To Lepto or not Lepto? That is the Question
A global infection of both humans and animals, leptospirosis is on the tip of most owners and dog professional’s tongue. Caused by the pathogen icleptospira spp. it is a major zoonosis, with infection acquired from wild and domestic animals. Canine leptospirosis presents very similarly to the syndromes presented in other species with hepatic, renal and pulmonary ramifications. In short, it’s pretty rough, but vaccine induced immunity is restricted to serologically related serovars and is generally very short-lived; therefore, needing annual revaccination. If there are more than 230 serovars belonging to at least ten pathogenic species, does the vaccine even pose benefits? Or do the risks outweigh them? We are going to look at the science and explore both sides to this story. Fancy coming along for the journey? Leptospirosis is characterised by fever, jaundice, vomiting, diarrhoea, renal failure, haemorrhages and ultimately death. However, for those who recover, they may become asymptomatic renal carriers for extended periods and shed infectious leptospires into the environment. This is a large source of infection, as rats can be carriers but do not show signs of infection. Whilst treated dogs can shed leptospires, so can vaccinated dogs. This raises the first red flag; is this potentially increasing exposure? Most signs of leptospirosis become apparent in the first week after infection; younger dogs, less than 1 year of age tend to get the most severe forms of leptospirosis and 87-100% of infected dogs will have some degree of renal implication. There do appear to be different clinical parameters of the infection: Peracute Disease: super-sudden onset which usually affects younger dogs with an overwhelming exposure. The large amount of toxin causes rapid death before the kidney or liver disease even occurs. Acute Disease and Subacute Disease: this is the classic form which manifests as fever with bruising and bleeding, general muscle pain and painful abdomen from kidney and/or liver disease. There may be jaundice and inflammation in the eyes. Chronic Disease: recurring fevers, chronic hepatitis, chronic kidney disease, uveitis, poor appetite and weight loss. However, leptospira interrogans sensu lato is sensitive to doxycycline which is a readily available antibiotic. Leptospires are cleared from the blood within 24 hours of starting antibiotics. But it does take around 7 days to clear from the urine. Prognosis, depending on organ damage is 80-90% with appropriate treatment. There are, however, other serovars, like the pomona which is associated with more severe disease and in severe kidney cases, dialysis can be required which is often limited. So, whilst treatment is largely effective, if started soon enough, there was clearly enough concern to develop a vaccine. Vaccination against leptospira interrogans sensu lato is available for the seravars canicola, grippotyphosa, pomona and icterohaemorragiae. Some vaccines coverall four serovars, whereas some cover two of the four. This is where you will recognise the common lepto two or four vaccine. Vaccination against canicola and icterohaemorragiae has been traditional for dogs and vaccination overall, has been seen to reduce the severity of the disease, but will not prevent infected dogs from being carriers. Note, it supposedly reduces severity, it doesn’t necessarily prevent occurrence. The leptospirosis vaccine was soon associated with a higher chance of vaccine reactions. This is a result of human research into leptospirosis. In the U.K. in 2014 , over 2000 reports of Novibac L4 adverse reactions have been reported to the VMD (Veterinary Medicine Directive) and around 120 suspected deaths related to vaccinosis. In addition to this, data suggested that the severity of the disease was associated with the intensity of the immune response. In short, the more intense and early the response, the more severe the disease. Findings here If our immune system, and our dog’s, is primed to take out antigens and protect, why does a more intense response seem to make things worse? An intense immune response induces a high level of inflammatory cytokines which can result in severe tissue lesions. Immunity is like the porridge in Goldilocks. It can sometimes be too cold (lacking) and sometimes too hot (overzealous). Ideally, we want it, just right. There are many things that affect immune responses, in the case of lepto, a more intense response was associated with previous infection. Fever was induced by virulent injection in previously immunised rabbits whereas non-immunised rabbits exhibited no fever after injection. So, in this case, the immunised rabbits fared poorer than non-immunised rabbits. See where we might be going with this? So we are vaccinating to potentially reduce, not prevent the severity of infection but here it appears those rabbits immunised, had a more severe reaction to exposure. But, stress, nutrition and the environment can all affect immune responses too. So too, can genes. This can help explain why some animals are more, or less susceptible to pathogens (or vaccines) than others. And explain the age-old statement, but my dog was fine! It therefore raises no eyebrows when reports appear of clinical leptospirosis in numerous dogs when they had previously been vaccinated. You’ll remember this from earlier, when it was deemed to reduce severity, not necessary prevent occurrence. This was however, associated with vaccine type. In short, the dogs were vaccinated against only two of the many pathogenic serovars. So, in walked Lepto 4. But these new vaccines were associated with further increases in vaccine reactions, not limited to local swelling or hypersensitivity, but including cardiac abnormalities. Specifically, heart murmurs appearing between first and second vaccination. Findings here What is particularly interesting in studies exploring the use of lepto 4 vaccines, is that dogs demonstrated antibodies to serovars not vaccinated against. Researchers have therefore concluded that natural exposure (not vaccine exposure) to serovars provide positive titre results. Not only that, but in cases of vaccinations up to 1745 days previously, some dogs still demonstrated antibodies. This raises a question around the need for such frequent booster vaccinations. The take home from this particular study was “seroconversion following vaccination differed considerably among individual dogs.” Yet they still concluded that, “in the light of the high incidence and
