/pubmed/3577489
Zentralbl Bakteriol Mikrobiol Hyg A. 1986 Dec;263(1-2):29-33.

Borrelia transfer by ticks during their life cycle. Studies on laboratory animals.

Stanek G, Burger I, Hirschl A, Wewalka G, Radda A.

Abstract

Ticks of the species Ixodes ricinus were cultured in the laboratory. Yellow silver rabbits, gerbils and white mice served as blood hosts. Borrelia burgdorferi could be detected by means of an IFA test in homogenates of female ticks, their eggs as well as the respective larval and nymphal ticks. Blood infection of splenectomized gerbils and ordinary white mice or of ordinary white mice alone has been demonstrated after feeding of larval or nymphal ticks on them, respectively. Spirochetemia started 5 to 8 days after feeding and lasted for ca 3 weeks. Two distinct peaks in the cell count of spirochetal organisms per ml blood plasma could be observed on days 11-13 (5 X 10(5) to 2 X 10(6) cells/ml) and 17-19 (10(5) cells/ml), regardless whether splenectomized gerbils or white mice were used. The results display that B. burgdorferi is vertically from the female ticks to their eggs and transstadially transmitted. The transmission-rate from larval to nymphal ticks is 100%. These findings show the tick itself as a main reservoir of B. burgdorferi. The established mouse-model appears to be a useful tool to detect Borrelia carrying ticks.

PMID:
3577489
[PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/pubmed/7628234
Exp Appl Acarol. 1993 Aug;17(8):581-6.

Ability of transovarially and subsequent transstadially infected Ixodes hexagonus ticks to maintain and transmit Borrelia burgdorferi in the laboratory.

Toutoungi LN, Gern L.

Source

Institut de Zoologie, University of Neuchâtel, Chantemerle 22, CH-2000 Neuchâtel, Switzerland.

Abstract

In a previous study, transstadial and transovarial survival of Borrelia burgdorferi in Ixodes hexagonus and transmission to laboratory mice via the bite of infected females were demonstrated. Here, we report the ability of I. hexagonus progeny infected transovarially to maintain and transmit the spirochaete to the host. Ticks were examined for spirochaetes by direct immunofluorescence antibody test. I. hexagonus larvae derived from the parental transstadially infected females were fed on two white mice: 21/54 (38.9%) of these ticks examined as unfed nymphs were infected. I. hexagonus nymphs were fed on three white mice and examined for spirochaetes after moulting as adults: 7/25 (28%) were found to harbour the spirochaete. The success of B. burgdorferi transmission to the mice by larval and nymphal I. hexagonus was determined by xenodiagnosis using I. ricinus larvae: 20/50 (40%) and 30/99 (30.3%) of the I. ricinus larvae fed on the mice infected by I. hexagonus larvae and nymphs respectively became infected. This study shows that B. burgdorferi can be maintained through transovarial and subsequent transstadial transmissions in I. hexagonus.

PMID:
7628234
[PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/pubmed/8433348
J Med Entomol. 1993 Jan;30(1):80-6.

Efficiency of transovarial transmission of the Lyme disease spirochete, Borrelia burgdorferi, in the western blacklegged tick, Ixodes pacificus (Acari: Ixodidae).

Schoeler GB, Lane RS.

Source

Department of Entomological Sciences, University of California, Berkeley 94720.

Abstract

The efficiency of transovarial transmission of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner was evaluated in Ixodes pacificus Cooley & Kohls collected from two areas of northern California where Lyme disease is endemic. In total, 132 (8.8%) of 1,499 replete females examined by direct immunofluorescence were demonstrated to be infected with B. burgdorferi. Larvae or eggs from 119 of these females were examined for the presence of spirochetes by direct immunofluorescence, placing them in culture, or both; none was found to contain B. burgdorferi. The fecundity of 20 midgut-infected (mean = 874.2) and 20 uninfected (mean = 1,048.3) I. pacificus females did not differ statistically. Likewise, the fertility of infected (mean = 87.0%) and uninfected (mean = 89.9%) females and the mean engorged weights of both groups (infected, 120.8 mg versus uninfected, 132.7 mg), were comparable. The fecundity, fertility, and mean weights of six replete females having ovarian infections, six females having midgut-restricted infections, and six uninfected females were also similar. We conclude that transovarial transmission is not efficient for maintaining B. burgdorferi in populations of I. pacificus, a known vector of that pathogen. Infection with the spirochete does not appear to affect either feeding or reproductive success adversely in females of this tick.

