Outbreaks of
emerging infectious diseases have been increasing in frequency as human populations expand and encroach on previously undisturbed or uninhabited areas.
Vector-borne diseases have presented significant challenges to maintaining public health over the past century. Furthermore,
arthropod-borne diseases have been at the forefront of vector-borne diseases, bringing
epidemics of
plague,
tularemia,
yellow fever,
malaria,
Japanese encephalitis,
Eastern equine encephalitis,
West Nile Virus disease,
leishmaniasis, and several others. Epidemiologically-relevant transstadial transmission is primarily observed in mites, ticks, and mosquitoes that serve as arthropod vectors of disease.
Transstadial transmission of pathogens in arthropod vectors Lyme Disease (Borrelia burgdorferi) Lyme disease, caused by the bacterium
Borrelia burgdorferi, is spread to humans via the bite of an infected
blacklegged tick, also known as a deer tick (
Ixodes scapularis).
B. burgdorferi is considered
enzootic, meaning that it is perpetuated in animals in the environment, outside of humans. In the cycle from ticks to animals, an uninfected tick larva feeds on an infected host, such as a
deer or a
mouse, leading to infection of the tick. The infection is transstadial in ticks because the bacterium will persist in the tick as it molts from a larva to a nymph. Humans are a dead-end host for
B. burgdorferi and do not function in the natural cycling of the bacterium in the environment.
B. burgdorferi contains a
1Mb linear
chromosome with multiple linear and circular
plasmids with
genes encoding
lipoproteins that become activated under various conditions. Additionally,
B. burgdorferi is an
auxotroph for all
amino acids,
nucleotides, and
fatty acids, and does not contain genes encoding proteins for use in the
tricarboxylic acid cycle or
oxidative phosphorylation. When the tick engages in its nymphal bloodmeal,
B. burgdorferi undergoes many changes in
gene expression, upregulating protein generation for use in attachment to the host and establishing infection.
Virulence genes are also activated in concert with tick
saliva production, further advancing the ability for the bacterium to become established in the new host.
La Crosse Virus La Crosse virus is primarily transmitted via the Eastern Treehole mosquito (
Aedes triseriatus). Disease caused by La Crosse virus can result in serious
neurological complications, such as
La Crosse Encephalitis, most often occurring in children and is endemic to the eastern United States. La Crosse virus undergoes transovarial transmission in mosquitoes, passing from one generation to the next. Additionally, after infection of the mosquito egg, the virus remains in the mosquito as it progresses through its life stages, completing transstadial transmission. Mosquitoes may become infected by feeding on the blood of reservoir hosts in the environment, allowing for the transmission of the virus in the genetic line of the mosquitoes in the environment.
Anaplasma spp. Anaplasma is a bacterial genus causing costly economic losses worldwide, particularly in the food animal agricultural sector. Infection by
Anaplasma results in
anaplasmosis, a disease which can cause both serious and
subclinical disease.
Anaplasma is another arthropod-vectored disease and is also spread through the bites of infected ticks, particularly
Ixodidae ticks and potentially mosquitoes as well
. Numerous scientific reports present claims of transovarial and transstadial transmission of
Anaplasma in ticks. Ruminants are the primary reservoir for
Anaplasma spp., but the bacteria can also be found in wild animals. In ticks,
Anaplasma spp. can be transmitted transstadially, and the ticks become infected by feeding off infected animals, allowing for transmission to un-infected animals. Recent research, however, has built evidence for transovarial transmission of at least some
Anaplasma species in ticks. == Transstadial transmission and fungal communities in mosquitoes ==