cankering

[Guest]

hi ive been told i should treat for canker every 6-8 weeks. what dos canker look like ?  ( i dont want to have to treat whats not there) :-/

[madmaxlofts]

Trichomoniasis (pigeon canker) is the most common disease of pigeons. Approximately 80 percent of pigeons are infected with this organism. The organism is a microscopic flagellate classified as a protozoan. Different strains, Trichomonas gallinae or Trichomonas columbae , vary greatly in their ability to cause disease. The disease occurs worldwide in warm climates or during warm weather. It may occur at any time of the year in commercial squab operations. Adult pigeons frequently carry the trichomonads without showing signs of disease. When the adult pigeon is stressed, however, the organisms may multiply profusely. A mild infection can then turn into a serious condition. Stresses include other diseases, parasitic infestations, or overbreeding.

 

Affected pigeons in a loft may cease to feed, become listless and ruffled in appearance, and lose weight before death. Pigeons often have difficulty when closing their mouths because of lesions in the oral cavity. They drool and make repeated swallowing movements. Watery eyes may be apparent in birds with lesions located in the sinuses or tissues around the eyes. Diarrhea, increased water intake, and respiratory distress may be noted. Birds may die suddenly due to suffocation if the lesion blocks the opening of the trachea. The disease becomes more severe in birds that are noticeably emaciated. The thin weakened bird loses the inclination to fly and will "take to the wing" reluctantly.

 

Pigeons that are carriers often transmit trichomonads to their young during feeding. The disease is common in 10- to 24-day-old squabs. As a method of feeding their young, pigeons regurgitate the sloughed, fat laden cells lining the crop (crop milk) into the oral cavity of the squabs. If squabs are infected with only small numbers of the protozoan, they may develop immunity which is maintained by constant low-level exposure. If squabs are infected with large numbers, a severe outbreak may occur and endanger the entire young generation.

 

Lesions of canker are usually most extensive in the mouth, pharynx, or esophagus but may occur at other sites including the crop, proventriculus, or sinuses. The infection is promoted by minor injuries to these tissues. The spelts and awns from grains can easily cause small lesions. The lesions first appear as small, circumscribed, and elevated areas on the surface of the oral mucosa. They may be surrounded by a thin red zone. The lesions may increase in size and coalesce. The build-up of white to yellow/tan caseous material may be sufficiently extensive to partially or completely block the lumen of the esophagus. Organisms may also enter the body through the unhealed navel of squabs. In this form, necrotic tumor-like swellings occur under the skin adjacent to the navel. Lesions can spread to various internal organs, particularly the liver. Large, well-defined, and yellowish areas of hepatic necrosis may be found on necropsy examination.

 

Typical signs and lesions are very suggestive of the disease. Demonstration of large numbers of organisms in the oral fluids is usually considered enough evidence for diagnosis. The small plaques in the mucosa should be differentiated from pox, vitamin-A deficiency, or candidiasis.

 

Since the organism is transmitted from parent to squab, every effort should be made to treat or remove infected birds from the flock. If possible, depopulate at regular intervals and thoroughly clean and disinfect the premises.

 

In addition, the following preventive measures should help: practice a high standard of sanitation at all times; do not add birds to an established flock since they may be carriers (if birds are added, quarantine for 30 days); and provide a source of clean, fresh water eliminating all sources of stagnant water.

 

The antiprotozoal drugs which were used successfully in treating this disease, such as dimetridazole and metronidazole, have been removed from the market. Experimentally, a number of drugs are active against trichomonas infection. Use of 0.1% copper sulfate (100 mg per 100 ml of drinking water), 0.5% hydrochloric acid or 0.02% mercuric chloride (sublimate) is worth investigating. The optimum time to treat breeding pairs is at the initiation of egg production.

 

 

 

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Footnotes

[Guest]

hi, thanks for your reply it is most helpful. one more question as there are a lot of treatments on the market which one would you recommend? ;D

[Wiley]

flagyll or rondizole

[speedy]

i can quite honestly say i have taken mad max comments on canker and pinned them in the loft although your advice was for someone else it has been most interesting and useful so thanks mad

[Guest]

hi ive been told i should treat for canker every 6-8 weeks. what dos canker look like ?  ( i dont want to have to treat whats not there) :-/

 

All pigeons carry canker,worms and cocci,you need to treat for all 3 reguarly,anyone who says they don't treat either has very poor results or is lying,fact.If you look back on some of the threads on here you will find lots of info.