PMID:
8433348
[PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/pubmed/7628258
Exp Appl Acarol. 1994 Sep;18(9):531-42.

Infection rates of Borrelia burgdorferi in different instars of Ixodes ricinus ticks from the Dutch North Sea Island of Ameland.

Rijpkema S, Nieuwenhuijs J, Franssen FF, Jongejan F.

Source

Laboratory of Bacteriology and Antimicrobial Agents, National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands.

Abstract

Between 1988 and 1993, a total of 7173 I. ricinus ticks, predominantly, were collected from the vegetation on the Dutch North Sea Island of Ameland. A proportion of the ticks (n = 547) was screened for the presence of Borrelia by immunofluorescence. Infection rates of Borrelia varied, in nymphs (n = 347) from 13% to 46% and in adults, (n = 122) from 20% to 43%. The infection rate in larvae (n = 84) collected in 1993 was 21%, showing that transovarial transmission of B. burgdorferi occurs in the I. ricinus population on Ameland. Two tick-naive sheep seroconverted for B. burgdorferi after field-collected adult or nymphal I. ricinus were allowed to feed on them. Larval progeny (n = 168) of 15 female adult ticks fed on one of these sheep were free from B. burgdorferi. B. burgdorferi was isolated in culture from field-collected adult ticks. Serotyping using monoclonal antibodies against outer surface proteins A and C indicated that both isolated belonged to genospecies B. garinii, and this was confirmed by DraI restriction analysis of the variable DNA sequence between the 5S and 23S rRNA genes.

PMID:
7628258
[PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/pubmed/8972683
Epidemiol Infect. 1996 Dec;117(3):563-6.

Detection of four species of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks collected from roe deer (Capreolus capreolus) in The Netherlands.

Rijpkema SG, Herbes RG, Verbeek-De Kruif N, Schellekens JF.

Source

Research Laboratory for Infectious Diseases, National Institute of Public Health and the Environment, Bilthoven, The Netherlands.

Abstract

Roe deer (Capreolus capreolus) were investigated for their value as sentinel animals for Lyme borreliosis in the Netherlands. Serum was obtained from 114 roe deer, and 513 Ixodes ricinus, predominantly females (72%), were obtained from 47 animals (41%). The polymerase chain reaction was used to detect DNA of Borrelia burgdorferi sensu lato in a total of 190 ticks, comprising 106 engorged ticks and 84 non-engorged ticks. Borrelia DNA was detected in 24 engorged ticks (23%) and 26 non-engorged ticks (31%). This difference was not significant (P = 0.25). Four species of B. burgdorferi sensu lato were identified in the ticks. B. burgdorferi sensu stricto, Borrelia garinii, Borrelia afzelii and group VS116. B. afzelii was most commonly found and present in 13 mixed infections, and in 28 single infections. Fifteen sera (13%) contained antibodies to Borrelia spp. Ticks are more appropriate sentinel animals for Lyme borreliosis than roe deer, an important host for I. ricinus. Although the viability of borrelia spirochaetes in engorged ticks collected from roe deer was not assessed, a bloodmeal taken from roe deer did not eliminate borrelia spirochaetes from the tick. The relevance of this finding for transovarial transmission of borrelia spirochaetes in ticks is discussed.

