Your cat has been lethargic for a few days. She's barely eating. Her eyes look dull. You check for ticks you don't find any. So you assume it's not a parasite problem.

But ticks aren't the only way a blood parasite can reach your cat. In India, there's a disease spread by ordinary biting flies the kind buzzing around your home and garden every monsoon. It's called surra, and most Indian cat owners have never heard of it.

Key Takeaways

• Surra is a blood disease caused by the parasite Trypanosoma evansi, spread by biting flies like horseflies and stable flies not ticks.
• India is one of the most endemic countries for surra in the world, with significant incidence recorded across Haryana, Punjab, Rajasthan, Maharashtra, Karnataka, and other states.
• Surra was actually first described in India in 1880 it has been here longer than most people realise.
• Cats usually experience a milder form of surra than horses or camels, but can still suffer progressive anaemia, eye problems, and swelling and can silently pass the parasite to other animals.
• Diagnosis requires laboratory testing; symptoms alone are not enough to confirm surra.
• Treatment is prescription-only under a vet's supervision. Reducing biting fly exposure around your home is the key prevention step.

What Is Surra?

Surra is a disease of animals caused by a microscopic parasite called Trypanosoma evansi. The word itself comes from Hindi it means "rotten" a stark clue to how long this disease has been known in India.

T. evansi is a haemoflagellate a single-celled organism that lives in the bloodstream and has a whip-like tail (flagellum) it uses to move. Once it enters an animal's blood, it circulates freely, multiplying by splitting in two. The body mounts an immune response. The parasite evades it by changing its surface coat a trick called antigenic variation that prevents the immune system from ever fully clearing the infection.

The result is a cycle of flare-ups: the parasite surges, the immune system fights back, the parasite changes its disguise, the cycle starts again. Over time, this wears the animal down through progressive anaemia, immune suppression, and organ stress.

According to the Merck Veterinary Manual, surra affects animals mainly in tropical and subtropical regions, and the disease is found across North Africa, the Middle East, Asia, the Far East, and Central and South America.

Think of it this way: while babesiosis is the tick-borne blood parasite most cat owners know about, surra is the fly-borne blood parasite most have never heard of. Both destroy the blood. Both make your cat very sick. The difference is in how they get there.

The India Connection: Why This Matters for Cat Owners

India is one of the most endemic countries for surra in the world and this isn't a new problem.

The first trypanosome ever discovered was identified in India. In August 1880, British veterinarian Griffith Evans was stationed at Dera Ismail Khan (then British India, now Pakistan) investigating a mysterious illness killing army horses. He found worm-like parasites in blood samples from every diseased horse. That parasite was Trypanosoma evansi the cause of surra. India literally wrote the opening chapter of this disease's history.

Today, surra remains endemic across much of the country. A comprehensive review by researchers cited in the WOAH (World Organisation for Animal Health) Surra Technical Manual confirms that significant surra incidence has been reported from Haryana, Punjab, Rajasthan, Madhya Pradesh, Uttar Pradesh, Gujarat, Maharashtra, Tamil Nadu, Kerala, Assam, Andhra Pradesh, and Karnataka. The incidence is comparatively higher in the north and northwest, but the disease is a pan-India reality.

The parasite is most known as a disease of horses, camels, and cattle. The economic losses to India's livestock sector are substantial surra is a notifiable disease precisely because of its impact. But where livestock animals carry and sustain the parasite, pet dogs and cats in the same ecosystem can be exposed too.

If your cat lives in a semi-urban area, has access to a balcony or garden, or shares a neighbourhood with horses, working animals, or cattle surra is a disease worth knowing about.

How Does Surra Spread? The Biting Fly Route

This is what makes surra different from most blood parasite diseases pet owners know about. There are no ticks involved.