[shalis lofts]

hi can you tell me where you can purchase these products to and are both of them jut for canker or cocci andworms as well i would much apreiciate suggestions and info

        yours in sport shalis lofts : ;D

[little sam]

AS SOON AS THEY ARE WEANED OVER MINE WILL RECIVE IT IN TABLET FORM SO WILL THE OLD BIRDS AFTER THERE SEPERATED THEN WHEN RACING THEY WILL HAVE IT IN THE WATER AFTER EVERY RACE  

[Back garden fancier]

You can buy the products on line, or most corn/pigeon stockists will have them in.

[shalis lofts]

thanks m8 information much appreciated

[Back garden fancier]

See if you can find the thread on Milton, that has some good ideas and is good for canker. It costs pence to use.

[Guest]

if ur lazy ;D then u could get emtryl to put in the water , thats ok for canker.pm me ill tell u where u can get it....paul

[Guest]

 

All pigeons carry canker,worms and cocci,you need to treat for all 3 reguarly,anyone who says they don't treat either has very poor results or is lying,fact.If you look back on some of the threads on here you will find lots of info.

 

Neither Dr Gordon Chalmers nor Dr Colin Walker can be called liars nor can they be said to have poor results.

 

I contacted Gordon Chalmers a long time ago about canker, his reply is the first two para below, and he attached a rather long article about it, which follows his reply:-

 

"Trichomoniasis - there is quite a range of strains, from the very mild to the very deadly. It has been well established that mild strains will protect against more pathogenic strains, which is why I have been reluctant to treat against the condition. My feeling is that I'd prefer to use the hopefully mild strains of the organism present in my birds to deal with any possible introduction of a pathogenic strain. My references, which go back many years, don't discuss the means by which the organism causes disease, but I'd suspect powerful enzymes or toxins at the root of the problem.

 

What do they consume? I don't know but again would suspect local nutrients such as glucose, perhaps even some bacteria. A lot of the answers might be gleaned from studies on the human reproductive trichomonad, as I am not aware of such studies in the organism in pigeons. For your information, I have attached an article that distils a lot of the information in my trichomonas file. "

     

 

Canker:  Strains of the Causative Organism

 

Gordon A Chalmers, DVM Lethbridge, Alberta, Canada. Email:  gacdvm@telus.net

 

An article that I read recently asked if there was a new strain of canker, and it reminded me that there are indeed strains of the canker-causing organism.  Canker is the name of the disease caused by the tiny parasite called Trichomonas gallinae.  It occurred to me then that, as a reply to the question asked by this article, I might present some background information on strains of Trichomonas gallinae, and their importance to all of us.  I have drawn the information in this article from a number of important old and some fairly current scientific papers selected from my files.  Incidentally, in the following material, when I refer to the canker organism, I will likely use the terms "Trichomonas gallinae, T. gallinae (the latter is simply a shortened form of the full scientific name), trichomonad, trichomonas and canker organisms" interchangeably -- all mean the same thing.

 

Infection by this organism was first identified in Europe in 1878 by a researcher named Rivolta.  Many years later in the USA, a scientist named Robert Stabler, conducting research in the state of Colorado, pioneered extensive work on the organism in pigeons -- in fact in 1938, he gave the organism its scientific name, Trichomonas gallinae.  

 

In a 1948 publication on the subject, he noted that not all pigeons that harbour the organism die of the infection, or even have internal changes to indicate the presence of this organism.  As well, he found that youngsters from some parents in a loft nearly always died of canker in a few days or weeks after hatching, whereas certain other parents, although infected, raised healthy youngsters indefinitely.  Obviously these facts gave rise to the idea that there were strains with differing abilities to cause disease, a suggestion that had also been proposed by other scientists who had worked on canker in pigeons.

 

To test this idea, Dr Stabler then set up an experiment in which he used canker organisms that he arbitrarily designated as "strains" (see explanation in the next paragraph), from five different sources:  Strain 1 from an infected wild youngster, Strain 2 from a healthy adult King (a meat variety of pigeon), Strain 3 from a healthy adult Carneaux (a meat variety of pigeon), Strain 4 from an adult racing pigeon that had a history of transmitting lethal canker to his youngsters and to at least three successive hens, and Strain 5 from the mouth of a peregrine falcon that had died with severe canker of the mouth.  (Note that canker caused by T. gallinae occurs in birds of prey in which it is called "frounce".  Broadly related organisms in this group also cause infections, variously, in the reproductive systems of humans, cattle, and sheep, and in the digestive tracts of domestic chickens and turkeys.  I have also seen it in devastating outbreak form in small aviary finches in which the disease very much resembled that seen in the oral cavity of young pigeons.)  

