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  Discussion on Gedoelstia hasleri
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New Member:
Mwpennya

Posted on Thursday, Nov 3, 2005 - 1:26 am:

Hi There
My 4 year old half warmblood mare in kyalami, Johanneburg,South Africa, has just had a gedoelstia fly deposit larvae in her eye. this has resulted in severe ulcers on the cornea as this larvae apparently has vicious mouthparts and eats into the eye.I had never heard of this before but we got the eye clinic out and they showed us the actual larvae causing migratory tracts in the eye.They sprayed a permethrin spray into the eye and a local anaesthetic DrOp and actually scraped off what larvae they could.The three horses at our yard that were affected are extremely uncomfortable and in severe pain. We have to put in DrOps every 2 hours and they are on bute.they have to remain stabled due to the atropine eyeDrOps effect on the pupil and the sun.They are rubbing a lot. This fly's natural host is apparently the wildebeest but due to people bringing game into the area, these flies have come with them and although rare, do attack horses from time to time. I am having a difficulty in finding any literature on this fly and apparently the larvae can migrate into the bloodstream, heart,brain and usually sinus's.Would Ivermectin work systemically on these larvae and kill them? I would love to know more about this fly and the effects.
Moderator:
DrO

Posted on Thursday, Nov 3, 2005 - 9:21 am:

Hello Penny,
Gedoelstia is a specie of bot fly Penny and I cannot find any information of the effectiveness of ivermectin against it. This was the most informative reference that I find:

Onderstepoort J Vet Res. 1977 Jun;44(2):113-8.
Parasites of domestic and wild animals in South Africa. III. Oestrus spp. and Gedoelstia hassleri in the blesbok.
Horak IG, Butt MJ.

Four blesbok culled in the Rietvlei Nature Reserve, Pretoria, District during May 1972 were found to harbour large burdens of 1st instar Oestrus spp. larvae and from 16-37 3rd instar larvae of Oestrus macdonaldi. They were also infested with large numbers of 1st instar Gedoelstia hassleri larvae but only 2 harboured 3rd stage larvae of this species. During an 18-month period 34 blesbok were culled in pairs in the Percy Fyfe Nature Reserve, Potgietersrus District. These antelope harboured peak numbers of 1st instar Oestrus spp. larvae during February, July and December but few if any during early October. Third instar Oestrus variolosus larvae were generally recovered from July-February and those of O. macdonaldi during July 1972 and from May-September 1973. Some 1st instar larvae of these flies appeared to undergo a pulmonary migration before returning to the naso-pharyngeal area to mature. The pupal period of O. variolosus varied from 67 days during the spring to 35 days during the summer. G. hassleri larvae reached peak numbers from October 1972-January 1973 and during May and June 1973. The lowest numbers were recovered from August-October 1973. Recovery and measurement of 1st instar larvae indicated that they either undergo an ocular-cranial or ocular-vascular-pulmonary migration before reaching the naso-pharyngeal area. Pupal periods varied from 46 days for flies hatching during October to 22 days for those hatching during December.

We know in the normal bot fly larvae of horses that the later stages of the larvae are sensitive to ivermectin while the earlier stages (the 1st instar they refer to above) are resistant. I am also uncertain that if given orally it penetrates into the internal structures of the eye and the cornea but with the inflammation present it would not surprise me if it did. Another concern is if the ivermectin is effective there will be inflammation from the dead larvae. This may require aggressive antiinflammatory therapy to prevent loss of the eye from the inflammation. If the larvae have penetrated to the brain there may also be a encephalitis from killing them.

Consult with your vets and if they approve and if there are no better choices you could try an aggressive therapy of ivermectin after first trying several low doses to see if there is an adverse reaction.
DrO
Member:
Mrose

Posted on Thursday, Nov 3, 2005 - 9:31 am:

Sure learn a lot of interesting things here! And...glad I don't live where these flys do!
New Member:
Mwpennya

Posted on Thursday, Nov 3, 2005 - 11:28 am:

Dear Dr O

Thank you for your input. I also remember now that the eye specialist said he battled to find literature on this and will be publishing a paper shortly (if this is the correct terminology)as it is one of his particular interests due to the fact that it is occurring more and more frequently in Johannesburg, even though most game farms are well outside Johannesburg. He also said that uveitis is a risk as a secondary problem largely a reaction to the pain involved. However, on the positive side, the horses look much better this morning. The swelling around the eye is down and there is less discharge, all after Jean who stables them, got up every two hours throughout the night to treat them. I have given my horse the ivermectin based on advice from the vet. The amazing part was that the horses were fine at about 9am and by 11am the same day the eyes were already swollen and mucky.The vet was there by 12 so we did catch it fast.
Member:
Jgordo03

Posted on Thursday, Nov 3, 2005 - 12:57 pm:

Penny,
I'm so glad to hear your horses are healing quickly. Would fly masks be effective against the gedoelstia fly in conjunction with the Ivermectin for a future treatment? Is this a year round problem or is it a seasonal problem like it is in the USA? Keep us updated and share your eye specialist's paper on the subject when it's published.
New Member:
Mwpennya

Posted on Saturday, Nov 5, 2005 - 7:25 am:

Hi Judith

I forgot to add that we have now ensured that all our horses have fly masks on during the day, although I am told that the chances of any further attacks are remote. The affected horses have fly masks with additional fabric stitched onto the outside of the mask over the affected eye to protect them against uv damage. We are putting them out in the paddocks from 5-9am and 4-6pm which is not the most ideal time as we have african horse sickness here which is carried by midges usually most active early in the morning. We vaccinate against it but there have been many cases in and around Kyalami in the last couple of years due to new strains. It is a pity we were not aware of this gedoelstia fly, or we would have ensured all horses had fly masks all along.Most people I have come across have never heard of it either.Apparently the Gedoestia fly is only really a danger in October and November.It can attack dogs,sheep and apparently humans too.
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