Summary The period 1973‐76 saw additions to knowledge of Australian arboviruses in several directions. A large epidemic of Murray Valley encephalitis (MVE) allowed evaluation of serological diagnostic techniques not available in previous major outbreaks, and also added to knowledge of clinical features and epidemiology. Its wide geographical distribution, with cases recognized for the first time in central Australia, suburhan Adelaide and east central Queensland, possibly associated with what has been described as “the most extraordinary set of weather conditions to affect Australia in this century”, triggered new consideration of epidemic prediction and vector control. The recognition of regular summer‐autumn occurrence of epidemic polyarthritis in southern Australia suggested the possibility of year‐round survival of Ross River virus, and perhaps of other togaviruses, in that area. Further evidence was obtained for previous suggestions that Kunjin virus might cause febrile disease of man. Bovine ephemeral fever was repeatedly epizootic and its epidemiology became a major focus of investigation, with accent on possibilities of control by vaccination. Important progress was made in Japan and then in Australia in linking Akabane virus with a disease of domestic animals. The continuation of field programmes in Queensland and Western Australia, and the commencement of new ones in Northern Territory, the Murray Valley of Victoria and elsewhere, led to the discovery of “new” viruses and extended the known host and geographic range of other viruses, adding complexity to the Australian arbovirus pattern. An ambitious programme of serological surveillance of virus infection in sentinel cattle herds covered a wide area of Australia and New Guinea and produced important results which could well be supplemented in other hosts. Progress in this period does not contradict the previous suggestion that complete elucidation of the epidemiology of arboviruses in Australia is a distant goal within the limits of current techniques, but it does suggest that collaboration between units and between disciplines can provide steady and useful progress.

SUMMARY Sixty strains of 11 viruses were isolated from 25,901 mosquitoes of 32 species collected at Mitchell River Mission, Cairns and Normanton in 1960 and 1961. The viruses, the local prototype strains and the mosquito species, geographical location and year of repeatable isolations, were: Group A: Sindbis (MRM39) from Culex annulirostris and Aedes normanensis at Mitchell River (1960) and Cairns (1961); AMM2021 (N544) from Anopheles amictus amictus and Culex bitaeniorhynchus at Normanton (1961). Group B: Murray Valley encephalitis virus from C. annulirostris at Mitchell River (1960 and 1961); Kunjin (MRM16) from C. annulirostris at Mitchell River (1960); Kokobera (MRM32) from C. annulirostris at Mitchell River (1960 and 1961); Edge Hill (C281) from Aedes vigilax and C. annulirostris at Cairns (1961); Stratford (C338) from Ae. vigilax at Cairns (1961). Koongol group: Koongol (MRM31) from C. anulirostris at Mitchell River (1960) and Normanton (1961); Wongal (MRM168) from C. anulirostris at Mitchell River (1960 and 1961). Ungrouped: MRM1 (found resistant to ether and sodium desoxycholate) from C. anulirostris at Mitchell River (1960); Mapputta (MRM186) from Anopheles meraukensis at Mitchell River (1960) (not reisolated). C. annulirostris was the commonest mosquito collected (12,124) and the source of 44 of the virus strains. Eight of the viruses appear to be new. One (Murray Valley encephalitis virus) has previously been isolated from man in Australia and two (Sindbis and AMM 2021) from mosquitoes elsewhere.

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Sttmmtry.Ml.MS mosquitoes and 4^53 ofhcr anhropods coltcctetJ at three cenires in QueenslaiKJ in I972>1976 yiekfcd ISl strains or 18 viruses. CuJex annuiirossm was the m^jor source of virus noUtion but 42 strains from AeJes nurmoitemis indicate it IO Iw a vector of importance. Ross River and Kokobera viruses *trc isdatod at Kownnyama in the dry season, a finding of inicmt a^ being compariNc %kith yearround \urvival in vector-vertebrate cyiiies. Cule.v fatigam has in pan replaced Culex an/iuliroitrii in pchdomestic breedmg sites at Kouanyama: the inrrcquency or virus botatlon from ii ^uggc^I^ that this replacement may lower arK>viriis infcLtian rales. Twelve Mrainv were iJcntified as viruses antigenically diMlnci from any previously Motnted in Australia or NCNV Guinea: 0)16129. shown by the Intcrniitional Reference Centre for Arboviruses to be a previously undescribed nKnibcr of the Sinibu Group (f-awy's Paddock virus). Chl631.1 (Murwch). ChI9.S20 (Parker's I arm) iitid Chl9546 (Little Sussex). The remaining strains were idcntilicd ns viruses previously known in Au-ilrnthi, hut included many new host or geographical record**.

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