PMID:
8972683
[PubMed - indexed for MEDLINE]
PMCID:
PMC2271641
Free PMC Article
The full article is here (in the form of a scanned copy of the original print version):
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2271641/

http://www.afpmb.org/sites/default/file ... 169235.pdf
Experimental & Applied Acarology, 22 (1998) 249-258

Review

The ecology of ticks transmitting Lyme borreliosis

J.S. Gray*

Department of Environmental Resource Management, University College Dublin, Belfield 4,
Dublin, Republic of Ireland

(Received November 1996; accepted 6 February 1998)

ABSTRACT

The main vectors of Borrelia burgdorferi sensu lato, the cause of Lyme borreliosis, are ixodid
ticks of the lxodes persulcatus species complex. These ticks, which occur throughout the northern
temperate zone, have very similar life cycles and ecological requirements. All are three-host ticks,
with the immature stages mainly parasitizing small to medium-sized mammals and birds and the
adult females parasitizing large mammals such as deer, cattle, sheep and hares. The host-seeking
stages show a distinct seasonality, which is regulated by diapause mechanisms and there appear to be major differences in this respect between the Old World and New World species. Most
cases of human borreliosis are transmitted in the summer by the nymphal stages, with the
exception of the Eurasian species, I. persulcatus, in which the adult females are mainly
responsible. The ticks acquire the spirochaetes from a wide variety of mammals and birds but
large mammals do not seem to be infective, so that ticks that feed almost exclusively on large
mammals, for example in some agricultural habitats, are rarely infected. The greatest tick
infection prevalences occur in deciduous woodland harbouring a diverse mix of host species and
the diversity of the different genospecies of B. burgdorferi s.1. is also greatest in such habitats.
There is evidence that these genospecies have different host predilections but, apart from the fact
that I. persulcatus does not seem to be infected by B. burgdorferi sensu stricto, they do not seem
to be adapted to different tick strains or species.

Exp Appl Acarol 22:249-258 (C) 1998 Chapman & Hall Ltd

[snip]

THE TRANSMISSION OF LYME BORRELIOSIS

Much remains to be learned about the details of Borrelia burgdorferi transmission,
but some facts are now well-established. In most unfed ticks, the spirochaetes
inhabit the midgut and during feeding they penetrate the midgut wall and translocate
to the salivary glands via the haemolymph. They then pass into the feeding
lesion with the saliva. The migration of spirochaetes from the gut to the salivary
glands during feeding means that most infections do not take place for at least 2
days after attachment; however, in a proportion of unfed ticks the spirochaetes are
already present in the salivary glands and transmission can take place much sooner
(Korenberg et al., 1994; Leuba-Garcia et al., 1994). At one time regurgitation of
the gut contents into the feeding lesion was considered to be possible and could
explain early transmission, but so far no convincing evidence has appeared to
support this hypothesis. Trans-stadial transmission (stage to stage) rather than
transovarial transmission (from an infected female to her eggs) normally takes place
so that the infection is usually acquired from a reservoir host by the larvae or
nymphs, and transmitted by the nymphs or adults. Transovarial transmission is
uncommon and the larval infection rates are usually less than 1% so that the larvae
are not considered to be a significant source of infection for humans. However, in
an attempt to explain the fact that in Europe rodents seem to become infected
despite feeding few infecting nymphs, it has been suggested that transovarial
transmission may have a considerable role in maintaining the circulation of the
spirochaete in nature (de Boer et al., 1993). So far no consistent experimental
transmission of spirochaetes by the larvae has been shown
and the precise role of
rodents in the circulation of spirochaetes between the hosts and ticks remains to be
determined.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC106822/

[full article]
Appl Environ Microbiol. 1998 August; 64(8): 3089–3091.
PMCID: PMC106822

Failure of Ixodes Ticks To Inherit Borrelia afzelii Infection

Franz-Rainer Matuschka,1,2 Thomas W. Schinkel,1 Birte Klug,1 Andrew Spielman,2 and Dania Richter1,2,*

Institut für Pathologie, Charité, Medizinische Fakultät der Humboldt-Universität zu Berlin, 12249 Berlin, Germany,1 and Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 021152

*Corresponding author. Mailing address: Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115.

