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Don’t cancel the Rio Olympics because of Zika

Aerial view of the Christ the Redeemer statue in Rio de Janeiro

Aerial view of the Christ the Redeemer statue in Rio de Janeiro, with Rocinha and the Leblon neighbourhood in the background. By Chensiyuan – Own work, CC BY-SA 4.0,

The Harvard Public Health Review has published a piece titled “Off the Podium: Why Public Health Concerns for Global Spread of Zika Virus Means That Rio de Janeiro’s 2016 Olympic Games Must Not Proceed.” The author is Amir Attaran, DPhil, LLB, MS. Faculty of Medicine and Faculty of Law, University of Ottawa. I believe he is incorrect and the facts bolster that belief. The Rio Olympics should not be cancelled due to any risk from Zika.

The Summer Olympics begin in Rio de Janeiro Aug. 5, week 31. Dr Attaran offers five reason to cancel the Olympics this August.

Rio is not on the fringes of the outbreak, but inside its heart.

Will the mosquito population of the Rio region be active enough and infected enough to create an unusual risk to those attending the Olympics?

Two mosquito species are vectors for dengue, chikungunya and Zika in Brazil. The females of both species need a blood meal to complete their reproductive cycle. Aedes albopictus, the Asian Tiger mosquito, is a sylvan species and feeds on animals as well as humans. Aedes aegypti, the Yellow Fever mosquito, is an urban mosquito and feeds almost exclusively on humans.

Any threat to the Olympics from Zika viral illnesses would be through Aedes aegypti. Several studies seem to show that the numbers of that mosquito species vary little during the year in the Rio area. [1] [2]

Mosquito behavior

Dr. Attaran states that the number of dengue cases in the Rio area are much higher for 2016 than they were in 2015. He suggests that a higher baseline for dengue infections means that there is a greater risk of mosquito transmission.

The problem is that increased infections does not mean that there are greater numbers of mosquitoes. Aedes aegypti is a “sipping” mosquito and will bite three to five humans on average before its blood meal is complete.

Graphic showing the cycle of infection between mosquitoes, humans and the dengue virus

The cycle of infection

Data from Brazil, displayed graphically, suggests that there is a seasonality to mosquito transmitted viral infections such as dengue, chikungunya and Zika. The Olympics will begin in early August, in week 31 of the year. The graphs show that estimated cases are at their lowest during the summer, in and around week 31 to 35.

Estimated number of chikungunya, dengue and Zika cases in Pernambuco state, Brazil, from 2015-2016.

Estimated number of chikungunya, dengue and Zika cases in Pernambuco state, Brazil, from 2015-2016.

estimated cases of dengue in Brazil

Weekly number of estimated cases of dengue in Brazil for 2014-1016.

What could account for the drop in estimated cases of mosquito borne illness during the summer if the number of mosquitoes remains level? In Brazil, that would be the weather. It is winter in Brazil. reports that the average high temperature for Rio de Janeiro in August is 26 degrees and the average low is 19. The average rainfall is 5.1 cm.

Many studies have been done that predict the behaviors of Aedes aegypti at specific temperatures. [3] [4]

It appears that the average weather in Rio de Janeiro during the months of July and August contributes to a lower level of mosquito reproduction and a reduction in the mosquito’s ability to transmit a viral illness.


Dr. Attaran discusses the “microcephaly” outbreak. He cites a flawed paper on the Zika outbreak in Polynesia. [5] That paper concluded that seven cases of microcephaly were produced by Zika infections in pregnant women during the period of wide spread infection. The study failed to investigate other potential causes for microcephaly and failed to account for the wide geographic dispersal of the population on islands. He then cites two studies from Brazil that claimed both an unusual number of cases of microcephaly and a causal relationship to Zika infections.

Microcephaly is a rare birth defect which is often accompanied by other central nervous system defects and other pre-natal fetal injuries. Brazil has maintained, officially, that it had about 150 cases per year before the arrival of Zika. No one believes that statement since data is easily found that demonstrates that far more cases are the norm. Our work can be seen here:

The resources and data that has been cited in those articles demonstrate that Brazil’s baseline level of microcephaly cases was probably 20 times higher than the official level.

Brazil continues to investigate reported cases of microcephaly. From Oct. 2015 through May 7, 2016, the Ministry of Health has received 7,438 reports. It has investigated 54 percent of those cases and discarded 2,679 of the reports as unfounded.

The Ministry has confirmed 1,326 cases of microcephaly which is believes were caused by an infection. While the Ministry believes that all the mothers with microcephalic children were infected with Zika, it has only confirmed the infection in 205 cases.

