Published Date: 2012-11-11 19:50:16
Subject: PRO/AH/EDR> Yellow fever - Africa (13): Sudan (Darfur, Khartoum): control
Archive Number: 20121111.1404679
YELLOW FEVER - AFRICA (13): SUDAN (DARFUR, KHARTOUM) CONTROL
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 11 Nov 2012
From: Paul Reiter <firstname.lastname@example.org>
The news from Darfur must surely be treated as an international emergency; 3.5 million refugees are housed in camps in the province and water is an increasing problem. The virus has now reached Khartoum (pop. more than 5 million); a major epidemic could spawn the global catastrophe that entomologists and other public health specialists have been predicting for decades.
The most frightening aspect of this emergency is the critical need for refugees to store water. According to the African Union - United Nations Mission in Darfur (UNAMID):
"Understanding that the scarcity of water is one of the lead causes of conflict in Darfur, UNAMID has carried out a large number of projects aimed at helping rural and urban communities in the region gain access to this invaluable resource.
"Recent efforts include helping to organize an international conference on water, bringing together more than 200 experts in water use and distribution and leading development specialists and donors in Khartoum on 27 Jun 2011. This is the first major international effort to build an innovative and sustainable water service system for all communities in Darfur".
_Aedes aegypti_, which is undoubtedly the principal vector in this epidemic, is a container-breeding species. Water storage containers are classic sites. They have been the root cause of some of the most devastating outbreaks of yellow fever in history.
It is irrelevant whether, as reports suggest, a "new species of mosquito" is present, just as the "nature of the disease" is also irrelevant. Yellow Fever has been identified: Yellow Fever vaccination should begin immediately and energetic anti-mosquito measures should also be implemented.
Just as worrying are other articles on the UNAMID pages. For example:
"At the request of the North Darfur State Ministry of Education, the Mission will provide potable water to nearly 12 000 students at examination centers and dormitories for the next 16 days. UNAMID also delivered water earlier in the year for 8th graders taking their secondary school entrance exams".
"As more than 400 000 children nationwide today sat to take their Secondary Certificate Examinations, UNAMID began the first daily delivery of more than 30 000 litres to students in El Fasher, many of whom had travelled from smaller villages".
Once delivered, this water will not come out of a tap. It will be put into pots or drums. Women will carry pots to their homes and to neighboring villages.
Susceptibility of the mosquito(s) to insecticide is the only basic information that is needed. If the mosquito larvae are susceptible to temephos, this should be used to treat water in storage jars. The method has been routinely used for decades in the Caribbean, Latin America and SE Asia. Treatment is simply by dropping a teaspoonful (or other suitable measure) of the granular formulation into each container. Treatment will last at least three weeks, more so if the water is fairly clean
Vehicle-mounted "fogging machines" that dispense insecticidal aerosols to kill adult mosquitoes are very expensive and have little or no impact on _Ae. aegypti_, mainly because the species rests indoors. I suspect this is the case in Darfur, where the humidity outdoors is very low. [Mosquitos resting outdoors would quickly become fatally dehydrated. - Mod.JW.]
Hand-operated foggers inside buildings can be very effective but the treatment is labour-intensive and slow. Treatment could begin in areas known to be affected by the virus.
In the 1960s, the Pan American Health Organization declared the _Aedes aegypti_ eradication campaign an outstanding success; the species had been eradicated from 22 countries. The method used was "focal treatment" of breeding sites: DDT was sprayed into and for 50cm around each container that was positive for mosquito larvae. DDT and the other residual insecticides kill by contact when the insect alights on the treated surface. The method was fast, safe and practical to apply, clearly a vital advantage in this pending catastrophe.
If the mosquito is susceptible to DDT then this would be the method and insecticide of choice: cheap, safe and highly effective. If resistance to DDT is significant, there may well also be resistance to residual pyrethroids such as permethrin and deltamethrin, in which case, the only rapidly available insecticide would be one of the carbamates. All these insecticides are cheap and easy to apply.
During the eradication campaign, treatments remained effective for at least 4 months. The astonishing success of the project was probably driven by the behaviour of the mosquito; females fly from site to site, depositing a few eggs here and there. In this way, even if all the positive breeding sites are not treated, the probability is high that an egg-laying female will hit a treated site [and its eggs will never develop. - Mod.JW]
In Darfur, spray-men with simple, portable hand-pumped sprayers would simply apply insecticides to the sides and surrounding of the water storage jars. No need to search for other sites, no need to inspect for the presence of larvae.
Bed-nets are not generally recommended for protection against _Ae. aegypti_ because the species bites more during daylight than at night. Nevertheless, bed-nets over suspected cases may reduce the numbers of mosquitoes that become infected and the number of infective bites; they should be installed in hospitals and similar sites. Infants can also be protected by bed-nets.
Mosquito screens are expensive to install but should be essential in hospitals and other places where patients are present.
In theory, "Source reduction" -- the elimination of breeding sites -- is an effective approach to suppress the mosquito population but clearly, in a land where water is worth gold, the refugees are not going to empty water storage jars. In theory, jars can be covered, but covers must be a tight fit because mosquitoes are adept at finding the tiniest gaps.
In summary, it is hard to overestimate the seriousness of this situation. As mentioned, the virus has already reached Khartoum (population of the city and adjoining cities over 5 million); water storage is widespread, especially in residential areas.
If transmission becomes epidemic in Khartoum then the world is open to catastrophe; the number of vaccines available is limited and the global dispersion of the virus could affect any place where dengue and chikungunya are transmitted, whether by _Ae. aegypti_, _Ae. albopictus_ or other species.
In other words, more than 2.5 billion people throughout the tropics and subtropics would be at risk.
***These notes are my own opinion: they are not necessarily in agreement with recommendations of my employer or other institutions and organizations.
Paul Reiter, PhD, FRES
Unit "Insectes et Maladies Infectieuses"
25-28 rue du Dr Roux
Tel: +33 (0) 1 44 38 95 62
Sec: +33 (0) 1 45 68 89 67
Fax: +33 (0) 1 45 68 87 28
Mobile: +33 (0) 6 08 36 16 70
[***"More than 2.5 billion people throughout the tropics and subtropics would be at risk."
Although DDT has been banned in some developed countries, its use in an emergency like this would be well justified.
The Greida refugee camp, south-east of the Darfur town of Nyala, Sudan:
Location of Darfur refugee camps in 2007: