Follow Ups | Post Followup | Back to Discussion Board | VegSource
See spam or
inappropriate posts?
Please let us know.

From: TSS ()
Subject: Transmission of TSEs through ectoparasites i.e. P. tenuis and CWD
Date: May 3, 2007 at 9:05 am PST

SEAC 97/2
Annex 2

Other organisms

Transmission of TSEs through ectoparasites has been postulated by Lupi5. Post et al6
fed larvae of meat eating and myiasis causing flies with brain material from scrapieinfected
hamsters. Two days after eating infected material, the larvae showed high
amounts of PrPSc by Western blot. In further studies, the inner organs of larvae, which
had been fed with scrapie brain, were extracted and fed to hamsters. Six out of eight
hamsters developed scrapie. Two out of four hamsters fed on scrapie infected pupae
subsequently developed scrapie.

I AGAIN raise the possibility of that damn brain eating worm in elk and CWD transmission via elk, deer, and other critters eating that worm. ...tss

Immunodiagnosis of experimental Parelaphostrongylus tenuis infection in elk
Oladele Ogunremi, Murray Lankester, and Alvin Gajadhar
Centre for Animal Parasitology, Canadian Food Inspection Agency, 116 Veterinary Road, Saskatoon, Saskatchewan S7N 2R3 (Ogunremi, Gajadhar); Department of Biology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1 (Lankester).

Elk infected with the meningeal worm, Parelaphostrongylus tenuis (Protostrongylidae), do not consistently excrete larvae in feces, making the current method of diagnosing live animals using the Baermann fecal technique unreliable. Serological diagnosis could prove more useful in diagnosing field-infected animals but depends on the identification and availability of good quality antigen. To mimic field infections, 2 elk were inoculated with 6 infective L3 larvae of P. tenuis, and another 2 with 20 L3 larvae. Fecal samples were examined for nematode larvae using the Baermann technique and serum samples taken were tested for anti-P. tenuis antibody with ELISAs by using the excretory-secretory (ES) products of L3, and sonicated adult worms as antigens. One animal passed first-stage larvae in its feces 202 days postinoculation, but passed none thereafter. The remaining 3 inoculated animals did not pass larvae. In contrast to parasite detection, antibodies against larval ES products were detected in all animals starting from 14 to 28 days postinoculation and persisted until the termination of the experiment on day 243 in 2 animals that harbored adult worms. Antibodies against somatic antigens of the adult worm were not detected until day 56 but also persisted until the end of the experiment in the animals with adult worms. In 2 elk that had no adult worms at necropsy, anti-ES antibodies were detected transiently in both, while anti-adult worm antibodies were present transiently in one. These findings confirm the superiority of P. tenuis larval ES products over somatic adult worm antigens as serodiagnostic antigens, as previously observed in studies of infected white-tailed deer, and extend the application of the newly developed ELISA test in diagnosing and monitoring cervids experimentally infected with P. tenuis.

Subject: TSE & insects as a vector of potential transmission
Date: October 26, 2006 at 12:50 pm PST

i try to keep an open mind about any other routes and sources that we may be overlooking. i mean, there is enough TSE protein in circulation now VIA the FDA, just in 2006 alone, and the oral route has been proven with BSE, and the non-forced oral consumption of scrapie to primate, as to not worry about a natural route of a few worms that have maybe been feasting on a deer that's brain is infected with CWD, then excreted out, and then passed on to another worm hungry deer looking for that feast. i suppose maybe just another potential route and source for a TSE, and possibly even a 'double dose' so to speak from not only the worm in the feces (maybe triple with feces), but the soil as well (see soil and prion study as well below) following that are some other studies that may be of interest ;

Myiasis as a risk factor for prion diseases in humans

Journal of the European Academy of Dermatology and Venereology
Volume 20 Page 1037 - October 2006
Volume 20 Issue 9

