Non-Core Vaccines

 When veterinary bodies announced that we don’t need to vaccinate annually, I was overjoyed, believing that this would vastly reduce the number of life-threatening vaccine reactions visited upon dogs.  Then I realised that, so long as pet owners are persuaded to over-use the ‘non-core’ vaccines, annual vaccination simply won’t go away, and neither will vaccine adverse events.

The World Small Animal Veterinary Association has split canine vaccines into three groups, namely ‘core’, ‘non-core’, and ‘not recommended’.  Vaccines for the core viral diseases – distemper, parvovirus and adenovirus/hepatitis – provoke long-term, and potentially lifelong, immunity, so annual shots are out (or should be).    

My analysis of the non-core vaccines is that they have been designated non-core for three reasons.  One is that they don’t work.  Two is that they are dangerous.  Three is that it’s hard to justify recommending these vaccines in the light of one and two.  Looking at the non-core vaccines, I personally believe they should be on the ‘not recommended’ list – if only to remove them as an excuse to vaccinate dogs annually as is currently happening.  I would, incidentally, have no problem with annual shots of any type if there weren’t serious safety concerns. 

Unfortunately, important caveats in the WSAVA guidelines are being ignored, namely that non-core vaccines are “those that are required by only those animals whose geographical location, local environment or lifestyle places them at risk of contracting specific infections.”  The WSAVA also advises that “the practitioner should obtain informed client consent to provide that client, and the animal, with a current evidence-based vaccination schedule.”  There is no informed consent, and there no evidence to support these vaccines.    

So let’s look at the non-core vaccines and the issues surrounding them. 

Leptospirosis

Leptospirosis is a zoonotic disease, which means that it can be transmitted to humans.  It is present around the world, but is most likely to cause problems in places that lack adequate sanitation, in tropical climates, in flood areas, amongst farm workers, and amongst people who spend time in water, either for work or leisure.  The majority of dogs with known leptospirosis have been found to be without symptoms – they live with it without getting ill. 

This isn’t to say that leptospirosis can’t cause illness in dogs.  In some cases lepto can be fatal.  However, in the 1996 Canine Health Concern vaccine survey 100% of dogs with leptospirosis had been vaccinated within three months prior to infection.  This can only be because a) the vaccine caused the disease, or b) the vaccine didn’t contain the serovar that caused the illness, or c) the vaccine contained a non-local serovar that the dog hadn’t adapted to, or d) it just didn’t work. 

Despite being zoonotic and theoretically a notifiable disease, I have – after extensive research – been unable to find any public recording system for leptospirosis incidence in the UK for dogs or humans.  Leptospirosis used to be a reportable disease in the United States, but it was removed from the national CDC list, although it is reportable in some states, most notably Hawaii.  This would indicate that it’s not that much of a problem in most places. 

If your vet recommends a lepto shot, you need to ask him two questions.  The first is whether he has seen a case of lepto in the last, say, six months (i.e., is the vaccine necessary?).  The second is which serovar is involved, and is that serovar in the vaccine?  For if it’s not, the vaccine won’t help.  There are over 200 versions of leptospirosis and vaccination against one form will not provide protection against the others.     

The WSAVA VGG states that “the leptospirosis vaccine is the one least likely to provide adequate and prolonged protection, and therefore must be administered annually or more often for animals at high risk. Protection against infection with different serovars is variable. This product is associated with the greatest number of adverse reactions to any vaccine. In particular, veterinarians are advised of reports of acute anaphylaxis in toy breeds following administration of leptospirosis vaccines. Routine vaccination of toy breeds should only be considered in dogs known to have a very high risk of exposure.”

If you take time to understand the above advice from the VGG, you would have to conclude that the vaccine doesn’t work and is dangerous, but that the door is left open to give it annually or more frequently.  I don’t support this logic, and can’t help but speculate whether there have been heated discussions between VGG experts and the VGG’s vaccine industry sponsors before the lepto vaccine made it to the ‘non-core’ list.  If something doesn’t work and is dangerous, why  keep doing it?  It makes less sense when you know that leptospirosis, if diagnosed and treated, responds well to antibiotics and it can be treated prophylactically with antibiotics in outbreak areas.  If you use holistic therapies, there is also good evidence to support the leptospirosis nosode, and anti-bacterial herbal products.  There are alternatives to this useless, dangerous, vaccine. 

The WSAVA VGG states, “In the USA, the four serovars responsible for most, if not all, cases of leptospirosis are canicola, icterohaemorrhagiae, pomona and grippotyphosa. Therefore, the four component product is recommended. In many other countries there is insufficient knowledge of which serovars are circulating in the canine population. The VGG would encourage collection of such data.”

No-one seems to know what they’re vaccinating against outside the US!  So if you’re anywhere else in the world, the leptospirosis vaccine can provoke a serious adverse reaction, but might not even cover the serovar that may, or may not, be a threat to your dog in your local area.  Even in the US, if a dog is exposed to a version of lepto that isn’t in the vaccine, then he’s not protected. 

The VGG adds:  “Leptospira vaccines provide short-term immunity (e.g. 3–12 months) and the efficacy is often less than 70%. Also Leptospira products often prevent clinical disease but fail to protect against infection and shedding of the bacteria, especially when infection occurs more than 6 months after vaccination. The immunity among the serovars varies and immunity varies among vaccinated dogs. Persistence of antibody after vaccination will often be only a few months and immunological memory for protective immunity is short (e.g. 1 year or less). Thus, revaccination may be required as often as every 6–9 months for dogs at high risk.”

So it doesn’t protect a third of dogs; it might not protect any if the form of lepto in your area is different to the form in the vaccine; an annually vaccinated dog can be unprotected for up to nine months of the year; and infected dogs – irrespective of vaccination – are hidden infective reservoirs, capable of spreading lepto to humans and other animals.  And yet – despite all this – leptospirosis is still a very rare disease in most parts of the world.  There are virtually no records of dogs passing lepto onto humans, and we don’t hear of dogs with lepto often. 

Commercial vaccines against leptospirosis in humans have been produced in France and Cuba. However, these vaccines do not induce long-term protection against infection and do not provide cross-protective immunity against heterogenous leptospiral serovars.  No human vaccine is currently available in the United States or the UK.  Why, do you think?

The Lancet, Infectious Diseases Vol 3 December 2003 might explain why:   

”Several problems confront the development of a vaccine to prevent human leptospirosis. First, an unacceptable side effect profile of killed bacterial vaccines has often been reported. Second, the killed bacteria vaccines are likely to provide only short-term and possibly incomplete protection, similar to that reported with anti-leptospiral vaccines in animals. Third, the locally varying patterns of Leptospira transmitted may preclude the development of a suitably generalisable vaccine. Fourth, there is theoretical potential for inducing autoimmune disease such as uveitis and, lastly, there is incomplete knowledge of mechanisms of protective immunity against leptospiral infection.”

The Lancet also stated:  “Vaccination of animals such as dogs or cattle may prevent illness but not leptospiruria and hence transmission to human beings.” 

Scientists have been trying to develop a human leptospirosis vaccine for decades – one that is safe and effective and which governments will license around the world.  They have failed.  But a dangerous, ineffective, substandard canine vaccine is out there, and will remain out there until pet owners educate themselves of the risks. 

What is the leptospirosis vaccine doing on the WSAVA non-core list?  It has no place there.  It should be on the ‘not recommended’ list.  Leptospirosis is not even a vaccinatable disease, and the vaccine can kill!   

 Ask Alison Lovell what she thinks of this vaccine.  Her beautiful GSD puppy was a perfectly normal little man the day before she was persuaded to give him the lepto shot.  The day after he was brain dead, and the week after he was literally dead.

Ask Sue and Zoe Lewsley whose Champion Doberman, Tommy, experienced inflammation in his entire body after a lepto shot.  Tommy was screaming in pain and couldn’t move.  Within three months, despite extensive veterinary support, the nerve damage in Tommy’s body was so severe that he had to be legally killed.  An adverse vaccine event report was filed by Tommy’s vet.  Please note that neither a GSD nor a Doberman is a toy breed.  

Lyme disease

As with leptospirosis, Lyme disease is also caused by a bacteria, but is transmitted through tick bites.  Lyme disease exists in most states in America, but is rare here in the UK.  As with leptospirosis, not all dogs who test positive for Lyme disease suffer symptoms, and the disease can be treated with antibiotics or good holistic care. 

The society of veterinary internists, the ACVIM, stated in 2005, The ACVIM diplomates believe the use of Lyme vaccines is still controversial and most do not administer them.”  Neither do the American veterinary schools recommend the Lyme vaccine. 