To define conditions promoting inherited infection by Lyme disease spirochetes in Ixodes ticks, we variously infected ticks with Borrelia afzelii and examined their progenies by dark-field microscopy, immunofluorescence, PCR, and serial passage. No episode of inherited infection was evident, regardless of instar or gender infected or frequency of exposure. We suggest that these spirochetes rarely, if ever, are inherited by vector ticks.
http://folia.paru.cas.cz/pdfs/showpdf.php?pdf=20695
FOLIA PARASITOLOGICA 51: 67–71, 2004

Studies on the transovarial transmission of Borrelia burgdorferi sensu lato in the taiga tick Ixodes persulcatus

Valentina V. Nefedova, Edward I. Korenberg, Nataliya B. Gorelova and Yury V. Kovalevskii
Gamaleya Research Institute for Epidemiology and Microbiology, Russian Academy of Medical Sciences, 18 Gamaleya Street, 123098 Moscow, Russia

Key words: Borrelia burgdorferi, Ixodes persulcatus, ticks, transovarial transmission

Abstract. The possibility of vertical transmission of Borrelia burgdorferi sensu lato in Ixodes persulcatus Schulze, 1930 ticks was studied in the progeny of 20 females collected from the vegetation in an active focus of ixodid tick-borne borrelioses (ITBB) located in the Perm oblast, Russia, where Borrelia garinii and B. afzelii are circulating. The presence of Borrelia DNA was detected by the PCR method after feeding and egg laying in 16 engorged females (80.0%), as well as in 36.5 ± 7.2% samples containing 20 eggs each and in 21.4 ± 4.2% samples containing 10 eggs each. The respective rates of individual egg infection were 0.4−8.0% and 0.5−23.0%. PCR analysis of 370 eggs (one egg per sample) and 781 unfed larvae hatched from the same egg masses (1, 10, 20, 40, and 50 larvae per sample) failed to reveal the presence of Borrelia DNA. Negative results were also obtained in experiments on inoculating the BSK II medium with the egg and larval materials. Microscopic analysis of 1,683 smear preparations of eggs and 1,416 preparations of unfed daughter larvae revealed spirochete-like cells in 7 (0.4 ± 0.3%) and 13 (0.9 ± 0.5%) preparations, respectively; typical Borrelia cells were found in seven preparations of larvae (0.5 ± 0.4%). Only 1 out of 16 infected females transmitted Borrelia vertically, through the eggs to the larval progeny. The infection rate in this progeny was about 7%, and the prevalence of Borrelia in individual larvae was 0.4−0.8 cells per 100 microscopic fields. These data do not allow the conclusion that transovarial transmission of B. burgdorferi sensu lato in the I. persulcatus tick is an established fact. However, they show that, even if such transmission is possible, its probability is very low.
http://www.ct.gov/caes/cwp/view.asp?a=2815&q=376732 (2005 ?)
Transmission of the Lyme Disease Spirochete

EN025 (11/05)

Transmission of the Lyme Disease Spirochete

By Louis A. Magnarelli
Department of Entomology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106

[snip]

The rise in deer populations over several decades in and near forests is correlated with substantial increases in blacklegged ticks and corresponding amplification of the disease organism in nature. Although deer are important hosts for adult blacklegged ticks, they do not serve to infect ticks. White-footed mice are considered the chief reservoirs for the Lyme disease agent. Larval and nymphal blacklegged ticks acquire the pathogen when they feed on these rodents and possibly other hosts, such as chipmunks and some birds. The disease organism can then be passed from larvae to nymphs to adults during the developmental process. There is occasional passage of the disease agent from infected females to larvae (via the eggs), but this form of pathogen transmission is not considered to be epidemiologically significant.1

[snip]

References

1. Magnarelli, L.A., J. F. Anderson, and D. Fish. 1987. Transovarial transmission of Borrelia burgdorferi in Ixodes dammini (Acari: Ixodidae). Journal of Infectious Diseases 156:234-236.

2. Piesman, J., T. N. Mather, R. J. Sinsky, et al. 1987. Duration of tick attachment and Borrelia burgdorferi transmission. Journal of Clinical Microbiology 25:557-558.

3. des Vignes, F., J. Piesman, R. Heffernan, et al. 2001. Effect of tick removal on transmission of Borrelia burgdorferi and Ehrlichia phagocytophila by Ixodes scapularis nymphs. Journal of Infectious Diseases 183:773-778.

