Ticks, Heartworm and Parasites You Forgot About in the UK

If your pet's previous life was in the UK, North America or northern Europe, you probably had a flea treatment you used in summer, a tick check you did after walks in the woods, and a heartworm preventative your vet may not have even mentioned. That's all about to change.

This piece walks through the parasite categories that come up in nearly every first vet appointment for a newly arrived pet: fleas, ticks and the diseases they carry, heartworm, intestinal worms and protozoa, and the bacterial infection that sits alongside them in this climate. It's general information — your vet will have local, specific recommendations that should override anything generic, and nothing here is a substitute for an examination.

The actual reason prevention is year-round here

Ask a vet in Singapore or Bangkok why prevention doesn't stop in the cooler months and you'll get a version of the same answer: there are no cooler months, at least not from a parasite's point of view.

In a temperate climate, winter does most of the work. Cold weather suppresses mosquito activity, drives flea populations down, and pushes tick life cycles into dormancy. That seasonal collapse is what makes seasonal prevention defensible in the UK. It doesn't happen in the tropics. Air temperature and humidity in Singapore, Kuala Lumpur, Bangkok and — for most of the year — Hong Kong stay inside the range in which fleas complete their life cycle, ticks quest and feed, and mosquitoes breed. Nothing gets a break.

Heartworm makes the point most precisely. Dirofilaria immitis cannot develop inside a mosquito unless it stays warm enough for long enough: American Heartworm Society guidance describes development to the infective third larval stage taking roughly ten to fourteen days at around 27°C, and slowing as temperatures fall. In much of the UK, that threshold is rarely sustained long enough for transmission to establish. In tropical Asia it is met permanently. The seasonality that underwrites a temperate protocol simply isn't there.

The practical consequence is that "monthly, without gaps" isn't your new vet being cautious or commercially minded. It's the protocol matched to the environment. Regional guidance from bodies like the Tropical Council for Companion Animal Parasites is built around continuous cover for exactly this reason.

What changes when you arrive from the UK

Three things, usually.

1. Heartworm prevention gets added. Most UK dogs have never been on it, because D. immitis is not established in the UK and ESCCAP's UK and Ireland guidance treats it as a travel-related risk rather than a domestic one. Here it becomes the backbone of the monthly plan.
2. Flea and tick cover becomes continuous. Not "from April" and not "after we've seen one".
3. The specific products often change. Licensing differs by country, and your vet will have a view on what is actually working in their patient population — which is not always the same thing as what is available.

Bring the box, or a photograph of it, to your first appointment. "Some kind of spot-on, the blue one" is a genuinely common answer and it makes the conversation harder than it needs to be. If you have only just landed, our guide to the first thirty days with a newly arrived pet puts this appointment in the wider arrival sequence.

Fleas

Fleas in temperate climates are seasonal and household-dependent. Fleas in tropical Asia are continuous and close to universal. The dominant species on both dogs and cats is the cat flea, Ctenocephalides felis — the name is misleading, because it is the flea you will find on almost every dog too.

The part owners underestimate is that most of the flea population is not on the pet. Eggs, larvae and pupae live in the environment — bedding, sofa fabric, the gaps between floorboards, the corridor outside a condo unit — and warm, humid conditions are close to ideal for completing that cycle. Treating the animal alone, once, when you notice scratching, is why infestations recur.

Fleas also matter beyond the itching. Flea allergy dermatitis is a hypersensitivity reaction to antigens in flea saliva, which means a single bite can trigger a disproportionate inflammatory response in a sensitised animal; it is one of the most common skin presentations in this region. Fleas are also the intermediate host for the tapeworm Dipylidium caninum, which a pet acquires by swallowing an infected flea during grooming, and they are implicated in the transmission of Bartonella henselae — the organism behind cat scratch disease in people — and Rickettsia felis.

Flea allergy dermatitis is also the reason a lot of owners in this region end up in the supplement aisle. The coat looks terrible, so the coat gets treated — which is backwards. Sort the fleas out first, and treat the environment as well as the animal. If the skin is still unhappy three months later, our coat and skin supplements guide covers which ingredients have evidence behind them and which are marketing.

Ticks

The headline tick across tropical Asia is the brown dog tick, long referred to as Rhipicephalus sanguineus. Worth knowing that the taxonomy has moved: the globally distributed "tropical lineage" of that complex was formally recognised in 2022 as Rhipicephalus linnaei. You will see both names in circulation, sometimes in the same clinic, and for practical purposes they refer to the tick you are dealing with here.