Trypanosoma evansi spreads through the bites of blood-sucking flies, primarily:

• Horseflies (Tabanus species) — the large, aggressive flies common near water, grass, and livestock areas during summer and monsoon
• Stable flies (Stomoxys calcitrans) — smaller, fast-biting flies that can look like houseflies but bite sharply

The mechanism is mechanical transmission meaning the fly doesn't need to be infected in any biological sense. It feeds on an infected animal, picks up parasite-containing blood on its mouthparts, then bites another animal within minutes. The parasite is transferred directly. No complex life cycle inside the fly is required.

This is exactly why surra has spread so widely across the globe. As the Merck Veterinary Manual explains, unlike the trypanosome that causes African sleeping sickness — which requires tsetse flies and cannot exist without them T. evansi does not need tsetse flies. Any horsefly or stable fly is a potential carrier.

There is also a secondary route of transmission specific to cats and dogs: eating infected prey or carcasses. Cats that hunt birds, rodents, or other small animals in rural or semi-rural areas can ingest the parasite directly. Wild animals can serve as silent reservoirs carrying the parasite without showing obvious disease.

What this means practically: You can do everything right for tick prevention, and your cat could still be exposed to surra if there are biting flies in your home's environment during monsoon season especially if you live near parks, fields, gardens, or a building complex that shares outdoor space with livestock.

What Are the Symptoms of Surra in Cats?

The Merck Veterinary Manual is direct on this: cats usually have mild disease compared to horses and camels. But mild relative to a dying horse still means a sick cat and there is another dimension that makes feline surra particularly tricky.

The clinical signs are non-specific. They look like dozens of other conditions. Without lab testing, surra can masquerade as general illness, anaemia from any cause, or even a kidney or liver problem.

According to the WOAH Technical Manual on Surra and clinical case reports published in PMC/NCBI, the documented signs in infected cats include:

The eye signs are worth noting specifically. Research on natural T. evansi infection in cats in Southeast Asia including a case documented in Indonesia and reviewed on PMC/NCBI found that corneal opacity and eyelid oedema appeared consistently during peaks of parasitaemia. As the parasite levels rose, eye symptoms worsened; as they fell, eyes improved. This cyclical pattern can be a clue to the diagnosis.

An important clinical note from the same research: the disease often progresses in waves. A cat may seem to stabilise or even improve briefly, then relapse as the parasite switches its surface coat and avoids the immune response again. This cyclical fever and relapse is characteristic of trypanosomiasis.

"The symptoms of parasitemia appeared moderate at the beginning of the first peak, such as loss of appetite, lethargy, coarse, dry hair, and fever. During the second peak of parasitemia, fever is followed by edema in one part of the eyelid." Detection of Trypanosoma evansi in a naturally infected cat, PMC/NCBI

The gum check always. Press your finger on your cat's upper gum, release, and watch for colour return within 2 seconds. White or very pale gums = anaemia, and that is always a reason to go to the vet that day, not tomorrow.

How Is Surra Diagnosed?

Because the symptoms overlap with many other conditions, diagnosis is never possible by observation alone. Your vet needs laboratory confirmation.

The Merck Veterinary Manual — Professional Version on Trypanosomiasis describes the key diagnostic approaches:

Blood smear examination. A drop of blood is spread thin on a glass slide, stained (typically with Giemsa), and examined under a microscope. If parasitaemia is high enough, the vet can see the characteristic elongated, flag-shaped Trypanosoma evansi parasites moving or stained in the sample. This is the most accessible method. Its limitation is sensitivity at low parasite levels, the blood smear can appear normal even in an infected animal.

Buffy coat examination. Blood is spun in a centrifuge tube (PCV tube). The buffy coat the thin layer between the red blood cells and plasma concentrates white blood cells and any parasites. Examining this layer as a wet mount for motile organisms is more sensitive than a standard smear. Per the Merck Veterinary Manual Professional Version, this is the most sensitive rapid method available.

Complete Blood Count (CBC). A standard blood panel will reveal the degree of anaemia (low haematocrit), changes in white blood cell count, and platelet levels. This helps assess severity and guides treatment decisions.

