16/06/2016

Zika: The Spread to Americas and the implications for the Olympic Games in Brazil
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Amidst eager anticipation of the 2016 Olympic Games, the Zika virus outbreak has taken the world by surprise. Questions surrounding the virus’s transmission and its contributions to birth defects are abound, while researchers are fervently working to find a vaccine. Here PhD candidate Enny S. Paixão, from London School of Hygiene and Tropical Medicine, outlines what is currently known about the virus and its transmission, and describes the measures taken to keep further spread to a minimum leading up to the Olympics.
 Amidst eager anticipation of the 2016 Olympic Games, the Zika virus outbreak has taken the world by surprise. Questions surrounding the virus’s transmission and its contributions to birth defects are abound, while researchers are fervently working to find a vaccine. Here PhD candidate Enny S. Paixão, from London School of Hygiene and Tropical Medicine, outlines what is currently known about the virus and its transmission, and describes the measures taken to keep further spread to a minimum leading up to the Olympics.


Zika is a mosquito-borne disease, not described outside Africa and Asia regions until an outbreak was reported in Micronesia in 2007. In the last three years, this disease has emerged in French Polynesia, Cook Islands, and more than 20 American countries - fuelling concern as its link to severe birth defects and neurological syndromes becomes more probable. 

The emergence or re-emergence of some infectious diseases has been changing the epidemiological pattern in many countries – especially the emergence of diseases caused by virus transmitted by mosquitoes of the genus Aedes (Stegomyia). These vectors have great ability to transmit a number of infectious agents and are very difficult to control, so vector-borne diseases that once were restricted to some areas are now apparent in several previously unaffected regions. Zika is one such disease. The first evidence of humans infected with Zika is from 1952(1)  and since then this disease circulated almost silently until 2007, when there was a large outbreak in Yap, Micronesia (2).

Outbreaks of  Zika have a high rate of transmission, estimated at 73%, and a high rate of asymptomatic disease with just one in five infected patients developing clinical symptoms. When symptoms occur, they generally are characterized by acute fever, rash, arthralgia, conjunctivitis and oedema. According to information from previous outbreaks, hospitalizations and deaths are rare (2). Before the outbreak in French Polynesia and Brazil the symptoms of this disease were described as mild and limited to the individual. However more recently Zika has aroused the fears of the society and public health authorities because it is suspected of causing microcephaly in several infants born to women who were infected during pregnancy (3). Guillain-Barré syndrome has been linked to Zika outbreaks as well (4). However, more studies are required to prove a causal relationship between Zika and microcephaly and Guillain-Barré syndrome, as well as the spectrum of outcomes that could be associated with this disease.

The Zika virus (ZIKV) was detected in Brazil for the first time in early 2015 (5) and later in the same year epidemiological evidence suggested that ZIKV infection of pregnant women in Brazil might be associated with the increasing numbers of microcephaly. Despite the connection between ZIKV and congenital defects, according to the World Health Organization (WHO), athletes and sports fans should not fear travelling to Olympic Games in Rio de Janeiro this(?) August. A study that analysed the risk of dengue during the 2014 FIFA World Cup in Brazil showed that football fans were unlikely to get dengue during the competition period, because dengue is a seasonal disease and during the dry season its incidence decreases and the density of cases becomes residual even in North-Eastern Brazil, the epicentre of the outbreak. The study found that in Rio de Janeiro, located in south-eastern Brazil, risk of dengue infection is close to zero (6). As Zika is transmitted by the same mosquito as dengue, a low risk of tourists and athletes contracting Zika infection can be assumed as well. According to some public health experts the fact that the games are held in a single city during a cold and dry month means that the risk of Zika will be reduced to an acceptable level.

To assure the safety of travelers, Brazilian authorities have announced plans to prevent the spread of Zika during the games, and the British Olympic Association will be monitoring the situation over the coming months to ensure that the athletes are receiving medical advice along with information on mosquito bite prevention strategies (7).         

