This document summarizes the current epidemiology of the Zika virus. It describes how the virus originated in Africa and has since spread to Asia and the Americas. The virus is primarily transmitted by Aedes mosquitoes. While most infections are asymptomatic, it can cause mild flu-like symptoms. Complications include microcephaly in fetuses of infected mothers and Guillain-Barré syndrome. Public health efforts focus on mosquito control and prevention through avoiding bites and pregnancy in infected areas. Vaccine research is ongoing but no vaccine currently exists.

1. 3/9/2016
The current
epidemiology of Zika
virus
George W. Rutherford, M.D.
Global Health Sciences
March 7, 2016

2. The current epidemiology of Zika
virus
George W. Rutherford, M.D.
Global Health Sciences
March 7, 2016

5. Zika virus epidemiology
• Zika virus originally isolated from primates in
the Zika forest of Uganda in 1947
• First detected serologically in humans in
Nigeria in 1968
• Endemic across Western, Central and Eastern
tropical Africa
• Spread to Asia by 2007
• Basically follows the Aedes spp footprint

6. Range of Ae. aegypti

7. From: Hayes EB. Zika virus outside Africa. Emerg Infect Dis 2009; 15:1347-50.

8. More recent epidemiology
• Spread across the Pacific
– Yap Island (Micronesia) 2007
– French Polynesia 2013
– Cook Islands, New Calendonia 2014
– Easter Island February 2014
– Now in American Samoa, Samoa and Tonga
• First Latin American cases in Brazil in May 2015
• Spread through tropical Latin America and the
Caribbean

9. 1948
Expansion other countries in Africa 1947-1948

10. 1977
Pakistan, Malaysia, Indonesia 1977-1978

11. 1978
Pakistan, Malaysia, Indonesia 1977-1978

12. 2007
Yap Island (Micronesia) and Guam, 2007
2007

13. 2014
New Caledonia (FR) and Cook Islands, 2014Easter Island (CHILE), 2014

14. 2015
Brazil, May 2015

15. 2016
Active transmission in the Americas 2016 (and other areas worldwide in previous 15 months, ECDC)

16. May 2015

17. October 2015

18. November 2015

19. December 2015

20. January 2016

21. Zika virus in the United States
• Reported from:
– Yap Island, Federated States of Micronesia (180)
– American Samoa (4)
– Puerto Rico (102)
– U.S. Virgin Islands (1)
– 154 travel-associated cases (not autochthonous
transmission) in US states and Puerto Rico
• Florida (42)
• New York (23)
• Texas (15)
• California (10)

22. Countries in the Americas with current
Zika virus transmission
Latin America
• Boliva
• Brazil
• Costa Rica
• Dominican
Republic
• Colombia
• Ecuador
• El Salvador
• French Guiana
• Guatemala
• Guyana
• Haiti
• Honduras
• Mexico
• Nicaragua
• Panama
• Paraguay
• Suriname
• Venezuela
Caribbean
• Aruba
• Barbados
• Bonaire
• Curacao
• Guadeloupe
• Jamaica
• Martinique
• Puerto Rico
• Saint Martin
• Saint Vincent and the
Grenadines
• Trinidad and Tobago
• US Virgin Islands

23. Sexual transmission
• 8 cases of male-to-female transmission
– Intercourse few days before onset of symptoms
• 3 cases of replication-competent Zika virus isolated
from semen 2-10 weeks after illness onset (persisted
longer than in blood)
• In all cases men were symptomatic and had
hematospermia
• CDC recommends abstinence or condoms for men
who may have been exposed and their pregnant
sexual partners
• Unknowns:
– Transmission without symptomatic infection
– Transmission from women to men

24. Why Zika and why now?
• Zika is a “new” pathogen that has been
introduced into a non-immune population and
has spread rapidly
• Aided in this case by widespread presence of
Ae. aegypti in the tropical Americas
• Zika will likely remain endemic as have West
Nile virus and yellow fever

28. Zika virus
• Single stranded RNA virus
• Mosquito-borne flavivirus
• Replicates in dendritic
cells at site of inoculation,
spreads to lymph nodes
and blood stream
• Can be found in blood
from day of onset of
clinical illness to 11 days
post onset

29. Flaviviridae
• Flavivirus
– Dengue virus
– Japanese encephalitis virus
– St. Louis encephalitis virus
– Tick-borne encephalitis virus
– West Nile virus
– Yellow fever
– Zika virus
• Hepacivirus
– Hepatitis C virus
• Pegivirus
– GBV-C (hepatitis G)
• Pestivirus
– Hog cholera

30. Zika virus transmission
• Primarily mosquito-
borne
– Aedes aegypti, Ae.
africanus, Ae.
apicoargenteus, Ae.
vitattus, Ae. furcifer, Ae.
polynesiensis
• From infected mother
to her fetus
• Blood transfusion
• Sexual transmission

31. Zika virus clinical manifestations
• 80 percent of infections are asymptomatic
• When symptomatic, generally mild
– Fever
– Rash
– Arthralgia
– Conjunctivitis
– Lasts several days to a week
• No specific treatment, avoid aspirin in children
• NIAID is screening antiviral compounds

32. From: Duffy MR, Chen T-H, Hancock T, et al. Zika virus outbreak on Yap Island, Federated States of Micronesia. N Engl J
Med 2009; 360:2536-43.

