African Swine Fever Virus Infection in the Iberian Soft Tick, Ornithodoros (Pavlovskyella) marocanus (Acari: Argasidae) R. G. ENDRIS,i W. R. HESS,* AND J. M. CAIADO^ Plum Island Animal Disease Center, USDA-ARS-NAA, P.O. 848, Greenport, New York 11944-0848
J. Med. Entomol. 29(5): 874-878 (1992)
KEY WORDS Arachnida, Ornithodoros (P.) marocanus, arbovirus, African swine fever virus
DELETERIOUS VIRUS-INDUCED effects on arthro-
pod vectors appear to be an uncommon feature of the vector/pathogen relationship, particularly in the case of tick-borne viruses. It has often been suggested (Hess 1981, 1988) that African swine fever virus (ASFV), a double-stranded DNA virus assigned to the Iridoviridae, is of tick origin. It is remarkable that the other members of the Iridoviridae are either insect pathogens or associated with insects, and ASFV is the only member of the genus known to infect mammals. Recently, this virus has been shown repeatedly to cause mortality in experimentally infected argasids. ASFV-induced mortality has been observed in a nearctic species, Ornithodoros coriaceus Koch (Groocock et al. 1980, Hess et al. 1987) and a neotropical species, Ornithodoros puertoricensis Fox (Endris et al. 1992). Hess et al. (1989) reported ASFV-induced mortality in the Iberian soft tick, Ornithodoros erraticus (Lucas) [=Ornithodoros (Pavlovskyella) marocanus Velu] and in the "natural" African vector, Ornithodoros moubata Murray, although other workers have not reported virus-induced mortality in either O. moubata (Plowright et al. 1969a, b, 1 Merck Research Laboratories, P.O. Box 2000, Rahway, NJ 07065-0900. 2 395 Gillette Drive, East Marion, NY 11939. 3 Laboratorio Nacional de Investigacao Veterinaria, Lisboa, Portugal.
1970a, b, 1974; Greig 1972) or Ornithodoros savignyi (Audouin) (Mellor & Wilkinson 1985). Other sublethal effects of ASFV infection on the vector have not been reported. The virus strains used in all of these studies were characterized as moderately to highly virulent and hemadsorbing (Pan & Hess 1984). It has been observed that in Portugal, swine infected with ASFV exhibit symptoms ranging from acute, lethal infections to chronic infections characterized by erythematous skin lesions with persistent lymphatic involvement (Galo 1988). Pan & Hess (1985) proposed an explanation for this diversity of symptoms: ASFV populations consist of clones capable of producing significantly different courses of disease in swine infected with a single plaque-derived clone. The effects of tick passage on these ASFV clones and mixtures of clones with pathogenic differences manifested in the arthropod and mammalian hosts have yet to be explored in the detail that showed reassortment of segmented viruses in ixodid ticks (Davies et al. 1987). Here, we report the effects of a recent field-collected, highly virulent, hemadsorbing ASFV strain on the argasid vector, O. marocanus, with which it has been associated for more than 30 yr. In addition, data are presented for the first time on the biology of O. marocanus fed exclusively on pigs.
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ABSTRACT One thousand six hundred Ornithodoros (Pavlovskyella) marocanus Velu larvae were fed on a pig infected with African swine fever virus (titer: 107'4 HAd50/ml), and 1,600 larvae were fed on an uninfected pig. Ticks in each group were compared for mortality rates, mean time to death for ticks that died, mean time from feeding to either molting or eclosion, percentage of ticks that eclosed or molted, and the number of blood meals per nymph or instar. Cumulative virus-induced mortality for all immature stages (larvae to adult) of O. marocanus that had been fed as larvae on a pig infected with African swine fever was ca. 73% over a 390-d period. In contrast,
J. Med. Entomol. 29(5): 874-878 (1992)
KEY WORDS Arachnida, Ornithodoros (P.) marocanus, arbovirus, African swine fever virus
DELETERIOUS VIRUS-INDUCED effects on arthro-
pod vectors appear to be an uncommon feature of the vector/pathogen relationship, particularly in the case of tick-borne viruses. It has often been suggested (Hess 1981, 1988) that African swine fever virus (ASFV), a double-stranded DNA virus assigned to the Iridoviridae, is of tick origin. It is remarkable that the other members of the Iridoviridae are either insect pathogens or associated with insects, and ASFV is the only member of the genus known to infect mammals. Recently, this virus has been shown repeatedly to cause mortality in experimentally infected argasids. ASFV-induced mortality has been observed in a nearctic species, Ornithodoros coriaceus Koch (Groocock et al. 1980, Hess et al. 1987) and a neotropical species, Ornithodoros puertoricensis Fox (Endris et al. 1992). Hess et al. (1989) reported ASFV-induced mortality in the Iberian soft tick, Ornithodoros erraticus (Lucas) [=Ornithodoros (Pavlovskyella) marocanus Velu] and in the "natural" African vector, Ornithodoros moubata Murray, although other workers have not reported virus-induced mortality in either O. moubata (Plowright et al. 1969a, b, 1 Merck Research Laboratories, P.O. Box 2000, Rahway, NJ 07065-0900. 2 395 Gillette Drive, East Marion, NY 11939. 3 Laboratorio Nacional de Investigacao Veterinaria, Lisboa, Portugal.
1970a, b, 1974; Greig 1972) or Ornithodoros savignyi (Audouin) (Mellor & Wilkinson 1985). Other sublethal effects of ASFV infection on the vector have not been reported. The virus strains used in all of these studies were characterized as moderately to highly virulent and hemadsorbing (Pan & Hess 1984). It has been observed that in Portugal, swine infected with ASFV exhibit symptoms ranging from acute, lethal infections to chronic infections characterized by erythematous skin lesions with persistent lymphatic involvement (Galo 1988). Pan & Hess (1985) proposed an explanation for this diversity of symptoms: ASFV populations consist of clones capable of producing significantly different courses of disease in swine infected with a single plaque-derived clone. The effects of tick passage on these ASFV clones and mixtures of clones with pathogenic differences manifested in the arthropod and mammalian hosts have yet to be explored in the detail that showed reassortment of segmented viruses in ixodid ticks (Davies et al. 1987). Here, we report the effects of a recent field-collected, highly virulent, hemadsorbing ASFV strain on the argasid vector, O. marocanus, with which it has been associated for more than 30 yr. In addition, data are presented for the first time on the biology of O. marocanus fed exclusively on pigs.
Downloaded from http://jme.oxfordjournals.org/ by guest on March 25, 2016
ABSTRACT One thousand six hundred Ornithodoros (Pavlovskyella) marocanus Velu larvae were fed on a pig infected with African swine fever virus (titer: 107'4 HAd50/ml), and 1,600 larvae were fed on an uninfected pig. Ticks in each group were compared for mortality rates, mean time to death for ticks that died, mean time from feeding to either molting or eclosion, percentage of ticks that eclosed or molted, and the number of blood meals per nymph or instar. Cumulative virus-induced mortality for all immature stages (larvae to adult) of O. marocanus that had been fed as larvae on a pig infected with African swine fever was ca. 73% over a 390-d period. In contrast,