Guillain-Barré syndrome

Dr. Attaran also bring up the apparent connection between cases of Guillain-Barré syndrome and Zika infections. According to the Merck Manual, in about two thirds of the cases, the onset of Guillain-Barré syndrome “begins 5 days to 3 wk after a banal infectious disorder, surgery, or vaccination.” Common infections that are prequel to the condition include “Campylobacter jejuni , enteric viruses, herpesviruses (including cytomegalovirus and Epstein-Barr virus), and Mycoplasma sp.”

“The most frequently identified cause of GBS is Campylobacter jejuni infection, which has been identified in up to 41% of patients and is associated with more severe disease and prolonged disability.” Also: [6]

Reports of GBS in Brazil include no information about testing for Zika or for any other potential cause. [7] Acute exanthematous illness is assumed to be Zika in the absence of “clinical and epidemiologic characteristics (which) did not satisfy the criteria for dengue, chikungunya, measles, or rubella.”

Our analysis suggests a baseline mean number of GBS cases in Brazil of 3,478, pre-Zika. There is evidence that a dengue illness can result in Guillain-Barré syndrome. [8] As Dr. Attaran notes, dengue is epidemic in Brazil in 2016.

Detecting Zika viral illnesses

Zika viral illnesses are described as laboratory confirmed or as one of several other terms, probable, suspected, potential. If a Zika illness is not discovered through testing, it is diagnosed by clinical means. Those diagnoses make up the greatest number of cases in the Americas but there are serious defects in diagnosing Zika by signs and symptoms.

Two recent studies highlight the massive error rate connected with clinical diagnosis of a Zika Illness. In one study, 1,541 patients who had traveled to Zika affected areas reported one or more signs or symptoms consistent with Zika. Over 85 percent tested negative for the virus. [9] In another study, from Puerto Rico, 6,157 tests were conducted on patients who could have contracted the viral illness. Some 683, 11 percent, were positive for Zika. [10]

The two studies involved over 10,000 patients who had reason to suspect that they might have contracted a Zika viral illness. The vast majority had not. It is fair to conclude that the same situation obtains with clinical diagnoses being made in Brazil. This massive error rate affects the reported number of Zika cases by the Ministry of Health as well as the presumed causation of microcephaly or GBS by a Zika infection.

Other disease threats to the Olympics in Brazil

Yellow Fever and Malaria
Leprosy [11]
Toxoplasmosis [12]
Cytomegalovirus [13] [14]
Saint Louis encephalitis virus [15]
Mayaro virus [16]
Oropouche Orthobunyavirus [17]
Baggio–Yoshinari syndrome (Brazilian lyme-like disease) [18]

Illnesses that could be brought to Brazil

West Nile
Sindbis virus disease
Rift Valley fever


The evidence that Zika viral illnesses pose a threat to the tourists and participants in the 2016 Summer Olympics in Rio de Janeiro is slim. Clearly, the vector for the illness will be somewhat active in the region. The activity level should be low but weather conditions could change that. There are many other diseases that are endemic or epidemic in Brazil which could also pose a threat to those attending the Olympics. Some are mosquito borne while others have different vectors.

It is also important to note that the many people traveling to Brazil may be bringing with them any number of illnesses that are not found in that country. The blonde Swedes and Finns could be bringing the Sindbis virus. Athletes from the United States could import West Nile. Modern travel patterns mean that any contagious illness is just a few hours away.

The notion, as advanced by Dr. Attaran, that Zika illnesses could spread to other countries and continents due to the Olympics runs solidly into two facts. The first is that Zika has already spread, into Asia and the Pacific from its origins in Africa. The second fact is that thousands of people infected with Zika have already traveled from Central and South America to countries that do not currently have the illness locally transmitted. It’s too late to close that barn door.

The Rio Olympics should go on as planned. The participating countries would be wise to provide mosquito repellent and window screens to their personnel. Tourists should abide the cautions from the Centers for Disease Control and the World Health Organization.

