Myiasis-producing flies?

Question 1

What is myiasis?

Answer 1

The parasitism of living animals by the larvae of dipteran spp.

Question 2

How can myiasis be classified?

Answer 2

Facultative or Obligatory

Cutaneous, nasal or somatic

Question 3

What are the Hypoderma spp. more commonly known as?

Answer 3

Warble flies

Question 4

How can warble flies be distinguished from bumble bees?

Answer 4

They only have ONE pair of wings.

Question 5

Describe the general life cycle of a warble fly.

Answer 5

The female adult lays egg(s) around the belly and legs of cattle between June and August. These are attached to the animal firmly by a terminal clasp and cement. After a few days larvae hatch and crawl into hair follicles or existing skin wounds. They migrate first towards the diaphragm and then to their WINTER RESTING SITES after about 3 months. Here they moult to L2 stage before continuing migration in early spring to their site in the subcutis. Here they develop to L3 and breath through breathing holes. After 4-10 weeks they drop to the ground and pupate.

Question 6

Why don’t adult flies last very long?

Answer 6

They have vestigeal mouthparts and don’t feed so only survive for a couple of weeks.

Question 7

What is the difference between the lifecycles of the two spp.?

Answer 7

H. bovis rest in the epidural fat and H. lineatum in the wall of the oesophagus. H. lineatum are also on the wing 6-8 weeks before H. bovis.

Question 8

What are the consequences of warble fly infection?

Answer 8

Down-grading/condfemnation of hides
Gadding leading to reduced milk yield/injury
Losses at meat inspection
Larval death can lead to paraplegia or bloat.

Question 9

When should treatment for warble fly larvae be carried out?

Answer 9

Either before they reach their winter resting sites or after they have migrated away from them

Question 10

What are the major species that cause blowfly strike?

Answer 10

Lucilia sericata (greenbottles)
Phormia terra-novae (blackbottle)
Calliphora erythrocephala (bluebottle)
C. vomitoria (bluebottle)

Question 11

Which family do the above belong to?

Answer 11

Calliphoridae

Question 12

How are the maggots of different species identified?

Answer 12

By looking at the spiracles at the rear end of the larvae.

Question 13

How long does it take for the life cycle to go from egg to adult?

Answer 13

In 24hrs eggs hatch and larvae crawl to the skin. They moult twice and are mature in 1-2 weeks. Larvae fall to the ground to pupate and adults emerge within 1 week in warm conditions.

Question 14

What are the epidemiological categories of blow fly?

Answer 14

Primary - can penetrate intact skin
Secondary - colonise already penetrated skin, extending the wound.
Tertiary - lesions on the carcasses of struck sheep.

Question 15

What are the factors that predispose an animal to blowfly strike?

Answer 15

Temperature - environmental and microclimate in the fleece
Rainfall - wet fleeces are more attractive to adult flies.
Putrifactive odours - urine/diarrhoea
- injuries (shearing)

Question 16

What are the two phases of strike in

a) highland, and,
b) lowland sheep?

Answer 16

a) 1 - June in unshorn adults
2 - August/september lambs with longer fleece

b) 1 - less obvious as shorn earlier
2 - July lambs

Question 17

What is the pathogenesis of strike?

Answer 17

Severe initial skin lesions lead to secondary attack and then bacterial infection. All of the above result in a variety of production losses.

Question 18

What are the clinical signs?

Answer 18

Often weight loss is the first as maggots hard to spot. Sheep also appear dull and tend to stand away from the rest of the flock.

Question 19

How can it be diagnosed?

Answer 19

From the above clinical signs and then confirming the presence of maggots by parting the fleece (as the maggots are present on the skin).

Question 20

How is it controled?

Answer 20

1. Prophylactic treatment using insecticides
2. IGRs
3. a) worm control (to prevent diarrhoea)
   b) removal of excess wool from the breech area
   c) sergical removal of breech skin
   d) tail docking of lambs
   e) proper carcasss disposal