4. Piesman, J. and M. C. Dolan. 2002. Protection against Lyme disease spirochete transmission provided by prompt removal of nymphal Ixodes scapularis (Acari: Ixodidae). Journal of Medical Entomology 39:509-512.
http://wwwnc.cdc.gov/eid/article/8/2/01 ... rticle.htm
Perspective

Vector Interactions and Molecular Adaptations of Lyme Disease and Relapsing Fever Spirochetes Associated with Transmission by Ticks

Suggested Citation

Tom G. Schwan* and Joseph Piesman†
Author affiliations: *National Institutes of Health, Hamilton, Montana, USA; †Centers for Disease Control and Prevention, Fort Collins, Colorado, USA

Abstract

Pathogenic spirochetes in the genus Borrelia are transmitted primarily by two families of ticks. The Lyme disease spirochete, Borrelia burgdorferi, is transmitted by the slow-feeding ixodid tick Ixodes scapularis, whereas the relapsing fever spirochete, B. hermsii, is transmitted by Ornithodoros hermsi, a fast-feeding argasid tick. Lyme disease spirochetes are generally restricted to the midgut in unfed I. scapularis. When nymphal ticks feed, the bacteria pass through the hemocoel to the salivary glands and are transmitted to a new host in the saliva after 2 days. Relapsing fever spirochetes infect the midgut in unfed O. hermsi but persist in other sites including the salivary glands. Thus, relapsing fever spirochetes are efficiently transmitted in saliva by these fast-feeding ticks within minutes of their attachment to a mammalian host. We describe how B. burgdorferi and B. hermsii change their outer surface during their alternating infections in ticks and mammals, which in turn suggests biological functions for a few surface-exposed lipoproteins.

[snip]

Spirochete Multiplication

The principal tick vectors of Lyme disease spirochetes in North America are I. scapularis and I. pacificus; the developmental stage of the former species that transmits most human infections is the nymph. Although transmission by adult I. scapularis or transovarially infected larvae remains possible, our review focuses on tick-spirochete interactions within nymphal I. scapularis. Larval ticks ingest spirochetes from infected reservoir hosts, molt, and emerge as nymphs. When spirochetes are ingested by larvae, they rapidly multiply in the replete tick until the nymphal molt, when a precipitous drop in spirochete numbers occurs (10,11). Thus, at the time questing nymphs are likely to contact their potential victims, spirochete numbers are at their lowest and generally restricted to the lumen of the midgut. When nymphal feeding begins, a pronounced multiplication of spirochetes takes place in the tick. Nymphal I. scapularis take approximately 3 to 4 days to complete feeding. Spirochete numbers are reported to increase >300- fold during this feeding period, increasing from a mean of 496 spirochetes in unfed nymphs to 166,575 at 72 hours after attachment (12). Along with this rapid multiplication, other changes are taking place in the spirochete population that may lay the groundwork for eventual transmission to the host.

[snip]

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Page last updated: July 14, 2010
Page last reviewed: July 14, 2010
http://www.ncbi.nlm.nih.gov/pubmed/21923267
Vector Borne Zoonotic Dis. 2012 Jan;12(1):21-7. Epub 2011 Sep 16.

Absence of Lyme disease spirochetes in larval Ixodes ricinus ticks.

Richter D, Debski A, Hubalek Z, Matuschka FR.

Source

Abt. Parasitologie, Institut für Pathologie, Charité Universitätsmedizin Berlin, Berlin, Germany

Abstract

To determine which kind of spirochete infects larval Ixodes ricinus, we examined questing larvae and larvae derived from engorged females for the presence of particular spirochetal DNA that permitted species differentiation. Borrelia miyamotoi was the sole spirochete detected in larval ticks sampled while questing on vegetation. Questing nymphal and adult ticks were infected mainly by Borrelia afzelii, whereas larval ticks resulting from engorged females of the same population were solely infected by B. miyamotoi. Since larvae acquire Lyme disease spirochetes within a few hours of attachment to an infected rodent, questing larvae in nature may have acquired Lyme disease spirochetes from an interrupted host contact. Even if transovarial transmission of Lyme disease spirochetes may occasionally occur, it seems to be an exceedingly rare event. No undisputable proof exists for vertical transmission of Lyme disease spirochetes, whereas B. miyamotoi appears to be readily passed between generations of vector ticks.

