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Lyme Disease Transmission and Maintenance within the environment
Lyme Disease (LD) is described as a vector-borne disease as it is spread via the bite of arachnids (ticks). It should also be noted that there are some methods of transmission that are subject to speculation and controversy. These methods include:
1. Evidence that blood sucking insects (other than ticks) are able to transmit Lyme disease;
2. Contact (urine passed) transmission has been noted in mice, and;
3. Human to human transmission : sexual and mother to baby (vertical).
These controversial areas are outlined briefly, before going on to focus on the well known ability of the tick to spread Lyme disease in order to address the problems with lack of recognition in Australia.
Other blood sucking insects:
In clinical cases of Lyme Disease, biting flies (1-3), mosquito’s (3,4) and mites (5) are suggested to have been responsible for the infection. Borrelia has been found in: numerous species of mites (6) ; fleas (6-8) ; biting flies, ie: bot flies, deer flies, horse flies (6,7, 9-11) ; and mosquito’s (8, 9, 11-14), indicating that these insects are capable of maintaining the bacteria within the environment and are potential vectors.
Contact transmission:
Borrelia spirochetes have been found in the urine of infected dogs (15,16), horses (17,18), cattle (18) and mice (19,20). Studies on mice have found that the spirochetes in urine remained viable for 18-24 hours and concluded that “Urine may provide a method for contact non-tick transmission of B. burgdorferi in natural rodent populations particularly during periods of nesting and/or breeding” (19: pg 40). Evidence for direct contact transmission has been demonstrated in mice (20). These findings suggest that further research is needed to ascertain whether, like the spirochete that causes Leptospirosis, the borrelia spirochete is able to spread by the urine of infected animals to humans.
1. Evidence that blood sucking insects (other than ticks) are able to transmit Lyme disease;
2. Contact (urine passed) transmission has been noted in mice, and;
3. Human to human transmission : sexual and mother to baby (vertical).
These controversial areas are outlined briefly, before going on to focus on the well known ability of the tick to spread Lyme disease in order to address the problems with lack of recognition in Australia.
Other blood sucking insects:
In clinical cases of Lyme Disease, biting flies (1-3), mosquito’s (3,4) and mites (5) are suggested to have been responsible for the infection. Borrelia has been found in: numerous species of mites (6) ; fleas (6-8) ; biting flies, ie: bot flies, deer flies, horse flies (6,7, 9-11) ; and mosquito’s (8, 9, 11-14), indicating that these insects are capable of maintaining the bacteria within the environment and are potential vectors.
Contact transmission:
Borrelia spirochetes have been found in the urine of infected dogs (15,16), horses (17,18), cattle (18) and mice (19,20). Studies on mice have found that the spirochetes in urine remained viable for 18-24 hours and concluded that “Urine may provide a method for contact non-tick transmission of B. burgdorferi in natural rodent populations particularly during periods of nesting and/or breeding” (19: pg 40). Evidence for direct contact transmission has been demonstrated in mice (20). These findings suggest that further research is needed to ascertain whether, like the spirochete that causes Leptospirosis, the borrelia spirochete is able to spread by the urine of infected animals to humans.
Human to human transmission:
Sexual transmission:
There is no direct evidence for sexual transmission, although spirochetes have been found in semen (21), suggesting that it is a possibility. Lyme disease has also been likened to another spirochetal disease, syphilis, which is a sexually transmittable infection (22).
Mother to baby:
The possibility of placental transmission is acknowledged, although there are mixed reports regarding exactly what health risk congenital Lyme disease poses to the foetus/newborn. A brief dialogue regarding some examples and the quoted passages below: Allan MacDonald notes that adverse reactions, such as fetal death and cortical blindness, have been associated with gestational Lyme disease and suggests the need for further research in order to ascertain whether the associations are co-incidental or related to the infection (23); The International Disease Society of America (IDSA) guidelines typically downplays any risk, associated with Lyme, and in this regard notes that “there is little evidence that a congenital Lyme disease syndrome occurs” (24); The Centre for Disease Control (CDC) notes that while “Lyme disease can be dangerous for your unborn child”, and “may lead to infection of the placenta and may possibly lead to stillbirth” (25,26), it follows the IDSA guidelines that “favorable outcomes can be expected when pregnant women with Lyme disease are treated with standard antibiotic regimen”; Contrary to this statement, there are reports of adverse outcomes, including the death of newborns, with (27) or without (28) antibiotic treatment of the mother; The National Institutes of Health, puts it short and sweet: “If you are pregnant, be especially careful to avoid ticks in Lyme disease areas because you can pass on the infection to your unborn child” (29:pg 15). Which leads us back to the original message, further research is urgently required.