Serological testing. Tests like CATT (Card Agglutination Test for T. evansi) or ELISA detect antibodies to the parasite in the blood. These are useful for population-level screening and for cases where the blood smear is negative but clinical suspicion remains high.

PCR testing. The most sensitive and definitive method. Detects T. evansi DNA in blood even at very low levels. Not always available at every clinic in India, but veterinary diagnostic labs and teaching hospitals can process these samples. If your vet suspects surra but cannot confirm it, ask about PCR referral.

The key diagnostic message: a cat in a surra-endemic region of India showing fever, anaemia, and unexplained eye changes needs surra included in the differential diagnosis even if no flies were observed biting it.

How Is Surra Treated in Cats?

Treatment is prescription-only and must be managed by a veterinarian. The drugs used for surra are not available over the counter and require careful dosing because, as the Merck Veterinary Manual explicitly notes, most have a narrow therapeutic index — meaning the difference between a therapeutic dose and a toxic dose is small.

The key treatment drugs documented for trypanosomiasis in animals include:

Diminazene aceturate A trypanocidal drug widely used in livestock. Must be used with extreme caution in cats; dosing in carnivores is very different from cattle and can cause neurological side effects at incorrect doses.

Quinapyramine sulphate Listed in the Merck treatment table as applicable to dogs and horses for T. evansi. Dosing and use in cats should only be under direct veterinary supervision.

Suramin Used in horses, camels, and dogs for T. brucei and T. evansi. Again, only under veterinary supervision.

Supportive care is a critical part of treatment regardless of which drug is used:

• IV or oral fluids to manage dehydration
• Supportive nutrition for anorexic cats a cat that stops eating for even 24 hours is at risk of hepatic lipidosis (liver fat accumulation)
• Anti-inflammatory medication if indicated
• Treatment of secondary infections, which surra can trigger by suppressing the immune system

Drug resistance is a known issue with surra treatment. If a cat does not respond to initial treatment, your vet may need to consider alternative drug protocols. This is not a disease to treat at home or with guesswork.

Do not attempt to treat your cat with any human medicine or any drug sourced without a vet prescription. The liver enzyme differences between cats and humans mean that many drugs safe in people are fatal in cats. If you want to understand exactly why, our blog on Is It Safe to Give Human Medicines to Dogs and Cats? explains it in detail.

Can Surra Kill a Cat?

For cats specifically, the Merck Veterinary Manual places them in the category of animals that usually have mild disease unlike horses, camels, and dogs, where surra can be fatal.

However, there are important qualifiers:

Severe disease has been documented in cats. Clinical reports from Asia describe cats infected with T. evansi showing malaise, fever, generalised oedema, corneal opacity, anaemia, liver enlargement, and rapid progression to death, per ScienceDirect's review of T. evansi infections in companion animals. These are not isolated anecdotes they appear in documented case reports.

Immune suppression is a significant risk. Surra's most dangerous and underappreciated effect is its ability to weaken the immune system. A cat with active T. evansi infection becomes more vulnerable to every other infection it encounters bacteria, viruses, secondary parasites. According to the global review published in PMC/NCBI on T. evansi distribution, surra has even been associated with failure of vaccination against other diseases in affected animals. A surra-infected cat may not mount a full immune response to its annual vaccinations.

Some cats become chronic, asymptomatic carriers. They show no obvious disease but harbour the parasite. According to the Merck Veterinary Manual, some animals with surra "show no clear symptoms but still carry the parasite." This is both a welfare concern and a public health one a carrier cat feeding biting flies is a source of infection for other animals in the household or neighbourhood.

The bottom line: mild in cats is a relative term. An untreated cat in poor condition, with concurrent illness or immunosuppression, can deteriorate significantly.

Can Cats Spread Surra to Other Animals?

Yes and this is the most practically important thing Indian multi-pet and rural household owners need to understand.

