Transmission of Crimean-Congo hemorrhagic fever virus in two species of Hyalomma ticks from infected adults to cofeeding immature forms.

Crimean-Congo hemorrhagic fever (CCHF) virus was transmitted from infected adult Hyalomma ticks to uninfected larval and nymphal Hyalomma ticks while cofeeding on a guinea pig host that did not have a detectable viremia. When tested after feeding with infected adults, three (0.8%) of 370 H. truncatum larvae contained detectable CCHF virus (mean virus titer 10(1.6) plaque-forming units [PFU]/tick). The virus was transmitted transstadially from infected larvae and was detected in 15 (1.2%) of 1,253 nymphs and 12 (0.1%) of 2,049 adults. Virus was recovered from 18 (1.9%) of 931 H. impeltatum nymphs, which originated from larvae that cofed with infected adults. After H. impeltatum nymphs cofed with infected adults, CCHF virus was detected in 21 (4.3%) of 449 (mean virus titer 10(1.7) PFU/tick) fed nymphs, but none of 886 adults tested after molt. Results of this study indicate that a small proportion of either larvae or nymphs may acquire CCHF infection while cofeeding on a host without a detectable viremia.