Parasitology - Myiasis-producing flies Flashcards Preview

BVM2 > Parasitology - Myiasis-producing flies > Flashcards

Flashcards in Parasitology - Myiasis-producing flies Deck (24)
Loading flashcards...
1
Q

What is myiasis?

A

Parasitism of living animals by the larvae of dipteran insects (flies). Of interest is the parasitic larval stage – also called a maggot – instead of the adult fly.

2
Q

Myiasis can be classified in a couple of different ways:

  1. By the parasiitic behaviour of the maggots

or

  1. By the location of the parasitism on the host

What are the classifications?

A
  1. Facultative or Obligatory - based on whether the larvae must become parasitic to complete its life cycle (obligatory) or whether the parasitic stage is optional (facultative)
  2. Cutaneous, Nasal or Somatic - based on location of larval parasitism on the live animal; note that myiasis-causing flies are NOT all parasites of the skin. Some are respiratory and GIT parasites.
3
Q

What are the two main FAMILIES of Diptera (order) that have myiasis-producing flies?

A

Oestridae & Calliphoridae

4
Q

Which family of flies is facultative myiasis-producing, and which is obligatory myiasis-producing?

A

Calliphoridae flies are faculative: eg., greenbottles, bluebottles

Oestridae flies are obligatory: eg. warble flies, bot flies

Oestridae are truly grosser of the two.

5
Q

Genera of the Oestridae family are obligatory myiasis-producing flies. What are these genera, and which is the one that affects skin?

A

Warble flies (species Hypoderma) - this is the one that leaves big holes in the skin

Horse bot fly (Gasterophilus) - targets GIT

Sheep nasal bot fly (Oestrus) - targets URT (nose)

6
Q

What are some of the species of warble fly?

A
  • Hypoderma bovis, H. linneatum* - cattle (eradicated in the UK)
  • H. diana* - deer, sheep & horses (rare in UK)
7
Q

How would you recognise a warble fly?

A

It is LARGE (13-15 mm).

Looks like a bumble-bee but with only ONE PAIR OF WINGS.

See photo.

8
Q

What is the life cycle of the typical warble fly that affects cattle?

A

ONE GENERATION PER YEAR:

Eggs laid in summer around host belly & legs, attached to hair by clasp & cement

few days later larvae hatch,
enter skin via insect-bite wounds

migrate SQ to diaphragm via mouth hooks & enzymes

3 months later reach
WINTER RESTING SITES:
epidural fat in spinal canal for H. bovis & oesophagus for H. linneatum

moult to L2 stage during winter (Nov.-March)

Spring: migrate to midline of back, bore breathing hole, moult to L3 “warbles” (see below)


4-10 weeks later, larvae emerge, fall to ground, pupate under veg

1 month later, adults emerge, copulate, lay eggs & die w/i one-two weeks (vestigial mouths, live off fat reserves)

9
Q

What are the main differences between the life cycles of the two Oestridae warble-fly species, **Hypoderma bovis & H. linneatum? **

A

1. Winter resting sites:

  • H. bovis* rests in epidural fat of the spinal canal - think of the damage to the spinal cord
  • H. lineatum* rests in the wall of the oesophagus - think of bloat
    2. H. lineatus adults emerge about six-eight weeks before H. bovis
10
Q

What are the main veterinary &/or economic issues behind cattle infection by warble flies?

A
  1. Downgrading of hides by warbles’ bore holes
  2. Production losses & injury due to gadding (running away, freaking out at sight of warble flies)
  3. Trimmed-meat losses - green-coloured butcher’s jelly around larvae due to eosinophils around oesophagus (H. linneatum) & warbles under skin
  4. ** Paraplegia due to larval death & toxin release** / pressure on spinal cord with H. bovis
  5. Bloat due to luminal blockage in oesophagus from dying larvae with H. linneatum
11
Q

Warble fly (H. bovis) has been eradicated since 1978 legislation made it a notifiable disease, the introduction of Ivermectin and cooler summers.

What is used to treat it now (even though it’s eradicated in UK)?