 

Dr Stabler defined "strain" as the particular canker organisms removed from the mouth of an individual bird, even though he recognised the possibility that any given bird might harbour more than one strain.  The results he obtained seemed to justify the use of the organisms from a particular bird as "a strain", at least in terms of their ability to cause disease.  He maintained the five individual strains mentioned previously by inoculating them by eyedropper into the mouths of clean pigeons, and took great care to be sure that the different strains weren't accidentally mixed.  The clean pigeons he infected with these five strains came from his own loft of racing pigeons that he knew were free of canker-causing organisms.  

 

In the first experiment, he used 25 of his own young birds, aged 6 weeks, 5 1/2 weeks, 5 1/2 months, 7 months, and 9 months, with five birds in each group.  One bird in each age group was inoculated by mouth with Strain 1, one in each group received Strain 2, and so on.  Results showed that the Strains 1, 4, and 5 caused severe signs of disease that ended in the death of all except two youngsters, a 7 and a 9-month-old bird infected with the Strain 4.  These two birds had severe canker for over a week, but they recovered.  Strains 2 and 3 either didn't produce signs of disease in the youngsters they infected, or the infection was very slight and lasted only 2-4 days.  

 

In follow-up work, Dr Stabler showed that Strain 1 (which became known in trichomonad circles as his famous "Jones' Barn" strain) obtained from the wild youngster with canker, was the most deadly of the five strains, killing 12 of 13 birds inoculated with it in an average of 10.6 days.  Over all, he was able to show that, of 119 pigeons infected successively with this potent strain, 114 (95.8%) died in 4 to 18 days.  In later work, he showed that Strain 1 was deadly even if only one organism was placed in the mouths of susceptible pigeons.  Obviously, this single organism multiplied rapidly into the thousands or more to cause serious illness.

 

These results showed that there was a marked difference in the ability of these five different strains of T. gallinae to cause disease in pigeons.  These strains varied from those that caused little or no disease to those that caused high losses.  Obviously, there were also strains that were intermediate in their ability to cause canker, since they were able to cause serious illness from which most birds eventually recovered.

 

In important later studies, Dr Stabler was able to show that mild strains of the canker organism were able to protect birds against more deadly strains, a finding that continues to have practical application today.  To confirm these results, he first gave eight of his own trichomonas-free youngsters the relatively potent Strain 5 obtained from the peregrine falcon.  All developed severe canker of the mouth, six birds recovered and two died.  Fifty-four days after the initial infection with Strain 5, the six survivors were given the very deadly Strain 1.  None of them developed evidence of disease during the following month.  These six birds were then killed and examined at post mortem.  There was evidence of scarring of the liver of three birds, findings that suggested infection from the previous dose of organisms.  The other three birds were almost completely free of signs of infection.  The only significant finding in these birds was the loss of the palatal fringe on the roof of the mouth.  (Dr Stabler believed that, in every case examined, this change was highly characteristic of evidence that the canker organism was the cause.)  

 

He then repeated this experiment with eight more clean youngsters that were first given the mild Strain 3 from the adult Carneaux.  Only two youngsters developed a mild form of the disease.  About a month later, all eight birds were given the deadly Strain 1.  In the next three weeks, only two of the eight birds developed signs of canker.  One had a mild form of the disease, and the other had a severe form from which it eventually recovered.

 

Post mortem examinations of these eight birds determined that tissues of seven birds were completely normal, and that the bird that developed severe canker had severe changes of canker in the liver.  At the same time, as a control, Dr Stabler inoculated 13 youngsters from his own loft of trichomonas-free birds with deadly Strain 1; 12 of the 13 birds died.  Thus, these experiments demonstrated that infection by a mild strain of T. gallinae conferred protection against a more deadly strain of the organism.  However, the duration of that immunity wasn't determined at that time.