Cornell University found long-term side effects from the Lyme vaccine.  Dr Patricia Jordan writes: “In some cases, dogs develop Lyme disease despite the vaccine, or maybe because of the vaccine. Research dogs develop all the symptoms of Lyme disease up to six weeks after receiving the shot, while tests for the Lyme disease bacteria show up as negative. Left untreated more concerning issues develop.”

“Cornell University’s School of Veterinary Medicine researchers suspect long-term side effects are associated with the Lyme disease vaccine for dogs, but nothing definitive has been documented or exhaustively studied”, says Allen Schoen, a doctor of veterinary medicine in Sherman, Connecticut. “These side effects may vary from rheumatoid arthritis and all the major symptoms of Lyme disease to acute kidney failure.”

There is some controversy about how long a tick must be on your dog before it injects the Borellia bacterin that causes Lyme disease into him.  Some say five hours, others say up to 70 hours.  Therefore the safest and most effective ‘vaccine’ would be to inspect your dogs daily and remove ticks before they attach, or as quickly as possible.  Other preventative measures include keeping your lawn short, not feeding wildlife near your garden, and using tick preventatives.  Diatomaceous Earth, Neem and household vinegar can be effective.

Given the evidence, it is difficult to imagine why the Lyme vaccine is on the WSAVA VGG non-core list rather than the ‘not recommended’ list.   

Kennel Cough Vaccines

Kennel cough is caused by a variety of agents including – but not limited to – parainfluenza virus, adenovirus, and the Bordetella bronchiseptica bacterin.  The WSAVA informs us that, “it is important to realize that not all members of the Kennel Cough complex have a vaccine. Also, because Kennel Cough is a localized infection (meaning it is local to the respiratory tract), it is an infection that does not lend itself to prevention by vaccination. Vaccination must be regularly boosted and often vaccination simply muffles the severity of infection without completely preventing it.”

Putting this is plain English, the WSAVA VGG seems to be saying that kennel cough vaccines don’t work, or that kennel cough is not a vaccinatable disease. 

Most combination canine vaccines contain injectable parainfluenza as well as adenovirus, expressed as ‘DHPPi = (D) Distemper, (H) Hepatitis/adenovirus, (P) Parvovirus and (Pi) Parainfluenza. 

The Bordetella bronchiseptica vaccine is a live avirulent bacteria, given up the nose.  It is generally combined with intranasal parainfluenza. The WSAVA advises that, “the Bordetella vaccine may promote transient (3–10 days) coughing and sneezing, and nasal discharge may occur in a small percentage of vaccinates”.  The implication of this, and the evidence suggests, that kennel cough vaccines cause kennel cough outbreaks.    

B. bronchiseptica is closely related to B. pertussis which causes whooping cough in humans.  Datasheets warn that vaccinated dogs can spread B. bronchiseptica for up to six weeks following vaccination, and that immunocompromised humans should avoid contact with vaccinated dogs for up to six weeks.  Although thought to be rare, this vaccine can actually give vulnerable humans a life-threatening infection.

B. bronchiseptica has also been associated in humans with endocarditis (inflammation of heart lining), peritonitis (inflammation of the lining of the abdomen), meningitis (inflammation of the linings of the brain and spinal cord) and wound infections. In some cases, a direct connection to animals is obvious.

As stated earlier, apart from the ability to infect humans, one dog vaccinated against B. bronchiseptica has the ability to infect many dogs.  Christine Sandiford of the Hazel Corner Boarding Kennels was quoted in Kennel and Cattery News:  “For the last 3 to 4 years, I have insisted that kennel cough vaccines be done a minimum of a month before dogs come into the kennels.  We have had no kennel cough outbreaks since we introduced this policy.”

Pam Gee of Daisybank Kennels said:  “Our experience has been that kennel cough outbreaks often originate from dogs that have been recently vaccinated.  Therefore ten years ago we began to advise our clients that they should not have their dogs vaccinated less than six weeks prior to them entering the kennels.”

Alison Hunt of the Tor View Kennels wrote to me this morning saying,  “We have just had a kennel cough case, meaning our workload goes into overdrive to isolate /disinfect even more. I’ve now found out that her owners were persuaded to have ‘up the nose’ drops on the 4th.  The bitch came to us 16th, and started it all on 26th.

