Disease in Dogs pt. 2

Bacterial diseases

A number of Leptospira sp. bacteria atop a 0.1. µm polycarbonate filter

Bacterial diseases in dogs are usually not contagious from dog to dog; instead they are usually the result of wound colonization, opportunistic infections secondary to decreased resistance (often the result of viral infections), or secondary to other conditions (pyoderma secondary to skin allergies or pyometra secondary to cystic endometrial hyperplasia). These examples are not considered infectious diseases because they do not satisfy Koch's postulates - for example Staphylococcus intermedius, a commonly isolated bacteria from skin infections in dogs, would not cause pyoderma when introduced to a healthy dog. In all likelihood that type of bacteria is already present on the skin of a healthy dog.

There are some bacteria that are contagious from dog to dog. The most notable of these are Bordetella bronchiseptica, one of the causes of kennel cough, Leptospira sp, which cause leptospirosis, and Brucella canis, cause of brucellosis in dogs. There are also common tick-borne bacterial diseases, including Lyme disease, ehrlichiosis, and Rocky Mountain spotted fever.

Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira. Humans and dogs become infected through contact with water, food, or soil containing urine from infected animals. This may happen by swallowing contaminated food or water or through skin contact, especially with mucosal surfaces, such as the eyes or nose, or with broken skin. In dogs, transmission most commonly occurs by drinking puddle, pond, or ditch water contaminated by urine from infected wildlife such as squirrels or raccoons. The liver and kidney are most commonly damaged by leptospirosis. Vasculitis can occur, causing edema and potentially disseminated intravascular coagulation (DIC). Myocarditis, pericarditis, meningitis, and uveitis are also possible sequelae. ^[13]

Ixodes scapularis

Brucellosis in dogs is caused by Brucella canis. It is a sexually transmitted disease, but can also be spread through contact with aborted fetuses. The most common sign is abortion during the last trimester or stillbirth. Other symptoms include inflammation of the intervertebral disc and eye (uveitis), and inflammation of the testicle (orchitis) and prostate (prostatitis) in males.^[14]

Tick-borne diseases are common in dogs. Lyme disease, or borreliosis, is caused by Borrelia burgdorferi and spread by Ixodes pacificus on the West coast of the Umited States and by I. scapularis (deer tick) in the rest of the U.S. Signs and symptoms include fever, joint swelling and pain, lameness, and swelling of the lymph nodes. It has been diagnosed in dogs in all 48 states of the continental U.S.^[15] Ehrlichia canis, which causes canine ehrlichiosis, and Rickettsia rickettsii, which causes Rocky Mountain spotted fever, are both spread by the American dog tick, Dermacentor variabilis, and the brown dog tick, Rhipicephalus sanguineous.^[16]

Fungal diseases

One of the most common fungal diseases in dogs is ringworm, or dermatophytosis, an infection of the skin, hair, or nails. There are three fungal species that cause ringworm in dogs. About 70 percent of infections are caused by Microsporum canis, 20 percent by M. gypseum, and 10 percent by Trichophyton mentagrophytes. Signs include hair loss and scaling of the skin. Treatment for localized ringworm is not always necessary as the disease is self-limiting, but the cliinical course can be shortened by using topical miconazole or clotrimazole. Generalized infections, most commonly seen in immunocompromised dogs, can be treated with oral antifungal drugs such as griseofulvin or itraconazole. Infection can spread to humans.^[17]

Blastomyces dermatitidis

There are several fungal diseases that are systemic in nature, meaning they are affecting multiple body systems. Blastomycosis, caused by Blastomyces dermatitidis, is a fungal disease that affects both dogs and humans, although it is only rarely zoonotic. It is found mainly in the United States in the Mississippi River and Great Lakes areas. Signs include weight loss, cough, fever, enlarged lymph nodes, draining skin lesions, blindness, and lameness. Because dogs are ten times more likely to become infected from the environment than humans, they are considered to be sentinels for the disease.^[18]

Histoplasmosis, caused by Histoplasma capsulatum, is a disease with a worldwide distribution. In the United States it is mainly found in the Mississippi and Ohio River areas, most commonly in bird and bat feces. Signs include weight loss, cough, fever, enlarged lymph nodes, and gastrointestinal symptoms.^[19] Coccidioidomycosis, caused by Coccidioides immitis, is found in arid and semi-arid regions of Central and South America, Mexico, and southwestern United States. Signs include weight loss, fever, cough, enlarged lymph nodes, and lameness.^[20]

Parasites

External parasites

• Fleas and ticks of various species can be acquired and brought home by a dog, where they can multiply and attack humans (and vice versa). This is particularly important, now that tick-borne Lyme Disease has become endemic throughout a large area, in addition to other similar diseases such as Rocky Mountain Spotted Fever. Although dogs do not seem to be as susceptible to such diseases as humans, similar rickettsial diseases have been spread by dogs to humans through such mechanisms as a dog killing an infected rabbit, then shaking itself off in the house near enough to its owners to fatally infect most of the family.
• Fleas and ticks are common parasites for which there are many effective preventive measures.
• Various mites cause skin problems such as mange.

Internal parasites

• Parasites, particularly intestinal worms such as hookworms, tapeworms and roundworms, can be transmitted in a dog's feces. Some tapeworms have fleas as intermediate hosts: the worm egg must be consumed by a flea to hatch, then the infected flea must be ingested (usually by the dog while grooming itself, but occasionally by a human through various means) for the adult worm to establish itself in the intestines. The worm's eggs then pass through the intestines and adhere to the nether regions of the dog, and the cycle begins again.
• Intestinal worms cause varying degrees of discomfort.
• Heartworm is a dog parasitoid. It is hard to eliminate and can be fatal; prevention, however, is easily achieved using medication.

  As the name suggests, an infected mosquito injects a larva into the dog's skin, where it migrates to the circulatory system and takes up residence in the pulmonary arteries and heart, growing and reproducing to an alarming degree. The effects on the dog are quite predictable, cardiac failure over a year or two, leading to death. Treatment of an infected dog is difficult, involving an attempt to poison the healthy worm with arsenic compounds without killing the weakened dog, and frequently does not succeed. Prevention is much the better course, via heartworm pills which are fed to the dog and contain a compound which kills the larvae immediately upon infection without harming the dog. Often they are available combined with other parasite preventives.

• Hydatidosis is caused by a cestode Echinococcus. This is usually noticed among dogs, wild dogs, foxes, etc. Due to its importance as a zoonosis, these worms are important to treat. Preventing hydatidosis is an easier task than treating the same. Anthelmintics such as praziquantel may help prevent this condition. Prohibition of the feeding of dogs with uncooked offals may be the best prophylactic measure against these tapeworms.

As rewritten from Wikipedia