Two things make it a different problem to the ticks you knew in the UK. The first is that it is unusually well adapted to living indoors and in kennels — it does not need woodland, and it will happily establish in a home or a condo compound. The second is the list of pathogens it carries:

• Ehrlichia canis — canine monocytic ehrlichiosis, the "tick fever" your vet will mention by name.
• Anaplasma platys — cyclic thrombocytopenia, often subclinical, sometimes found incidentally on bloodwork.
• Babesia vogeli — a protozoal parasite of red blood cells. Note that Babesia gibsoni, the more aggressive species seen in this region, is a different transmission story: it is associated with Haemaphysalis ticks and, importantly, with direct dog-to-dog transmission through bite wounds and through transfused blood.
• Hepatozoon canis — acquired not through the bite but by the dog ingesting an infected tick, which is a useful thing to know if your dog chews at itself.

Tick prevention takes two forms: medication and physical inspection. Both matter, and neither substitutes for the other. The reason inspection alone is insufficient is timing — experimental work has shown E. canis being transmitted within a few hours of attachment, far quicker than the multi-day windows quoted for some other tick-borne diseases. A tick found on the evening check may already have done its work.

If you find an attached tick, remove it promptly. Use fine-tipped tweezers or a purpose-made tick hook. With tweezers, grasp the tick as close to the skin as possible and pull steadily upward without crushing the body; a tick hook is designed to be slid underneath and rotated, so follow the technique for the tool you actually have rather than mixing the two. Do not burn it, do not smother it in petroleum jelly or alcohol, and do not try to make it "back out" — all of these are slower than simply removing it and risk the tick regurgitating into the wound. Keep the tick in a sealed container if you can; identification is occasionally useful, and so is a date.

Tick fever: what it actually looks like

Ehrlichiosis is worth understanding because it does not behave like a single illness. It has three recognised phases. The acute phase, some weeks after infection, brings fever, lethargy, appetite loss, enlarged lymph nodes and often a low platelet count, and many dogs appear to recover from it. That apparent recovery is the subclinical phase, which can last months to years with the organism persisting. In a proportion of dogs the infection then progresses to a chronic phase involving bone marrow suppression — the severe form historically described as tropical canine pancytopenia, which is the same disease process rather than a separate one. German Shepherds are frequently cited as over-represented in the severe form.

The reason this matters to you as an owner is that "he had a fever, we gave him something, he was fine" is not necessarily the end of the story, and a dog that was treated for tick fever three years ago in Bangkok is a dog whose history your new vet needs. Ask for the records, and keep them.

Heartworm

Heartworm is transmitted by mosquitoes, which act as an obligate intermediate host — the parasite cannot complete its life cycle without them, and it cannot pass directly between dogs. Infective larvae are deposited on the skin as the mosquito feeds and enter through the puncture wound. From there they migrate through the tissues and, over roughly six to seven months, mature into adult worms that live in the pulmonary arteries and the right side of the heart.

Adult heartworm infection is serious, expensive to treat, and sometimes fatal. The treatment itself carries real risk, because killing adult worms creates fragments that must be cleared through the pulmonary circulation, which is why treated dogs are strictly exercise-restricted for weeks. None of that is a scenario you want to reach.

Prevention is straightforward by comparison. The monthly products belong to a drug class called the macrocyclic lactones — ivermectin, milbemycin oxime, moxidectin and selamectin are the actives you will see named — and they work by killing the immature larval stages the animal has picked up over the preceding weeks. They do not repel mosquitoes and they do not kill adult worms. That is why the dosing interval is not a suggestion: a missed month is not "slightly more risk today", it is a window in which larvae acquired during that period can survive to a stage the product no longer touches.

That six-to-seven-month prepatent period is also why testing sits where it does. A heartworm test before starting prevention is standard, and annual testing thereafter is the norm even for dogs on consistent cover — partly because no product and no owner is perfect, and partly because a test done too soon after exposure will read negative regardless. If your pet has just arrived, your vet will factor the timing of the move into when they test.

Cats are a genuinely different picture. Feline heartworm involves fewer worms, is harder to diagnose, and the significant disease is respiratory rather than cardiac — it is described as heartworm-associated respiratory disease. There is no adulticide treatment approved for cats, which makes prevention the entire strategy rather than a first line of defence. Cats in this region need a conversation about it, indoor or not.

Intestinal worms and protozoa

Roundworms, hookworms, whipworms, tapeworms and Giardia are all more present in tropical climates than in colder ones. Hookworm is the one worth singling out: the larvae develop in warm, moist soil, which means urban grass, park verges and shaded ground in Singapore or Bangkok are a more productive environment for them than the equivalent in London or Toronto.