Myiasis as a risk factor for prion diseases in humans
O Lupi *


Prion diseases are transmissible spongiform encephalopathies of humans and animals. The oral route is clearly associated with some prion diseases, according to the dissemination of bovine spongiform encephalopathy (BSE or mad cow disease) in cattle and kuru in humans. However, other prion diseases such as scrapie (in sheep) and chronic wasting disease (CWD) (in cervids) cannot be explained in this way and are probably more associated with a pattern of horizontal transmission in both domestic and wild animals. The skin and mucous membranes are a potential target for prion infections because keratinocytes and lymphocytes are susceptible to the abnormal infective isoform of the prion protein. Iatrogenic transmission of Creutzfeldt–Jakob disease (CJD) was also recognized after corneal transplants in humans and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes could also be important in prion infections. Some ectoparasites have been proven to harbour prion rods in laboratory experiments. Prion rods were identified in both fly larvae and pupae; adult flies are also able to express prion proteins. The most common causes of myiasis in cattle and sheep, closely related animals with previous prion infections, are Hypoderma bovis and Oestrus ovis, respectively. Both species of flies present a life cycle very different from human myiasis, as they have a long contact with neurological structures, such as spinal canal and epidural fat, which are potentially rich in prion rods. Ophthalmomyiases in humans is commonly caused by both species of fly larvae worldwide, providing almost direct contact with the central nervous system (CNS). The high expression of the prion protein on the skin and mucosa and the severity of the inflammatory response to the larvae could readily increase the efficiency of transmission of prions in both animals and humans.

International Journal of Dermatology
Volume 42 Page 425 - June 2003
Volume 42 Issue 6

Could ectoparasites act as vectors for prion diseases?
Omar Lupi, MD, PhD

Prion diseases are rare neurodegenerative diseases of humans and animals with a lethal evolution. Several cell types found on the human skin, including keratinocytes, fibroblasts and lymphocytes, are susceptible to the abnormal infective isoform of the prion protein, which transforms the skin to produce a potential target for prion infection. Iatrogenic transmission of Creutzfeldt-Jakob disease was also recognized after corneal transplants in humans, and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes, as well as cerebral inoculation and oral ingestion, could be important in prion infections. Animal prion infections, such as scrapie (sheep) and "mad cow disease" (cattle), have shown a pattern of horizontal transmission in farm conditions and several ectoparasites have been shown to harbor prion rods in laboratory experiments. Fly larvae and mites were exposed to brain-infected material and were readily able to transmit scrapie to hamsters. New lines of evidence have confirmed that adult flies are also able to express prion proteins. Because ocular and cerebral myiases and mite infestation are not rare worldwide, and most cases are caused by fly larvae or hay mites that usually affect sheep and cattle, it is important to discuss the possibility that these ectoparasites could eventually act as reservoirs and/or vectors for prion diseases.

P. tenuis – The White-tailed Deer Parasite

“Brain worms” (meningeal worms) can affect sheep, goats, llamas, alpacas, moose and other exotic small ruminants

M. Kopcha, D.V.M., M.S., J. S. Rook, D.V.M. & D. Hostetler, D.V.M

MSU Extension & Ag. Experiment Station

Michigan State University

College of Veterinary Medicine

Many livestock producers are familiar with internal parasites that invade the digestive system (the abomasum, small or large

intestines), liver, and lungs. An internal parasite which may not be so well-recognized is one that invades the central nervous system

(brain and spinal cord). Commonly called the “brain worm” or meningeal worm (the meninges are a thin membrane that covers the

brain and spinal column), the scientific name for this parasite is Parelaphostroneylus tenuis (P. tenuis), and its natural host is the

White-tailed deer. Usually, P. tenuis completes its life cycle in

the deer (Figure 1) without causing noticeable problems.

However, when P. tenuis is ingested by unnatural, or aberrant

hosts such as, llamas, sheep, goats, moose, elk, caribou, and

other susceptible ruminants, the parasite moves into the brain

and/or spinal cord, damaging delicate nervous tissue.

Neurologic problems result.

White-tailed deer may he parasitized by P. tenuis year-round.

However, the neurologic disease seen in aberrant hosts has a

seasonal occurrence that starts in the late summer and continues

until a hard freeze occurs. A cool, moist summer and/or a mild

winter may extend the period during which the disease occurs.

How does it occur?