33. Ae. aegypti range, United States

35. Reported complications for Zika virus
infection
• Microcephaly
• Guillain-Barré syndrome
• Thrombocytopenic purpura
• Leukopenia
• In French Polynesian outbreak in 2013, of
10,000 registered cases, there were 70 (0.7%)
severe cases

36. Microcephaly
• Abnormally small cranial vault secondary
to abnormal brain growth
• Clinical manifestations
– Seizures, developmental delay, intellectual
disability, problems with movement and
balance, dysphagia, hearing and vision loss
• Incidence 2-12/10,000 live births in the
U.S.
• Causes
– Infection (rubella, toxoplasmosis,
cytomegalovirus)
– Severe malnutrition
– Toxin exposures (e.g., alcohol)

38. Microcephaly cases by head diameter,
Pernambuco State, Brazil, 1999-2015
0
100
200
300
400
500
600
700
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
32-33 cm
<32 cm
Source: SENAC, SES-PE. Courtesy of PAHO
<32 cm is <3rd percentile, z-score ≤-3; 32-33 cm is <15th percentile, z-score <-2

39. Epidemic curve of microcephaly cases among at-term newborns and
preceding Zika virus circulation in: Pernambuco State, Brazil, 2015
Outbreak Rash & Fever
Detected by EBS
DEN test (-) ZIKV lab confirmed

40. Isolation of Zika virus from brains and
fetal tissue
• Zika isolated by RT-PCR from
brains of two infants with
microcephaly (36 and 38 weeks
gestation) who died within 20
hours of birth and from
products of conception of two
first trimester stillbirths from
Rio Grande do Norte state
• All four mothers had clinical
illnesses compatible with Zika
virus infection
• Newborn brains had
parenchymal calcification,
microglial nodules, gliosis, cell
degeneration and necrosis

41. Prevention
• Avoidance of areas with active transmission
• Avoiding Aedes mosquito bites
– Long-sleeved shirts and pants
– Permethrin-treated clothing
– Insect repellents
• DEET, picaridin and IR 3535 safe to use during pregnancy
– If infected, don’t feed the mosquitos
• Avoiding pregnancy (five countries)
• Condoms if potential for sexual exposure

42. Prevention
• Immunization
– Three strategies being pursued at NIAID:
• DNA vaccine (strategy similar to WNV vaccine)
• Attenuated live virus vaccine (similar to dengue vaccine)
• Genetically engineered VSV (similar to Ebola vaccine)
– Phase I trials in 2016?
• Natural infection to achieve immunity before
becoming pregnant
• Herd immunity (some evidence from Polynesia)

43. New mosquito control strategies
• Release of Insects carrying Dominant Lethal
genes (RIDL)
– Males carry lethal dominant trait
– Can be treated with artificial diet
– Released into wild and mate with WT females
– Offspring do not survive
• Endosymbiotic bacteria (Wolbachia)
– Inhibit replication of flaviviruses without affecting
Aedes fitness
Phuc, HK, Andreasen, MH, Burton, RS et al. Late-acting dominant lethal genetic systems and mosquito control. BMC
Biology. 2007; 5: 1–11.
Carvalho, DO, McKemey, AR, Garziera, L et al. Suppression of a field population of Aedes aegypti in Brazil by sustained
release of transgenic male mosquitoes. PLoS Neglect Trop Dis. 2015; 9: e0003864.
Walker, T, Johnson, PH, Moreira, LA et al. The wMel Wolbachia strain blocks dengue and invades caged Aedes aegypti
populations. Nature. 2011; 476: 450–453.

44. Mosquito control involves larviciding and adulticiding. The other strategy is to
remove habitat where standing water can facilitate mosquito breeding.

45. Guidelines for pregnant women
• Two scenarios:
– Pregnant women with history of travel to an area
with ongoing Zika virus transmission
– Pregnant women residing in an areas with ongoing
Zika virus transmission
• With or without symptomatic infection

49. There are 30 million passengers who fly to the United States each year from Zika-endemic
countries in Latin America and the Caribbean. 2.7 million from Brazil alone.

50. Why Zika and why now?
• This is a 21st century example of the Columbian
exchange although it came from West not East