Mosquito-Borne Diseases

Mosquito-Borne Diseases


Zika Virus

What is Zika Virus and How Does it Spread?

Zika virus (ZIKV) was first discovered in 1947 in the Zika Forest of Uganda. ZIKV is a flavivirus similar to yellow fever, dengue, Japanese encephalitis, and West Nile virus.  Prior to 2007, it had only been detected in central Africa and throughout Southeast Asia. However, in 2007, it was associated with a disease outbreak on Yap Island in the South Pacific, representing the first time it had spread outside of Asia.  From there, it spread to South America with human cases first reported in 2014. ZIKV is transmitted by Aedes mosquitoes. In the Americas, it has only been linked to transmission by Aedes aegypti.  Ae. aegypti is also responsible for the transmission of dengue virus, yellow fever virus, and chikungunya virus.  Recently in Africa, the virus was detected in Aedes albopictus or the Asian tiger mosquito; hence, it is possible that Ae. albopictus could vector the virus in the Americas.

Symptoms of Zika Infection

Most people who contract the Zika virus show no symptoms of the infection.

When symptoms occur, they typically begin with a mild headache and fever.

Within a day or two, a maculopapular rash may appear and can cover many parts of the body.

Following the rash, people generally report continued fever, malaise, and body aches.

Other symptoms can include diarrhea, constipation, abdominal pain, and dizziness

Treatment of Zika Infection

Currently, there is no vaccine or cure for ZIKV.

Treatment for symptoms includes rest and the use of acetaminophen to relieve fever.

Patients should also be advised to drink plenty of fluids if diagnosed.

If anyone has recently traveled to a known endemic area and are displaying any of the symptoms of Zika infection, they should consult their physician immediately.

Concerns with Pregnancy and Perinatal Infections

If a pregnant woman is infected with Zika virus, it may result in microcephaly, a birth defect causing underdevelopment of the head and brain in newborn children.

 The CDC has officially linked Zika virus to microcephaly; however, they are waiting for additional studies to confirm if cases of Guillain-Barré syndrome can also be linked to the virus. The World Health Organization has announced their belief that the virus can contribute to both diseases.

Zika and the United States

A portion of the United States is at a higher risk because of climate and the presence of Aedes mosquitoes. Both Ae. aegypti and Ae. albopictus are limited in their distribution in the U.S. Therefore, although select areas of the country are at a higher risk, it is unlikely that ZIKV will become a disease that circulates in the local mosquito populations throughout the U.S. Most U.S. cases were imported from travelers who contracted the virus in other countries and returned to the U.S. while infected. One of the factors accelerating the spread of Zika virus throughout the Americas could be that it does not appear to require an animal reservoir host, like West Nile virus. In other words, non-infected mosquitoes are able to acquire the virus after feeding directly on infected people, which allows ZIKV to spread rapidly where abundant, competent vector mosquitoes and humans are present together.

West Nile Virus


West Nile Virus (WNV)

West Nile virus (WNV) is a mosquito-borne arbovirus that was discovered in 1927 in the West Nile sub-region of Uganda. The first serious outbreaks of WNV occurred in the mid-1990s in Algeria and Romania. The virus was introduced in the United States in 1999, with the first case being identified in New York City. That year, 62 human cases, 25 horse cases, and countless bird diagnoses were reported in New York State. The CDC has since received more than 40,000 reports of people affected with WNV in the lower 48 states, making it the most common virus transmitted by mosquitoes to humans in the U.S. Because only a portion of all cases are reported, the CDC believes the actual number of illnesses may be as high as 700,000. 

WNV is typically transmitted to humans by mosquitoes that have previously fed upon an infected bird. While over 150 species of mosquitoes have been known to carry the virus, the main vector species in the U.S. are Culex pipiens, Culex tarsalis, and Culex quinquefasciatus. These mosquitoes are all active at night, and most cases of infection occur during the summer months. Transmission of the virus has occurred in a very small number of cases through blood transfusion, organ transplant, and breastfeeding; however, WNV is not transmitted from person-to-person or from animal-to-person through casual contact.

Symptoms of West Nile Virus Infection

The majority (4 out of 5) of people infected with West Nile virus will experience no symptoms.

Approximately 20% of people affected by the virus will experience flu-like symptoms including fever, headache, nausea, muscle pain, and swollen lymph glands.

Other symptoms may include a stiff neck, rash, sleepiness or disorientation.

Less than 1% of those infected will develop West Nile Encephalitis or Meningitis, which can lead to coma, tremors, convulsions, paralysis, and even death.

Treatment of West Nile Virus Infection

Rest and acetaminophen can be used to treat the symptoms associated with West Nile virus infection.

There is currently no WNV vaccine available.

People with mild symptoms typically recover completely within several weeks.

Those with severe symptoms are often hospitalized to receive supportive treatment and close care.

If you believe that you or a family member might have a West Nile virus infection, consult a physician immediately.

Severe Neurological Diseases Caused by West Nile Virus\

Severe cases of WNV infection can affect the central nervous system and result in a number of serious neurological diseases.

West Nile encephalitis, West Nile meningitis, and West Nile poliomyelitis are all diseases that cause inflammation of the brain and/or spinal cord and the surrounding tissues. These diseases can be debilitating or, in some cases, even deadly. 

West Nile Virus and the United States

In 2015, 48 out of 50 states reported WNV infections in people, mosquitoes, or birds. In those states, 2,060 cases of WNV were reported in humans, and there were 119 confirmed deaths (5.8%) in 2015, which is in-line with data from recent years. In 2015, states reporting greater than 50 cases of WNV neuroinvasive disease included Arizona, California, Colorado, and Texas.


 Eastern Equine Encephalitis


Eastern Equine Encephalitis (EEE)

What is Eastern Equine Encephalitis Virus and How Does it Spread?

Eastern equine encephalitis virus (EEEV) is a zoonotic alphavirus and arbovirus, and was first recognized in horses in 1831 in Massachusetts. The first confirmed human cases were identified in New England in 1938. EEEV is present today in North, Central and South America, and the Caribbean. In rare cases, those that contract the virus will develop the serious neuroinvasive disease, Eastern equine encephalitis (EEE). From 2004 to 2013, an average of eight cases of EEE were reported annually in the U.S. EEE may also be commonly referred to as Triple E or sleeping sickness. EEEV is a vector-borne disease that is transmitted to humans through the bite of an infected mosquito. Culiseta melanura is the primary vector among birds, but this mosquito species does not typically feed on humans. It is believed that EEEV is mainly transmitted to humans and horses by bridge vectors that have contracted the virus by feeding on infected birds. Bridge vector species of mosquitoes may include Coquillettidia pertubans, Aedes sollicitans, and Ochlerotatus canadensis. The risk of contracting the EEE virus is highest during the summer months, and those who live and work near wetland and swamp areas are at higher risk of infection. EEEV is only spread to humans via mosquito bite, and cannot be transmitted directly by other humans or horses. There is an EEEV vaccine available for horses, and owners are encouraged to discuss vaccination with their veterinarian. 

Symptoms of EEE Infection

Symptoms typically occur four to ten days after a bite from an infected mosquito and include fever, headache, vomiting, muscle aches, joint pain, and fatigue.

In rare cases, infection occurs in the brain and spinal cord leading to sudden high fever, stiff neck, disorientation, seizures, and coma.

The mortality rate of those that develop EEE is about 33%, the highest among arboviruses transmitted in the U.S.

Treatment of EEE Infection

There is no human vaccine for EEE or anti-viral drugs for treatment of EEE.

For severe illnesses, supportive treatment includes hospitalization, IV fluids, and respiratory support.

Eastern Equine Encephalitis: A Rare but Serious Neuroinvasive Disease

EEE is a rare but very serious disease that involves inflammation and swelling of the brain. Fortunately, only 5% of human EEEV infections result in EEE. However, one out of three people who develop EEE will die, and many survivors have mild to severe brain damage.

 Of those who contract the EEE virus, the elderly (ages 50 and older) and young (ages 15 and younger) are at the greatest risk of developing encephalitis. 

Eastern Equine Encephalitis and the United States

Between five and ten cases of EEE are reported every year in the U.S., with most cases being reported in Florida and Massachusetts. Transmission of the virus is most common in swampy areas in the Atlantic and Gulf Coast states. Cases have also been reported in the Great Lakes region.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

A Global View of Eastern Equine Encephalitis

EEE affects areas throughout North and South America, with outbreaks occurring mainly in the eastern coastal areas of the United States and Canada, the Caribbean, and Argentina.




What is Chikungunya Virus and How Does it Spread?

Chikungunya (chik-en-gun-ye) is one of the lesser known viruses transmitted to humans by mosquitoes, but it is gaining notoriety in the Western Hemisphere since its introduction to the Americas in 2013 on several Caribbean islands. Certain parts of Africa, Southeast Asia, and India report the largest number of cases each year. Areas with known transmission should consider extra preventative measures for newborns, older adults (65+), and people with medical conditions such as diabetes, high blood pressure, and heart disease. Chikungunya disease can result in painful and disabling symptoms, but it is rare to see complications resulting in death. If a person has been infected, their body will likely build a tolerance for protection against future infections.  

Symptoms of Chikungunya Infection

Chikungunya symptoms typically begin with a fever three to seven days after exposure.

Following the fever, individuals experience significant joint pain or stiffness usually lasting for weeks or months.

Other symptoms can include muscle pain, headache, rash, or joint swelling.

Treatment of Chikungunya Infection

Currently, no specific medications exist to treat chikungunya virus infection or disease.

Treatment for symptoms includes rest and the use of acetaminophen to relieve fever and pain.

Patients should also be advised to drink plenty of fluids if diagnosed.

If anyone has recently traveled to a known endemic area and are displaying any of the symptoms of chikungunya infection, they should consult their physician immediately.

Chikungunya Misdiagnosed as Dengue

Chikungunya infection has symptoms similar to dengue infection and can be misdiagnosed in areas where dengue is common. Both infections can result in fever, headache, and muscle aches. Lingering joint pain, with some adults experiencing months of arthritis, is the main difference for individuals with a chikungunya infection. 

Chikungunya and the United States

Beginning in 2014, the United States began reporting cases from citizens who had contracted the disease in South America and the Caribbean and traveled back to the U.S. before symptoms had begun (Imported Cases). Local transmission of chikungunya (citizens that have contracted the disease in the U.S.) has now been confirmed in Florida, Puerto Rico, and the U.S. Virgin Islands. In 2015, a total of 679 chikungunya virus disease cases were reported to ArboNET (the national arboviral surveillance system managed by the CDC) from 44 U.S. states, all of which occurred from imported cases. U.S. territories reported 202 cases of locally-transmitted cases of chikungunya virus from Puerto Rico and the U.S. Virgin Islands. There is a risk that the virus will continue to spread to new areas by infected travelers in the years to come. Unlike the more commonly recognized mosquito-borne viruses in the United States, which have an animal reservoir, chikungunya virus is a human virus. Mosquitoes become infected when they feed on a person already infected with the virus and then spread the virus by feeding on other humans. A portion of the United States is at a higher risk because of climate and the presence of certain Aedes mosquitoes.

A Global View of Chikungunya

Chikungunya is most often transmitted by Aedes aegyptiand Aedes albopictus mosquitoes. These species are also responsible for the transmission of dengue virus, yellow fever virus, and more recently Zika virus. The below maps highlight parts of the world that provide a suitable environment for each species. 




What is Dengue and How Does it Spread?

Dengue virus is transmitted by certain Aedes mosquitoes and considered a major global threat as our world’s urban landscape grows. Beyond the increase in desirable habitats for the container-breeding species, the virus has four strains (multiple serotypes) making it complicated for medical professionals to manage. Chikungunya virus shares similar symptoms to dengue and provides those bitten with immunity from future chikungunya infections. Unfortunately, with multiple strains of dengue, an individual is more likely to be hospitalized or die if infected with more than one serotype. Those previously infected or individuals with a weakened immune system should take even greater precautions.  

Symptoms of Dengue Infection

When symptoms occur, they typically begin with a high fever (104°F) three to seven days after exposure.

Along with the high fever, individuals usually experience at least two of the following symptoms: headaches, pain behind the eyes, significant joint and muscle pain, fatigue, nausea, vomiting, skin rash two to five days after the onset of the fever.

Other symptoms can include mild bleeding and easy bruising. 

Treatment of Dengue Infection

Currently, no specific medications exist to treat dengue virus infection or disease.

Treatment for symptoms includes rest and the use of acetaminophen to relieve fever and pain. Avoid aspirin.

Patients should also be advised to drink plenty of fluids if diagnosed.

If anyone has recently traveled to a known endemic area and are displaying any of the symptoms of dengue infection, they should consult their physician immediately.

Severe dengue (dengue hemorrhagic fever) can occur with warning signs three to seven days after symptoms began. If temperature declines and the following symptoms surface seek immediate medical attention: severe abdominal pain, continued vomiting (may include blood), bleeding nose or gums, rapid breathing, or fatigue. 

New Dengue Fever Vaccine

There is still no cure for dengue fever; however, in April 2016, the World Health Organization (WHO) endorsed the world’s first-ever vaccine for dengue fever. Many governments are reviewing the vaccine for approval in their country and manufacturers are determining how to manage supply and demand issues. The vaccine is given over the course of a year via three injections. While additional details continue to emerge on the vaccine, the development is a great step for a virus that threatens to infect nearly half of the world’s population. 

Dengue and the United States

The United States has experienced local outbreaks in Florida, Hawaii, and near the Texas-Mexico border. Florida has reported local cases annually since 2009 and Hawaii experienced an outbreak in 2015/2016. Larger outbreaks have occurred within U.S. Territories such as Puerto Rico, the U.S. Virgin Islands, and U.S.-affiliated Pacific Islands. A portion of the United States is at a higher risk because of climate and the presence of certain Aedes mosquitoes. 

A Global View of Dengue

Dengue is most often transmitted by Aedes aegyptiand Aedes albopictus mosquitoes. These species are also responsible for the transmission of chikungunya virus, yellow fever virus, and more recently Zika virus. The below maps highlight parts of the world that provide a suitable environment for each species. 




What is Malaria and How Does it Spread?

Malaria is a disease caused by a plasmodium parasite. It is believed that malaria, or a disease resembling malaria, was recorded in ancient Chinese writings as early as 2700BCE. Outbreaks have been recorded worldwide throughout history and the disease has been responsible for the decline of many populations. Charles Louis Alphonse Laveran was credited with the official discovery of the malaria parasite in 1880. 17 years later, Ronald Ross proved that malaria could be transmitted to humans by infected mosquitoes. The vector-borne disease is widespread in poor tropical and subtropical areas. In 2015 there were an estimated 214 million cases of malaria worldwide, resulting in an estimated 438,000 deaths according to World Health Organization statistics. Although historically more prevalent, today in the United States an average of 1,500 cases of malaria are reported annually. Virtually all of these cases are in recent travelers or immigrants coming from countries where the disease is widespread.

Malaria is most commonly transmitted to humans through the bite of certain infected Anopheles mosquitoes. Mosquitoes in this genus usually feed from dusk throughout the night. Although rare, it is possible for infected mothers to transmit the parasite to their baby during pregnancy. It is also possible to contract malaria through blood transfusion or the shared use of contaminated needles. Malaria cannot be sexually transmitted or spread from person to person through casual contact

Symptoms of Malaria

Flu-like symptoms typically develop about two weeks after being bitten by an infected mosquito and include fever, chills, sweating, and fatigue.

A common symptom of malaria is paroxysmal attacks, which involve recurring sudden coldness and shivering followed by fever and sweating every two to three days.

Other common symptoms are vomiting, diarrhea, headache, and mental confusion.

In severe cases, malaria can cause yellow skin, seizures, coma or even death.

Severity often depends on the species of parasite. 

Treatment of Malaria

There are a variety of antimalarial drugs. Treatment often depends on the species of malaria parasite, the part of the world where it was acquired, and the severity of the disease.

Oral or intravenous medications may be used, depending on severity.

Severe cases of malaria will require hospitalization for supportive treatment and care to manage high fever, seizures, and respiratory complications.

Traveling to Countries Where Malaria is Present

It is important to take appropriate prevention measures when traveling to known malaria-endemic regions of the world. Depending on the destination, malaria prevention medicines may be needed and travelers should discuss options with their healthcare provider. Other prevention measures include the use of repellents and insecticide-treated bed nets while staying in countries with known malaria risk. 

Malaria and the United States

Through economic development and public health measures, the United States has succeeded in eliminating malaria. While malaria was officially considered to be eliminated from the U.S. in the 1950s, approximately 1,500 cases are still reported every year. This is primarily attributed to individuals becoming infected while traveling and then returning to the U.S. When this happens, rapid diagnosis and treatment are extremely important in preventing outbreaks. And since the vector mosquito species Anopheles is still present in many parts of the county, ongoing surveillance is vital to helping us accurately track the distribution of these mosquitoes and to identify at-risk areas for potential disease transmission.

A Global View of Malaria

Approximately half of the world’s population lives in areas that are at risk of malaria transmission. Malaria is most prevalent in developing nations within tropical and subtropical regions of the world. Africa is the most affected area, with the most vulnerable persons being young children and pregnant women. And because of the high cost of intervention, malaria is a leading cause of death in many of these poor countries. Global efforts are under way to help control malaria and reduce the number of malaria-related cases and deaths. Control measures include the diagnosis and treatment of patients as well as prevention interventions such as insecticide-treated nets, indoor residual spraying, and larval and adult vector control. These efforts have led to a 45% decrease in malaria mortality over the past decade. 


Know Your Anopheles Mosquitoes

The Anopheles genus of mosquito is mainly responsible for the transmission of malaria in humans. There are about 430 known species of Anopheles that can be found worldwide (except Antarctica). Of these species, around 35 are known vectors of malaria. Adult Anopheles can be identified by their unique resting position where their abdomen is raised in the air. The Anopheles gambiae complex, which comprises at least seven morphologically indistinguishable species, is the primary vector of malaria throughout tropical Africa.  None of these species occur in the United States; however historical vector species that are still prevalent in the U.S. include Anopheles quadrimaculatus, An. freeborni, and An. pseudopunctipennis.


Controlling Anopheles Mosquitoes and Malaria





 Yellow Fever

Yellow Fever

What is Yellow Fever and How Does it Spread?

Yellow fever is an acute viral disease. The yellow fever virus is a Flavivirus with a 400-year history. The disease originated in Africa and then spread to South America in the 1600s. The first reports of yellow fever in the U.S. occurred in Charleston, SC and Philadelphia, PA in 1699. Today, yellow fever is found in South America and Africa and causes around 200,000 infections and 30,000 deaths each year. Fortunately, there is an effective vaccine against yellow fever.

Yellow fever is spread through three transmission cycles; urban, sylvatic, and intermediate. The disease is mainly transmitted to humans through the bite of an infected mosquito, Aedes aegypti, and these mosquitoes acquire the virus by feeding on other infected humans. This is known as the urban cycle. The sylvatic, or jungle, cycle involves transmission of the virus through non-human primates in the wild. Humans can then become infected by these mosquitoes when visiting or working in the jungle. Vectors involved in the jungle cycle include Aedes africanus in Africa or mosquitoes of the genus Haemagogus and Sabethes in South America. An intermediate cycle exists where semi-domestic mosquitoes of the Aedes species serve as vectors, and both human and non-human primates serve as reservoirs for the disease. 

Symptoms of Yellow Fever

Most people infected will experience no symptoms.

For those who do become ill, symptoms include fever, chills, headache, nausea and loss of appetite. Other symptoms may include muscle pains, particularly in the back.

Most patients recover after about 4 days, though approximately 15% experience a second, more serious, phase of the illness.

The second phase of yellow fever involves high fever and liver damage that causes yellow skin. Failure of multiple organs may occur as well. Mortality rate among severe cases of the disease is estimated at 20 to 50%.

Treatment of Yellow Fever Infection

There is no cure for yellow fever.

Treatment is symptomatic and involves making the patient more comfortable.

Yellow Fever Vaccine

There is a vaccine for the disease, and it is strongly recommended or required for those traveling to high-risk areas in South America and Africa.

The CDC maintains a list of specific countries where yellow fever vaccination is required or recommended for travelers. The vaccine is recommended for those nine months of age and older. Reactions to the vaccine are typically rare and mild, though there are risks of more severe reactions. Travelers should consult their healthcare provider to discuss vaccination if they are planning to travel to areas at risk for the disease.

Yellow Fever and the United States

Yellow fever was introduced in the U.S. in the late 1600s, with major epidemics occurring from 1793 through 1905. Today, endemic areas are restricted to Africa and South America. However, Aedes aegypti mosquitoes are found in the southern coastal states and the risk of individuals becoming infected while traveling and then returning to the U.S. does exist.

A Global View of Yellow Fever

In sub-Saharan Africa, yellow fever occurs in regular epidemic patterns and accounts for the vast majority of all human cases and deaths attributable to yellow fever. However, there are also periodic, more unpredictable outbreaks of urban yellow fever throughout the continent. At least 32 African countries are now considered at risk of yellow fever, with a total population of 610 million people at risk.

Yellow fever is also endemic in 10 South and Central American countries and on several Caribbean islands. Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela are considered at greatest risk. Although the disease usually causes only sporadic cases and small outbreaks, nearly all major urban centers in the American tropics have been re-infested with Aedes aegypti. Due to the loss of organized mosquito control programs and subsequent re-infestation of the primary vector, Latin America is now at greater risk of urban epidemics than at any time in the past 50 years.

Map is from the CDC website. Current as ofJuly 2015.This map, which aligns with recommendations also published by the World Health Organization (WHO), is an updated version of the the 2010 map created by the Informal WHO Working Group on the Geographic Risk of Yellow Fever.

Know Your Aedes Mosquiotes

Aedes aegypti, the yellow fever mosquito, is characterized by a silvery-white “lyre-shaped” pattern of scales on its thorax. It is a peridomestic species found not far from human dwellings. They are primarily early morning or late afternoon feeders, but females can also take a bloodmeal at night under artificial illumination. Typically, Ae.aegypti fly only a few hundred yards from their breeding sites.

The species utilize containers to breed, and educating the public on how to eliminate their backyard larval habitats is one key to keeping these invaders under control. Larvae can be found in a variety of artificial containers, including buckets, tires, cans, and flower pots. Homeowners should also inspect rain gutters for clogs, gardening equipment, and backyard children’s toys.


 St. Louis Encephalitis

St. Louis Encephalitis

What is St. Louis Encephalitis and How Does it Spread?

St. Louis encephalitis virus (SLEV) belongs to the virus family Flaviviridae and is related to Japanese encephalitis virus. The virus was first recognized in 1933 when an epidemic in St. Louis, Missouri resulted in over 1,000 cases of encephalitis. Several epidemics have occurred sporadically throughout the U.S. since then, with the majority of cases occurring in eastern and central states. 

SLEV is transmitted to humans through the bite of an infected mosquito. Mosquitoes from the genus Culex contract the virus when feeding on infected birds, and then pass the virus to humans. Wild birds, such as sparrows, pigeons, blue jays, and robins, are the primary hosts of SLEV. Humans are dead-end hosts, meaning that once infected with the virus they cannot transmit it to other humans. Transmission of the virus occurs primarily in late summer and early fall in temperate areas, and occurs year-round in the south.  

Symptoms of St. Louis Encephalitis Virus Infection

Most people infected with SLEV will show no symptoms and only a small number of cases result in St. Louis Encephalitis (SLE) disease.

Those who do become ill may experience fever, headache, nausea, and tiredness.

Severe infections will result in high fever, neck stiffness, disorientation, and possibly coma, tremors or even death.

Mortality ranges from 3% to 30% in those that develop SLE disease, and is largely dependent on age. 

Treatment of St. Louis Encephalitis Virus Infection

Care is based on symptoms, as there is no cure or specific treatment for SLE disease.

For severe cases of illness, supportive treatment includes hospitalization, IV fluids and respiratory support.

St. Louis Encephalitis Disease and the Elderly

SLE disease is a rare but very serious disease that involves inflammation and swelling of the brain.

The elderly are at a greater risk for both developing the disease as well as experiencing severe complications as a result of the disease. Mortality is estimated between 7% and 24% for those with SLE and over 50, where it is less than 5% for those under 50. 

St. Louis Encephalitis Disease and the United States

Prior to the introduction of West Nile Virus in 1999, SLEV was the most important epidemic mosquito-borne viral disease in the U.S. Annual reports of SLEV cases fluctuate widely, due to periodic epidemics that occur. Most cases occur in east and central states. From 2004 to 2013, an average of seven cases of SLE disease were reported annually. The last major epidemic occurred in 1975 along the Ohio-Mississippi River Basin when nearly 2,000 cases and 142 deaths were reported.

Source:  ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

A Global View of St. Louis Encephalitis

St. Louis Encephalitis virus mainly affects the U.S., though occasional cases have been reported in Mexico and Canada.


 Heartworm Disease

Heartworm Disease

What is Heartworm Disease and How Does it Spread?

Dirofilaria immitis, commonly referred to as heartworm, is a parasitic roundworm that infects a variety of mammals. Heartworm is found throughout the world and has been reported in all states in the U.S. The natural host for heartworms is dogs but heartworms may also live in cats, ferrets, and humans. Infection in dogs can lead to heartworm disease, a serious condition that may result in death. Cats are an atypical host since most worms in cats don’t survive to the adult stage. If cats become infected, however, they may develop serious health problems. Although isolated human infections have been reported, heartworm is not currently recognized as a human health problem. 

Hosts for heartworm include domestic dogs, wolves, foxes, and raccoons. Heartworm is spread by mosquitoes that bite an infected host and then pass the parasite to another host during a blood meal. Aedes, Anopheles, and Mansonia species of mosquito are all capable of transmitting heartworm. Humans and other mammals are accidental hosts and cannot play a role in spreading heartworm as the worms do not produce the microfilariae necessary for transmission. Heartworms are only spread by the bite of a mosquito and cannot be passed directly from one dog to another. And people cannot get heartworms from their pets.

 Symptoms of Heartworm Disease in Dogs

It takes about seven months for the parasite to develop into an adult heartworm once a dog is bitten by an infected mosquito. So, initially, dogs will show little to no symptoms.

As infection persists, dogs may experience a persistent cough, fatigue, decreased appetite, and weight loss.

Heavy worm burden can stop blood flow to the heart and cause a condition called caval syndrome, which leads to heart failure.  

Treatment and Prevention of Heartworm Disease in Dogs

Both topical and intravenous drugs exist to treat heartworms. The specific treatment plan will depend on severity and stage of the disease.

For dogs that develop caval syndrome, surgical removal is the only treatment option.

Without proper treatment or surgical removal, most dogs will die from heartworm disease.

Fortunately, there are FDA-approved products to prevent heartworms in dogs. Most are given monthly and require a veterinarian’s prescription.  

Heartworms in Cats

Though cats are not as susceptible to infection as the worms don’t thrive as well in their bodies, they are still at risk for the disease. In cats, heartworms don’t live as long and rarely mature into adult worms. Signs of heartworm may be hard to detect and include coughing, wheezing, periodic vomiting, or weight loss. Unfortunately, there is no approved drug treatment for heartworm in cats and the goal is to stabilize the cat through long-term treatment. There are, however, FDA-approved products for the prevention of heartworms in cats.

  Meet the Heartworm

 Adult heartworms grow to 12 inches in length and have the appearance of cooked spaghetti. Heartworms have a lifespan of five to seven years and an infected dog may have anywhere from 1 to 250 worms.

Heartworm Life Cycle



 Source: American Heartworm Society, Heartworm Life Cycle for Pet Owners, 2014