Dogs are susceptible to various diseases, ailments, and poisons, some of which can affect humans. To defend against many common diseases, dogs are often vaccinated. There are many household plants that are poisonous to dogs, such as poinsettias, begonia and aloe vera. A mixed-breed terrier Some breeds of dogs are prone to certain genetic ailments such as elbow or hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two serious medical conditions particularly affecting dogs are pyometra, affecting unspayed females of all types and ages, and bloat, which affects the larger breeds or deep-chested dogs. Both of these are acute conditions, and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, and mites, as well as hookworm, tapeworm, roundworm, and heartworm. Dogs are highly susceptible to theobromine poisoning, typically from ingestion of chocolate. Theobromine is toxic to dogs because, although the dog's metabolism is capable of breaking down the chemical, the process is so slow that even small amounts of chocolate can be fatal, especially dark chocolate. Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis. A zoonosis (pron.: /?zo?.no?s?s/) (also spelled zoonosis) is an infectious disease that is transmitted between species (sometimes by a vector) from animals other than humans to humans or from humans to other animals (the latter is sometimes called reverse zoonosis or anthroponosis). In direct zoonosis the agent needs only one host for completion of its life cycle, without a significant change during transmission. In a systematic review of 1,415 pathogens known to infect humans, 61% were zoonotic. The emergence of a pathogen into a new host species is called disease invasion or "disease emergence". The emerging interdisciplinary field of conservation medicine, which integrates human and veterinary medicine, and environmental sciences, is largely concerned with zoonoses. Programs supporting regular vaccination of dogs have contributed both to the health of dogs and to the public health. In countries where routine rabies vaccination of dogs is practiced, for example, rabies in humans is reduced to a very rare event. Currently, there are geographically defined core v ccines and individually chosen non-core vaccine recommendations for dogs. A number of controversies surrounding adverse reactions to vaccines have resulted in authoritative bodies revising their guidelines as to the type, frequency, and methods/locations for dog vaccination. Theobromine poisoning or chocolate poisoning is an overdose reaction to the alkaloid theobromine, found in chocolate, tea, cola beverages, acai berries, and some other foods. Cacao beans contain about 1.2% theobromine by weight, while processed chocolate, in general, has smaller amounts. The amount found in highly refined chocolate candies (typically 1.4–2.1 g/kg or 40–60 mg/oz) is much lower than that of dark chocolate or unsweetened baker's chocolate (> 14 g/kg or > 400 mg/oz). In general, the amount of theobromine found in chocolate is small enough such that chocolate can be safely consumed by humans. However, occasional serious side effects may result from the consumption of large quantities, especially in the elderly. In extreme cases, emergency room treatment may be required. Serious poisoning happens more frequently in domestic animals, which metabolize theobromine much more slowly than humans, and can easily consume enough chocolate to cause chocolate poisoning. If large numbers of filled chocolate candies are consumed another serious danger is posed by the fat and sugar in the fillings which can sometimes trigger life threatening pancreatitis several days later. The most common victims of theobromine poisoning are dogs, for which it can be fatal. The toxic dose for cats is even lower than for dogs. However, cats are less prone to eating chocolate since they are unable to taste sweetness. Theobromine is much less toxic to rats and mice, due to their relative genetic similarity to primates; they and humans all have an LD50 of about 1,000 mg/kg. Toxic (LD50) doses of theobromine have only been published for humans, cats, dogs, rats, and mice; these differ by a factor of 6 across species (see the table in this article). The toxicity for (pet) birds is not known, but it is typically assumed that chocolate is dangerous for birds. The first signs of theobromine poisoning are nausea, vomiting, diarrhea, and increased urination. These can progress to cardiac arrhythmias, epileptic seizures, internal bleeding, heart attacks, and eventually death.