{"version":"1.0","provider_name":"TBE Book","provider_url":"https:\/\/tbenews.com\/tbe","author_name":"IT","author_url":"https:\/\/tbenews.com\/tbe\/author\/brianong\/","title":"Chapter 5: TBEV-transmission and natural cycles - TBE Book","type":"rich","width":600,"height":338,"html":"<blockquote class=\"wp-embedded-content\" data-secret=\"F5K5jXVonG\"><a href=\"https:\/\/tbenews.com\/tbe\/chapter-5-tbev-transmission-and-natural-cycles\/\">Chapter 5: TBEV-transmission and natural cycles<\/a><\/blockquote><iframe sandbox=\"allow-scripts\" security=\"restricted\" src=\"https:\/\/tbenews.com\/tbe\/chapter-5-tbev-transmission-and-natural-cycles\/embed\/#?secret=F5K5jXVonG\" width=\"600\" height=\"338\" title=\"&#8220;Chapter 5: TBEV-transmission and natural cycles&#8221; &#8212; TBE Book\" data-secret=\"F5K5jXVonG\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\" class=\"wp-embedded-content\"><\/iframe><script>\n\/*! This file is auto-generated *\/\n!function(d,l){\"use strict\";l.querySelector&&d.addEventListener&&\"undefined\"!=typeof URL&&(d.wp=d.wp||{},d.wp.receiveEmbedMessage||(d.wp.receiveEmbedMessage=function(e){var t=e.data;if((t||t.secret||t.message||t.value)&&!\/[^a-zA-Z0-9]\/.test(t.secret)){for(var s,r,n,a=l.querySelectorAll('iframe[data-secret=\"'+t.secret+'\"]'),o=l.querySelectorAll('blockquote[data-secret=\"'+t.secret+'\"]'),c=new RegExp(\"^https?:$\",\"i\"),i=0;i<o.length;i++)o[i].style.display=\"none\";for(i=0;i<a.length;i++)s=a[i],e.source===s.contentWindow&&(s.removeAttribute(\"style\"),\"height\"===t.message?(1e3<(r=parseInt(t.value,10))?r=1e3:~~r<200&&(r=200),s.height=r):\"link\"===t.message&&(r=new URL(s.getAttribute(\"src\")),n=new URL(t.value),c.test(n.protocol))&&n.host===r.host&&l.activeElement===s&&(d.top.location.href=t.value))}},d.addEventListener(\"message\",d.wp.receiveEmbedMessage,!1),l.addEventListener(\"DOMContentLoaded\",function(){for(var e,t,s=l.querySelectorAll(\"iframe.wp-embedded-content\"),r=0;r<s.length;r++)(t=(e=s[r]).getAttribute(\"data-secret\"))||(t=Math.random().toString(36).substring(2,12),e.src+=\"#?secret=\"+t,e.setAttribute(\"data-secret\",t)),e.contentWindow.postMessage({message:\"ready\",secret:t},\"*\")},!1)))}(window,document);\n\/\/# sourceURL=https:\/\/tbenews.com\/tbe\/wp-includes\/js\/wp-embed.min.js\n<\/script>\n","thumbnail_url":"https:\/\/tbenews.com\/tbe\/wp-content\/uploads\/2024\/06\/Chapter-5-TBEV-TRANSMISION_N-CYLE_-scaled.jpg","thumbnail_width":2560,"thumbnail_height":1709,"description":"Chapter 5:TBEV-transmission andnatural cycles Lidia Chitimia-Dobler Key points Introduction Ticks play a critical role in the transmission of a wide variety of viral, bacterial, and protozoan pathogens to humans and animals.1,2 In the case of humans, infection is accidental as these transmission cycles are invariably enzootic with the natural hosts most frequently being wild birds and mammals.1 In order to be tangentially affected by such cycles, humans must be bitten by a vector tick species found in habitats visited by humans, as well as the tick\u2019s usual hosts, as the dispersal of ticks not attached to hosts covers only very short distances. In addition, the tick has to accept humans as a suitable host, meaning that the species involved usually have a broad host spectrum. Nevertheless, these tick species may only be part of the transmission cycle, with eco-epidemiologically significant sub-cycles involving tick species not commonly in contact with humans.3,4 Thus, the transmission of tick-borne pathogens often comprises a complex network of interactions involving several tick and host species. Below, we provide background to the biology of ticks and how this can influence, specifically, the eco-epidemiological cycle of tick-borne encephalitis virus (TBEV). Structure and morphology Ticks are a group of hematophagous ectoparasites with about 989 living species.5 They belong to the phylum Arthropoda, the class Arachnida, the superorder Acarina, and the order Ixodida, and they are exclusively parasitic. The Ixodida contain 3 families: the Ixodidae with 15 genera (hard ticks), the Argasidae with 15 genera (soft ticks), and the Nuttalliellidae, represented by only one species, Nuttalliella namaqua.6-9, A summary of tick taxonomy and the two groups is presented in Figure 1. All the tick species involved in the eco-epidemiological cycle of TBEV belong to the Ixodidae. Details of