New World Screwworm

Ready Reference Guide―Maps & Timelines 

November 2016

USDA APHIS Veterinary Services • National Preparedness and Incident Coordination (NPIC)

4700 River Road Unit 41 • Riverdale, MD 20737

1

New World Screwworm Eradication Programs, by Start Date

New World Screwworm Eradication Programs Timeline, by Duration

The following map identifies countries that were infested 

with New World screwworm (NWS) and have 

successfully eradicated the pest from within its borders. 

This map indicates the program start date—the length of 

the eradication program is provided in the timeline 

below. In all cases, the sterile insect technique (SIT) was 

used to eradicate the NWS from the geographical region. 

In 1995, NWS were reintroduced to Curaçao; the country 

mounted a second SIT eradication program after over 40 

years of NWS freedom. Similarly, NWS were 

reintroduced into the United States in 2016, infesting the 

Florida Keys. As of November 2016, eradication activities 

continue in those islands, located in the southeast 

United States. 

This timeline shows the length of NWS eradication programs which occurred in North America, the Caribbean, and Central America 

from the mid 1950’s to the present. Curaçao was the first country to implement an SIT eradication program, and successfully 

eradicated NWS in 1954. The duration of any eradication program depends on many factors, including the geographical extent of

the infestation, NWS status of neighboring countries, and the characteristics of the SIT eradication program (e.g., number of sterile 

flies that can be released). Please note that the official “NWS-free” date may be slightly after the dates pictured below.

Panama, north of the Darien 

Gap, was the southernmost 

country to eradicate NWS in 

Central America. This Darien 

Gap area now serves as a 

“barrier” for NWS from 

entering Central or North 

America from South America.

Dates from Vargas-Teran et al. (2005). “Impact of Screwworm Eradication Programmes Using the Sterile Insect Technique.” In Dyck et al. Sterile Insect Technique: Principles and Practices 

in Area-Wide Integrated Pest Management, 629-250. 
USDA APHIS Veterinary Services • National Preparedness and Incident Coordination (NPIC)

4700 River Road Unit 41 • Riverdale, MD 20737

 2

New World Screwworm

Ready Reference Guide―Maps & Timelines 

Country of Origin for Recent New World Screwworm Detections into the United States

November 2016

New World Screwworm and Old World 

In the past three decades, NWS has been detected in the United 

States (including Puerto Rico) 27 times. In addition, there was a 

single U.S. detection of Old World Screwworm (OWS) from Singapore 

(not pictured at left). In many cases, the country of origin of the NWS 

detection is known because cases are detected in imported animals 

while they are in quarantine (13 of the 28 NWS/OWS detections 

were while in import quarantine). Three additional cases were in 

humans. But in two cases—1998 and 2016—the country of origin 

remains unknown. USDA is currently investigating the origin of the 

2016 detection.

The map at left shows the country of origin for each U.S. NWS 

detection by year. The darker the red color of a country, the more 

recent the import of NWS into the United States. After the initial 

eradication of NWS in the United States throughout the 1950’s and 

1960’s, subsequent NWS detections have resulted in only a single 

infested animal. Intensive surveillance efforts did not yield 

identification of further infestations. In three cases (including in the 

Puerto Rico case), out of an abundance of caution, sterile flies were 

released to ensure NWS did not re-establish in the United States 

(occurred in April 1987, August 1987, and September 1989).

However, this changed with the NWS introduction in 2016, when 

NWS again established itself in the United States. In part due to 

delayed identification, NWS infested a specific area in the Florida 

Keys. To-date, over 130 Key Deer have been affected, as well as 

approximately 5 domestic animals. While the country of origin (as of 

November 2016) is currently unknown, this introduction has resulted 

in an extended and continuing SIT eradication program against the 

established infestation in the Florida Keys. 

This timeline provides another visualization of the data pictured in the map above; it illustrates U.S. NWS detections and the 

respective country of origin. One block represents one case. In two incidents, this origin country is unknown. The OWS detection 

from Singapore is also illustrated below. 
USDA APHIS Veterinary Services • National Preparedness and Incident Coordination (NPIC)

4700 River Road Unit 41 • Riverdale, MD 20737

 3

New World Screwworm

Ready Reference Guide―Maps & Timelines 

New World Screwworm and Old World Screwworm in the United States, by Species Affected 

(Presumptive and Confirmed Cases)

Historically, NWS has been detected in animals that have been recently imported into the United States. This timeline illustrates 

the species affected by NWS and OWS detections in the United States; it includes both presumptive and confirmed NWS and OWS 

cases. Both autochthonous and imported cases are shown below. Because of the geographical proximity of NWS to the United 

States, NWS is significantly more common than OWS. To-date, the 2007 case of OWS is the only known finding of an OWS larvae 

in the Western Hemisphere. 

Three human detections are pictured; all individuals had recently traveled to an area with NWS. There has never been a NWS or

OWS detection or introduction in livestock in the United States; horses and dogs are most commonly infested. All NWS and OWS 

detections in the United States have been traced back to imported animals or recent foreign travel for humans, except the 1998 

case in a Texas goat and the current 2016 infestation. In 1998, while one larvae was identified as NWS, the animal had never been 

outside of the United States and no other cases were found or reported. There was no history indicating a likely source of the 

NWS. It remains unclear whether this was indeed NWS; this detection was not confirmed. 

Then, in 2016, NWS has been detected in both wild and domestic animals in the infested area of the Florida Keys. Not yet tied to a 

country of origin, animals affected (presumptive or confirmed infestations) include domestic dogs, pet pigs, domestic cats, as well 

as wild Key Deer and a raccoon. The numbers illustrated below are current as of November 21, 2016, and may change.

November 2016

The Darien Gap, Panama

The Darien Gap region of Panama is considered the “barrier zone” between South America, 

where NWS remains endemic and Central America/North America which is free from NWS. 

USDA APHIS International Services (IS) leads the operation of a sterile fly production facility 

within this region. This production facility is critical to 1) maintain this barrier zone in 

Central America, and 2) provide sterile flies as required by detections in NWS-free 

countries. It is currently providing the sterile flies for the 2016 response in the Florida Keys.