PMID:
21923267
[PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov/pubmed/22230951
Nat Rev Microbiol. 2012 Jan 9;10(2):87-99. doi: 10.1038/nrmicro2714.

Of ticks, mice and men: understanding the dual-host lifestyle of Lyme disease spirochaetes.

Radolf JD, Caimano MJ, Stevenson B, Hu LT.

Source

Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.

Abstract

In little more than 30 years, Lyme disease, which is caused by the spirochaete Borrelia burgdorferi, has risen from relative obscurity to become a global public health problem and a prototype of an emerging infection. During this period, there has been an extraordinary accumulation of knowledge on the phylogenetic diversity, molecular biology, genetics and host interactions of B. burgdorferi. In this Review, we integrate this large body of information into a cohesive picture of the molecular and cellular events that transpire as Lyme disease spirochaetes transit between their arthropod and vertebrate hosts during the enzootic cycle.

PMID:
22230951
[PubMed - indexed for MEDLINE]
PMCID:
PMC3313462
Free PMC Article
The full article is here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3313462/

http://www.ncbi.nlm.nih.gov/pmc/article ... figure/F1/
The enzootic cycle of Borrelia burgdorferi. Ixodes spp. ticks undergo a three-stage life cycle — larva, nymph and adult — with one blood meal per stage. Although some Borrelia spp. that cause relapsing fever can be passed from adult to egg (transovarial transmission), this does not occur with B. burgdorferi, so each generation of tick must acquire a B. burgdorferi infection anew. Larval ticks feed on many different animals, including Peromyscus spp. mice, squirrels and birds. B. burgdorferi infection is acquired by feeding on an infected reservoir animal, and the bacterium is retained during the subsequent stages (that is, trans-stadially) after each blood meal and moult7,10. Nymphs feed on a similar range of hosts to larvae; transmission of spirochaetes to a competent reservoir host by a feeding nymph perpetuates the enzootic cycle for the next generation of larval ticks. Although small mammals are usually thought of as the primary reservoirs for Lyme disease spirochaetes, studies have called attention to the importance of migratory birds as disseminators of spirochaetes over large distances7,10. Adult ticks are not generally important for maintenance of B. burgdorferi in the wild, as they feed predominantly on larger animals such as deer, which are incompetent hosts for B. burgdorferi7. However, deer are important for maintenance of the tick population because adult ticks mate on them. Although all three stages of Ixodes scapularis can feed on humans, nymphs are responsible for the vast majority of spirochaete transmission to humans. It is unknown whether infected humans can transmit spirochaetes to feeding larvae, and humans are generally considered dead-end hosts and not part of the enzootic cycle. Dogs are probably incidental hosts and not part of the enzootic cycle.

Pandora
Posts: 252
Joined: Tue 20 Mar 2012 14:58

Re: Transovarial Transmission

Post by Pandora » Sun 16 Dec 2012 0:55

Comparison of the local structural stabilities of mammalian prion protein (PrP) by fragment molecular orbital cal
culations.
http://www.ncbi.nlm.nih.gov/pubmed/23232497
The structural stability of 6 mammalian PrPs, including human, cattle, mouse, hamster, dog and cat, was analyzed.

We then evaluated intramolecular interactions in PrP by fragment molecular orbital (FMO) calculations.

Despite similar backbone structures,

the PrP side-chain orientations differed

among the animal species examined.

The pair interaction energies between secondary structural elements in the PrPs varied considerably,

indicating that the local structural stabilities of PrP varied among the different animal species.
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If this is true for "normal" prp(C) and PrP(Sc) would it not be presumtious of us to think borrelia PRION LIKE PROTEINS do not exhibit the same?

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