tick biology generally can be found in a variety of publications, for example in Nicholson et al.,9 Petney et al.,10 and Sonenshine and Roe,11 and a list of valid species names in Guglielmone and Nava.12 The following genera of ticks contain species known to transmit TBEV or in their species TBEV was detected. &nbsp; Figure 1: The Ixodidae family The Ixodidae family is divided in two groups: Prostriata, which includes only the genus Ixodes and which is characterizad by an anal groove encircling the anus anteriorly (blue arrow); and Metastriata, including 14 genera, which all have an anal groove behind the anus (red arrow). Click the image above to enlarge Ixodes is the largest tick genus, with 266 described species worldwide.5 Ixodes species are characterized by a distinct groove that encircles the anus anteriorly and a lack of eyes. Males have seven sclerotized ventral plates that are absent in the males of other genera. The genus Ixodes has been subdivided in roughly 15 subgenera (e.g., Ixodes, Pholeoixodes) on the basis of morphology.13,14 The genus has a worldwide distribution, including parts of Antarctica.9 Some species are particularly important as vectors of TBEV: Ixodes ricinus the castor bean tick or sheep tick in Europe and middle Asia, Ixodes persulcatus the taiga tick in northeastern Europe and northern Asia, and Ixodes ovatus in the forest belt of middle Asia and Japan. The genus Dermacentor has 44 species worldwide.9 The basis capitulum appears rectangular when viewed dorsally. A pair of medially directed spurs occurs on the first pair of coxae. The palps are short and thick. The scutum is almost always ornamented, eyes present. Dermacentor species are found mostly in Europe, Asia, and North America.[9] In Europe, TBEV has been recovered from 2 species, Dermacentor reticulatus (the ornate dog tick), Dermacentor marginatus (the ornate sheep tick), and in Asia from Dermacentor nuttalli. Haemaphysalis Haemaphysalis is the second largest (176 species) tick genus.5 This eyeless genus can, in most cases, be identified by a pronounced lateral projection of palpal segment 2, which extends well beyond the basis capitulum. In Europe, TBEV has been recovered from Haemaphysalis punctata (the red sheep tick), Haemaphysalis concinna in Europe and Asia, and from Haemaphysalis longicornis in Asia.9 The genus Hyalomma is relatively small with 27 species of small- to large-sized ticks.14 They are characterized by their elongated palps, which are at least twice as long as wide. The distinct eyes are located in sockets adjacent to the postero-lateral edges of the scutum that is unornamented. The distribution of Hyalomma species is limited to the Old World, primarily to arid or semiarid habitats. Hyalomma marginatum (the Mediterranean Hyalomma) is the only member of this genus from which TBEV has been recovered.15,16 The biology of hard ticks All the species known to transmit TBEV have a 3-host life- cycle (Figure 2). Each postembryonic life stage requires a blood meal from a suitable host, after which the tick detaches and molts in the leaf litter. The arrows with broken lines in the figure show the potential transmission paths to humans. The line from larvae to humans indicates that transovarial trans-mission from an infected female can happen which results in infective larvae. Infection of the tick can occur when larvae, nymphs, or females feed on an infective host (see below). The larva, nymph, and adult (female or male \u2013 Figures 3a, 3b, 3c, and 3d) are active stages that require a host (this is not the case for males of the genus Ixodes, which can mate off-host without feeding).17 Larvae are easily recognizable by the presence of only 3 pairs of legs, and absent spiracular and genital apertures (Figures 4a and 4b). Nymphs have 4 pairs of legs and spiracles (Figures 5a and 5b). Adult females have 4 pairs of legs, and spiracles, a genital aperture, and porose areas on the dorsal surface of the basis capituli (Figures 3a and 3b). Adult males have 4 pairs of legs, the scutum covers the entire dorsal surface, and seven hard sclerotized plates cover the ventral body surface of some species (Figures 3c and 3d). &nbsp; Table 1: Tick species, habitats, and involved hosts in relation to the TBEV subtype and distribution ES, European subtype (TBEV-EU); FES, Far Eastern subtype (TBEV-FE); SS, Siberian subtype (TBEV-Sib)* Reference for"}