The Merck Veterinary Manual states it clearly: "infected cats can help spread the parasite to other species."

Here is how it works. A biting fly lands on your cat which may have surra with no visible symptoms. The fly takes a blood meal. The fly, now carrying T. evansi on its mouthparts, bites your dog, your horse, or a calf nearby. The parasite is transferred.

In this way, a mildly affected cat can silently sustain the transmission cycle in a household or farm environment. For families in Maharashtra, Rajasthan, Gujarat, or other states where surra is endemic and where pets coexist with working animals or livestock this is a concrete, real concern.

If you have multiple animals and one is diagnosed with surra, ask your vet whether the others should also be tested.

How to Protect Your Cat from Surra

Unlike tick-borne diseases, where applying a tick spot-on is a direct and reliable preventive measure, surra prevention is more about reducing the overall environment of biting flies around your pet. There is currently no licensed vaccine for surra in cats.

1. Reduce biting fly populations in your home and surroundings

Biting flies like horseflies and stable flies breed in moist organic matter waterlogged soil, decomposing plant material, animal waste areas, standing water. Practical steps:

• Clear standing water from pots, tyres, drains, and containers especially after monsoon rains
• Keep garbage and organic waste covered
• Clean up animal faeces promptly in homes with multiple pets
• Trim dense grass and overgrown garden corners flies rest in cool, damp, shaded spots
• Stable flies are particularly common near livestock if your building compound has a guard's horse or dairy cattle nearby, this is a real exposure risk

2. Keep your cat indoors during peak fly activity

Biting flies are most active during daylight hours, particularly in the morning and late afternoon. Monsoon season (June–September) in India sees the highest fly populations. Limiting your cat's outdoor time during these windows reduces exposure.

3. Use a vet-approved ectoparasite preventive on your cat

While cat spot-on treatments are primarily designed for fleas and ticks, the Fipronil-based products work by protecting the skin surface from insect contact. Any biting insect that contacts the treated coat is killed on contact this extends to flies as well. Consistent monthly use also reduces the overall burden of ectoparasites that can act as co-vectors or secondary stressors.

Cat-safe spot-on options available on Animeal all with up to 15% OFF:

• FRONTLINE PLUS CAT SPOT ON by Boehringer Ingelheim — the globally trusted Fipronil + (S)-Methoprene combination. Kills adult fleas and ticks on contact within 24-48 hours. Safe for cats from 8 weeks and 1 kg.
• FIPROFORT PLUS CAT SPOT ON by SAVA VET Fipronil + S-Methoprene, one month protection. Kills adult parasites while disrupting the lifecycle of immature stages.
• SAFELINE SPOT ON SOL 0.50ML by Hester Biosciences Fipronil 9.8% w/v + S-Methoprene 11.8% w/v, monthly application. Four weeks of continuous parasite protection.

Important reminder: Never apply a dog-formulated spot-on or any product containing permethrin to a cat. Permethrin is highly toxic to cats. Only use products specifically labelled for felines.

4. If you live near livestock — stay alert

Surra is primarily a disease of horses, camels, and cattle in India. If your home, building, or neighbourhood has livestock nearby a common situation in semi-urban and rural India the risk of fly-mediated transmission to your cat is meaningfully higher. In this context, regular vet check-ups that include blood smear examination during the monsoon and post-monsoon months are a practical precaution.

5. Prevent hunting and scavenging

Cats that hunt rodents, birds, or other small animals can ingest T. evansi directly from infected prey. Reducing your cat's opportunity to hunt (keeping them indoors, particularly at night) lowers this route of exposure.

Can Humans Get Surra?

This is a reasonable concern, and the answer requires nuance.

Surra is not considered a major human health risk, per the Merck Veterinary Manual. However, "very rarely reported in people" is not the same as impossible.

A small number of documented human surra cases exist from India and Vietnam, among other countries confirmed by the PMC/NCBI global systematic review on T. evansi. India is one of the countries where human cases have been reported. People can theoretically be infected through the bite of a fly that has recently fed on an infected animal.

