Hidden Offenders - Infectious and Parasitic Causes of Vomiting in Dogs

Why Not Every “Gastric Case” Starts in the Gut 
Vomiting is one of the most frequent presenting complaints in small animal practice. While diet changes and gastritis are often blamed, a significant number of “gastric cases” in Indian clinics have an infectious or parasitic origin. 
From tick-borne fevers to heavy worm loads, these hidden offenders can induce vomiting long before their classic systemic signs appear. Recognizing these early clues can transform clinical outcomes — especially in resource-limited or first-contact settings. 

1. Viral Causes — When Vomiting Is the First Warning 

Canine Parvovirus (CPV) 
The classic culprit in young, unvaccinated pups. 
Vomiting usually precedes diarrhea and is often projectile, frequent, and associated with severe lethargy. 
A rapid CPV antigen test (fecal ELISA) confirms the diagnosis — but early suspicion and isolation are critical to prevent spread and fatal dehydration¹. 

Clinical cue: In canine parvoviral enteritis, persistent vomiting (even when the stomach is empty), rapid dehydration (characterized by sunken
eyes and tacky mucous membranes), and foul or acidic-smelling gastrointestinal secretions are common findings ². 

Field reminder: In India, seasonal spikes post-monsoon are common due to higher environmental virus survival. 

Canine Distemper Virus (CDV) 
Primarily known for respiratory and neurologic signs, distemper can initially manifest as vomiting and inappetence in partially vaccinated or adult dogs³. 
Look for serous ocular/nasal discharge or hyperkeratosis of nose or paw pads before ruling it out³. 

Clinical tip: Mixed CPV–CDV infections are not rare. Always consider co-testing in kennels or shelters with multi-dog outbreaks³. 

2. Parasitic Infiltrators — The Most Overlooked Cause 

Gastrointestinal Helminths (Toxocara, Ancylostoma, Strongyloides) 
Heavy infestations can cause vomiting due to gastric irritation, intestinal obstruction, or larval migration. 
Typical signs include a pot-bellied abdomen, dull coat, intermittent vomiting, and good appetite⁴. 

Vet insight: Always perform a fecal flotation or deworming trial before initiating advanced diagnostics in a vomiting pup. Many “mystery gastritis” cases resolve after a proper anthelmintic protocol³. 

Giardiasis — The Persistent Nuisance 
Giardia spp. infection leads to vomiting and soft, foul-smelling stool, especially in dogs exposed to stagnant water, kennels, or shelters. 
Diagnosis can be made via fecal smear, antigen ELISA, or immunofluorescence assay⁵. 

Treatment with metronidazole (25 mg/kg BID for 5–7 days) or fenbendazole (50 mg/kg for 3–5 days) is typically effective, though reinfection is common⁵. 

Prevention: Stress hygiene and disinfection of bowls and bedding. Reinforce clean water access, especially during monsoons. 

3. Tick-Borne Infections — Systemic Diseases Masquerading as Gastritis 

Ehrlichiosis and Babesiosis 
These vector-borne infections can present with vomiting, inappetence, and lethargy even before hematologic or febrile signs appear. 
If vomiting coexists with fever, pale mucosa, lymphadenopathy, or thrombocytopenia, always prioritize tick-borne screening (CBC, smear, or PCR^)6. 

Red flag: A vomiting dog with low platelet count is not a primary gastric case⁷. 

Field note: Subclinical or chronic ehrlichiosis is increasingly being recognized in India — early doxycycline therapy prevents organ involvement⁸. 

4. Bacterial and Fungal Offenders — Beyond the Obvious 
While less frequent, infections such as leptospirosis, campylobacteriosis, and systemic mycoses can produce vomiting secondary to hepatic or renal compromise⁹. 
In endemic regions, suspect Leptospira when vomiting occurs with icterus, azotemia, or hemoglobinuria¹⁰. 

Early action: Initiate doxycycline (5 mg/kg BID) pending results to reduce mortality and zoonotic risk¹¹. 

Bonus insight: Mycotic infections like aspergillosis or blastomycosis can occasionally cause vomiting due to disseminated visceral involvement — think of them in unresponsive or relapsing cases¹². 

