Jean-Louis Camicas

Sexual and transovarian transmission of Crimean-Congo haemorrhagic fever virus in Hyalomma truncatum ticks

Male Hyalomma truncatum ticks were inoculated with Crimean-Congo haemorrhagic fever (CCHF) virus, hypostomectomized and then allowed to mate with uninfected females feeding on a naive rabbit. After mating, CCHF virus was reisolated from 2 out of 3 males tested and from 4 of 6 mated, engorged females (titre greater than or equal to 2.2 log LD50/ml). Vertical transmission was then demonstrated by virus reisolation from a portion of 2 of the 6 batches of eggs laid by the positive females. From these 2 positive egg batches, 6 larvae pools were tested with successful virus reisolation from one. Attempts to reisolate CCHF virus from 15 nymph pools of this positive batch of larvae were unsuccessful. Virus reisolation from gonopore-closed female H. truncatum which cofed with preinfected males demonstrated transmission in the absence of copulation. Rabbits that served as bloodmeal sources seroconverted after infestation by infected male ticks. However, CCHF virus was not reisolated from 3 gonopore-closed, engorged females, nor from their eggs, after feeding with hypostomectomized preinfected males. Transmission of CCHF virus during mating or cofeeding of adult H. truncatum, and subsequent transovarial transmission, appear to represent additional mechanisms of infection in the tick population, and may contribute to the maintenance of transmission in nature.

Ecology of ticks as potential vectors of Crimean-Congo hemorrhagic fever virus in Senegal: epidemiological implications

At least 30 tick species from 7 genera have been found naturally infected with Crimean-Congo hemorrhagic fever (CCHF) virus worldwide. To this list we add Rhipicephalus guilhoni. In the sub-Saharan Africa, 17 tick species have been implicated as vectors, of which 12 are present in Senegambia or Mauritania. We studied the five principal species that appear to be the most important in CCHF virus transmission in Senegal, namely Amblyomma variegatum, Hyalomma impeltatum, H. marginatum rufipes, H. truncatum, and Rhipicephalus guilhoni. We report on the distribution, host associations, seasonal activity patterns and CCHF virus infection of these ticks, as well as the epidemiological implications for human disease. Despite similarities in ecological characteristics, not all of these species are equally likely to be important in the transmission cycle. The most important vectors in enzootic and epidemic transmission throughout Senegal appear to be Hyalomma truncatum and Amblyomma variegatum.

Host-passage-induced phenotypic changes in Crimean-Congo haemorrhagic fever virus

Changes in virulence of Crimean-Congo haemorrhagic fever (CCHF) virus toward intracerebrally inoculated suckling mice (SM) were studied in relation to different host-passage histories. Two CCHF virus strains, one isolated from a human and the other from a tick, were passaged through various vertebrate and tick hosts and then reisolated and tested for their virulence toward SM. In various experiments, SM were inoculated with 12 different viral suspensions, each having a specific passage history. Survival curves of SM, which may reflect differences in viral strain characters, were established using an actuarial life table; differences were evaluated with the log-rank test. Regardless of the origin of the strain, CCHF viruses exhibited pathogenicity when passaged among SM. However, virulence, as measured by the proportion of deaths in SM, was altered following passage through another vertebrate host or tick. The final host seems to have a major influence on virulence. Because CCHF virus strains appear to vary little in their antigenic characters, it is hypothesized that hosts can induce phenotypic changes that modulate viral virulence.

Epidemiology of Crimean-Congo hemorrhagic fever in Senegal: temporal and spatial patterns

Aspects of the spatial and temporal patterns of transmission of Crimean-Congo hemorrhagic fever (CCHF) virus were studied in Senegal, West Africa. A country-wide serological survey of domestic animals indicated that transmission was most intense in the northern dry sahelian zone and least in the southern, more humid guinean zone. Human IgG prevalence, ranging from nearly 20% to < 1% among 8 sites throughout the region, also was greatest in the north. A fatal human case of CCHF from Rosso, Mauritania in 1988 was studied and an accompanying serosurvey of human contacts and domestic animals indicated epidemic transmission during that period. Systematic samples of adult ixodid ticks on domestic animals allowed us to analyze the distribution and relative abundance of potential CCHF virus vectors, demonstrating that Hyalomma spp. predominated in those biotopes where transmission was most intense. A prospective study of CCHF virus infection and tick infestation in sheep exposed a period of epizootic transmission in 1988 that corresponded temporally with increased abundance of adult H. truncatum and H. impeltatum. Four strains of CCHF virus were isolated from pools of these ticks and of Rhipicephalus guilhoni. Our results suggest that CCHF virus is focally endemic throughout the region, although highly variable in time and space, and that the relative abundance of Hyalomma ticks may be the primary determinant of epidemic transmission.

Crimean-Congo haemorrhagic fever virus replication in adult Hyalomma truncatum and Amblyomma variegatum ticks

The kinetics of the replication of the Crimean-Congo haemorrhagic fever virus (CCHFV) was studied in intra-anally inoculated adult Hyalomma truncatum and Amblyomma variegatum ticks. The virus was re-isolated by suckling mouse inoculation and revealed by antigen capture with ground ticks and indirect immunofluorescence of haemolymph. The virus was detected in ticks in the first hours post-inoculation (p.i.) and its replication was observed from 36 h p.i. onwards. Virus titre reached a maximum within 3-5 days then decreased slowly to a level of at 2 log LD50/ml for several months until the end of observations. Several specific, non-identified factors seem to favour CCHFV replication in H. truncatum. Long-term virus persistence seems to occur in CCHFV-infected adult ticks.

Développement de souches sauvages et vaccinales du virus de la fièvre jaune dans les cellules de aedes aegypti et transmission au souriceau

Summary The development and transmission of yellow fever virus in Aedes aegypti mosquito were studied after feeding or intrathoracic inoculation. Five different viral strains were examined: two vaccinal strains, one strain isolated from man in South America, two African wild strains isolated respectively from ticks and mosquitoes. Depending on the examined wild strains, the results show great differences in the time of latency in the mosquito before it transmits the virus to the suckling mouse. It appears that the virus strains isolated in South America have a much longer time of latency than the African ones. Vaccinal strains do not develop in the mosquito fed on infected suckling mouse (table I, column 3). On the other hand, the mosquito is infected when intrathoracically inoculated. In that case transmission to suckling mouse is possible. These experiments reveal the part of the intestinal barrier in the infection of A. aegypti mosquitoes, when fed with vaccinal strains. A comparative study of these five viral strains was made in vitro in A. aegypti-cloned cells but with no greatly different specific results.

Caractéristiques des souches du virus de la fiévre jaune isolées des ceufs et des larves d'une tique Amblyomma variegatum, récoltée sur le bétail à Bangui (Centrafrique)

Abstract The authors reported briefly the isolation circumstances of six strains of yellow fever virus from eggs and larvae of a tick, Amblyomma variegatum , collected from cattle at the slaughterhouses in Bangui, and from sera of a monkey infected with these larvae. Isolation conditions and characteristics of these strains are compared to strains previously isolated in Central Africa. Their viral and immunological properties are similar. The epidemiological interest of these isolements which demonstrate the transovarial and transtasial transmission of the yellow fever virus in A. variegatum was suggested.