“You can imagine the explanations and advice we’ve had to give to every other owner.  It’s very time consuming.  Hopefully we have controlled things, cordoning off areas, the staff spraying themselves, and so on.  We’re taking a mass of precautions.  Thankfully we’ve only had two cases, which we’ve been treating.  We’ve also given the kennel cough nosode to every incomer.”

Although kennel cough is not a serious disease for the majority of dogs, it is a serious disease for kennel owners.  Their reputation and livelihood can be irrevocably damaged by vaccine-induced kennel cough outbreaks. 

In its Guidelines document, the WSAVA states,Although the development of an adverse reaction is often dependent on the genetics of the animal … certain vaccines have a higher likelihood of producing adverse reactions, especially reactions caused by Type I hypersensitivity. For example, bacterins (killed bacterial vaccines), such as Leptospira, Bordetella [kennel cough], Borrelia [Lyme] and Chlamydophila are more likely to cause these adverse reactions than MLV viral vaccines.”

Type I hypersensitivity reactions involve an immune mediated reaction that releases potent inflammatory mediators and other chemicals that trigger an anaphylactic reaction in the affected animal. The reactions are usually acute, with the clinical signs appearing within minutes or hours of vaccination. Typical signs reported are facial oedema, shock, lethargy, respiratory distress and diarrhoea. Severe anaphylactic reactions may result in death. Urticaria (hives), facial oedema and anaphylactic shock are specific clinical manifestations of Type I hypersensitivities.

Ann wrote to me to tell me what happened to her dog Yogi, when he received a kennel cough vaccine.  On the night of the vaccine he was lethargic and quiet, hiding out in his kennel.  The next day he was struggling to breathe and panicking, and an x-ray revealed an inflamed and collapsed wind pipe.  A battery of tests costing £2,500 revealed no known cause, although the vaccine manufacturer offered £1,000 towards the bill.  Ann told them where to stick their offer, feeling that they should be held responsible for the entire bill. 

Once again, there is compelling evidence to suggest that kennel cough vaccines should be on the VGG ‘not recommended’ list.  Kennel cough is a transient disease and the vaccine causes outbreaks and risks more serious adverse reactions.  The only positive benefit for its existence is that it keeps booster income flowing.    

References

1. Gomez, L. et al. 1998. Bacterial pneumonia due to Bordetella      bronchiseptica in a patient with acute leukemia. Clin. Infect. Dis.      26:1002-1003.

2. Gueirard, P. et al. 1995. Human Bordetella bronchiseptica      infection related to contact with infected animals: persistence of      bacteria in host. J. Clin. Microbiol. 33:2002-2006.

3. Re, V.L. et al. 2001. Infected branchial cleft cyst due to Bordetella      bronchiseptica in an immunocompetent patient. J. Clin. Microbiol.      39:4210-4212.

4. Sastre, J. et al. 1991. Pneumonia due to Bordetella      bronchiseptica in a patient with AIDS. Rev. Infect. Dis. 13:1250-1251.

5. Tamion, F. et al. 1996. Bordetella bronchiseptica      pneumonia with shock in an immunocompetent patient. Scand. J. Infect. Dis.      28:197-198.

6. Viejo, G. et al. 2002. Bordetella bronchiseptica      pleural infection in a patient with AIDS. Scand. J. Infect. Dis.      34:628-629.

7. Wallet, F. et al. 2002. Pneumonia due to Bordetella      bronchiseptica in a cystic fibrosis patient: 16S rRNA sequencing for      diagnosis confirmation. J. Clin. Microbiol. 40:2300-2301.

8. Woolfrey, B.F. et al. 1991. Human infections associated with      Bordetella bronchiseptica. Clin. Microbiol. Rev. 4:243-255.

 

 

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Understanding Bordetella bronchiseptica vaccines

Bordetella is a family of closely related bacterins which include Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica. Pertussis and Parapertussis can cause whooping cough in humans. It’s also accepted that Bordetella bronchiseptica (kennel cough) can infect humans.

As its name suggests, kennel cough causes dogs to cough and it’s usually picked up from kennel environments, or from places where dogs are crowded together. This is what they would like you to believe, anyway – but the reality is that the vaccine itself is a source of infection. It’s also possible that when a human is diagnosed with whooping cough, they actually have kennel cough.

An inconvenient but rarely life-threatening disease in dogs

I took the following description of kennel cough from a typical veterinary practice – http://www.vetstream.co.uk: “Most dogs are not really unwell when they have the disease although occasionally they have a high temperature and are a bit ‘out of sorts’ for a day or two. The cough is dry and hacking and it often sounds as if your dog is choking on something stuck in his throat. The cough gets worse for a few days and then gradually goes away after about three weeks.

