Tarāpunga Tick Paralysis
DUNEDIN WILDLIFE HOSPITAL · CASE STUDY
From presentation and treatment to rehabilitation and release
An unexpected outbreak
In November 2022, we began admitting unusually large numbers of weak and dying tarāpunga/red-billed gulls from Taiaroa Head on the Otago Peninsula and surrounding areas. Some birds were simply quiet and weak, while others were unable to stand or were already critically unwell by the time they reached the Dunedin Wildlife Hospital.
Against the backdrop of the global spread of highly pathogenic avian influenza (HPAI), the sudden appearance of multiple sick and dying seabirds was understandably concerning. The Ministry for Primary Industries (MPI) was contacted and samples were collected from a number of affected birds for testing.
Thankfully, HPAI was ruled out. Instead, the investigation pointed to a very different cause: tick paralysis.
What is tick paralysis?
Following the MPI investigation, the ticks found on affected birds were identified as Ixodes laridis, a relatively recently described tick species associated with New Zealand seabirds. It has now been recorded from at least 14 bird species, including gulls, terns, gannets, shags, albatross, petrels and spoonbills.
Exactly how these ticks cause paralysis remains uncertain. The clinical pattern appears consistent with a toxin-mediated process, particularly because the severity of disease seems to be related to the number of ticks relative to the size of the bird. Some tarāpunga may have only one tick and still show signs of weakness, while others can carry more than 20. In contrast, Ixodes laridis can be found in low numbers on much larger seabirds such as albatross without apparent clinical disease.
Another possibility is that paralysis could be associated with pathogens carried by the ticks. Saumarez Reef virus and Kaikōura bunyavirus have both been detected in Ixodes laridis from Kaikōura, although at present we consider this a less likely explanation for the clinical syndrome we see.
There is still much to learn about this newly recognised disease.
What do affected birds look like?
Affected tarāpunga present with a wide spectrum of clinical signs. Mildly affected birds may simply appear depressed, weak or reluctant to move. As paralysis progresses, they may sit back on their hocks, become unable to stand and stop eating. In the most severe cases, birds can become moribund, unable to pass faeces and may die.
Interestingly, body condition can vary considerably. Some affected birds arrive underweight, while others are still in relatively good body condition, suggesting that the paralysis can progress rapidly.
During examination, ticks are generally concentrated around the head and face. Tick burdens vary enormously: some birds have only a single tick, while others have more than 20. The ticks themselves can also be surprisingly difficult to find, ranging from tiny pin-point-sized individuals to large, fully engorged ticks.
Finding and removing every tick is therefore an important part of treatment.
Treatment
Tick removal
Ticks are removed using a small plastic tick-removal tool, available from Kahuvet, which hooks underneath the tick and allows it to be gently rotated and removed. We avoid crushing or squeezing the body of the tick and aim to remove it intact, including the embedded mouthparts.
Very small ticks can be more challenging to remove mechanically. Where necessary, veterinary staff may carefully apply a small amount of fipronil (Frontline) directly around the attachment site using a cotton tip to assist with removal.
Supportive care
Removing the ticks is only the beginning. Many affected birds are weak, depressed or even moribund when they arrive and require intensive supportive care while the effects of the paralysis resolve.
Birds that are unable to maintain their body temperature are housed in warm brooders until their condition improves. Supportive treatment may include oral fluids, analgesia where clinically indicated and nutritional support with fish slurry until they are strong enough to eat independently.
A small blood sample is also collected to assess packed cell volume (PCV) and total protein (TP). Across the affected birds assessed, the average PCV was approximately 39.4%. Where an individual bird is anaemic, iron supplementation may be provided based on its clinical and blood results.
The road to recovery
Recovery following tick removal can be remarkably variable.
Mildly affected birds may recover within three to four days, while moderate cases can take a couple of weeks to regain normal strength and mobility. Watching this recovery occur gives us a fascinating insight into the progression—and reversal—of the paralysis.