Severe illness in humans is more likely in those with a weakened immune system or a removed spleen. Most people who might be exposed through occupational contact with infected animals veterinarians, livestock handlers, farmers show either no symptoms or very mild illness.

You cannot catch surra from petting or living with your cat. You cannot catch it from your cat's urine, faeces, saliva, or direct contact. The transmission route is through a biting fly intermediary. The most practical hygiene measure is minimising fly populations at home which protects both your pet and your family.

FAQ

Is surra the same as sleeping sickness?
No. Surra and sleeping sickness are both caused by trypanosomes, but different species. African sleeping sickness in humans is caused by Trypanosoma brucei rhodesiense or T. brucei gambiense, spread by tsetse flies found only in sub-Saharan Africa. Surra is caused by Trypanosoma evansi, spread by horseflies and stable flies, and is found across Asia, Africa, the Middle East, and South America including India. T. evansi is not transmitted by tsetse flies and does not cause sleeping sickness.

My cat is an indoor cat. Can she still get surra?
Technically yes, though the risk is much lower. Biting flies can enter homes through open windows, doors, and gaps. Cats with access to a balcony or open courtyard are at meaningful risk, especially near livestock areas. The more your cat is confined to genuinely enclosed indoor spaces, the lower the risk but a single fly bite during a brief outdoor moment is theoretically enough.

How is surra different from babesiosis in cats?
Both are blood parasite diseases that cause anaemia. Babesiosis is caused by Babesia parasites and spread by tick bites. Surra is caused by Trypanosoma evansi and spread by biting flies and oral ingestion of infected prey. Babesiosis primarily damages red blood cells. Surra circulates in the blood and also suppresses the immune system and can cause eye signs (corneal opacity) that are not typically seen in babesiosis. Both require lab diagnosis and prescription treatment. Both are present in India.

Does regular deworming protect against surra?
No. Deworming treats intestinal worms roundworms, tapeworms, hookworms. Surra is a blood parasite, not an intestinal worm. Standard deworming has no effect on Trypanosoma evansi. If you want to learn about all parasite prevention your cat needs, speak to your vet about a full parasite prevention plan covering both internal and external parasites.

If a fly bites my cat, does that mean she will definitely get surra?
No. The fly must first have fed on an infected animal within a short window (minutes) before biting your cat. The risk goes up in areas with high livestock populations carrying the parasite, and during peak fly season (monsoon and post-monsoon). In typical urban apartment settings in India, with no nearby livestock, the risk is low but not zero. If you're in a high-risk area or your cat shows unexplained illness, ask your vet to include surra in the differential diagnosis.

References

1. Nick Roman, DVM, MPH — Surra in Cats, Merck Veterinary Manual (Reviewed March 2026). https://www.merckvetmanual.com/cat-owners/blood-disorders-of-cats/surra-in-cats
2. Silvina E. Wilkowsky, PhD — Trypanosomiasis in Animals (Professional Version), Merck Veterinary Manual (Reviewed March 2026). https://www.merckvetmanual.com/circulatory-system/blood-parasites/trypanosomiasis-in-animals
3. WOAH (World Organisation for Animal Health) — Surra in All Species (Trypanosoma evansi Infection), Technical Manual Chapter 3.1.21. https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/3.01.21_SURRA_TRYPANO.pdf
4. Pruvot M. et al. — Systematic Review and Meta-analysis on the Global Distribution, Host Range, and Prevalence of Trypanosoma evansi, PMC/NCBI. https://pmc.ncbi.nlm.nih.gov/articles/PMC6357473/
5. Sawitri Prihatini et al. — Detection of Trypanosoma evansi in a Naturally Infected Cat in Indonesia Using Bioassay and Molecular Techniques, PMC/NCBI. https://pmc.ncbi.nlm.nih.gov/articles/PMC10206981/