To understand this disease and how to prevent or minimize its

occurrence, it is important to understand the life cycle of P.

tenuis in the White-tailed deer and what happens when the

parasite is ingested by susceptible ruminants. The life cycle is

as follows (Figure 1): adult meningeal worms live in the deer's

central nervous system (brain and spinal cord) and produce

eggs which hatch into larvae. The larvae migrate from the deer's

central nervous system to the lungs, where they are coughed

into the mouth, swallowed and passed from the intestinal tract

with the manure. This portion of the life cycle takes

approximately three months (Figure 1 - numbers 1 and 2).

After excreted in the manure, larvae must continue their

development in an intermediate host (certain land-dwelling

snails and slugs) for another three to four weeks until they reach

their infective stage (Figure 1 - numbers 3 and 4).

White-tailed deer become infested with P. tenuis by eating

these snails or slugs that contain the infective stage of the larvae

(Figure 1 - number 5). Once ingested, the larvae migrate

through the deer’s gut and eventually move into their central

nervous system where they mature into adults, produce eggs,

Figure 2 The Angora goat in the

center of the picture had a mild

lameness in its left forelimb

(arrow). The presumptive

diagnosis was meningeal worm

infestation. Mild cases such as

this one may recover


Figure 3 This Angora goat was

probably affected with

meningeal worms and was able

to use its hindlimbs, but was

unable to rise onto its


Figure 4 This alpaca had been

paralyzed by meningeal worms.

Notice that despite the paralysis,

the animal appears alert. This is

typical for a brain worm

infestation that affects the spinal

cord and not the brain.

Figure 6: This Suffolk sheep was one of several

sheep from a flock that were affected with

Parelaphostrongylus tenuis. The posture that this

animal is displaying is referred to as a

“dogsitting” position.

Figure 5: This alpaca

displayed weakness in both

hindlimbs and was unable to

stand without assistance. The

presumptive diagnosis was

brain worm infestation. This

animal eventually recovered.

and the cycle begins again.

When P. tenuis-infected snails and slugs are ingested by aberrant hosts, the larvae migrate into the brain and/or spinal cord, but

do not mature into adults. Instead, these immature larvae wander through the central nervous system causing inflammation and

swelling which damages sensitive nervous tissue producing a variety of neurologic signs. Because these larvae do not mature into

adults in aberrant hosts, they cannot produce eggs that would mature into larvae which would then pass outside the animal with the

feces. This is why sheep, goats, llamas and other unnatural hosts are considered dead-end hosts for P. tenuis. Dead end hosts

infected with P. tenuis larva cannot spread the disease to other aberrant hosts or back to deer - i.e. infected sheep or

goats can not bring the disease to your flock or herd.

The neurologic signs observed in infected llamas,

sheep, goats and others depend upon the number of

larvae present in the nervous tissue and the specific

portion of the brain or spinal cord that has been

affected. For example - a mild infestation in a very

local area may produce a slight limp (Figure 2)) or

weakness in one or more legs (Figure 3,4,5, & 6). A

more severe infestation may cause an animal to

become partially or completely paralyzed. If the

parasites are located only in the spinal cord, an

affected animal will appear bright and alert, and have

a normal appetite, despite the altered gait or

paralysis. When larvae migrate through the brain, they

may cause blindness, a head tilt, circling, disinterest in

or inability to eat, or other signs that can mimic brain

diseases caused by bacteria, viruses, nutritional

deficiencies, trauma, or toxins. Table I lists some of

the diseases that P. tenuis can mimic when the

parasites migrate through nervous tissue.

Table 1_Included in this table are various diseases that can look similar to

“brain worm” infestation. Also listed are the target species that are

susceptible to each of the diseases.


Disease Llamas and


Sheep Goats

Listeriosis X X X

Caprine Arthritis-



Scrapie X Rare*

Rabies X X X

Trauma X X X

Copper Deficiency X X X

Vitamin E/Selenium



Spinal Cord or Brain



Polioencephalomalacia X X X

Could it happen on my farm?

Animals pastured in lowland areas frequented by infected White-tailed deer are prime candidates for exposure to snails containing

P. tenuis larvae. When such animals develop neurological problems during the late summer through early winter in the Upper

Midwest (the season for exposure may be longer in other parts of the country), “brain worms” are a likely possibility.