The abstracts of the above referenced readings and further information on Human to Human transmission are provided in the Transmission Controversy section of LARA website.
Sexual transmission:
There is no direct evidence for sexual transmission, although spirochetes have been found in semen (21), suggesting that it is a possibility. Lyme disease has also been likened to another spirochetal disease, syphilis, which is a sexually transmittable infection (22).
Mother to baby:
The possibility of placental transmission is acknowledged, although there are mixed reports regarding exactly what health risk congenital Lyme disease poses to the foetus/newborn. A brief dialogue regarding some examples and the quoted passages below: Allan MacDonald notes that adverse reactions, such as fetal death and cortical blindness, have been associated with gestational Lyme disease and suggests the need for further research in order to ascertain whether the associations are co-incidental or related to the infection (23); The International Disease Society of America (IDSA) guidelines typically downplays any risk, associated with Lyme, and in this regard notes that “there is little evidence that a congenital Lyme disease syndrome occurs” (24); The Centre for Disease Control (CDC) notes that while “Lyme disease can be dangerous for your unborn child”, and “may lead to infection of the placenta and may possibly lead to stillbirth” (25,26), it follows the IDSA guidelines that “favorable outcomes can be expected when pregnant women with Lyme disease are treated with standard antibiotic regimen”; Contrary to this statement, there are reports of adverse outcomes, including the death of newborns, with (27) or without (28) antibiotic treatment of the mother; The National Institutes of Health, puts it short and sweet: “If you are pregnant, be especially careful to avoid ticks in Lyme disease areas because you can pass on the infection to your unborn child” (29:pg 15). Which leads us back to the original message, further research is urgently required.
The abstracts of the above referenced readings and further information on Human to Human transmission are provided in the Transmission Controversy section of LARA website.
In order to address the problems with lack of recognition of Lyme disease, the focus of the following information is on the well known ability of the tick to spread and transmit Lyme disease / borreliosis.
To maintain Lyme disease within the environment requires the tick (the vector that carries and spreads the disease) and host animals. The host animals may be thought of as either reservoir hosts, which are small to medium size animals that carry/maintain the spirochete infection within their blood, and the larger host animal for which the adult of a particular species of tick has an affinity(30). There is some question as to whether or not larger mammals, such as sheep, deer, horses and cattle simply serve to amplify the infection within the environment by providing the tick with a host blood meal or whether they also serve as reservoir hosts of borrelia. In general, the studies show mixed conclusions. These findings are discussed further in the ‘Tick vectors in Australia' section. With regards to the smaller/medium animals, there are over 50 mammalian and avian species that are reservoir hosts of borrelia (31) and include various mammal species such as: mice, rats, hares, rabbits, squirrels and dogs, as well as numerous species of marine and land birds including puffins, blackbirds, pheasants and ducks.
Ticks and Human Disease:
Ticks are classified as arachnids (eg: spiders, mites, scorpions), as they have eight legs, rather than six as with insects. Arachnids are a group of arthropods (this term is sometimes used in relation to Lyme disease and its vectors) which account for over three quarters of all known animal species (32). There are approximately 850 species of ticks worldwide that are divided into two families, the Ixodidae (hard ticks) and Argasidae (soft ticks). Both are vectors for human disease, though in the case of Lyme disease it is the Ixodidae family that has been associated with transmission. The family of Ixodidae tick itself has approximately 650 different species, divided into 13 genera including; Ixodes, Amblyomma, Haemaphysalis, Rhipicephalus and Dermacentor (33). The first ticks that were found to be competent vectors of borrelia were of the Ixodes genera: I. Scapularis (Previously known as I. dammini, before being shown to be same species), and I. Pacificus (Black-legged Tick), commonly known as deer ticks in America. In Europe and Asia, the vectors were found to be the I. Ricinus (Castor Bean/Sheep Tick) and I. Persulcatus (Taiga Tick). Since these early investigations, many more species of ticks have been identified as vectors. This includes over a dozen more species of Ixodes ticks, as well as ticks from other Ixodidae genera’s including, Amblyomma, Haemaphysalis, Rhipicephalus and Dermacentor.
