Screw Worm Fly: new threat to livestock in Yemen

Dr. Mohammed al-Haddad

Livestock in a number of the Yemeni governorates, especially al-Mahweet, are increasingly threatened by a serious pest called the Old World Screw Worm Fly (SWF). In order to obtain more information on this disease and it’s effects on those governorates infected by the disease, the Yemen Observer met Dr. Mohammed Ahmed al-Haddad, Director of the General Administration of Animal Health and Veterinary Quarantine in the Ministry of Agriculture and Irrigation.   

Yemen Observer (YO): Could you give us a brief description about the epidemic and where and when it began in Yemen? 
Dr. Mohammed al-Haddad (Dr. M.A): The first cases of animals infected with the Old World Screw Worm Fly (SWF) were recorded by the Yemeni Ministry of Agriculture and Irrigation in Sa’ada governorate in December 2007. The disease then spread to infect Hajjah and al-Hodeidah, and reached al-Mahweet governorate in March 2008. The disease has infected all groups of animals, including dogs, in five districts including Al-Mahweet -Al- Khabt, Khamis Bani S’ad, Malhan, and Hafash. After tracking the course of the disease, we found that the epidemic spread from north to south, where the climate has helped this parasite proliferate easily.  

Y.O: How did your ministry respond to the urgent situation and what was done to contain the spread of the epidemic from al-Mahweet governorate?  Dr. M.A: The Ministry of Agriculture and Irrigation - the General Administration of Animal Health and Veterinary Quarantine - took all emergency preventive actions. The Ministry prepared and sent field veterinary teams with spraying cars to investigate and control the spread of the disease in cooperation with the Agriculture and Irrigation office and other related bodies in al-Mahweet governorate. 

Y.O: You told me that the ministry took some measures to control the spread of the disease among animals, could you mention the main measures?
Dr. M.A: Control measures began in al- Mahweet’s infected districts by sending three teams to do the following:
• Treat the infected animals.
• Spray animals and folds with insecticides.
• Distribute posters and educate farmers on this disease and how to prevent their animals from being infected. Teams also trained farmers to test their livestock and make periodic inspections of their animals, and encourage them to report any new infected cases to the nearest veterinary center or the central operations room in Sana'a. Training farmers on the treatment of livestock and providing them with the necessary medicines and requirements was essential as we believe that it is only through the participation of farmers' that we were able to combat this epidemic among their animals.
• The Ministry also intensified its efforts in the field and in the area of laboratory surveillance in infected governorates, especially al-Mahweet. • Collecting samples of the Screw Worm Fly’s larvae and diagnosing them in the Central Veterinary Laboratory in Sana’a to confirm the presence of the Old World Screw Worm Fly.
 
Y.O: What were the achievements of measures established to control the SWF?
Dr. M.A: Control measures continued in these districts from April to November 2008 to survey 1,107 villages. It was found that 557 of the villages surveyed were infected with the SWF. Through great efforts, we prevented the disease in 242,694 animals, treated 2,622 of the infected animals, sprayed 8,445 folds, and collected 208 samples. Unfortunately, around 1,465 of infected animals in al-Mahweet’s districts died but we averted what would have been a far greater crisis.  

This photo shows a healthy sheep before infection, while the second shows a sheep in the later stages of infection.

Y.O: Does the ministry have any future plans to control this disease and stop it from re-appearing in the near future?  
Dr. M.A: A team including Dr. Mohammed al-Ghashm, Deputy Minster of Agriculture and Irrigation - Agricultural Services Sector, and some other specialists from the General Administration of Animal Health and Veterinary Quarantine made a field visit to al-Mahweet governorate in November 2008. The visit was aimed to evaluate the situation in the infected districts, and specify the constraints of work and future needs of teams. The field teams were then enhanced by another four teams with spraying cars, and necessary medicines and requirements for the prevention and control. The Ministry continues to place this issue at the forefront of its agenda and is making every effort to combat this epidemic and reduce the economic hazard it poses to the livestock sector. 

Y.O: Did you receive any foreign help? 
Dr. M.A: Many international and regional organizations responded to this urgent situation and provided us with technical assistance, and expertise in our struggle against the SWF. We still communicate with many of these bodies and organizations, there are many and I cannot mention them all.  

Y.O: In your view, what are the factors that caused this screw worm fly to appear and re-appear in Yemen?  
Dr. M.A: Yemen, especially southern areas, has suitable climatic conditions (temperature, humidity, vegetation cover) that help the SWF proliferate and spread, in addition to the geographical position of our country which makes Yemen one of the high-risk epidemiological areas. The screw worm fly is able to fly for long distances. So, this facilitates the spread and expansion of this epidemic to encompass many other areas. The infected wild animals and stray dogs are considered an important factor in the transfer and spread of this epidemic among livestock because of their ability to move freely through areas.    

Workers spray at risk livestock to prevent an outbreak of Old World Screw Flies in the flock.

Y.O: To give the readers more information about the screw-worm fly, what is it?
Dr. M.A: The screw-worm fly is an insect parasite with a shiny blue-green body and red eyes that whose larvae feed off the flesh of warm-blooded animals, including humans. It prefers hot, humid climates and cannot survive in frost-prone areas. There are two species of screw-worm fly: ‘Old World’ (Chrysomya bezziana) and ‘New World’ (Cochliomyia hominivorax). 

Y.O: What are its effects?
Dr. M.A: Screw-worm flies breed in the wounds on mammals, including humans. The female screw-worm fly lays up to 250 eggs on the edge of an injury, scratch, branding mark or castration wound. Larvae (maggots) hatch within 24 hours, enter the wound and chew their way into healthy underlying flesh to feed. The wound becomes a mass of maggots, causing extensive tissue damage and leaving the flesh susceptible to a secondary fly strike. After about a week the larvae drop from the wound to pupate in the soil. Adults emerge in another seven days to mate and repeat the cycle. If left untreated, infested animals can die from infection and loss of tissue fluid.

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