5. Clinical Insight — Think Beyond the Gut 
Infectious causes of vomiting often worsen with empirical “gastro-protective” or antiemetic therapy, because the primary pathology lies outside the stomach. 
Simple, rapid diagnostics — CBC, fecal analysis, vector-borne disease panel, and antigen testing — can help differentiate infection-driven vomiting from benign gastritis within a single consultation. 

Bottom Line for Practitioners 
When routine gastric management fails, it’s time to look beyond the gut. 
Viruses, parasites, and tick-borne pathogens remain the silent culprits behind many “simple vomiting” cases across Indian clinics. 

Practical takeaway: Early screening, isolation, and empirical deworming or vector control can save both lives and costs — especially in high-volume OPD and shelter medicine settings. 

References  

1. Li H, Shengnan L, Pan Y, Shi Q. Decoding canine parvovirus: biomarkers for diagnosis and advances in vaccine development to address emerging challenges. Frontiers in Veterinary Science. 2025 Aug 6;12:1624275. 

2. Botha WJ, Goddard A, Pazzi P, Whitehead Z. Haemostatic changes associated with fluid resuscitation in canine parvoviral enteritis. Journal of the South African Veterinary Association. 2020 Jan 1;91(1):1-9. 

3. Costa VG, Saivish MV, Rodrigues RL, Lima Silva RF, Moreli ML, Krüger RH. Molecular and serological surveys of canine distemper virus: A meta-analysis of cross-sectional studies. PloS one. 2019 May 29;14(5):e0217594. 

4. Parmar D, Sharma D, Singh E, Katoch A, Ahuja A, Verma S. TOXOCARIASIS IN PUPPY-MORPHOLOGICAL DESCRIPTION AND CLINICAL MANAGEMENT. Exploratory Animal & Medical Research. 2023 Dec 1;13(2). 

5. Ciuca L, Pepe P, Bosco A, Caccio SM, Maurelli MP, Sannella AR, Vismarra A, Cringoli G, Kramer L, Rinaldi L, Genchi M. Effectiveness of fenbendazole and metronidazole against Giardia infection in dogs monitored for 50-days in home-conditions. Frontiers in Veterinary Science. 2021 Mar 26;8:626424. 

6. Rautenbach Y, Schoeman J, Goddard A. Prevalence of canine Babesia and Ehrlichia co-infection and the predictive value of haematology. Onderstepoort Journal of Veterinary Research. 2018 Jan 1;85(1):1-5. 

7. Dhliwayo S, Chihambakwe B, Taonezvi K, Chikerema SM, Tivapasi MT, Pfukenyi DM. Seroprevalence of Canine Ehrlichiosis and Microscopic Screening for Canine Babesiosis in Dogs in Harare, Zimbabwe, 2016‐2017. Veterinary medicine international. 2019;2019(1):4130210. 

8. Cardoso SP, Honorio-França AC, França DC, Silva LP, Fagundes-Triches DL, Neves MC, Cotrim AC, Almeida AD, França EL, Sousa VR. Effects of doxycycline treatment on hematological parameters, viscosity, and cytokines in canine monocytic ehrlichiosis. Biology. 2023 Aug 16;12(8):1137. 

9. Ashmi M, Sanjana AK, Nikunjkumar P. A review on bacterial infectious diseases of dogs. Acta Scientific Veterinary Sciences (ISSN: 2582-3183). 2022 Jul;4(7). 

10. Andrade MC, Oliveira LB, Santos ÁF, Moreira MV, Pierezan F, Ecco R. Differential diagnoses in 83 dogs with icterus. Pesquisa Veterinária Brasileira. 2020 Jun;40(6):451-65. 

11. Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. Journal of Veterinary Internal Medicine. 2023 Nov;37(6):1966-82. 

12. Tutun H, Sababoglu E, Ayan A, Sevindik M. Fungal Diseases and Therapy in Dogs. InFungal Diseases in Animals: From Infections to Prevention 2021 Jun 23 (pp. 105-126). Cham: Springer International Publishing.