Viraemic transmission of Crimean-Congo haemorrhagic fever virus to ticks

Abstract

SUMMARYIn order to determine the way in which vertebrates infected with CrimeanCongo haemorrhagic fever (CCHF) virus and potential ixodid tick vectors interact in nature, immature and adult ticks of several species were fed on viraemic mammals and then assayed for virus content at varying times after feeding. CCHF virus was not isolated from ticks of six species tested after feeding as adults and immature forms on sheep with viraemia of 102 -32 LD 50/ml, nor from larval ticks fed on guinea-pigs and white-tailed rats with viraemia of 1019-27 LD 50/ml. In contrast, virus was isolated from 10 of 152 pools of engorged adult ticks of 5 species that fed on cattle with viraemia of 101'-27 LD 50/ml and from 3 of 137 female ticks after oviposition. Infection was transmitted to larval and nymphal Hyalomma truncatum and H. marginatum rufipes, but not to Rhipicephalus evertsi evertsi, from a scrub hare with viraemia of 1042 LD 50/ml but only nymphal H. truncatum and H. m. rufipes became infected from scrub hares with viraemia of 102 6-2 7 LD 50/ml. Infection was transmitted trans-stadially in H. m. rufipes and H. truncatum infected as nymphae, and adult H. m. rufipes transmitted infection to a sheep. No evidence of transovarial transmission was found in larval progeny of ticks exposed to CCHF virus as adults on sheep and cattle or as immatures on scrub hares.

Crimean-Congo hemorrhagic fever: History, epidemiology, pathogenesis, clinical syndrome and genetic diversity

“…Competent tick vectors of CCHFV are defined by their ability to support viral replication in their tissues during metamorphosis from larva to nymph to adult, to transmit the virus from adult females to their eggs and from adult males to females during copulation (Dohm et al, 1996;Gordon et al, 1993;Logan et al, 1990;Shepherd et al, 1991;Gonzalez et al, 1992). Following its ingestion by a competent vector in a blood meal, CCHFV replicates in the lining of the tick's midgut, then spreads to many different tissues, reaching the highest titers in the salivary glands and reproductive organs (Dickson and Turell, 1992).…”

“…sufficiently high blood viral titer to efficiently infect ticks (Shepherd et al, 1989a;Shepherd et al, 1991). Tick species also differ in the quantity of ingested virus that is required to initiate infection of the lining of the midgut (Shepherd et al, 1991).…”

“…Tick species also differ in the quantity of ingested virus that is required to initiate infection of the lining of the midgut (Shepherd et al, 1991).…”

Ectoparasitic Viral Zoonoses in the Southern African Context

“…Various stages of the ticks feed on small animals and birds, while the adult ticks feed on larger animals such as sheep and cattle [9,15,27]. When animals are slaughtered during the viraemic phase, the infection can be transmitted to humans and certain occupations may be susceptible or at an increased risk for infection with CCFHV [9,27]. Transmission occurs by the following main mechanisms:…”

“…International Health Regulations require that certain diseases be notified. Notification is a form of passive surveillance but active surveillance can be done by testing the tick viral vectors and infected animals [27]. In South Africa, CCHF is a notifiable medical condition in terms of the National Health Act (Act 61 of 2003).…”