A

**Systemic organophosphorous (OP) insecticides: **transdermally injected; NB OP can only be used while larvae migrating from diaphragm (before Dec. 1) or when they’ve left winter resting sites (in spring) or it can cause anaphylaxis

Avermectins & Milbemycins - antimicrobials injectible & pour-on

Before, people used to just “pop out” the warbles under the hides, but there was a danger of rupture that could cause bronchospasm/anaphylactic shock

12
Q

While Oestridae (family) are the disgusting obligatory myiasis-producing flies (warble flies, horse & sheep bot flies), the family Calliphoridae includes facultative myiasis-producing flies that cause “blowfly myiasis”.

What are the main blowfly species in Europe?

A

Greenbottles - Luciata sericata

Blackbottles - Phormia terra-novae

Bluebottles - Calliphora erthyrocephala & C. vomitoria

13
Q

What veterinary species is most affected by Calliphora blow-fly species in the UK?

A

Sheep

14
Q

What does it mean to say a sheep is blown?

What does it mean to say a sheep is struck?

A

Calliphora species such as greenbottles, blackbottles or bluebottles have laid eggs in the fleece.

A struck sheep means the eggs have moulted to larvae deep within the fleece.

15
Q

What is the danger to sheep that have been struck by a blowfly?

A

Severe skin damage

Skin lesions extended & deepened by secondary blowflies

Secondary bacterial infection

Production losses

16
Q
A
17
Q

What is the life cycle of a Calliphora blow fly?

A

Life cycle from egg to adult is about two weeks minimum.

Yellow-egg clusters laid in wounds, soiled fleece or carrion

24 hrs later, larvae hatch, crawl to skin, grow & moult 2x - this is when they cause lots of damage

1-2 weeks later, fully mature maggots ↓
fall to ground, pupate


1 week later (summer), adult emerges (pupae can also overwinter)

female reaches sexual maturity when she has protein meal, lays eggs

adults live ~ 1 month
(4-10 generations/year)

18
Q

How do the lengths of life cycle differ between obligatory myiasis-producing flies and facultative?

A

Obligatory (Oestridae - warble flies & bots): one generation a year

Facultative (Calliphorae - blowflies): 4-10 generations a year

19
Q

Define the terms primary, secondary, tertiary blowfly in the context of facultative cutaneous myiasis.

A

Primary, secondary & tertiary refer to the blowfly’s ability to initiate a strike in a host & thus create a wound. The three types can work together to worsen a strike.

Primary blowfly: Larvae can penetrate intact skin, initiating a strike. Eg. Lucilia spp & Phormia spp.

Secondary: Can’t initiate, can only attack area already struck & extend area of damage. Eg. Most Calliphora spp & Chrysomya spp

Tertiary: Attack struck, dry carcass. Eg. Musca spp, Sarcophaga spp.

20
Q

What are environmental and hygiene factors that pre-dispose sheep to a primary blowfly strike?

A
  • Temperature: Warmth of spring & early
    summer determine when pupae hatch
  • Rainfall: Wet fleece attractive to adult
    female laying eggs
  • Host susceptibility: urine, faeces on
    fleece, shearing & other wounds,
    wrinkly skin
21
Q

What is pizzle rot?

A

Blow-fly strike in sheep penile sheath.

22
Q

How can blow-fly strike be prevented?

How can a blown sheep be treated?

A

Prevention:

Prophylactic insecticide treatment - kill larvae with hand spray, plunge dip, spray race, jetting

Treatment:

Insect Growth Regulators - hormone analogues that prevent further devt of larval stages. Eg. Cyromazine (pour- on, up to 2 months’ protection), Dicyclanil (pour-on, up to 4 months’ protection)

23
Q

What do Lucilia seratica (greenbottles) blow flies look like?

Note especially colour of thorax and abdomen & wings.

A

As adults, they’re medium sized (less than 10 mm long) with green metallic sheen to thorax & abdomen. They are very common.

They have clear wings.

24
Q

What do the maggots (larvae) of the blow flies look like? How are they identified?

A

They are smooth.

About 10-15 mm long.

They have spiracles and stigmatic plates on the tail, which are used for identification of species.

Decks in BVM2 Class (88):