Presently there is no definitive test

that can be performed on a live

animal to confirm P. tenuis

infestation. Since the larvae do not

mature to adulthood in aberrant

hosts, and therefore, cannot

produce eggs or pass larvae in the

feces, a fecal examination is not

useful. Also, these parasites cannot

be detected by blood testing.

A test that can help support

suspicions of brain worm infestation

is evaluation of cerebrospinal fluid

(CSF), which is the fluid that

bathes the brain and spinal cord.

Disease that occurs in these areas

may cause changes in the CSF

detectable by various tests.

Normal CSF contains very few

cells and little protein. An animal

that has parasites migrating in the

brain or spinal cord, often will have

a larger number of cells, especially

a certain type of cell called an

eosinophil. Also, the protein

concentration may be increased.

Therefore, finding eosinophils in a

CSF tap taken from an animal with

neurologic abnormalities is very supportive evidence for “brain worm” infestation. If eosinophils are not found, this does not rule

out the possibility of a “brain worm” problem. Currently, the only way to confirm this diagnosis is by finding the parasite in the

nervous system, which requires a necropsy examination.

Obtaining CSF from sheep, goats, and llamas is somewhat more involved than obtaining a blood sample. Two areas used most often

for CSF collection are just behind the poll or over the hips, in the area called the lumbosacral junction. We prefer the lumbosacral

site because the test can be performed using local anesthetic only (rarely would a tranquilizer be required), and the animal can be

standing or lying down, whichever is most comfortable. The head site usually requires that the animal be heavily tranquilized or


The procedure can be performed in a hospital setting or on the farm, and must be done in a sterile manner. This includes removal

of the hair or wool from a small area where the puncture will be made, scrubbing the site with surgical disinfectant and rinsing with

alcohol. Sterile gloves and equipment are used.

After the site has been scrubbed, an injection of a local anesthetic is placed under the skin and into the deeper tissues where the

spinal needle will be placed. The needle is inserted through the anesthetized area. The animal may notice slight discomfort when the

needle enters the spinal canal. However, having a quiet person at the animal's head (in some cases the best person is the owner or

handler) will provide a calming effect. The needle does not penetrate the spinal cord. In many animals, the cord ends just ahead of

where the needle is placed. Once fluid has been obtained, the needle is withdrawn. The amount of fluid collected depends on the

animal's size. Usually, 5 to 8 cc's are withdrawn and submitted to a clinical laboratory for analysis. This is a very safe procedure

if performed properly.

What about treatment?

Many different drugs including thiabendazole, levamisole, fenbendazole, albendazole, and ivermectin have been used in an attempt

to treat “brain worm” infestation. However, to date, no controlled studies have confirmed or refuted the efficacy of various treatment

recommendations. Some anthelmintics can kill P. tenuis larvae while they migrate from the stomach to the brain or spinal cord, but

are unable to enter the central nervous system because of a structure called the blood-brain barrier. Therefore, they do not have

an effect on parasitic larvae once the parasite has migrated across the blood-brain barrier and is in the central nervous system. Other

anthelmintics may be able to kill the larvae regardless of their location in the body. An important point to remember is that once the

parasite begins to migrate within the nervous tissue, damage occurs that is usually irreversible. Although some drugs may kill the

worms, thus pre venting further damage, treatment does not repair nervous tissue. Some animals with mild clinical signs may recover

without treatment. At this time, the best recommendation for treatment is "do no harm." Perhaps some medications are helpful,

however, remember that drugs used at higher-than-usual levels or more frequently than usual may cause toxicity problems.

The best approach to “brain worm” infestation is prevention. This s achieved by keeping the life cycle in mind. Animals kept in

pastures that have wetlands and White-tailed deer should be removed from these pastures in the late summer and until the first hard

freeze. If this is not possible, strategic deworming is the second best approach. This would involve either continuously providing

an anthelmintic in feed or mineral mix throughout the “brain worm” season, or deworming with an oral or injectable product every

10 to 14 days - starting in late summer and continuing through early to mid-winter, depending on the severity of the freezing


The 10- to 14-day schedule recommendation is based on experimental evidence that demonstrated the parasites' ability to reach

the brain and/or spinal cord in this amount of time after an animal eats the snails containing P. tenuis larvae. Thus, this is a "window

of opportunity" to kill the worms before they enter the central nervous system where they may be "safe" or protected from the killing

effect of drugs that cannot cross the blood-brain barrier.

