Neonatal Coccidiosis
LEVELS: Highly unlikely; No human illness; Already in the herd; Routine; Moderate; Negligible; Some; Needed but not available
| Register id | cystoisospora_suis |
| Type | parasite |
| Scientific name | Cystoisospora suis |
| NCBI taxid | 483139 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Cystoisospora suis causes neonatal coccidiosis, which the reference chapter calls the most important protozoal disease of swine. It is found wherever pigs are raised in confinement. Piglets scour at about seven to fourteen days of age, and the diarrhoea does not respond to antibiotics, which is often the first clue. Morbidity is high and mortality usually moderate, but affected pigs lose condition and grow more slowly, and that setback can carry through after weaning; with a concurrent bacterial, viral or parasitic infection, mortality can become extreme. The source is not the sow but the farrowing house itself — residual oocysts in the crate, where the warmth and moisture are ideal for them to become infective within a day, and once sporulated they resist most disinfectants. Diagnosis is quick: the oocysts in the faeces of affected piglets carry distinctive hazy bodies that no swine Eimeria has. Toltrazuril given once at three days of age is effective and cost-effective, and is essentially the only drug that works — nothing else has proved useful in nursing pigs, and treating the sow's ration is of little value. Improper dosing risks resistance. There is no vaccine, and no human infection is described.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Highly unlikely: Human infection with the agent has never been reported, or has been reported but is not attributed to pig or pork exposure
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l1, highly unlikely to infect humans"
Basis. Section 60.1.2 covers C. suis across six subsections -- clinical signs, pathology, diagnosis, epidemiology, immunity, treatment -- and makes no mention of human infection. Chapter 60 titles its final section "Other Protozoa of Minor Importance or Potentially Transmissible to Humans" and puts Giardia, Balantioides and Entamoeba there, which is where it collects the zoonoses.
How this level was decided
INFERRED from a structured silence that this chapter makes unusually legible: it has a section heading for the protozoa transmissible to humans, and C. suis is not in it. Cystoisospora suis is host-specific to pigs. Level 1.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l1, highly unlikely to infect humans so no clinical disease"
Basis. No human disease is described in section 60.1.2.
How this level was decided
INFERRED, on the same structured silence. C2 scores level 1 whenever the agent does not cause disease in people.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Corrected by Eric from L4 Extraordinary biosecurity required. Reason: MOVED L4 -> L1. Flagged for him on 2026-09-02 as an L4, L2 or L1 question, with the chapter contradicting itself -- "C. suis is endemic in most herds" against fewer than 3% of US pigs sampled shedding oocysts. He ruled on the first and on his own field experience: "c3l1 - present on all herds in my view, just not always clinically apparent." THE SURVEY FIGURE IS A SHEDDING PREVALENCE, NOT A HERD PREVALENCE, which is how the two reconcile: C. suis is excreted in phases and only by clinically affected piglets in the farrowing house, so a point- in-time sample of the general pig population finds almost none of it while the organism is still in the crates on most farms. Level 1 is the right level on the criterion as he defines it -- present in most herds, so there is no introduction event to prevent. CONSEQUENCE RECORDED SEPARATELY: this entry was the fourth worked example at C3 level 4 in criteria_levels.yml and he ruled it dropped rather than replaced.
Basis. ch60 60.1.2.4: "The source of clinical Cystoisospora infections in nursing pigs is most likely from residual oocysts in the environment of the farrowing facility rather than sow's feces." "once C. suis becomes established on a farm, it is probably transmitted through contaminated farrowing crates. The temperature (32-35 C) and moisture in the farrowing crate favor rapid sporulation." 60.1.1: "Once the oocysts are sporulated, they are resistant to most disinfectants."
How this level was decided
MOVED L3 -> L4 on 2026-09-01 by the five-level rework. The farrowing crate IS the habitat: the chapter traces clinical infection to residual oocysts in the farrowing facility rather than to the sow, and the supplemental heat the producer provides for the piglets is what sporulates them within twelve hours. Sporulated oocysts resist most disinfectants. Neither housing nor routine C&D closes this, which is L4. It is the worked example for that level in criteria_levels.yml. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable. FLAGGED FOR ERIC, 2026-09-02, AND THE LEVEL IS HELD RATHER THAN MOVED. He ruled cryptosporidium_spp down from L4 to L2 on the ground that C3 asks how the agent gets ONTO the farm rather than whether it recycles once inside, and he set out the general reading at the same time: housing a herd indoors is the FIRST STEP of a biosecurity programme, which is what L2 is. He also said the ruling does not generalise by itself -- "I may overrule on specific cases but in general" -- so this cell is put to him rather than moved with it. THE QUESTION IS WHETHER THE ANSWER IS L1 RATHER THAN L2. The chapter says outright that "C. suis is endemic in most herds", which is the level 1 label: present in most herds, so there is no introduction event to prevent. Against that, the same chapter reports fewer than 3% of US pigs sampled excreting C. suis oocysts, and sows on farms WITH a history of neonatal coccidiosis showing no detectable C. suis at all. Those two statements do not sit easily together. NOTE ALSO that Cystoisospora suis is the fourth worked example at C3 level 4 in criteria_levels.yml, so moving it is a criteria edit and needs a replacement example.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Routine: The disease would be suspected from clinical signs, history and epidemiology in normal practice, and confirmed by tests that local or regional laboratories run routinely
Basis. ch60 60.1.2.3: "Diarrhea in nursing pigs 7-14 days of age that does not respond to antibiotic treatment is suggestive of neonatal C. suis infection." "Diagnosis of C. suis can be achieved by finding C. suis oocysts in the feces of clinically affected piglets. This is the quickest method available for diagnosis." The oocysts carry "hazy bodies" which "are diagnostic for C. suis because none of the oocysts of the swine Eimeria species has this structure".