 

During the spring, summer and fall of 1950, there was a major outbreak of canker in wild mourning doves across much of the southern USA, with the greatest losses apparently in the state of Alabama where it was estimated that deaths might well run into the thousands in that state.  Dr Stabler obtained strains of trichomonads from several sources of these doves to see if the organisms from these doves could cause illness in pigeons.  He inoculated 50,000-100,000 organisms from different doves, into each of five pigeons from his clean colony.  For comparison, he inoculated only 3,000-10,000 organisms of his deadly Jones' Barn strain into another five clean pigeons, all of which subsequently died of canker of the liver.  The most deadly of the strains from the doves came from a bird collected in Alabama, and like the Jones' barn strain, this one proved to be equally deadly, killing all but one of the pigeons inoculated with it.   The other four strains obtained from the doves proved to be relatively mild when inoculated into pigeons, as most of these pigeons survived the infection.

 

The next question to resolve was this:  would pigeons that survived the infections with mild strains obtained from doves, be able to withstand infection by the deadly Jones' barn strain?  To test this idea, Dr Stabler inoculated all of these survivors with the Jones' barn strain.  The result was that all birds inoculated with the Jones' barn strain survived, findings that indicated good protection following infection with strains from the doves.  Did the fact that these birds survived mean that 1) the strains derived from doves had killed off the deadly Jones' barn strain, or 2) was the Jones' barn strain still present in these surviving birds, and if so, was it now altered so that it was now a mild strain, or 3) was the Jones' barn strain as powerful as ever for clean birds, but unable to cause illness in protected birds??

To test these ideas, Dr Stabler collected canker organisms from birds that had a combination of a mild strain and the deadly Jones' barn strain, and inoculated these organisms into clean pigeons.  The results were variable, as some of the newly infected clean birds had only mild changes of canker, whereas other birds either died of severe canker, or almost died.  These results indicated that the deadly Jones' barn strain continued to be present, and equally important, was as potent as ever.  Over all, of 13 birds infected, six died outright, one barely survived, and six had mild cases of canker.  Incidentally, Dr Stabler reported that the Jones' barn strain typically caused the most severe disease in the liver of infected birds, whereas milder strains produced only oral infections.

 

Although the procedure isn't too practical for us as pigeon fanciers, Dr Richard Kocan, working in the USA, found that blood plasma from pigeons infected with even a mild strain of T. gallinae could protect other pigeons infected with a deadly strain of the organism.  Much more practically, Dr Kocan was also able to demonstrate that previously infected pigeons that had been treated with the formerly used anti-canker drug Enheptin, were free of the organism for as long as 16 months, yet remained immune to infection when they were inoculated with deadly strains.  On this point, some of his other work showed that 172 of 313 wild pigeons and 54 of 66 mourning doves (all of the mourning doves captured were completely free of the canker organism) -- all trapped in his area, were resistant to the deadly Jones' barn strain.  His conclusions:  recovery from an infection with T. gallinae, even when the birds eventually completely eliminate the organism from their systems, results in long-term immunity to this parasite -- a fact that is of great importance to us as pigeon fanciers, one that we can use to advantage, especially in these days of apparent resistance by this organism to some of our modern, previously useful drugs.

 

The subject of drug resistance by the canker organism to modern drugs is also of major current importance to us.  Almost 10 years ago, in 1990, Drs Lumeij and Zwijnenberg of Utrecht University, Holland, demonstrated the fact that canker organisms recovered from a large flock of pigeons in that country, were uniformly resistant to all of our commonly used modern drugs -- Emtryl, Ridzol, Spartrix and Flagyl.  On the basis of that information, it seems likely that canker organisms in many other untested flocks of pigeons in Holland and indeed throughout Europe, and other countries, could have been similarly resistant at that time, likely, as these researchers pointed out, because of the common practice among fanciers, of continually under-dosing birds with these drugs.  

 

On the subject of under-dosing, especially with Emtryl, I find in my travels in the USA and Canada, that the dosage of the 40% water-soluble Emtryl, as recommended by several pigeon supply houses in North America is far below that recommended for pigeons by the producer of the drug.  (At one time, this company sold small 3-gram packets of Emtryl, the exact dosage for one Imperial gallon - 4.55 litres).  The fact that Emtryl is being recommended today at much lower dosages could certainly contribute to the problem of drug resistance mentioned in the previous paragraph, and may be a developing problem with major far-reaching consequences for us.  I would remind fanciers that the correct dosage of Emtryl for pigeons, as recommended by the company, is 3 grams (or one level teaspoon) per imperial gallon (4.55 litres) of drinking water for 5-7 days.  For the smaller US gallon (4 litres), this is about 3/4 teaspoon per gallon for the same treatment period.  

