Zika

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Zika virus and Zika fever are named after Zika Forest, a tropical forest in Uganda, where the virus was first isolated.

Zika is an emerging mosquito-borne arbovirus disease that has since 1947 caused sporadic human infections in some African and Asian countries, with usually mild symptoms of fever, rash, and arthralgia. It is now also found in the Americas.[1]

In 2015 a suggestion emerged that zika virus infection might explain an increase in reported cases of microcephaly in the Americas.[2][3][4] On 1st February 2016 WHO declared a public health emergency of international concern.

For more information on this, and extensive links to guidance, see the zika virus page from Public Health England.

Contents

Aetiology

Zika virus (ZIKV) causes in man Zika fever. It was first isolated from a rhesus monkey in the Zika forest of Uganda in 1947 but was not recognised to cause human disease until 1968 in Nigeria. In retrospect human cases are believed to have been described by 1952[5]. ZIKV antibody in man has now been found in many countries in tropical Africa, Asia, the Pacific and from 2013[6], in South America well before the 2014 world cup in Brazil. It is a fairly typical flavivirus and other similar arboviruses may be circulating in the same populations at any one time. Some genotypes are neurotrophic, a fact that was only recognised early in 2014 when the first report of Guillain-Barré syndrome was made[7] and more widely with the later October 2015 report of an association with fetal microcephaly where exposure in the mother has been about week 17. It is closely related to Spondweni virus (SPOV).

Genome

Its positive sense single-stranded RNA molecule is 10794 bases long with two flanking non-coding regions. This codes for a polypeptide that is cleaved into the capsid (C), precursor membrane (prM), envelope (E), and non-structural proteins (NS).

Taxonomy

.

Clinical

Causes a fever and flu like pain presentation in some about 5 days after exposure. Many infections are asymptomatic and only a very few have complications such as encephalitis. Intrauterine infection can be associated with microcephaly and possibly limb deformities.

Epidemiology

It is only relatively recently that RNA measurement in the urine has been validated as perhaps the most useful quick diagnostic test and previous reliance on serum samples means there continue to be gaps in our understanding. Viraemia lasts for up to 5 days after symptom onset but many infections are assymptomatic or associated with other viral co-infections further complicating epidemiology. The first recognised outbreaks were well described in eastern African monkeys in 1947 without proof of human transmission. It was rarely recognised as causing human disease before the Yap outbreak in 2007 and this might reflect differential strain virulence. Human to human transmission is very rare but has been suspected through sexual intercourse[8]

The outbreak that started in French Polynesia in October 2013 was associated with Guillain-Barré syndrome and meningo-encephalitis and not at that time recognised to cause foetal abnormalities. An outbreak occurred in 2015 in Venezuela, close to its border with Brazil[9] and in due course the larger naive to virus population affected allowed a better understanding of its potential clinical impact.

In the second decade of the 21st century the virus has been isolated and caused disease more widely and this has implications for transfusion medicine[10]. Concerns existed that the virus might spread more widely, including to the United States of America.[11]; and this appeared to have happened, at least in Florida by July 2016. In August 2016 an outbreak commenced in Singapore.

Current information on the spread of the virus is available at ProMED.

Transmission

Transmitted by Aedes luteocephalus mosquitoes predominantly historically with Aedes aegypti and to a lesser extent Aedes albopictus becoming more important as vectors as the virus spread. The Yap outbreak in 2007 was transmitted by Aedes hensilli showing that more widespread vector transmission is likely[12]. It is possible that sandflies might also transmit the virus. In Pakistan it seems to be as common as Japanese encephalitis although West Nile fever is twice as common[13]. The virus may persist in protected sites, like the testis, and it may be transmitted sexually (in semen) or potentially via blood transfusion.[14][15] Monkey bite has also been postulated as a pausable route of transmission[16]. Functional virus has also been isolated from saliva. One case of carer contact transmission has been reported where no other route of infection could be identified.

Transmission through sexual intercourse was proved in 2016[17].

Risk controversy

As with most illness there is the issue that publicity can be biased. For example the risk for visitors to the Rio de Janeiro Olympic Games in August 2016 of Zika virus infection is fifteen times less than that of contacting Dengue fever[18]. So calls for the Olympics to be rescheduled on the grounds of Zika virus risk to populations and individuals could be seen as illogical since a decision was made historically to hold the Olympic Games in a subtropical venue with its baseline infection risks in the first place. From the point of view of protecting unexposed populations, to a large extent it is too late given the likely timeframe to develop say an effective vaccine, so, all the Olympic Games might do is slightly alter the time course of the spread worldwide of the neurotrophic strains. Such observations will not stop controversy as risk benefit analysis has a large subjective element and public health is only one of the issues with regard to a large public event.

Investigations

Zika serology in those pregnant women with consistent travel who have microencephaly in exposed foetus has been recommended although causation is not yet definite[19][20]

Treatment

Prevention

  • Reduction mosquito exposure.
  • Condoms for at least 6 months (the virus has persisted for at least 181 days in semen so a year is probably more reasonable[21] )

Notification

Not currently listed as one of the notifiable diseases. Autochthonous transmission within the UK (i.e. if the condition is acquired from a UK source) would probably qualify as a suspected case "of other infections (“other relevant infection”) or contamination (“relevant contamination”) that present, or could present, significant harm to human health", and therefore become notifiable.