While clinical cases of meningeal worm infestation are rare, “brain worms” could affect your animals if they have access to wetlands

harboring P. tenuis-infected White-tailed deer. Wetlands contain a population of snails and slugs needed to complete the parasite's

life cycle if it is the season when P. tenuis infestation occurs. Remember: the success of treatment is variable - prevention is the best

means of control.

Titre du document / Document title
Characteristics of scrapie isolates derived from hay mites
Auteur(s) / Author(s)
CARP R. I. (1) ; MEEKER H. C. (1) ; RUBENSTEIN R. (1) ; SIGURDARSON S. (2) ; PAPINI M. (1) ; KASCSAK R. J. (1) ; KOZLOWSKI P. B. (3) ; WISNIEWSKI H. M. (3) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Department of Virology, NYS Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, New York, NY 10314-6399, ETATS-UNIS
(2) Department of Veterinary Diagnostics, University of Iceland, Keldur 112 Reykjavik, ISLANDE
(3) Department of Neurobiology, NYS Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, New York, NY 10314-6399, ETATS-UNIS

Résumé / Abstract
Previous epidemiological evidence suggested that in some instances a vector and/or reservoir is involved in the occurrence and spread of transmissible spongiform encephalopathies (TSEs). In a preliminary study, hay mite preparations from five Icelandic farms with a history of scrapie were injected into mice, and some ofthese mice became sick after long incubation periods. To confirm that the disease was scrapie, subsequent passages in mice were performed In addition, the characteristics of the disease process in these passages were assessed and the results compared to those findings with standard scrapie strains. As expected for scrapie, subsequent passages in the same host led to shortened incubation periods compared to those in primary isolate mice, and all mice had spongiform changes in brain. Results were similar for three of four isolates with regard to clinical manifestations, the incubation periods in mice of the three scrapie incubation-period genotypes (s7s7, s7p7, p7p7), and the PrP[Sc] Western blot (WB) pattern. The characteristics of the fourth isolate were markedly different from the other three isolates with regard to these parameters. Comparison of the characteristics of standard mouse-adapted scrapie strains and the four isolates revealed differences; these differences were particularly pronounced for the fourth isolate.
Revue / Journal Title
Journal of neuro virology (J. neurovirology) ISSN 1355-0284
Source / Source
2000, vol. 6, no2, pp. 137-144 (20 ref.)
Langue / Language

Editeur / Publisher
Taylor & Francis, London, ROYAUME-UNI (1995) (Revue)

Mots-clés anglais / English Keywords
Scrapie ; Scrapie agent ; Hay ; Reservoir ; Incubation ; Isolate ; Pathogenesis ; Comparative study ; Animal ; Mouse ; Prion ; Infection ; Rodentia ; Mammalia ; Vertebrata ; Nervous system diseases ; Central nervous system disease ; Cerebral disorder ; Spongiform encephalopathy ; Degenerative disease ;
Mots-clés français / French Keywords
Tremblante ; Agent tremblante ; Foin ; Réservoir ; Incubation ; Isolat ; Pathogénie ; Etude comparative ; Animal ; Souris ; Prion ; Acarien ; Infection ; Rodentia ; Mammalia ; Vertebrata ; Système nerveux pathologie ; Système nerveux central pathologie ; Encéphale pathologie ; Encéphalopathie spongiforme ; Maladie dégénérative ;

002b05c03 ;
Mots-clés espagnols / Spanish Keywords
Tembloroso ; Scrapie agent ; Heno ; Depósito ; Incubación ; Aislado ; Patogenia ; Estudio comparativo ; Animal ; Ratón ; Prión ; Infección ; Rodentia ; Mammalia ; Vertebrata ; Sistema nervioso patología ; Sistema nervosio central patología ; Encéfalo patología ; Encefalopatía espongiforme ; Enfermedad degenerativa ;
Localisation / Location
INIST-CNRS, Cote INIST : 26734, 35400008728405.0050

Copyright 2006 INIST-CNRS. All rights reserved

Toute reproduction ou diffusion même partielle, par quelque procédé ou sur tout support que ce soit, ne pourra être faite sans l'accord préalable écrit de l'INIST-CNRS.
No part of these records may be reproduced of distributed, in any form or by any means, without the prior written permission of INIST-CNRS.

