J.
Med. Entomol. Vol. 16, no. I: 59--66
12 September 1979 ©
1979 by
,he Bishop Moseum
QUANTITATIVE STUDIES OF THE VECTOR COMPETENCE OF AEDES AEGYPTI, CULEX ANNULIROSTRIS AND OTHER MOSQUITOES (DIPTERA: CULICIDAE) WITH MURRAY VALLEY ENCEPHALITIS AND OTHER QUEENSLAND ARBOVIRUSES1 By B. H. Kayl, J. G. Carley, I. D. Fanning and Cheryl Filippich2
Previous studies have demonstrated
that Aedes inoculation (Carley et al. 1973) to a wide range of Australian arboviruses and that Culex annulirostris Skuse can be infected orally (Kay et al. 1975) by these vIruses. Chamberlain et al. (1954£1, b, c) defined some basic quantitative terms as follows. Infl'ction rate-"the percentage (of all the mosquito specimens in the feeding series, regardless of ability to transmit) found to contain virus." Transmission rate-"the percentage of specimens of a given series transmitting infection by bite after ingesting a meal having a high virus titer and after a suitable extrinsic incubation."
aegyPli (L.) is susceptible by intrathoracic
'Based on part of a thesis submitted by B. H. Kay to the University of Queensland for the degree of Doctor of Philosophy. "Queensland Institute of Medical Research, BJ'amston Terrace, Herslon, Brisbane, Queensland 4006, Australia.
Threshold of infection-"the lowest concentration of virus capable of causing an infection in 1 to 5% of the specimens of a particular mosquito species ingesting." Extrinsic incubation period (E.I.P.)-"between the time of ingestion of virus-infected blood by an arthropod and the ultimate transmission of disease to a susceptible animal during refeeding." The impOl'tance of the E.I.P. to transmission of yellow fever virus was first recognized by Carter in 1900 (Strode 1951). Davis (1932) demonstrated that the duration of the E.I.P. was affected by temperature. Jones & Foster (1974) demonstrated that susceptibility to infection was determined genetically when they developed, by continuous selective inbreeding, lines of the biting midge Culicoides variiPennis (Coquillett) that showed different susceptibilities to bluetongue virus. These authors defined susceptibility rate as "the percentage of females capable of becoming infected by ingestion of a single blood meal that has sufficient virus concentration to infect all susceptible flies." The present study extends knowledge of both AI'. aegypti and Cx. annulirostris in 2 ways: (1) by defining parameters of vector competence, e.g., infection, susceptibility and transmission rates, threshold of infection and extrinsic incubation period in a colony of AI'. aegypti by feeding virus suspensions, and (2) using these studies as a model by evaluating the vector competence of a population of Cx. annulirostris from Brisbane with respect to Murray Valley encephalitis (MVE) virus and comparing its efficiency with that of a Victorian population studied by McLean (1953a). In doing this, fragmentary data were gathered on other wildcaught species and a newly established colony of Cx. fatigans Wiedemann. MATERIALS
AND METHODS
The colony of Ae. aegypti was established from Townsville, northern Queensland in 1957 and has
Downloaded from http://jme.oxfordjournals.org/ by guest on June 7, 2016
Abstract. Ten (Getah, Ross River, Murray Valley encephalitis, Kunjin, Kokobera, Edge Hill, Alfuy, Corriparta, Belmont, Ngaingan) of 28 known or unproven Queensland arboviruses, and chikungunya, known to be transmitted naturally elsewhere, showed some evidence of multiplication in colonized Aedes (//'gypti after oral infection. Parameters of vector competence (i.e., infection, susceptibility and transmission rates, threshold of infection, extrinsic incubation period) were determined for the I I viruses. Nine of these were transmitted by bite to infant suckling mice. Several patterns of response were evident which suggested loss of vector efficiency not only at the gut barrier but also in spread of virus to the salivary glands and in the salivary glands themselves. Different patterns of infection were achieved with viruses of different mouse passage level. This work provided a model on which to base studies of Culex anllIdirostris with Murray Valley encephalitis virus. Wild ex. annulimstris from Brisbane were highly efficient vectors of MVE virus. This efficiency was characterized by a low threshold (10"0 of 10"·9 LD511/mosquito),complete susceptibility to infection, and transmission to day-old chickens from 7 days, which reached 75-95% transmission by 10 days after ingestion of blood-virus mixtul·e. These results were considered comparable to those for a Murray Valley strain of ex. annulirostris studied previously by McLean. More limited investigations indicated that Aedes vigilax, AI'. linl'atupmnis and AI'. vittiger could also act as vectors of MVE virus.
J.