 

To avoid the problems of toxicity if birds drink excessive amounts of water especially during hot weather, try an Australian method that I know works well.  Make up the correct dosage of Emtryl and place it in front of the birds at, say, the evening feeding for a couple of hours or so.  After this time, throw out the medicated water and replace it with fresh water until the next evening.  Repeat the correct dosage for a couple of hours or so each evening for a total of 5-7 days.  This method insures firstly, that birds receive the correct therapeutic dose each day for the treatment period, and secondly, that problems with toxicity can be largely avoided.  It is important not to treat with Emtryl or other drugs of the same family during the pairing up period, because there is some suggestion that the drug can interfere with fertility.  It is also a good idea to change drugs each time you feel birds need to be treated, say, Emtryl for one 5-7 day treatment period, and another appropriate for the next one, etc., all at the correct dosage.

 

On the subject of canker and treatments, some fanciers subscribe to the idea that if it's not broken, don't fix it.  Dr Colin Walker, the Australian veterinarian who has written many excellent articles for racing pigeon magazines, seems to accept this idea.  In one of his books, he states that drugs alone will never control a canker problem.  He feels that it is important to allow developing youngsters enough exposure to the organism that they can develop natural resistance -- my idea for many years as well, based on the work of Dr Stabler.  

 

Dr Walker expands on this idea by stating that if birds in the stock loft (and presumably their youngsters) did not develop canker the previous year, no treatment is needed this year.  However, if canker did occur in stock birds and their youngsters last year, birds should be treated this year with a suitable drug prior to mating, and for two days every week after that.  Further, he suggests co-ordinating these two-day treatments with the hatching period when trichomonad shedding is the highest.  If the occasional youngster still develops canker, he recommends treating the parents and both youngsters in the nest with Spartrix or Flagyl for three days.  (Incidentally, some veterinary writers in the USA have some legitimate concerns about short periods of treatment because of the risks of resistance by the canker organism to these drugs.) Dr Walker also recommends avoiding the treatment of breeding pairs whose youngsters don't develop canker, so that there is no interference in the development of natural resistance, an idea that makes a great deal of sense to me.  

 

Speaking of natural resistance, I recall that when I worked in New Zealand during the early 1980s, a medical doctor there raced pigeons, but apparently didn't treat his birds for any disease.  Instead he preferred to rely on the development of natural resistance to any virus, bacteria or parasite his birds might encounter.  

 

For the past several years, I haven't used preventive canker treatments on any of my old or young birds, and touch wood(!), so far there hasn't been a detectable problem.  It is probable that the natural resistance developed in these birds by repeated exposure to the strains of canker organisms that very likely reside in my birds has (to date) been holding the disease at bay.  Based on information from Dr David Marx, one of the top pigeon veterinarians in the USA, I have also been examining the mouths of my birds during the racing season for evidence of reddening and excess stringy mucus, findings that could suggest multiplication of canker organisms and increased irritation of the oral cavity during this stressful time.  So far, on the basis of finding clean, pink throats, I haven't felt a need to treat preventively during the racing season, although it is possible that deeper areas such as the crop, which I didn't examine, may have been affected.  I acknowledge the possibility, however, that if I had treated periodically for canker in spite of these normal findings, some racing performances might have improved.  As far as canker is concerned, the idea "if it's not broken, don't fix it" seems to be working in my loft.  If things change for the worst, I am ready to treat if I have to.

 

I hope that this look at the historical background of strains may stimulate thought on this subject among fanciers.  As the risk of drug resistance by canker organisms (and other agents as well) increases steadily, I hope that fanciers may be better able to assess the facts surrounding natural immunity, and to use these facts to their advantage by recognising the biological benefits of using any mild strains of canker organisms that reside in their birds as a major defence against deadly strains.  In saying this, I also recognise the need to treat birds when or if the disease occurs.  A combination of judicious treatment when necessary, plus strategies to allow for the development of natural resistance may well be the best approach.  I also hope that information on the correct dosage of Emtryl -- and by extension, other drugs as well -- may help to reverse the trend of vastly underdosing our birds with these products.  

 

  

[Guest]

glad you answered that one bruno cause i couldnt be bothered to write all that down  ;D ;D ;D

[Guest malonebros]

hi all

what advice would you give on a bird that has a bad case of canker.ive tried a canker formula from a good vet but it aint working.

ive had a swab down its throat to clear some of the yellow cheese like substance.