A severely affected bird may initially be completely unable to stand. As strength begins to return, it will often use its wings for support before progressing to hock-sitting. From there, it begins standing for short periods, then walking normally. As its strength and coordination continue to improve, normal behaviours such as bathing, preening and eventually flying return.
If a bird shows little or no improvement within the first 24 hours, one of the first things we do is search again for ticks. A small engorged tick hidden among the feathers can easily be missed during the initial examination, and birds may fail to improve while ticks remain attached. If no further ticks are found, other causes of weakness or paralysis, such as spinal trauma, need to be considered.
Unfortunately, some birds arrive too severely affected to recover. In these cases, deterioration and death can occur within 12–24 hours of admission. We suspect that progressive paralysis eventually compromises respiratory function, although the precise mechanism responsible for death remains uncertain.
Rehabilitation
As the paralysis resolves, the focus gradually shifts from intensive supportive care towards getting the bird ready to return to the wild.
Nutrition
Initially, most affected birds receive fish slurry two to three times daily, with a structured refeeding programme used for underweight or debilitated patients where necessary. As their strength returns, they are transitioned onto whole fish.
Birds in good body condition that can sit upright, hold their head normally and feed strongly can often be offered whole fish relatively early in their recovery. Fortunately, tarāpunga tend to regain their appetite and begin self-feeding quite quickly once they start to feel better. Mazuri seabird tablets are added to the diet to provide appropriate vitamin and mineral supplementation during rehabilitation.
Getting waterproof again
Waterproofing varies considerably between individuals and is influenced by the severity of the paralysis, the length of time spent in care, the amount of handling required and whether the feathers have become soiled during supportive feeding. Birds that have experienced more severe paralysis often require more work to regain full waterproofing than mildly affected birds.
All tarāpunga are sprayed at least twice daily with a 3% saltwater solution to encourage preening and waterproofing and to help maintain normal salt-gland function.
Once a bird can stand reliably, it is provided with a shallow bathing dish. The size and depth of the water are gradually increased as its strength improves. Eventually, birds move into our outdoor pool enclosure, where they can continue waterproofing while also rebuilding their flight fitness.
Fortunately, tarāpunga can regain their waterproofing remarkably quickly, often over only a few days. They must still be monitored very closely when first given access to deeper water. A bird that is not completely waterproof can rapidly become waterlogged, and a weak or waterlogged bird may drown if it cannot leave the pool without assistance.
Ready for release
Before release, each bird must have a normal PCV, be in good body condition, be fully waterproof and demonstrate strong, normal flight.
Permanent identification bands are fitted under our Department of Conservation permit before the bird leaves the hospital. A metal E-band is placed on the right leg and an individually identifiable colour alphanumeric band on the left. These bands allow individual tarāpunga to be recognised if they are subsequently resighted in the wild, providing valuable information about their survival and movements after rehabilitation.
Once everything is ready, the bird is released as close as practicable to the location where it was originally found.
For birds that may have arrived unable even to stand, seeing them waterproof, flying strongly and heading back into the wild is an especially satisfying end to their rehabilitation.
Where are we now?
Interestingly, the number of tick-paralysis cases presenting to the Dunedin Wildlife Hospital dropped dramatically in 2024.
We suspect this may be associated with habitat changes at Taiaroa Head, including new rabbit-proof fencing and weed control. Ixodes laridis appears to favour shaded vegetation and humid microhabitats, so reducing this type of vegetation may also have inadvertently reduced suitable habitat for the ticks.
Continued monitoring will help us determine whether this reduction in cases is sustained and, hopefully, help us learn more about the ecology of Ixodes laridis and why tick paralysis occurs.
There is still much we don't know about tick paralysis in New Zealand seabirds. What we have learned, however, is that even a tarāpunga arriving profoundly weak and unable to stand can make a complete recovery. With careful tick removal, supportive veterinary care and rehabilitation, many of these birds can go from paralysis back to normal life in the wild.
Statistics of the past few years
Written for WReNNZ
by Angelina Martelli - DVN, Cert Avian Wildlife Health
Practice Manager/Senior Wildlife Veterinary Nurse - The Wildlife Hospital, Dunedin
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