External links

References

  1. The Lancet. Zika virus: a new global threat for 2016. Lancet 2016;387(10014):96.
  2. Petersen EE, Staples JE, Meaney-Delman D, Fischer M, Ellington SR, Callaghan WM, Jamieson DJ. Interim Guidelines for Pregnant Women During a Zika Virus Outbreak - United States, 2016. MMWR. Morbidity and mortality weekly report. 2016; 65(2):30-3.(Epub) (Link to article – subscription may be required.)
  3. Lavinia Schuler-Faccini, Erlane M. Ribeiro, Ian M.L. Feitosa, Dafne D.G. Horovitz, Denise P. Cavalcanti, André Pessoa, Maria Juliana R. Doriqui, Joao Ivanildo Neri, Joao Monteiro de Pina Neto, Hector Y.C. Wanderley, Mirlene Cernach, Antonette S. El-Husny, Marcos V.S. Pone, Cassio L.C. Serao, Maria Teresa V. Sanseverin. Possible Association Between Zika Virus Infection and Microcephaly — Brazil, 2015. 2016 (Jan 29) Morbidity and Mortality Weekly Report (MMWR) 2016 / 65(3);59–62.
  4. European Centre for Disease Prevention and Control. Rapid risk assessment: Microcephaly in Brazil potentially linked to the Zika virus epidemic – 24 November 2015. Stockholm: ECDC; 2015. (Associated press release "Microcephaly in Brazil potentially linked to the Zika virus epidemic, ECDC assesses the risk")
  5. Lopes MH, Miyaji KT, Infante V. Zika virus. Revista da Associação Médica Brasileira (1992). 2016 Feb; 62(1):4-9.(Link to article – subscription may be required.)
  6. Faria1 NR, Azevedo R, Kraemer MUG et al. Zika virus in the Americas: Early epidemiological and genetic findings. Science 24 March 2016. DOI: 10.1126/science.aaf5036
  7. Oehler E, Watrin L, Larre P, Leparc-Goffart I, Lastere S, Valour F, Baudouin L, Mallet H, Musso D, Ghawche F. Zika virus infection complicated by Guillain-Barre syndrome--case report, French Polynesia, December 2013. Euro surveillance : bulletin Européen sur les maladies transmissibles = European communicable disease bulletin. 2014; 19(9):.(Epub)
  8. Musso D, Roche C, Robin E, Nhan T, Teissier A, Cao-Lormeau VM. Potential sexual transmission of Zika virus. Emerging infectious diseases. 2015 Feb; 21(2):359-61.(Link to article – subscription may be required.)
  9. WHO situation report 3 December 2015 accessed 9 Dec 2015
  10. Marano G, Pupella S, Vaglio S, LiumbrunoE GM, Grazzini G. Zika virus and the never-ending story of emerging pathogens and transfusion medicine. Blood transfusion = Trasfusione del sangue. 2015 Nov 5; :1-6.(Epub ahead of print) (Link to article – subscription may be required.)
  11. Firger J. Zika virus is spreading outside Brazil and could threaten U.S. 2016; Updated 5 January 2016; Accessed: 2016 (January 8).
  12. Duffy MR, Chen TH, Hancock WT, Powers AM, Kool JL, Lanciotti RS, Pretrick M, Marfel M, Holzbauer S, Dubray C, Guillaumot L, Griggs A, Bel M, Lambert AJ, Laven J, Kosoy O, Panella A, Biggerstaff BJ, Fischer M, Hayes EB. Zika virus outbreak on Yap Island, Federated States of Micronesia. The New England journal of medicine. 2009 Jun 11; 360(24):2536-43.(Link to article – subscription may be required.)
  13. Darwish MA, Hoogstraal H, Roberts TJ, Ahmed IP, Omar F. A sero-epidemiological survey for certain arboviruses (Togaviridae) in Pakistan. Transactions of the Royal Society of Tropical Medicine and Hygiene. 1983; 77(4):442-5.
  14. Foy BD, Kobylinski KC, Chilson Foy JL, Blitvich BJ, Travassos da Rosa A, Haddow AD, Lanciotti RS, Tesh RB. Probable non-vector-borne transmission of Zika virus, Colorado, USA. Emerging infectious diseases. 2011 May; 17(5):880-2.(Link to article – subscription may be required.)
  15. Didier M, Claudine R, Emilie R, Tuxuan N, Anita T, Van-Mai C-L. Potential Sexual Transmission of Zika Virus. Emerging Infectious Disease journal 2015;21(2):359.
  16. Leung GH, Baird RW, Druce J, Anstey NM. ZIKA VIRUS INFECTION IN AUSTRALIA FOLLOWING A MONKEY BITE IN INDONESIA. The Southeast Asian journal of tropical medicine and public health. 2015 May; 46(3):460-4.
  17. DCHHS Reports First Zika Virus Case in Dallas County Acquired Through Sexual Transmission. Dallas County Health and Human Services press release 2 Feb 2016
  18. Castro MC. Zika virus and the 2016 Olympic Games - Evidence-based projections derived from dengue do not support cancellation. Travel medicine and infectious disease. 2016 Jun 27.(Epub ahead of print) (Link to article – subscription may be required.)
  19. Petersen EE, Staples JE, Meaney-Delman D, Fischer M, Ellington SR, Callaghan WM, Jamieson DJ. Interim Guidelines for Pregnant Women During a Zika Virus Outbreak - United States, 2016. MMWR. Morbidity and mortality weekly report. 2016; 65(2):30-3.(Epub) (Link to article – subscription may be required.)
  20. Tetro JA. Zika and microcephaly: causation, correlation, or coincidence? Microbes and infection / Institut Pasteur. 2016 Jan 13.(Epub ahead of print) (Link to article – subscription may be required.)
  21. Barzon L, Pacenti M, Franchin E, Lavezzo E, Trevisan M, Sgarabotto D, Palù G. Infection dynamics in a traveller with persistent shedding of Zika virus RNA in semen for six months after returning from Haiti to Italy, January 2016. Euro Surveill. 2016;21(32):pii=30316. DOI: http://dx.doi.org/10.2807/1560-7917.ES.2016.21.32.30316