  2. R. M. Lana, T. G. Carneiro, N. A. Hon0rio and C. T. Codeco. Seasonal and nonseasonal dynamics of Aedes aegypti in Rio de Janeiro, Brazil: Fitting mathematical models to trap data. Acta Tropica, vol. 129, no. 0, pp. 25-32, 2014
  3. Micieli, María Victoria, & Campos, Raúl Ernesto. (2003). Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) in subtropical Argentina. Memórias do Instituto Oswaldo Cruz, 98(5), 659-663.
  4. Douglas M. Watts, Donald S. Burke, Bruce A. Harrison, Richard E. Whitmire, and Ananda Nisalak. Effect of Temperature on the Vector Efficiency of Aedes aegypti for Dengue 2 Virus. Am J Trop Med Hyg 1987 36:143-152
  5. Cauchemez S, Besnard M, Bompard P, et al. Association between Zika virus and microcephaly in French Polynesia, 2013–15: a retrospective study. Lancet 2016: doi:10.1016/S0140-6736(16)00651-6.
  6. Jeremy H. Rees, Ph.D., M.R.C.P., Sara E. Soudain, B.Sc., Norman A. Gregson, Ph.D., and Richard A.C. Hughes, M.D. Campylobacter jejuni Infection and Guillain–Barré Syndrome. N Engl J Med 1995; 333:1374-1379November 23, 1995DOI: 10.1056/NEJM199511233332102
  7. Paploski IAD, Prates APPB, Cardoso CW, Kikuti M, Silva MMO, Waller LA, et al. Time lags between exanthematous illness attributed to Zika virus, Guillain-Barré syndrome, and microcephaly, Salvador, Brazil. Emerg Infect Dis. 2016 Aug [date cited].
  8. Santos, Nilse Querino, Azoubel, Ana Cláudia B., Lopes, Antonio Alberto, Costa, Gersonita, & Bacellar, Aroldo. (2004). Guillain-Barré syndrome in the course of dengue: case report. Arquivos de Neuro-Psiquiatria, 62(1), 144-146.
  9. Dasgupta S, Reagan-Steiner S, Goodenough D, et al. Patterns in Zika Virus Testing and Infection, by Report of Symptoms and Pregnancy Status — United States, January 3–March 5, 2016. MMWR Morb Mortal Wkly Rep 2016;65:395–399. DOI:
  10. Dirlikov E, Ryff KR, Torres-Aponte J, et al. Update: Ongoing Zika Virus Transmission — Puerto Rico, November 1, 2015–April 14, 2016. MMWR Morb Mortal Wkly Rep 2016;65:451–455. DOI:
  11. Henry M, GalAn N, Teasdale K, Prado R, Amar H, Rays MS, et al. (2016) Factors Contributing to the Delay in Diagnosis and Continued Transmission of Leprosy in Brazil – An Explorative, Quantitative, Questionnaire Based Study. PLoS Negl Trop Dis 10(3): e0004542. doi:10.1371/journal.pntd.0004542
  12. J. P. DUBEY, E. G. LAGO, S. M. GENNARI, C. SU and J. L. JONES (2012). Toxoplasmosis in humans and animals in Brazil: high prevalence, high burden of disease, and epidemiology. Parasitology, 139, pp 1375-1424. doi:10.1017/S0031182012000765.
  13. Linhares, M. I. S., De Andrade, G. P., Tateno, S., Eizuru, Y. and Minamishima, Y. (1989), Prevalence of Cytomegalovirus Antibodies in Brazilian and Japanese Populations in the North-East of Brazil. Microbiology and Immunology, 33: 975–980. doi: 10.1111/j.1348-0421.1989.tb00985.x
  14. Souza, Marli Adelina, Passos, Ana Maria, Treitinger, Arício, & Spada, Celso. (2010). Seroprevalence of cytomegalovirus antibodies in blood donors in southern, Brazil. Revista da Sociedade Brasileira de Medicina Tropical, 43(4), 359-361.
  15. Figueiredo, Luiz Tadeu Moraes. (2015). The recent arbovirus disease epidemic in Brazil. Revista da Sociedade Brasileira de Medicina Tropical, 48(3), 233-234.
  16. Mourão MPG, Bastos M de S, de Figueiredo RP, et al. Mayaro Fever in the City of Manaus, Brazil, 2007–2008 visit this web-site. Vector Borne and Zoonotic Diseases. 2012;12(1):42-46. doi:10.1089/vbz.2011.0669.
  17. Azevedo RSS, Nunes MRT, Chiang JO, Bensabath G, Vasconcelos HB, Pinto AYN, et al. Reemergence of Oropouche fever, northern Brazil. Emerg Infect Dis [serial on the Internet]. Jun 2007 [date cited]. Available from
  18. Gonçalves DD, Moura RA, Nunes M, et al. Borrelia burgdorferi sensu lato in humans in a rural area of Paraná State, Brazil. Brazilian Journal of Microbiology. 2015;46(2):571-575. doi:10.1590/S1517-838246220140097.
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