“Most dogs recover quickly from kennel cough. A young, otherwise healthy dog, should not be unwell with the disease and the cough should get better within 2-3 weeks. Very young or old dogs and dogs with other diseases may be much more severely affected by kennel cough. It would be very unusual indeed for a dog to die as a direct result of catching kennel cough.”

So vets think that kennel cough is not that big of a deal for dogs.

My three elderly previously-vaccinated dogs contracted kennel cough once and survived it; my two nine-month-old pups, who were being given nosodes, didn’t sneeze once – despite nose-to-nose contact. Just thought I’d throw that in!

The vaccine isn’t that great

Because B. pertussis and B. bronchiseptica are so closely related, a group of scientists seeking to understand why there has been a resurgence of whooping cough in vaccinated people used B. bronchiseptica and mice as their model. They found that natural infection induced protection in both the lungs and upper respiratory tract, whereas vaccines conferred protection only in the lungs. The authors suggested that naturally-induced protection is more effective than vaccine-induced protection, and that natural infection could prevent subsequent infections, whereas current vaccines cannot.

It seems that it would be better to let your normal healthy adult dog ‘risk’ contracting kennel cough and get over it, because nature provides better protection than the vaccine.

Most B. bronchiseptica vaccines also come with the parainfluenza virus, both of which are squirted up a dog’s nose. Vaccine company datasheets advise that, “mild discharges from the eyes and nose can occur from the day after vaccination, sometimes accompanied by sneezing and coughing. In some cases, this may persist for up to four weeks”. The datasheets add that antibiotics need to be given to dogs showing severe signs of vaccine-induced kennel cough. Additionally: “Cats, pigs and unvaccinated dogs may react to the vaccine strains with mild and transient respiratory signs.”

So, although kennel cough isn’t that big of a deal, vaccine manufacturers warn in their datasheets that a dog who has been given this vaccine can get a mild case of kennel cough. Vaccinated dogs can also can ‘mildly’ infect other dogs, cats and pigs. It seems to me that the use of the word ‘mild’ refers to the possibility that the lungs are protected but the upper respiratory tract isn’t. Also, it’s clear that dogs with ‘mild’ vaccine-induced kennel cough are still infecting other animals, which isn’t great for kennel owners’ reputations.

To add insult to injury, one paper identified that booster intranasal vaccines may not work for dogs previously exposed to or immunized against B. bronchiseptica! So by giving the Bordetella vaccine to your dog, you provide limited protection and may even give your dog kennel cough; you don’t get long-term immunity; and subsequent shots are unlikely to work. On this basis, it appears counterproductive to use this vaccine.

Vaccine danger to humans

Bordetella vaccine datasheets warn ‘immunocompromised’ humans to avoid contact with vaccinated dogs for six weeks. I mentioned this at one of my evening lectures, and a woman in the audience came up to me afterwards to tell me that she was just getting over whooping cough, and that – yes – it started just after her dog got a kennel cough vaccine.

One study gives credence to the notion that this lady may have contracted kennel cough from her vaccinated dog. The study states that since B pertussis and B. bronchiseptica are nearly identical, the gene detection kits for pertussis infection in humans can mistakenly identify a significant proportion of human kennel cough infections as whooping cough. Oh how ironic – you give your dog a kennel cough jab so he can go in kennels and you can go on holiday, and you end up sneezing and coughing through your vacation.

Another paper states: “B. bronchiseptica causes tracheobronchitis in dogs and atrophic rhinitis in swine; it also causes disease in rabbits and other mammals. B. bronchiseptica infection in humans is considered rare but has been documented in both healthy and immunosuppressed individuals. In healthy individuals, pertussis-like illness and chronic respiratory infection have been reported. Some cases of pertussis-like illness in humans have followed exposure to sick pets or farm animals. The disease is more likely to be severe in individuals who are immunocompromised, such as those with Hodgkin disease, cystic fibrosis, or HIV infection. Pneumonia, sepsis, and death have been reported after infection.”

