Zika Virus is a form of Mosquito-born Flavivirus (the group of RNA
Viruses that also includes the Yellow Fever and Hepatitis C Viruses),
which first emerged in Central Africa in 1947. Infection with Zika is generally associated with a rash and a fever, but symptoms are variable and include nonpurulent conjunctivitis, headache, pruritus, arthralgia, myalgia, or malaise. In 2007 an epidemic in Micronesia was associated with a new and worrying symptom, microcephaly, a severe congenital defect affecting infants born to women infected with the Virus, in which the brain fails to develop fully during pregnant, and the child is born with a much reduced cranium, leading to life-long disabilities. This symptom appeared again in a second outbreak that began in Brazil in April 2015 and which has since spread across much of the Americas.
In a paper published in the Centers for Disease Control and Prevention Prevention Morbidity and Mortality Weekly Report on 9 December 2016, a team of scientists led by Esther Liliana Cuevas of the Instituto Nacional de Salud in Bogotá present the results of a study which monitored the rise in the incidence of microcephaly associated with the spread of Zika Virus in Colombia in 2016.
Microcephaly, and other major birth defects, are routinely recorded in Colombia, so the country was already equipped with a system for monitoring the condition at the outset of the the epidemic. The first case of Zika was recorded in Colombia in August 2016; however the methodology by which the disease was diagnosed was variable and changed over the course of the epidemic, leading to some inconsistencies in the way data was recorded, so that not all cases of microcephaly were screened for Viral RNA.
Cuevas et al. examined data from 31 January to 12 November 2016, during which period 476 instances of microcephaly were recorded in Colombia, compared to 110 over the same period in 2015. This equates to 9.6 cases per 10 000 live births in 2016, compared to 2.1 cases per 10 000 live births in 2015. This is also higher than the 5.5 cases of microcephaly per 10 000 live births recorded in Brazil in 2015, where the Zika epidemic was already present, though in Brazil microcephaly was not routinely recorded before the epidemic, so it is likely that cases were missed.
Microcephaly was reported in 28 of Colombia's 33 reporting areas (33 departments plus the federal capitol area) for medical records, with the instances of the condition ranging from two cases per 10 000 live births in Nariño and Quindío departments to 29 cases per 10 000 live births in Amazonas Department. Interestingly, much of Colombia is more than 2000 m above sea level, at which altitude the Mosquitoes that spread the disease cannot survive, but these high altitude areas also suffered a rise in reported cases of microcephaly. If these cases were due to Zika Virus then they presumably either travel related infections (i.e. the mother had travelled to an area where the Virus could be transmitted by Mosquitoes) or instances of sexual transmission (like many Viruses, Zika can be transmitted by sexual intercourse with an infected person, though this is not the main means of transmition).
Prevalence of congenital microcephaly per 10,000 live births during epidemiologic weeks 5–45 (January 31–November 12), by reporting area — Colombia, 2016. Cuevas et al. (2016).
Due to the irregularities in the way
Zika infection was recorded, it was not possible to accurately assess
what proportion of these cases were infected with Zika, nor what
proportion of pregnant women infected with Zika produced babies with
microcephaly. However procedures were in place for screening cases for
other diseases which are known to cause microcephaly; Syphilis,
Toxoplasmosis, Rubella (German Measles), Cytomegalovirus, and Herpes
Simplex Virus. Of the 476 cases of microcephaly, 121 were screened for
these agents, 26 of which proved to have such an infection. Of these 15
were infected with Toxaplasmosis (14 of which were also confirmed to be
infected with Zika), six were infected with Herpes Simplex Virus (two of
which were also confirmed to be infected with Zika), four were infected
with Cytomegalovirus (one of which was also confirmed to be infected
with Zika) and one had Syphilis.
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