The basic implications of these findings is that there are many ticks (not just the deer tick, as is the popular myth) that are capable of carrying and transmitting the bacteria that causes Lyme disease. What all of the ticks typically have in common is that they are three-host ticks. This simply means that they attach to a different host in each stage of their life development. Once the tick egg hatches to the larvae, the larvae need to find a host to attach to for a blood-meal, it then drops off and molts into a nymph. The nymph repeats the action of finding a host for a blood-meal before molting into an adult. The final blood-meal is then sought by the adult before dropping off, with the females then laying eggs. It is due to the attachment on three different hosts that these ticks are able to firstly be infected and then spread/maintain the disease within their environment.
Typically the larvae and nymphs feed on smaller animals within the environment, with the adult ticks then attaching to larger hosts (ie: Deers for I. Scapularis or Sheep in the case of I. Ricinus). It is the smaller/medium sized animals that the larvae and nymphs feed on that act as reservoir hosts for the borrelia bacteria that play a large role in maintaining the infectious cycle. When the larvae or nymph ticks feed on the reservoir hosts, they are then infected, and upon attaching to their next host, may pass that infection on. Whilst humans are not the preferred host, if they inadvertently come into contact with ticks, (walking through bush or long grass) then they may be at risk. It is usually at the nymphal stage that humans are infected, as at this stage of its life, the tick is barely large enough to be noticed and it may feed and drop off without a person evening realizing. The ticks may feed without being noticed as when ticks attach, they inject an anaesthetic into the skin of the host. This action presumably reduces the chances that the host will notice the presence of the tick and thereby attempt to get remove it and interfere with its feeding.
The basic implications of these findings is that there are many ticks (not just the deer tick, as is the popular myth) that are capable of carrying and transmitting the bacteria that causes Lyme disease. What all of the ticks typically have in common is that they are three-host ticks. This simply means that they attach to a different host in each stage of their life development. Once the tick egg hatches to the larvae, the larvae need to find a host to attach to for a blood-meal, it then drops off and molts into a nymph. The nymph repeats the action of finding a host for a blood-meal before molting into an adult. The final blood-meal is then sought by the adult before dropping off, with the females then laying eggs. It is due to the attachment on three different hosts that these ticks are able to firstly be infected and then spread/maintain the disease within their environment.
Typically the larvae and nymphs feed on smaller animals within the environment, with the adult ticks then attaching to larger hosts (ie: Deers for I. Scapularis or Sheep in the case of I. Ricinus). It is the smaller/medium sized animals that the larvae and nymphs feed on that act as reservoir hosts for the borrelia bacteria that play a large role in maintaining the infectious cycle. When the larvae or nymph ticks feed on the reservoir hosts, they are then infected, and upon attaching to their next host, may pass that infection on. Whilst humans are not the preferred host, if they inadvertently come into contact with ticks, (walking through bush or long grass) then they may be at risk. It is usually at the nymphal stage that humans are infected, as at this stage of its life, the tick is barely large enough to be noticed and it may feed and drop off without a person evening realizing. The ticks may feed without being noticed as when ticks attach, they inject an anaesthetic into the skin of the host. This action presumably reduces the chances that the host will notice the presence of the tick and thereby attempt to get remove it and interfere with its feeding.
© Karen Smith, B. Psych (Hons), 2012 -2015
Further research with regards to the transmission & maintenance of Lyme can be seen on Lyme Australia Recognition & Awareness.
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