The New light of Myanmar
Thursday, 24 April, 2003

Animals and Public Health

(Continue from yesterday)

Cat scratch disease

The disease was also known as Cat Scratch Fever. The disease was associated with domestic cats, throughout the USA and worldwide. The disease was reported over 6000 cases, annually. Seen more often in men than in women. Have seen clusters of infection within families from 2 to 3 weeks, suggesting that shedding by cats may occur periodically. Other sources of infection have included scratches from other species including dogs, squirrels, and goats and from wounds induced by crab claws, barbed wire, and plant material. 90% of patients have been exposed to a cat. 75% of these have been bitten, scratched, or licked. Most affected individuals are <20 years of age.

In man a typical (CAT SCRATCH DISEASE—CSD) appear on neck or extremities, will develop in 50% of the cases and appear approximately 10 days after a bit or scratch. A pustule persists for 1-2 weeks. 10-14 days after the lesion appears, lymphadenopathy develops and usually regresses within 6 weeks. 30-50% of the enlarged nodes become supportive. Of the approximately 65% who develop systemic illness, fever and malaise are the symptoms most often noted. The disease is usually transient and most patients recover spontaneously without sequelae within 2-4 months. Many unrecognized cases probably occur. Disease appears to confer lifelong immunity.

DISEASEA TRANSMITED FROM DOG TO HUMAN

Rabies

Rabies is a preventable disease of animal origin, which is almost always fatal if not properly treated. Rabies affects many domestic and wild animals including bats and can be transmitted to humans. However, almost all human death in the world attributed to rabies are caused by dog bites. In addition, most of the 10 million post-exposure treatments (87% in Africa and 97% in Asia) are administered following dog bites. An estimated 35,000 to 50,000 human deaths are caused by rabies each year. It must be recognized however, that the true number of deaths is unknown. Gross under-reporting of human cases and deaths attributable to canine rabies is the rule in large areas of the developing world, not the exception. From age stratified incidence rates, on average between 30%-50% of human cases of rabies (and therefore rabies deaths) occur in children under 15 years of age (http://www.who.int/emc/diseases/zoo/rabies.html).

Rabies is caused by an RNA virus and is responsible for an estimated 100,000 human deaths each year, most in developing countries (Groves and Harrington, 1998).

Reservoirs are wild and domestic canidae, dogs, foxes, wolves, wild carnivores, raccoons, bats (vampires bats) and insectivores. Urban rabies is transmitted by dogs and accounts for most human cases; sylvatic rabies circulates among wild carnivores and bats and causes some spillover infection of dogs, cats and livestock. Rabies virus is abundent in saliva mostly transmitted to a bite inflicted by infected animals.

Rabid dogs shed virus in saliva 5-7 days before showing signs Rabies in dogs may be either furious or paralytic. The rabied dogs become agitated, restless and excitable in early furiuos stage. After aggressive stage, the dog attempting to bite objects, other animals or human and itself. Profuse salivation and the bark change to a horse howl.

Lyme disease

The disease was first implicated in 1982 as agent in a 1975 epidemic of juvenile inflammatory arthopathy in Old Lyme Connecticut. Cases have been reported from 46 states and the annual number of Lyme disease cases has increased 18 fold from 497 to 8803. It is now the most common tick transmitted disease in the USA. Also seen in Europe, England, Soviet Union, China, Japan, Southeast Asia, South Africa, Australia, and Canada.

The disease was transmitted by ticks (three host tick with a two to three year life cycle). Ixodes dammini  species has a broad range of hosts; adults prefer white tailed deer but will also parasitize dogs, horses, and humans. Larvae feed primarily on rodents, especially mice. Birds are an important reservoir and means of dispersal. Because of lack of any proof to the contrary it is generally believed at this time that any potential increased risk to human beings from infected animals is attributable to animals bringing ticks into areas of human habitation rather than any pet transmission. Dogs appear to be at greater risk than humans.

Serologic evidence has been reported in the dog, cat, horse, and ruminants. However, correlation with disease is lacking except in the dog. The dog exhibits the same symptoms as noted below for humans. Expanding skin lesions have been noted in mice and rabbits.

Multisystemic disease which may have chronic sequelae; an annular rash known as erythema chronicum migrans (ECM) develops in 60-80% of patients in the area of the tick bite. The symptoms are flu like, which resolve in about three weeks. 8-10% of people develop cardiac involvement several weeks later. Manifestations include atrioventricular block, cardiomyopathy, heart failure, myocarditis, and pancarditis. 15% develop neurologic disorders. Other manifestations include meningitis, cranial neuritis, radiculoneuritis, neuropathy, and encephalopathy. 60% develop the most common sequelae, arthritis.

Leptospirosis

Also known as Hemorrhagic jaundice (Leptospira icterohaemorrhagiae), canicola fever and dairy worker fever. Causal organism is Borreliae species, transmitted and maintained primarily by ticks.

Rats, mice, field moles, guinea pigs, gerbils, squirrels, rabbits, hamsters, reptiles, nonhuman primates, livestock, and dogs. In one study, 40% of stray dogs were seropositive. Rats and mice are common animal hosts for L. ballum. Infection in mice is unapparent and can persist for the animal’s lifetime. Rodents are the only major animal species that can shed leptospires throughout their life-span without clinical manifestations. Active shedding by lab animals can go unrecognized until personnel handling the animals become clinically ill.

Transmitted through handling affected animals, contaminating hands, or abrasions with urine, or aerosol exposure during cage cleaning are most common. The organism is often transmitted to humans by the urine of the reservoir host. The organism may also enter through minor skin lesions and probably via the conjunctiva. Many infections have followed bathing or swimming in infected waters.

In dogs and cats, gastroenteritis, jaundice, and nephritis may occur.

Symptoms in man ranges from inapparent infection to severe infection and death. Weakness, headache, myalgia, malaise, chills, & fever are common. Icteric leptospirosis (Weil’s syndrome-usually caused by L. icterohaemorrhagiae) is the most severe form of the disease, characterized by impaired renal and hepatic function, abnormal mental status, hypotension, and a 5-10% mortality rate. Signs and symptoms are continuous and not biphasic.

(Concluded)

Author : Dr Tin Tin Myaing (University of Veterinary Science, Yezin)