Nº notice refdoc (ud4) : 1361384

The Lancet 1999; 354:1969-1970


Fly larvae and pupae as vectors for scrapie
Karin Post PhD a, Detlev Riesner PhD a, Volker Walldorf PhD b and Heinz Mehlhorn PhD c

We analysed experimental transmissibility of the scrapie agent by natural vectors. A fly, Sacrophaga carnaria, fed with brains of scrapie-infected hamsters in different developmental stages caused scrapie in hamsters after they ate fly extracts.


a. Institut für Physikalische Biologie, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
b. Institut für Parasitologie, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
c. Biologisch-Medizinisches Forschungszentrum, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany

Prions Adhere to Soil Minerals and Remain Infectious
Christopher J. Johnson1,2, Kristen E. Phillips3, Peter T. Schramm3, Debbie McKenzie2, Judd M. Aiken1,2, Joel A. Pedersen3,4*

1 Program in Cellular and Molecular Biology, University of Wisconsin Madison, Madison, Wisconsin, United States of America, 2 Department of Animal Health and Biomedical Sciences, School of Veterinary Medicine, University of Wisconsin Madison, Madison, Wisconsin, United States of America, 3 Molecular and Environmental Toxicology Center, University of Wisconsin Madison, Madison, Wisconsin, United States of America, 4 Department of Soil Science, University of Wisconsin Madison, Madison, Wisconsin, United States of America

An unidentified environmental reservoir of infectivity contributes to the natural transmission of prion diseases (transmissible spongiform encephalopathies [TSEs]) in sheep, deer, and elk. Prion infectivity may enter soil environments via shedding from diseased animals and decomposition of infected carcasses. Burial of TSE-infected cattle, sheep, and deer as a means of disposal has resulted in unintentional introduction of prions into subsurface environments. We examined the potential for soil to serve as a TSE reservoir by studying the interaction of the disease-associated prion protein (PrPSc) with common soil minerals. In this study, we demonstrated substantial PrPSc adsorption to two clay minerals, quartz, and four whole soil samples. We quantified the PrPSc-binding capacities of each mineral. Furthermore, we observed that PrPSc desorbed from montmorillonite clay was cleaved at an N-terminal site and the interaction between PrPSc and Mte was strong, making desorption of the protein difficult. Despite cleavage and avid binding, PrPSc bound to Mte remained infectious. Results from our study suggest that PrPSc released into soil environments may be preserved in a bioavailable form, perpetuating prion disease epizootics and exposing other species to the infectious agent.

full text;

The BSE Inquiry / Statement No 526

Dr Alan Long

Issued 29/09/1999 (not scheduled to give oral evidence)


5. Possible Accessory or Alternative Factors

5.1. We drew analogies from the knowledge of zoonotic diseases as the connection with feed

was developed; accordingly, I wrote a survey in 1989 for the National Food Alliance.

School biology illustrates a familiar example of sequential and cyclic transmission in the

liver fluke (fascioliasis). Malaria offers a useful parallel: spread could be inhibited or

prevented by deterring mosquito attacks, killing the insects, or draining the swamps

where they breed. Any one intervention could break the chain, but the combination of

factors must be disrupted for eradication.

5.2. Tick-borne zoonoses are well-known and are affected by rises and falls of populations

with fluctuations in the weather. Lyme disease (borreliosis) was a tick-borne disease

increasing as BSE waxed; it is a bacterial infection transmitted by the ticks that also

carry a flavivirus causing louping ill, an encephalomyelitis resulting in bizarre behaviour,

in sheep. Could such insects transmit an infectious agent causing spongiform

encephalopathies and thus regulate transmission by their ability to bite their victims (and

inject their cargo of infection into the bloodstream, by-passing the protective

mechanisms of the digestive tract)?


Follow Ups:

Post a Followup

E-mail: (optional)


Optional Link URL:
Link Title:
Optional Image URL: