Your dog survived the monsoon with no obvious problems. Three weeks later, the vet tells you his red blood cells are being destroyed from the inside. His gums are pale. He hasn't eaten in two days. The culprit? The tick you almost missed behind his ear in September.

Key Takeaways

• Blood parasites are organisms protozoa, bacteria, or more complex pathogens that live in the bloodstream and are spread through tick bites, mosquito bites, biting flies, or even by dogs eating infected ticks.
• Babesiosis is the most dangerous tick-borne blood parasite disease affecting Indian dogs. Transmitted by the Brown Dog Tick, it destroys red blood cells and can kill within days without treatment.
• Hepatozoonosis is unusual dogs don't get it from being bitten by ticks. They get it by swallowing infected ticks while grooming. Prevention means discouraging scavenging and hunting.
• Hemoplasmas (Mycoplasma haemocanis) are tick-, mosquito-, and fly-spread bacteria that live on red blood cells. Most dogs don't show obvious signs unless their immune system is compromised.
• Surra (Trypanosoma evansi), spread by biting flies in Asia and the Middle East, can infect dogs in India particularly those in rural settings or around other livestock.
• Monsoon season is peak risk for both tick and mosquito activity across India year round prevention is not optional; it is the foundation of your dog's protection.

What Are Blood Parasites in Dogs?

A blood parasite is any organism that lives in the blood of its host. These can range from single-celled protozoa microscopic parasites that invade and destroy red blood cells to bacteria that attach themselves to the surface of those cells, to worms that ultimately take up residence in the heart and blood vessels.

According to the Merck Veterinary Manual, blood parasites in dogs can range from single-celled protozoa to more complex bacteria and rickettsiae. The method of transmission varies depending on the parasite, but they are most often transmitted through the bites of ticks or flies.

What makes blood parasites particularly dangerous is where they live. Once inside the bloodstream, they have direct access to every organ in the body. They can destroy the red blood cells that carry oxygen, trigger massive immune reactions, cause dangerous anaemia, damage the kidneys, liver, and heart, and sometimes kill within days.

The six main blood parasite diseases of dogs covered by the Merck Veterinary Manual are Babesiosis, Hemoplasmas, Hepatozoonosis, African Trypanosomiasis, Surra, and Chagas' Disease. Not all of them are present in India but several are, and they are responsible for some of the most serious blood emergencies seen in Indian dogs every year.

How Ticks and Mosquitoes Transmit Blood Parasites

Understanding how these parasites get from vector to dog helps you understand when your dog is at greatest risk and what prevention actually achieves.

Ticks as vectors: Ticks become infected when they feed on an already-infected animal. The parasite then develops inside the tick's body. When that tick later feeds on a new dog, it transfers the parasite through its saliva directly into the dog's bloodstream. For most tick-borne blood parasites, the tick needs to be attached for at least a few hours before transmission occurs. This is why removing ticks promptly matters and why keeping ticks off your dog in the first place is even better.

The Brown Dog Tick (Rhipicephalus sanguineus) is the most important tick species for Indian dog owners. It is found throughout India, thrives in warm conditions, lives in homes and kennels, and is the primary vector for Babesia canis vogeli, the most common cause of Babesiosis in Indian dogs. It is also a vector for Ehrlichia canis (Ehrlichiosis) and Hepatozoon canis (Hepatozoonosis).

Mosquitoes as vectors: Mosquitoes transmit blood parasites by picking up parasite larvae or microfilariae (microscopic early-stage larvae) when they bite an infected dog, then passing them on when they bite another dog. Unlike ticks, mosquito transmission is almost instantaneous there is no delay between bite and transmission. India's warm, humid climate means mosquito activity is year-round in many states, with a peak during and after monsoon season.

Biting flies: Certain blood parasites including Surra are spread mechanically by biting flies like horseflies (Tabanidae) and stable flies. Unlike ticks, these flies don't need to complete a biological cycle within their body. The fly simply picks up infected blood from one animal and introduces it into the next animal it bites.

Babesiosis — India's Most Urgent Tick-Borne Blood Disease

Of all the blood parasites that affect dogs in India, Babesiosis is the one every dog owner must know. It is common, it is severe, and it can kill a previously healthy dog within 48 hours if untreated.

How a Dog Gets It

Babesiosis is caused by protozoan parasites of the genus Babesia, and it is transmitted by ticks, according to the Merck Veterinary Manual. In India, the most relevant species is Babesia canis vogeli, transmitted primarily by the Brown Dog Tick. Any dog that spends time outdoors or even indoors in an area where ticks enter from clothing, other pets, or the environment is at risk.

What Babesia Does to the Blood

Once inside the dog's bloodstream, Babesia parasites invade red blood cells and multiply inside them. As they multiply, they burst the cells open to release new parasites, which then invade more red blood cells. The result is a cascading destruction of red blood cells haemolytic anaemia that can reduce the blood's oxygen-carrying capacity to dangerous levels in just a few days.

The dog's immune system also attacks the parasite-infected cells, sometimes so aggressively that it begins damaging its own healthy red blood cells as well (a process similar to immune-mediated haemolytic anaemia).

Signs — What You Will See

According to the Merck Veterinary Manual, signs vary from a mild illness that passes quickly to a severe disease that rapidly results in death. In some cases, the parasite causes a long-term disease with severe and progressive anaemia as the main symptom.

Watch for:

• Sudden, severe lethargy — your dog stops moving, lies down, and won't get up
• Pale or white gums — the clearest visible sign of severe anaemia
• Dark brown or red urine — haemoglobin from destroyed red blood cells spilling into the urine (called haemoglobinuria)
• High fever — often 39.5°C or above
• Loss of appetite — sometimes complete refusal of food and water
• Jaundice — yellowing of the whites of the eyes, gums, and skin, as the liver struggles to process the debris from destroyed red blood cells
• Weakness, stumbling, or collapse

Babesiosis can be confused with other conditions that cause fever, anaemia, red blood cell destruction, jaundice, or red urine, so laboratory tests a blood smear, CBC, and sometimes PCR testing are needed to confirm the diagnosis.

Diagnosis and Treatment

Your vet will typically start with a blood smear to look for the characteristic pear-shaped Babesia parasites inside red blood cells. More sensitive PCR testing confirms the diagnosis when the parasites are few in number.

Treatment involves antiparasitic medication prescribed by your vet. Supportive care is also important and may include anti-inflammatory drugs, antioxidants, and corticosteroids. In severely anaemic dogs, blood transfusions may be lifesaving a dog with Babesiosis may need an emergency blood transfusion to survive while medication takes effect.

A vaccine based on some types of Babesia is available, but it does not protect against all types, according to the Merck Veterinary Manual. The most effective protection is preventing exposure to ticks in the first place.

Zoonotic risk: A small number of human Babesiosis cases have been reported. It is not clear whether the species that infect dogs are identical to those infecting humans. Fatal cases in people have been linked to asplenia (removal of the spleen) or a weakened immune system.

Hepatozoonosis — The Disease Dogs Get by Eating Ticks

Hepatozoonosis is unusual among tick-borne diseases because the transmission route is not a tick bite. Dogs get it by eating an infected tick or by eating an animal that ate an infected tick.

According to the Merck Veterinary Manual, in most of the world including India, Africa, Southeast Asia, the Middle East, Southern Europe, and islands in the Pacific and Indian Oceans the disease is caused by Hepatozoon canis and is transmitted by the Brown Dog Tick. Infected dogs in these regions typically have no signs or only mild signs.

A dog with a healthy immune system that picks up H. canis may show no obvious illness at all. Having a suppressed immune system due to another disease appears to play an important role in the development of significant signs.

Signs, when they do appear, can include:

• Lethargy and weakness
• Fever
• Weight loss
• Muscle pain or stiffness
• Discharge from the eyes

Blood tests may show a significant increase in white blood cell count and mild to moderate anaemia.

Hepatozoonosis is a lifelong infection no known treatment completely clears the organism from the body. However, drug combinations have improved outcomes significantly, with remission now achievable in most dogs. The Merck Veterinary Manual notes that new drug combinations have resulted in a marked improvement in the outlook for dogs with hepatozoonosis.

Prevention is two-pronged: good tick control to prevent ticks from being on the dog, and discouraging dogs from eating prey animals or scavenging, which can also expose them to the parasite.

Hemoplasmas — When Bacteria Ride Ticks and Mosquitoes

Hemoplasmas are bacteria specifically Mycoplasma haemocanis that live on the surface of red blood cells. They are transmitted through multiple routes: biting lice, flies, ticks, and importantly, mosquitoes, according to the Merck Veterinary Manual. Infected blood transfusions and contaminated needles are also known transmission routes.

Most dogs with Mycoplasma haemocanis infection show no signs at all. The bacteria live on the red blood cells without causing obvious illness in immunocompetent (healthy-immune) dogs.

The risk group where hemoplasmas become dangerous: dogs that have had their spleens removed. Without a spleen, the dog loses a key organ for filtering damaged blood cells and mounting immune defence. In these dogs, hemoplasma infection can trigger red blood cell destruction (haemolysis) and serious anaemia.

Specific antibiotics can treat hemoplasma infections, but even after treatment, some dogs remain chronically infected. Blood transfusions may be necessary for dogs with significant anaemia. Screening blood donors before transfusions and controlling insects that transmit the bacteria are the main prevention strategies.

Surra — The Blood Parasite Carried by Biting Flies in Asia

Surra is caused by Trypanosoma evansi, a protozoan parasite transmitted primarily by biting flies including horseflies and stable flies rather than ticks. It occurs in North Africa, the Middle East, Asia, the Far East, and Central and South America, which includes India, making it directly relevant to Indian dog owners.

According to the Merck Veterinary Manual, Surra is mainly a disease of horses and camels, but all domestic animals are susceptible. It can be deadly, particularly in horses, camels, and dogs.

In dogs, Surra produces signs similar to African Trypanosomiasis: fever, anaemia, and weight loss. The eyes are often affected. Internally, the lymph nodes and spleen become enlarged. The infection is confirmed by laboratory testing to identify the trypanosomes in the blood.

Treatment is available, but following the correct dose exactly is critical drug resistance is a growing concern. Dogs most at risk are those in rural areas or in contact with cattle, horses, or camels animals that can carry T. evansi without necessarily showing severe illness themselves.

There is no vaccine for Surra. Controlling biting flies by using insecticide sprays, clearing brush, and protecting dogs from fly exposure in endemic areas are the main prevention tools.

Mosquitoes, Heartworm, and Other Blood Threats

The blog title names mosquitoes as vectors and while the Merck Blood Parasites page specifically includes mosquitoes as vectors for hemoplasmas, mosquitoes are also the only route of transmission for heartworm (Dirofilaria immitis) one of the most serious blood parasite diseases in India.

Heartworm is not classified the same way as the protozoan blood parasites it is a filarial worm that ultimately lives in the heart and pulmonary arteries rather than in the bloodstream cells themselves. But it is absolutely a blood-transmitted parasite and one that Indian dog owners need to know about.

How heartworm spreads: An infected dog carries microscopic larvae called microfilariae in its bloodstream. A mosquito bites the dog, picks up the microfilariae with its blood meal, and the larvae develop inside the mosquito. When that mosquito bites another dog, the infective larvae are deposited on the skin and enter through the bite wound. Over the next 6-7 months, they develop into adult worms that take up residence in the right side of the heart and pulmonary arteries.

Signs in dogs: Heartworm disease is often silent for a long time. Early signs include mild, persistent coughing, reduced exercise tolerance, and fatigue after activity. As the worm burden increases, signs worsen severe coughing, difficulty breathing, fainting, and eventually heart failure.

India's climate makes heartworm a year-round threat, especially in humid coastal states (Kerala, Tamil Nadu, West Bengal, Goa, Maharashtra's coastal belt), and in urban areas with significant mosquito activity. Year-round prevention with appropriate medication is strongly recommended.

Prevention: Monthly heartworm prevention medication such as MILBEMAX DOG TABLET by Elanco, which contains milbemycin oxime (effective against heartworm larvae before they can establish) keeps the larvae from developing into adult worms. Dogs must be tested for existing heartworm infection before starting preventive medication, as giving preventive medications to an already-infected dog requires careful vet management. Discuss the right schedule with your vet.

African Trypanosomiasis and Chagas' Disease: What Indian Pet Owners Should Know

Two other blood parasite diseases are covered by the Merck Veterinary Manual and while neither is currently a concern for pet dogs in India, understanding them helps you protect a dog that may travel or import/export.

African Tsetse-transmitted Trypanosomiasis is caused by Trypanosoma brucei and spread by tsetse flies which are restricted to sub-Saharan Africa. Indian pet owners do not need to worry about this disease for their home dogs, but dogs travelling to Africa or dogs imported from affected regions should be screened.

Chagas' Disease is caused by Trypanosoma cruzi and transmitted by "kissing bugs" (triatomine insects), primarily in Central and South America and the southern United States. It does not occur in India. However, its presentation inflammation of the heart muscle, sudden death, or long-term heart failure is worth knowing if you are rescuing or adopting dogs from other countries.

For Indian dogs, the diseases requiring active prevention are Babesiosis, Hepatozoonosis, Hemoplasmas, Surra (in rural areas), and Heartworm.

Blood Parasites Side by Side — A Quick Reference Table

Warning Signs That Mean Go to the Vet Today

If your dog has been exposed to ticks or mosquitoes which in India means virtually every dog at any time of year these signs require same-day emergency veterinary care:

• Pale, white, or yellow gums press and release; healthy gums return to pink in under 2 seconds. Pale gums mean dangerously low red blood cells.
• Dark brown, red, or cola-coloured urine haemoglobin from destroyed red blood cells is a blood emergency
• Sudden, severe collapse or extreme weakness inability to stand
• High fever (above 39.5°C) alongside any other symptom
• Rapid, laboured breathing at rest
• Sustained lethargy for more than 24 hours with reduced appetite

For signs that are less acute but still need a prompt vet visit this week:

• Mild but persistent lethargy reduced interest in walks or play, without explanation
• Gradual weight loss over several weeks
• Mild but persistent cough or fatigue during normal exercise
• Yellow tinge to the eyes or skin (jaundice)
• Evidence of a tick bite even a single tick finding warrants monitoring

Blood parasite disease is almost always faster to treat when caught early. Waiting until the dog collapses reduces the chances of survival significantly.

How to Protect Your Dog — Prevention That Works

Tick and insect prevention is the single most effective tool you have. Here is the practical breakdown.

Year-Round Tick Prevention

Oral tick prevention medications are the most reliable and consistent option for Indian dogs. According to Cornell University College of Veterinary Medicine, flea and tick preventatives are generally very well tolerated by pets and have a wide margin of safety.

BRAVECTO by MSD Animal Health provides up to 12 weeks of protection against multiple tick species including the Brown Dog Tick (Rhipicephalus sanguineus) that transmits Babesiosis and Hepatozoonosis with a single chewable tablet. This is especially practical in India where monthly compliance is challenging. A prescription from your vet is required. For a full breakdown of oral tick medicine options and comparisons for Indian conditions, see our complete tick medicines guide for dogs.

Ticks should also be physically removed promptly if found — grasp as close to the skin as possible, pull straight out without twisting, and disinfect the bite site. Never crush a tick between your fingers.

Heartworm and Broad-Spectrum Parasite Prevention

For the mosquito-borne threat, monthly heartworm prevention is the gold standard. MILBEMAX DOG TABLET by Elanco contains milbemycin oxime, which is effective against heartworm larvae (microfilariae) before they can develop into adult worms. It also covers roundworms, hookworms, whipworms, and tapeworms a comprehensive deworming alongside parasite blood protection. Your dog must be tested for existing heartworm infection before starting prevention; discuss timing and frequency with your vet.

Immune Support During and After Recovery

Dogs recovering from blood parasitic infections particularly Babesiosis have been through significant physiological stress. Their immune systems, red blood cell count, and organ function may take weeks to months to fully recover. During this period, targeted immune support can help the body rebuild.

IMMUNOL LIQUID by Himalaya uses Guduchi (Tinospora cordifolia) and Ashwagandha both established immunomodulators in Ayurvedic medicine to support the body's natural immune response during recovery. It is formulated for both dogs and cats and is safe for long-term use. Always use under veterinary guidance, especially during active infection or treatment.

Reduce Exposure at Home

• Keep grass short and garden areas clean ticks live in vegetation
• Avoid walking your dog through tall grass, scrubland, or areas near standing water during peak mosquito hours (dawn and dusk)
• Remove ticks from any human family members who may have been outdoors, as ticks can detach and find a new dog host indoors
• In multi-dog households, treat all dogs one untreated dog can sustain a tick population that then feeds on treated dogs

Don't Let Prevention Lapse After Monsoon

The monsoon brings peak tick and mosquito populations across India. But the risk does not end when the rains stop October and November are often high-risk months as ticks remain active in the cooler post-monsoon environment. Year-round prevention, not seasonal prevention, is the correct standard.

For a deeper dive into specific tick medicines, comparison charts, and Babesiosis-specific treatment information, see our guides on tick fever in dogs and our complete tick treatment guide.

FAQ

What are the signs of blood parasites in dogs?
The most visible signs of serious blood parasite disease are pale or white gums, dark brown or red urine, severe lethargy, high fever, weight loss, and jaundice (yellow-tinged eyes or gums). Babesiosis the most common blood parasite disease in Indian dogs can progress from normal to life-threatening in 48 hours. Any of these signs in a dog that has been exposed to ticks requires same-day veterinary care.

Can Babesiosis be cured?
With prompt treatment, most dogs with Babesiosis survive especially if caught before severe anaemia develops. Antiparasitic medication kills the parasites, and supportive care helps the dog recover. Blood transfusions are sometimes needed in very anaemic dogs. However, some dogs remain carriers after treatment, and reinfection is possible if tick prevention lapses.

How do dogs get Hepatozoonosis if it's not from tick bites?
Dogs get Hepatozoonosis by eating infected ticks typically while grooming themselves or scavenging prey. The Brown Dog Tick (Rhipicephalus sanguineus) is the main vehicle. This is why tick prevention alone isn't fully sufficient dogs that hunt or scavenge outdoors are at additional risk even if the tick never feeds on them directly.

Are blood parasites in dogs contagious to humans?
Most dog blood parasites are not directly transmissible from dog to human. However, the ticks and mosquitoes that carry them can also bite humans. Babesia species have occasionally been reported in humans, particularly in people with compromised immune systems or no spleen. Surra (T. evansi) is considered zoonotic. The safest approach is protecting your dog from parasites, which also reduces the parasite pressure in your environment.

When is tick season in India?
In most parts of India, ticks are active year-round. The Brown Dog Tick thrives in warm, humid conditions which describes most of India for most of the year. The highest-risk period is during and immediately after monsoon season (June through November), but ticks are never truly absent. Year-round prevention is more appropriate than seasonal prevention for Indian dogs.

How often should I give tick prevention medication?
It depends on the product. Oral preventives like NexGard require monthly dosing; BRAVECTO requires dosing once every 12 weeks (3 months). Spot-on treatments vary by product some are monthly, some last 6–8 weeks. Your vet will recommend the right option based on your dog's size, health history, and lifestyle. The most important thing is consistency gaps in protection are when infection risk spikes.

References

1. Multiple Authors (Alicja E. Tabor et al.). Blood Parasites of Dogs. Merck Veterinary Manual. Reviewed/Revised Dec 2017 | Modified Sept 2024. https://www.merckvetmanual.com/dog-owners/blood-disorders-of-dogs/blood-parasites-of-dogs
2. Merck Veterinary Manual. Babesiosis in Animals. Modified Mar 2026. https://www.merckvetmanual.com/circulatory-system/blood-parasites/babesiosis-in-animals
3. Merck Veterinary Manual. Trypanosomiasis in Animals. https://www.merckvetmanual.com/circulatory-system/blood-parasites/trypanosomiasis-in-animals