However, Brazil’s decision to go forward with the Games is not unanimously accepted. Arthur Caplan from New York University insists that it would be reasonable to postpone the games for at least 6 months, or even cancel them entirely. Caplan and Igel argue that young women cannot travel to Brazil safely and that men who are sexually active could transmit the disease to a partner. They insist that it would be irresponsible to host as important an event as the Olympic Games during a public health emergency of international concern (8). The US Centers for Disease Control and Prevention advised pregnant women to avoid travelling to countries affected by Zika (9).

There is no information about the extent to which an international event like the Olympics could contribute to the spread Zika. Travelers could be infected during the event and introduce the virus in their home countries, and imported cases might result in local transmission and spread the virus in areas that have the appropriate mosquito vectors already.
The current situation with regard to Zika is challenging, and according to Margaret Chan, the head of the WHO, ‘things may get worse before they get better’. There is no vaccine, no treatment, and no commercially available serological test. The only way to prevent Zika is to avoid mosquito bites, and even this does not remove the challenge of vector control. The Brazilian Minister of Health warned that the country is badly losing the battle against the mosquito. To reduce the risk of spreading Zika, attendees of the Olympics Games should take additional care and try to minimize their exposure to mosquito bites.

There are more questions than answers about Zika, but scientists from different areas are working to fill these gaps. Barreto et al (2016) suggested six central components to achieve success in battling Zika (10):

1) To increase the evidence of infection and potential outcome;
2) To develop a serological test – the test available now is the detection of viral RNA, which is present during the viraemia;
3) To control infestation by Aedes mosquitos;
4) To define protocols for treatment;
5) To develop a vaccine – because Zika is an emerging disease there is a lack of information about the immunological mechanisms involved in the infection, but current events have expedited the development of a vaccine;
6) To reprogramme the health-care system.

References 
1.     Fagbami AH. Zika virus infections in Nigeria: virological and seroepidemiological investigations in Oyo State. J Hyg (Lond). 1979;83(02):213–9. 
2.     Duffy MR, Chen T-H, Hancock WT, Powers AM, Kool JL, Lanciotti RS, et al. Zika virus outbreak on Yap Island, federated states of Micronesia. N Engl J Med. 2009;360(24):2536–43. 
3.     Schuler-Faccini L. Possible Association Between Zika Virus Infection and Microcephaly—Brazil, 2015. MMWR Morb Mortal Wkly Rep [Internet]. 2016 [cited 2016 Feb 23];65. Available from: http://www.cdc.gov/mmwr/volumes/65/wr/mm6503e2er.htm
4.     Ioos S, Mallet H-P, Goffart IL, Gauthier V, Cardoso T, Herida M. Current Zika virus epidemiology and recent epidemics. Med Mal Infect. 2014;44(7):302–7. 
5.     Campos GS, Bandeira AC, Sardi SI. Zika virus outbreak, Bahia, Brazil. Emerg Infect Dis. 2015;21(10):1885. 
6.     Aguiar M, Coelho GE, Rocha F, Mateus L, Pessanha JEM, Stollenwerk N. Dengue transmission during the 2014 FIFA World Cup in Brazil. Lancet Infect Dis. 2015;15(7):765–6. 
7.     Rio 2016 Organizing Committee for the Games of the XXXI Olympiad. The official website of the 2016 Rio Olympic Games. Available from http://www.rio2016.com/en/olympic-games -accessed February 29th 2016. 
8.     Caplan A, Igel L. With Zika, Is There Really A Case Against Postponing The 2016 Olympic Games in Rio? 2016 Feb 12; Available from http://www.forbes.com/sites/leeigel/2016/02/12/with-zika-is-there-really-a-case-against-postponing-the-2016-olympic-games-in-rio/#2f8d03b858b6; accessed February 24th 2016. 
9.     CDC. CDC issues advice for travel to the 2016 Summer Olympic Games. Available from http://www.cdc.gov/media/releases/2016/s0226-summer-olympic-games.html. 
10.     Barreto ML, Barral-Netto M, Stabeli R, Almeida-Filho N, Vasconcelos PF, Teixeira M, et al. Zika virus and microcephaly in Brazil: a scientific agenda. The Lancet [Internet]. 2016; Available from: http://www.sciencedirect.com/science/article/pii/S0140673616005456; accessed February 29th 2016.