60
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Med. Entomol. Vol. 16, no. I: 59--66
12 September 1979 ©
1979 by
,he Bishop Moseum
QUANTITATIVE STUDIES OF THE VECTOR COMPETENCE OF AEDES AEGYPTI, CULEX ANNULIROSTRIS AND OTHER MOSQUITOES (DIPTERA: CULICIDAE) WITH MURRAY VALLEY ENCEPHALITIS AND OTHER QUEENSLAND ARBOVIRUSES1 By B. H. Kayl, J. G. Carley, I. D. Fanning and Cheryl Filippich2
Previous studies have demonstrated
that Aedes inoculation (Carley et al. 1973) to a wide range of Australian arboviruses and that Culex annulirostris Skuse can be infected orally (Kay et al. 1975) by these vIruses. Chamberlain et al. (1954£1, b, c) defined some basic quantitative terms as follows. Infl'ction rate-"the percentage (of all the mosquito specimens in the feeding series, regardless of ability to transmit) found to contain virus." Transmission rate-"the percentage of specimens of a given series transmitting infection by bite after ingesting a meal having a high virus titer and after a suitable extrinsic incubation."
aegyPli (L.) is susceptible by intrathoracic
'Based on part of a thesis submitted by B. H. Kay to the University of Queensland for the degree of Doctor of Philosophy. "Queensland Institute of Medical Research, BJ'amston Terrace, Herslon, Brisbane, Queensland 4006, Australia.
Threshold of infection-"the lowest concentration of virus capable of causing an infection in 1 to 5% of the specimens of a particular mosquito species ingesting." Extrinsic incubation period (E.I.P.)-"between the time of ingestion of virus-infected blood by an arthropod and the ultimate transmission of disease to a susceptible animal during refeeding." The impOl'tance of the E.I.P. to transmission of yellow fever virus was first recognized by Carter in 1900 (Strode 1951). Davis (1932) demonstrated that the duration of the E.I.P. was affected by temperature. Jones & Foster (1974) demonstrated that susceptibility to infection was determined genetically when they developed, by continuous selective inbreeding, lines of the biting midge Culicoides variiPennis (Coquillett) that showed different susceptibilities to bluetongue virus. These authors defined susceptibility rate as "the percentage of females capable of becoming infected by ingestion of a single blood meal that has sufficient virus concentration to infect all susceptible flies." The present study extends knowledge of both AI'. aegypti and Cx. annulirostris in 2 ways: (1) by defining parameters of vector competence, e.g., infection, susceptibility and transmission rates, threshold of infection and extrinsic incubation period in a colony of AI'. aegypti by feeding virus suspensions, and (2) using these studies as a model by evaluating the vector competence of a population of Cx. annulirostris from Brisbane with respect to Murray Valley encephalitis (MVE) virus and comparing its efficiency with that of a Victorian population studied by McLean (1953a). In doing this, fragmentary data were gathered on other wildcaught species and a newly established colony of Cx. fatigans Wiedemann. MATERIALS
AND METHODS
The colony of Ae. aegypti was established from Townsville, northern Queensland in 1957 and has
Downloaded from http://jme.oxfordjournals.org/ by guest on June 7, 2016
Abstract. Ten (Getah, Ross River, Murray Valley encephalitis, Kunjin, Kokobera, Edge Hill, Alfuy, Corriparta, Belmont, Ngaingan) of 28 known or unproven Queensland arboviruses, and chikungunya, known to be transmitted naturally elsewhere, showed some evidence of multiplication in colonized Aedes (//'gypti after oral infection. Parameters of vector competence (i.e., infection, susceptibility and transmission rates, threshold of infection, extrinsic incubation period) were determined for the I I viruses. Nine of these were transmitted by bite to infant suckling mice. Several patterns of response were evident which suggested loss of vector efficiency not only at the gut barrier but also in spread of virus to the salivary glands and in the salivary glands themselves. Different patterns of infection were achieved with viruses of different mouse passage level. This work provided a model on which to base studies of Culex anllIdirostris with Murray Valley encephalitis virus. Wild ex. annulimstris from Brisbane were highly efficient vectors of MVE virus. This efficiency was characterized by a low threshold (10"0 of 10"·9 LD511/mosquito),complete susceptibility to infection, and transmission to day-old chickens from 7 days, which reached 75-95% transmission by 10 days after ingestion of blood-virus mixtul·e. These results were considered comparable to those for a Murray Valley strain of ex. annulirostris studied previously by McLean. More limited investigations indicated that Aedes vigilax, AI'. linl'atupmnis and AI'. vittiger could also act as vectors of MVE virus.
J.
60
1++
2:
0 C'l
0
~ \.l ''"" 15
-
't;:"
C'l
~ -r'l
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