Several hookworm species matter here. Ancylostoma caninum is the classic canine hookworm. A. braziliense is a well-known cause of cutaneous larva migrans in people — the intensely itchy, migrating skin track you may have seen described as a beach hazard. A. ceylanicum deserves particular attention: it is endemic in dogs and cats across Asia and is the only zoonotic hookworm species that establishes patent, egg-producing infections in humans, and molecular surveys have identified it as the second most common hookworm infecting people in South-East Asia. The reservoir is domestic and community dogs and cats.

Toxocara canis and Toxocara cati are the roundworms behind visceral and ocular larva migrans in humans, most often affecting young children. Trichuris vulpis (whipworm), Dipylidium caninum (the flea tapeworm) and Giardia round out the list your vet will be thinking about.

The point of listing the zoonoses is not to alarm you. It is that faecal picking-up, hand washing and routine deworming in this region are public health measures as much as pet health ones, particularly in a household with small children.

Most monthly heartworm preventatives also cover several intestinal species, but coverage varies by product and none covers everything. Routine faecal testing — at a frequency your vet sets based on lifestyle — picks up what prevention doesn't. Puppies, kittens and immunocompromised animals get monitored more often.

Leptospirosis: not a parasite, but it belongs in this conversation

Leptospirosis is a bacterial infection, so it sits outside the parasite list, but in the tropics it belongs in the same planning conversation. It is spread through the urine of infected animals — rodents are a major reservoir — and survives in warm, standing water and damp soil. Monsoon rain, flooding, drains and puddles are exactly the exposure route, which makes it a genuine urban risk in this region and not a rural curiosity. It is also zoonotic: people catch it, and can catch it seriously.

Vaccination exists and is widely used in tropical Asia, but it is worth understanding what it does. Leptospira comprises a large number of serovars, and a vaccine protects against the serovars it contains rather than against leptospirosis generally. WSAVA guidance frames the vaccine as one to be treated as core in regions where the disease occurs, the circulating serogroups are known and a suitable product is available — which is a more nuanced position than either "core everywhere" or "optional". Your vet's recommendation will reflect what is actually circulating locally, and it is a reasonable thing to ask about directly.

The products: what your UK vet gave you, and what's used here

You may name active ingredients in a conversation with your vet, and it helps to know the categories. Nothing below is a recommendation, and no dose appears here deliberately — dosing is a veterinary decision that depends on species, weight, age, breed and what else the animal is taking.

• Macrocyclic lactones (ivermectin, milbemycin oxime, moxidectin, selamectin) — heartworm prevention, with varying intestinal worm coverage depending on the product.
• Isoxazolines (afoxolaner, fluralaner, sarolaner, lotilaner) — oral and topical flea and tick products, widely used and generally well tolerated. The US FDA issued an alert in September 2018 noting neurologic adverse events including tremors, ataxia and seizures reported across this drug class, and required label updates. That is a reason to mention any seizure history to your vet, not a reason to avoid the class on your own initiative.
• Neonicotinoids and phenylpyrazoles (imidacloprid, fipronil) — older topical flea and tick actives, still in wide use, often in combination products.
• Pyrethroids and amidines (permethrin, amitraz) — used for tick repellency in some canine products. Permethrin is highly toxic to cats, and this is not a theoretical concern: cats have been poisoned by contact with a recently treated dog in the same household. If you have both species, say so before anything is prescribed.

One more thing worth raising if it applies to you: collies and related herding breeds carry a well-documented variant of the ABCB1 gene, still widely referred to as MDR1, that changes how certain drugs — including some macrocyclic lactones at higher doses — are handled. If your dog is a collie, an Australian shepherd or a related breed, mention it. Testing exists.

What vets in the region typically recommend

The pattern, allowing for individual variation, looks like this:

• Monthly broad-spectrum preventative covering heartworm, intestinal worms, and (depending on the product) fleas and ticks.
• Additional tick coverage for dogs that walk in vegetated areas — sometimes a separate product.
• Annual heartworm testing regardless of consistent prevention.
• Routine faecal testing at intervals your vet decides based on lifestyle.
• A vaccination plan built for this region, which is usually where leptospirosis enters the conversation and, in Singapore, where rabies drops out of it.

Specific products vary by city, by what's licensed locally, and by what your vet has seen work in their patient population. Asking "what do you put on your own dog?" is sometimes the most useful question you can ask in a first appointment. Our guide to finding a vet in Singapore covers the rest of that conversation, and the wider picture of what changes for a temperate-climate animal is in our primer on pet health in tropical Asia.

One last framing. Parasite prevention here is not an upsell and it is not anxiety. It is the cheapest, dullest, most effective thing you will do for your animal all year, and the alternative — treating ehrlichiosis, or adult heartworm, or a chronic flea allergy that has been running for eighteen months — is worse in every dimension that matters, including the financial one.