Zika virus is a global public health emergency, declares WHO

BMJ 2016; 352 doi: (Published 02 February 2016) Cite this as: BMJ 2016;352:i657

Re: Zika virus is a global public health emergency, declares WHO

Continuing my comments on men in white overalls spraying with DDT left right and centre, I’d like to remind readers of Rachel Carson’s “Silent Spring. New York: Houghton Mifflin: 1962)”.

In her book, Rachel Carson described a great number of harmful effects of spraying with DDT (and other similar toxic compounds) on the environment and its wildlife, as well as people and their food.

Dr Cristobal S. Berry-Caban (DDT and Silent Spring: Fifty years later. J Military and Veterans Health ; 19(4) October 2011) in the review article described how “One day in January 1958, Rachel Carson received a long, angry letter from her friend Olga Huckins, describing the deadly effect of DDT spraying for mosquito control over the Huckins’ private two-acre bird sanctuary at Powder Point, in Duxbury, Massachusetts. Not long afterwards Carson was a house guest at Powder Point when, late in the afternoon, a spraying plane flew over. The next morning she went through the estuary with the Huckins in their boat. She was sickened by what she saw - dead and dying fish everywhere, crayfish and crabs dead or staggering as their nervous systems appeared destroyed. She then realised that she would write about DDT.”

Even though the process was very slow (DDT was first synthesised in 1874), it was ultimately (in 1930s) established that DDT was insecticide. During WWII it was established that DDT had tremendous possibilities against several noxious insects, such as lice, mosquitoes and flies and ultimately against the malaria parasites, typhus and dysentery . This was found useful by the military. However, some cautioned that DDT must not be allowed to get into food or be ingested accidentally.

Berry-Caban also quoted Fred Bishop (1946. Present position of DDT in the control in insects of medical importance, Am J Publ Health. June; 36(6): 593-606), an American naturalist, who warned that the indiscriminate DDT spraying can upset the balance of nature and that 90% of all insects are beneficial.

Rachel Carson in her book (Silent Spring) wrote that DDT killed insects for weeks and months and not only the targeted ones but countless more, and remained toxic in the environment even after it was diluted by rainwater. She concluded that DDT had irrevocally harmed birds and animals and contaminated the entire world’s food supply. Additionally, the most devastating were the delayed kills, and the inhibition of reproduction, threatening entire species of birds and animals with extinction.

Carson pointed to the most damaging unintended effects of indiscriminate use of DDT: the extinction of birds and animals depending on certain insects and population explosion in other pests, with repercussions for humans because of DDT soaking into the soil and poisoning drinking water, and causing cancer.

The overuse of DDT in agriculture resulted in malaria –spreading mosquitoes developing resistance to DDT and other pesticides, similar to the well-documented bacterial resistance to sulpha drugs and antibiotics and, ultimately, to a vaccine-driven resistance of bacteria, viruses and other microorganisms.

Carson confirmed the phenomenal capacity of insects to adapt to new poisons; anything that kills a large proportion of an insect population ends up changing the insects’ genetics, favouring those that are most adaptable to new conditions. Susceptible populations can be rapidly replaced by the resistant ones. The survival intelligence of mosquitoes is demonstrated by an observation of strains of mosquitoes that can metabolise DDT into harmless by-products and others whose nervous systems became immune to DDT. There are even mosquitoes that learnt to avoid the toxic effects of DDT by resting between meals on the exterior walls of the houses not sprayed by DDT, avoiding the interior walls sprayed by DDT.

The little critters are arguably a 'superior intelligence'.

This all sounds elementary but nevertheless it indicates that humans, sadly, do not always learn from previous experience.

Competing interests: No competing interests

10 February 2016
Dr Viera Scheibner (PhD)
scientist/author retired
Blackheath NSW Australia