How this level was decided
Both halves of level 1, unusually cleanly. The clinical picture points here specifically -- diarrhoea in a defined age window that does not respond to antibiotics is the chapter's own trigger -- and confirmation is faecal flotation, which any practice or regional laboratory runs, with a morphological feature that is diagnostic on sight. NOTE: the chapter warns that piglets shed in phases and may be negative, and that detection alone does not establish clinical significance in an endemic herd. Those are interpretive cautions on an available and routine test, not barriers to getting one.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Basis. ch60 60.1.1: "Neonatal coccidiosis caused by C. suis is the most important protozoal disease of swine." 60.1.2.1: "Morbidity is high, but mortalities are usually moderate. Affected pigs often have loss of body condition with reduced growth rates, which may impact postweaning performance." "Concurrent bacterial, viral, or other parasitic infections may lead to extreme mortalities." 60.1.2: "Neonatal piglet coccidiosis has a cosmopolitan distribution and is found anywhere pigs are raised in confinement."
How this level was decided
Level 3. High morbidity with moderate mortality, plus lost condition and reduced growth carrying through into post-weaning performance, in a disease the chapter calls the most important protozoal disease of swine and which is found wherever pigs are confined. That is a measurable increase in cost of production that farms manage. NOTE: unlike most of the ch61 parasites, confinement does not remove this one -- the farrowing crate IS its habitat, so the standing note SCORING/production_cost_impact does not pull it down.
C6 Market impact
Duration of material disruption to pork and pig markets
Negligible: Little or no material disruption to supply or demand when disease occurs on one or more farms
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c6l1, common endemic disease, no impact on markets"
Basis. Section 60.1.2 records no trade measure, movement control or consumer response. The disease is non-zoonotic, endemic in most herds, and confined to nursing and newly weaned pigs.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact this is an agent long endemic and routinely diagnosed in US herds with no historical market response. Losses fall on the farrowing house and are scored at C5. Level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l2, effective extralabel product available and in common use"
Basis. ch60 60.1.2.6: "Toltrazuril is an effective means of treating coccidiosis in nursing piglets. A single dose of 20 mg/kg given at 3 days of age has been shown to decrease clinical signs and be cost effective." "Improper dosing can result in drug resistance to toltrazuril." "Controlled studies conducted to date in nursing pigs have not identified other effective coccidiostats." "using anticoccidial drugs in the sow's ration is of little value in controlling neonatal coccidiosis."
How this level was decided
INFERRED, and FLAGGED because it turns on a fact the folder does not carry. An effective, cost-effective, single-dose treatment exists and is named, which under the standing note SCORING/treatment_potential is level 1 if it is a labelled US product and level 2 if its use here is extralabel. Toltrazuril is licensed for piglet coccidiosis in the EU; the chapter does not say what its US status is. Scored level 2 on the assumption of extralabel use, with resistance from improper dosing as a second qualifier and no alternative coccidiostat identified. If Eric knows a US-labelled product, this is level 1.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l3, there would be demand for a vaccine if it were available, can cause persistent cost on production in some farms"
Basis. No vaccine is described in ch60 60.1.2.6, which addresses control through toltrazuril and sanitation. 60.1.2.5 records that experimental inoculation of sows before farrowing "resulted in partial protection of piglets against clinical disease", and that recovered pigs are solidly immune to challenge.
How this level was decided
INFERRED. No vaccine exists, and the reworded criterion asks whether one is warranted. It is: this is the most important protozoal disease of swine, present wherever pigs are confined, with high morbidity and lasting growth effects. The chapter also shows the target is tractable -- recovered pigs resist challenge, and inoculating sows partially protected their litters, so protective immunity is achievable. Needed but not available. Level 3.
Levels and evidence are generated from data/assignments/cystoisospora_suis.yml; the overview is authored in data/overviews/cystoisospora_suis.md. Do not hand-edit this page — corrections go in data/assignments/CORRECTIONS.yml.
Quoted material marked Basis is from Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine, 12th edition. Hoboken: Wiley Blackwell, 2025 — except where another source is named in the quotation itself.