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Viral Pathogens: A General Account
Published in Jagriti Narang, Manika Khanuja, Small Bite, Big Threat, 2020
Vinod Joshi, Bennet Angel, Annette Angel, Neelam Yadav, Jagriti Narang
This is an encephalitis virus of the genus Orthobunyavirus, discovered from the stored brain and spinal tissue of an infected child (then an unknown virus) in La Crosse of Wisconsin in 1960. The virus leads to a disease referred to as La Crosse encephalitis, leading to headache, coma, paralysis, and brain damage in severe cases. Normally people with no symptoms are also seen. The virus is known to be transmitted through the Aedes vector (Aedes triseriatus), which is a forest-dwelling species (Fig. 3.6). Since it dwells in forests, its reservoir hosts tend to be chipmunks, tree squirrels, etc. Transovarial transmission has also been reported for this virus. The infection has been reported in children under the age of 16 years as well as in immunocompromised individuals. At present no vaccine or treatment is available. Sometimes the disease goes undiagnosed where medical practitioners think it to be a case of aseptic meningitis (Thompson et al., 1965). In the United States, approximately 63 cases are reported each year due to this infection.
Classification of Hemorrhagic Fevers
Published in James H. S. Gear, CRC Handbook of Viral and Rickettsial Hemorrhagic Fevers, 2019
Most species are arboviruses in the biological sense. They infect a wide range of vertebrate hosts, causing a variety of diseases including yellow fever and dengue. Epitopes on the envelope protein E induce monoclonal antibodies which react with type, complex, or group specificity measurable by hemagglutination-inhibition or neutralization tests. Transovarial transmission of some species occurs in arthropods and transplacental transmission occurs in some mammals.
Biology and Distribution of Ticks of Medical Importance
Published in Jürg Meier, Julian White, Handbook of: Clinical Toxicology of Animal Venoms and Poisons, 2017
André Aeschlimann, Thierry A. Freyvogel
Several tick species contribute to the survival of pathogen populations in susceptible hosts by combining transstadial with transovarian transmission (Figure 6). Transovarian transmission is not possible for all pathogens; no transovarian transmission has been observed with either Theileria or Acanthocheilonema. Where it does occur, it may may take place through several consecutive tick generations. In this case the tick population simultaneously assumes the role of both vector and reservoir. How effective this is depends on the pathogens concerned. Transmission of rickettsiae is 100% transovarian, and of B. duttoni 40%. For B. burgdorferi, however, this route accounts for only 3 - 6% of transmission, and for encephalitis viruses only for 0.1%. Such figures provide some indication as to how relevant transovarian transmission may be under given epidemiological circumstances.
Modeling tick vaccines: a key tool to improve protection efficacy
Published in Expert Review of Vaccines, 2020
José de la Fuente, Agustin Estrada-Peña, Marinela Contreras
The conclusions from these models pointed at two important considerations for the control of CCHFv in natural foci: (i) a vaccination strategy targeting tick vector infestations and CCHFv infection/transmission would complement each other to produce the highest efficacy for reducing the risk of CCHF, and (ii) the overall efficacy of targeting vertebrates feeding the immature tick stages has a lower effect on CCHF than the delivery of the vaccine to ungulates. These results probably reflect the rates of transovarial transmission of the virus, coming from the infected females that feed on large ungulates and livestock. These results showed that no scenario promoted a complete eradication of the foci of the virus because the co-feeding transmission, which is known to occur in CCHFv to support persistent virus foci. In our scenarios, vaccines were not designed against the co-feeding virus transmission because it may occur in minutes and vaccination strategies blocking this transmission route are far from envisaged.
Scrub typhus and antibiotic-resistant Orientia tsutsugamushi
Published in Expert Review of Anti-infective Therapy, 2021
Chin-Te Lu, Lih-Shinn Wang, Po-Ren Hsueh
Adults pass O. tsutsugamushi to their offspring through transovarial transmission. Larva mites are the only parasite stage, while all other active stages are free-living; humans play no role in the Orientia mite life cycle and are dead-end hosts [9]. The occurrence of scrub typhus is frequently related to temperature, and sometimes to rainfall, with high transmission peaks before and after the rainy season in many regions of Southeast and East Asia; a regular year-round transmission is common in some tropical and subtropical regions [10–14]. Chiggers are abundant in locales with high relative humidity (60–85%), moderate temperature (20–30°C), low incidence of sunlight, and a dense substrate-vegetative canopy [11,15,16].