[majorpet]

hi all

what advice would you give on a bird that has a bad case of canker.ive tried a canker formula from a good vet but it aint working.

ive had a swab down its throat to clear some of the yellow cheese like substance.

 

IN MY OPINION I WOULDNT PERSEVERE WITH IT.

 

MAJORPET

[Guest]

 

IN MY OPINION I WOULDNT PERSEVERE WITH IT.

 

MAJORPET

 

I agree. Sorry, this is a danger to your other pigeons and isn't something you want in your loft - either the disease or a bird that can't cope with it / succumbed to it. Also you may have misdiagnosed the problem, but the correct way to solve it is to cull the bird, and clean and disinfect.

[Guest]

glad you answered that one bruno cause i couldnt be bothered to write all that down  ;D ;D ;D

 

A simple cut & paste job, Sammy.  8)

 

That's one of the things I like about electronic documents, they're so easily copied.

[Mike Lycett]

Canker lives & breeds in the crop - hence most the time you can't see it

 

The yellow cheesey form is excessive and deep rooted

 

A standard canker treatment OUGHT to shift it - if it doesn't I'd said there was something fundamentally wrong with pigeon - assuming you're using the product correctly

[Guest Greig the doo Drysdale]

 

All pigeons carry canker,worms and cocci,you need to treat for all 3 reguarly,anyone who says they don't treat either has very poor results or is lying,fact.If you look back on some of the threads on here you will find lots of info.

 

I dont treat for any and my results were the best in my club all young bird season last year and all old bird this year just check out pumpherston and district in the results section of this web site

[Guest]

Although this is 'Novices, Beginners & Young Fanciers' section, I think we as animal owners all get bombarded from time to time with statements like all pigeons, all dogs, all cats, have some or other parasite and should be treated 'regularly' for them. For example was in pet shop other week and shelves full of wormers for dogs and cats, and big sales signs 'use every 3 months'.

 

Well nobody can say with any authority that all 'anything' carries a parasite, and the same goes with pigeons. I have never treated my birds for worms and I know for a fact that they have none, because a recent dropping test has confirmed that. So anybody that says all pigeons have worms is wrong.

 

But there is statistical information on 'parasite & host' which also suggests that what we are being fed is a load of tosh - all animals aren't riddled with parasites as has been inferred - 70% of total pigeon parasite population can be found in 15% of the total pigeon population. So 85% of pigeons are either free from parasites, or have a very light burden.

 

http://www.aber.ac.uk/parasitology/Edu/ModelPar/ModelTxt.html

 

The Frequency Distribution of parasites in host populations

 

Or how parasites are distributed between different hosts in a population. There are three possibilities, random, regular (under dispersed) or clumped (over dispersed). If parasites are randomly dispersed, when you sample hosts you would find that the number of parasites per host follows a Poisson distribution. If the parasites were evenly distributed amongst their hosts, the number per host would follow a normal distribution. Finally if the parasites were clumped, sampling would give a negative binomial distribution (skewed). Most parasites show this last type of distribution and are over dispersed.

 

What this means is that you get more hosts than expected by chance with none or only a few parasites, but also more hosts with a lot of parasites. So most of the parasite population is present in relatively few hosts (70% of the parasite burden is typically found in 15% of the hosts). Parasites are not evenly distributed throughout the host population, and you get some individuals who are much more heavily infected than others. In control campaigns if you could identify those individuals that are heavily infected, you could target your chemotherapy more efficiently.

 

The factors that generate an over dispersed population of parasites in hosts can be divided into two sorts, density independent factors (ie do not depend on parasite numbers) and density dependent factors (ie depend on parasite numbers).

 

Density independent factors include:

i.     Genetic variation in the hosts, some hosts are more susceptible to infection than others.

ii.     Host behaviour, this may effect the degree of exposure of different individuals to infection.

iii.     Heterogenous environment, parasite transmission may be restricted to foci.

 

Density dependent factors are:

i.     Host immune response, the intensity of which can depend on parasite density.

ii.     Competition, both homospecific and heterospecific for nutrients and/or space can result in crowding effects, which affect growth rates and fecundity. Crowding effects have been noted in nematodes, digeneans, cestodes and acanthocephalans. A general observation is that worms from high-density infections are smaller and produce fewer eggs than worms from low density infections.

iii.     The level at which parasites start to kill their hosts. The importance of lethal levels in determining parasite population structure has been hotly debated, as has the importance of parasites in regulating host populations.