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Alert! Heartworm Disease Increasing in Dogs and Cats in LA ... Wildlife and Humans Also at Risk  


ANIMAL WATCH-Heartworm disease is a serious infection that results in severe lung disease, heart failure, other organ damage, and death in pets--mainly dogs--but also cats, coyotes, ferrets, wolves, sea lions, seals and other animals. And, occasionally it infects humans. The worms mature into adults, mate, and produce offspring while living inside the heart, lungs, and associated blood vessels of an infected animal.  

It is caused by a parasitic worm called Dirofilaria immitis, which is spread through the bite of a mosquito. Heartworm cases are increasing in Los Angeles, according to a report updated on April 26, 2016, by Los Angeles County Department of Public Health. 

This disease is NOT spread directly from animal-to-animal (or animal to human). Rather, infected animals are reservoirs for the disease but may not display symptoms. The transmission of the disease occurs when a mosquito bites and sucks the blood from an infected animal and then carries it to the next victim. 

Areas like California and Arizona, where heartworms have not been a problem, are now finding that building development and improved irrigation systems have also enabled mosquitoes to survive. Where there are mosquitoes, there are heartworms, experts advise. 

Three new species of drought-resistant mosquitoes are spreading throughout LA. County: the Australian backyard mosquito, the Yellow Fever mosquito and the Asian Tiger mosquito -- the latter two are also capable vectors for human viruses, such as West Nile and Zika, according to LA County officials. 

All three have transmitted heartworm in other countries, and therefore may spread heartworm here. They are black with white stripes, are “efficient” virus transmitters, biting multiple hosts, and are aggressive daytime biters.  They have a short flight range, averaging about one-quarter mile; however, strong winds can blow mosquitos a long way. 

Here are some tips to protect your pets, family and community. 

Mosquito Control.  Mosquitoes breed in standing water, so empty any outdoor containers in which water collects every two days and clean them thoroughly. This includes pet drinking bowls and birdbaths. Also, remove any uncovered bottles and jars or unused toys and planters in your yard. Throw away old tires lying in the backyard and clean gutters so rain will not be trapped. 

Mosquitoes lay their eggs on the inside of the container, just above the water level. The eggs can then lay dormant for up to several years while waiting for the right conditions to produce larvae. According to sgvmosquito.org, these mosquitoes can breed in a bottle cap of water. 

Unfortunately, Aedes have evolved in well-populated areas and like living in close contact with humans and in urban environments. So, the best prevention is to not make them welcome on your property or in your community. 

Keep Pets Inside your Home at Night.  Mosquitoes feed the most at dawn, dusk and at night, so keep your pet indoors. 

Coyote Control.  Infected coyotes can be reservoirs for the disease. Do NOT leave food or water for coyotes or any animal outside. This attracts rodents, other wildlife and feral cats, which attract coyotes. 

Have Your Pets Checked for Heartworm. In 15% of the heartworm cases confirmed in Los Angeles County, the animal was not treated. Untreated pets may become ‘reservoirs’ and infect mosquitoes, and then the mosquitoes can infect more pets and/or people. 

A human can be infected by a mosquito that has fed on an infected dog but human infections are rare, with the greatest danger being that it can create a small mass in the lungs. “The mass itself isn’t usually a problem, but if it gets seen on an x-ray, it may appear very similar to a lung tumor, potentially leading to the use of more invasive diagnostic techniques (e.g. lung biopsy) to rule out cancer,” warns WormsandGermsBlog.com.  

However, lest we take human infection too lightly, a paper published in the American Journal of Tropical Medicine and Hygiene in May 2001 reports the fourth case of heartworm infection confirmed in a California resident--all of which were males.  A 28-year-old man had become lost in a an Ohio state park for 18 hours, wearing only shorts and sandals and claimed to have been bitten numerous times by mosquitoes.  

Doctors eventually determined that an orchiectomy (removing a testicle) was necessary. “Histopathology revealed a well-preserved immature male D. immitis, the canine heartworm, in a branch of the spermatic artery,” the report states. (J. H. Theis, A. Gilson, G. E. Simon, B. Bradshaw, & D. Clark; Am J Trop Med Hyg May 2001vol. 64 no. 5 317-322).  

Getting back to more common dangers and the prevalence of heartworm disease in Los Angeles, of the 187 cases reported between 2005-2014, 53% were “Confirmed,” 41% were Probable, and 6% were “Suspected.” However, the 2005- 2015 total shows that veterinarians had reported 258 cases, in 18 cats and 240 dogs—an increase of 71 cases. The majority of the cases (75%) had no symptoms at the time they were diagnosed. 

The graph on the L. A. County Public Health site shows these cases by year and the alarming increase in 2014, when laboratories were required to begin reporting cases. 

Approximately 60 percent of dogs travel with their owners, thus increasing the potential for heartworm exposure,” says Robert Stannard, DVM, with the American Heartworm Society. [

 But, in 29% of the cases in L.A. County, owners indicated the pet had not traveled outside of Southern California, so they had acquired the infection locally. 

Sadly, sick dogs are being brought to Los Angeles—often surreptitiously-- by “rescuers” or brokers for foreign puppy mills.  They are transported from countries or states which are heartworm-endemic to California, where there is no requirement for heartworm testing and they can become reservoirs for mosquitoes.  

Heartworm Symptoms in Dogs: 

The disease is rare in dogs less than one year of age because the microfilariae take five to seven months to mature into adult heartworms after infection. 

Unfortunately, by the time clinical signs are seen, the disease is usually well advanced,” according to VCA Hospitals.  

“The most obvious clinical signs of heartworm disease are a soft, dry cough, shortness of breath, weakness, nervousness, listlessness and loss of stamina. All of these signs are most noticeable following exercise, when some dogs may even faint or become disoriented. …In advanced cases, congestive heart failure may be apparent and the abdomen and legs will swell from fluid accumulation. There may also be evidence of weight loss, poor condition and anemia. Severely infected dogs may die suddenly during exercise or excitement.” 

Heartworm Symptoms in Cats: 

"It is necessary for a cat to be bitten by an infected mosquito in order to become infected with heartworms," VCA Hospitals remind us that it is a wise to keep cats inside at all times. 

The most common signs are a sudden onset of coughing and rapid breathing, signs that can also be caused by several other diseases. Other common non-specific clinical signs include weight loss and vomiting. On occasion, an apparently normal cat may be found dead, or may develop sudden overwhelming respiratory failure and heartworm disease is diagnosed on a post-mortem examination.” 

Treating and Preventing Heartworms in Your Pet: 

“Your veterinarian will select the correct drug and administration time based on your pet's condition,” says Ernest Ward, DVM. 

You can prevent your dog from getting heartworms by using a heartworm preventive. When a dog has been successfully treated for heartworms, it is essential to begin a heartworm prevention program to prevent future recurrence. With the safe and affordable heartworm preventives available today, no pet should ever have to endure this dreaded disease.” 

(Animal activist Phyllis M. Daugherty writes for CityWatch and is a contributing writer to opposingviews.com. She lives in Los Angeles.) Prepped for CityWatch by Linda Abrams. 

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