As many of us know already, since October 2015 Brazil has seen an unexpected spike in cases of microcephaly, a condition where babies are born with smaller head sizes and negatively affected brain development. The country has reported over 3,000 cases of microcephaly in newborns in 2015 and over 1,000 so far this year, up from 150 in the whole of 2014. These have since been linked to infections with the mosquito-borne Zika virus. Women in Brazil, Jamaica and other countries have been advised to delay pregnancy until more is known about the risks to newborns, while the CDC has issued a travel warning for over 20 affected countries. The importance of heeding these warnings for US travellers has sadly been underscored by the birth of a microcephalic baby in Hawaii, whose mother was infected during time in Brazil, and two more pregnant women in Illinois confirmed to be infected. While the Zika virus usually causes only mild symptoms of fever, joint pain, rash and eye redness, many never know they were ever infected, and there is no (recognised) treatment.
Avoiding areas with epidemics of mosquito-borne infections is always advisable, however, there are natural alternatives to the conventional DEET repellents which can be used in everyday situations, especially if you react to it. One such natural substance is the essential oil of Apium graveolens seeds, or celery seeds. This was tested in one study for its repellent effects against adult Aedes aegypti mosquitoes, as well as for any larvicidal effects. A. aegypti is the species of mosquito that carries the Zika virus. In the larvicidal test, the lethal concentration for half of the mosquito larvae after 24 hours was 16.1 parts per million (ppm), and 29.08ppm for 90% of the larval population. Longer exposure increased the toxicity potential of the oil, with another 24 hours of exposure reducing the lethal concentration for half of the larvae to 13.22ppm. As for the repellency test, the celery essential oil resulted in 100% protection against mosquito bites in the first 150 minutes, which is two and a half hours. Protection was reduced to 88.8% (one bite recorded) in the next 15 minutes, and then to 77% (two bites) in the last 15 minutes. Direct application of the essential oil did not cause any skin irritation, unlike conventional chemical repellents. However, it did irritate the mosquitoes. No adult mosquitoes were able to tolerate exposure to 10% seed oil, whereas exposure to only 1% seed oil on paper was enough for them to begin flying away from the paper after four seconds. During the 15 minute contact irritancy test, only 2-3 flights from the alcohol-impregnated paper were recorded, while there was an average of 63.66 takeoffs from the essential oil paper.
Another essential oil that may protect against A. aegypti mosquitoes is peppermint oil. This study was also performed using the adult repellent and larvicidal tests, and like celery seed oil, peppermint oil was found to completely protect against bites for the first 150 minutes. In the next 30 minutes, only 1-2 bites were recorded for the treated participants as opposed to 8-9 for the control group. Peppermint oil was less effective than celery seed oil in killing off mosquito larvae, as the lethal concentration for 50% of the larvae was 111.9ppm; this was 295.18ppm for 90% of the larvae. The authors also stated that cinnamon, ginger and rosemary oils may be effective in repelling mosquitoes. Overall, evidence does recommend the use of essential oils to protect against mosquito bites, especially if there is hypersensitivity to conventional repellent, but standard precautions must still be taken and never ignored when there is the threat of irreversible harm such as birth defects. As new updates have stated that Zika may be transmissible through sexual intercourse, saliva and urine, avoiding infection is highly important.