Poverty, Disease & Disability

The links between poverty, diseases and disabilities are well known. These links can work in complex ways. This post is about studies in Brazil showing how Zika virus infection in pregnant women combined with a neurotoxin in contaminated water in drought affected areas to increase the incidence of microcephaly (smalll, less developed brain cortex) in their newborn babies, leading to cognitive disabilities.

Understanding how different factors combine together to produce an effect is important since it helps us to look for specific solutions even while we work to remove systemic disparities linked with poverty.

Zika Infection in Brazil

Though Zika virus had already been identified in 2013, it suddenly burst out as an epidemic in Brazil in 2014. Over the following 2 years, the disease quickly spread to many other countries of the Americas and pacific. The disease is transmitted mainly through a mosquito (Aedes aegypti), and also by sexual contacts and blood transfusions. That same mosquito is also responsible for spread of other diseases like Dengue, Chikangunya and Yellow Fever. Initially it was thought that Zika infection did not cause any serious complications, till October 2015 when first reports of children born with microcephaly started coming among the pregnant women who had had Zika infection. Within a month, the number of children born with microcephaly had increased ten times. Many other newborn children had other neurological problems. Other complications of Zika included congenital malformations, and paralysis due to Guillain-Barre syndrome.

By early 2017, the number of new cases of Zika had started decreasing all over, even if different countries keep reporting occasional cases. For example, in 2018, Rajasthan in India had reported a Zika outbreak. Different aspects related to this infection remain unclear including the reasons which had led to its sudden and explosive growth in 2014-15.

Drought and Water Contamination in Brazil

The Zika epidemic had coincided with a period of drought in the north-east of Brazil. With lack of rains and evaporation of water, the concentration of salinity and minerals in the water-bodies had increased, creating favourable conditions for the growth of Cyanobacteria. These bacteria produce a chemical called Saxitoxin, which damages the nerve cells. Shell fish from the water-bodies in the drought areas had higher concentrations of Saxitoxin.

Zika and Saxitoxin

An article in June 2020 issue of The Scientist explains how Zika infection had combined with Saxitoxin to increase the number of newborn children having microcephaly. It says, "While the incidence of Zika was higher in other regions of Brazil, the number of children being born with microcephaly was higher in the north-east." Fortesting, researchers infected neural cell-cultures with Zika and then exposed them to low concentrations of Saxitoxin. They found that brain cells exposed to both Zika and Saxitoxin had 2.5 times more dead cells and three times higher number of Zika virus. This meant that Saxitoxin increased virus replication and worsened its impact on the brain cells. These findings were also confirmed in animal studies.

This research also underlined the links between poverty and disability. Poor persons with Zika infection were more exposed to drinking of contaminated water and thus were disproportionately hit by higher numbers of children with microcephaly and other congenital neurological defects leading to cognitive and intellectual disabilities.

Conclusions

This case-study shows that natural conditions such as droughts can change the risks of contamination. In such situations, policies such as privatisation of water resources lead to negative consequences which disproportionately affect the poor families. For example, drinking water from deep tubewells, has created similar risks by arsenic contamination of the ground water in Bangladesh and some parts of India, which also disproportionately affects the poor.

Case studies like this are important to understand the different ways in which diseases and other negative environmental conditions can combine and cause diseases and disabilities, especially among the poor.

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