The paper goes on to state: “Bordetella pertussis, Bordetella parapertussis, and B. bronchiseptica are closely related species that all may cause respiratory tract infection in humans and other mammals and may express many similar virulence factors… With the advent of aerosol vaccination in veterinary clinics for companion animals, human exposure to B. bronchiseptica has likely increased in recent years. Physicians should ask patients presenting with pertussis-like illness whether they have visited a veterinary clinic or have been exposed to a sick or recently vaccinated animal during the week before the onset of symptoms. If the potential for exposure to B. bronchiseptica is present, performance of cultures should be considered before antibiotics are administered.

“Even when administered properly, there may be opportunity for human exposure, especially if the animal sneezes, which is a common occurrence after intranasal administration of a liquid. In addition, the animal may be able to transmit the vaccine strain during the period of active infection.”

One paper queried why pertussis (whooping cough) vaccines fail, and gave as one of its reasons the possibility that other Bordetella species might cause a coughing illness.

Counterproductive vaccine – you’d achieve more by attending to diet

As everyone knows, diet is the cornerstone of health, and good nutrition protects both humans and animals from infection. Whilst we might hypothesise that biologically appropriate food is a safer way of protecting our dogs, there is much science to support our common sense reasoning.

For example, malnutrition was assessed in relation to whooping cough in the UK. Mathematical modelling showed that epidemics were driven by seasonal weather conditions and increases in wheat prices. These two factors predicted the force of infection and the number of people who died. The same authors found a correlation between malnutrition, population size, weather, and measles epidemics.

Another paper states: “Infection and malnutrition have always been intricately linked. Malnutrition is the primary cause of immunodeficiency worldwide, and we are learning more and more about the pathogenesis of this interaction… There is a strong relationship between malnutrition and infection and infant mortality, because poor nutrition leaves children underweight, weakened, and vulnerable to infections, primarily because of epithelial integrity and inflammation.

“In 1968, the World Health Organization published “Interactions of Nutrition and Infection,” which suggested that the relationship between infection and malnutrition was a synergistic one. The Copenhagen Consensus project on hunger and malnutrition even suggested that efforts to provide vitamin A, iron, iodine, and zinc generates higher returns than do trade liberalization or malaria, water, and sanitation programs.”

Vitamin A deficiency increases the risk of developing respiratory disease and chronic ear infections. Vitamin A supplementation sustains gut integrity, lowers the incidence of respiratory tract infections, reduces mortality from diarrhea, and enhances immunity.

Vitamin E enhances immune function and is associated with significant improvement in resistance to influenza virus infection in aged mice and a reduced risk of acquiring upper respiratory infections.

Zinc plays a critical role in the structure of cell membranes and in the function of immune cells. Zinc deficiency reduces nonspecific immunity, including neutrophil and natural killer cell function and complement activity; reduces numbers of T and B lymphocytes; and suppresses delayed hypersensitivity, cytotoxic activity, and antibody production. (Zinc basically helps the immune system to fight disease.)

Patients who are prone to infections and are given high vitamin D doses for one year have a significantly lower risk of developing respiratory tract infections, according to a report in the British Medical Journal. Another study published in Pediatrics (August 2012) showed that incidence of respiratory tract infections among Mongolian children dropped when they were given vitamin D supplements.

Whether you use herbs or nutritional supplements, or feel a raw diet is enough for your dog – one thing is for sure: the Bordetella vaccine can get up your nose, and not necessarily in a good way.

References:

1. Different mechanisms of vaccine-induced and infection-induced immunity to Bordetella bronchiseptica, Microbes and Infection 9 (2007) 442e448

2. J Am Vet Med Assoc. 2002 Jan 1;220(1):43-8., Comparative efficacy of an injectable vaccine and an intranasal vaccine in stimulating Bordetella bronchiseptica-reactive antibody responses in seropositive dogs.

3. J Med Microbiol. 2007 Dec;56(Pt 12):1608-10. Misidentification of Bordetella bronchiseptica as Bordetella pertussis using a newly described real-time PCR targeting the pertactin gene.

4. Clinical Infectious Diseases, Volume 37, Issue 3, Pp. 407-414. Human Illness Associated with Use of Veterinary Vaccines

5. NeoReviews Vol. 129 No. 5 May 1, 2012, pp. 968 -970, (doi: 10.1542/peds.2011-2594)

6. Epidemiol Infect. 1998 Oct;121(2):325-34.

7. Theor Popul Biol. 1997 Oct;52(2):155-63. The dynamics of measles epidemics.

8. Clinical Infectious Diseases (Volume 46, Issue 10, pp 1582-1588)