Características de los aisladores comerciales

Drivers of livestock morbidity in FMD outbreaks

The median of the morbidities reported by each individual household surveyed (N = 118) was 42.9% (IQR: 21.9-68.8%) for cattle and 10.2% (IQR: 0 – 56.6%) for small ruminants, highlighting large variation in reported morbidity levels. Reported morbidity in the most recent FMD outbreak did not explain FMDV seroprevalence in the cross-sectional study herds (Table 3.8).

10 20 30

2012−01 2012−07 2013−01 2013−07 2014−01 2014−07 2015−01

Date

Km North Jittered

● ●

0 5 10 15 20 25 30

0.60.81.01.21.4

c(0, 30)

c(1, 1) SAT2 A SAT1 O Untyped Reported

Table 3.8: Morbidity is a poor explanatory variable for FMD seropositivity in livestock.

Explanatory variable dropped (whilst maintaining age

and random effect of herd) Difference in AIC LRT Χ² p

Reported cattle morbidity -0.86 1.14 0.286

Reported small ruminant morbidity -1.35 0.61 0.434

Livestock practice and herd size explained a small amount of the variation in cattle morbidity. Pastoralists reported higher morbidity (Median 67.7% [IQR: 33.5 – 95.4%]) compared to agropastoralists (Median 50.0% [IQR: 13.2 – 100.00%]) and households with larger herds reported lower morbidity (Table 3.9). However, much variation in morbidity remained unexplained (Deviance with random effects and intercept only: 956 on 112 degrees of freedom, residual deviance: 941 on 110 degrees of freedom).

Table 3.9: Variables explaining some of the variation in reported cattle morbidity using all available morbidity data.

Variable Difference in

AIC LRT Χ² p Estimate

(95% CI)

Odds ratio (95% CI)

Livestock practice -9.08 11.08 0.0009

Pastoral compared to

agropastoral 1.5 (0.6-2.3) 4.3 (1.9-10.0)

Herd size -3.3 5.3 0.021

Per extra ten cattle

-0.028 (-0.052--0.005)

0.972 (0.950-0.995)

Livestock practice had a large effect on reported small ruminant morbidity (Table 3.10), with agropastoralists reporting lower morbidity in their small ruminants (Median 0%, IQR:

0.0 -28.7%), compared to pastoralists (Median 50.0, IQR: 13.2 – 100.0%). Similarly to the cattle morbidity model, the small ruminant morbidity model failed to explain much of the variation in the data (Deviance with random effects and intercept only: 466.9 on 88 degrees of freedom, residual deviance: 441.8 on 86 degrees of freedom).

Table 3.10: Variables explaining some of the variation in reported small ruminant morbidity using all available morbidity data.

Variable Difference in

AIC LRT Χ² p Estimate

(95% CI) Odds ratio (95% CI)

Livestock practice -23.76 25.08 5.5 x 10 ^-7

Pastoral compared to

Per extra ten small ruminants

-0.12 (-0.206--0.034) 0.887 (0.814-0.967)

In order to increase the likelihood of accurate estimates for morbidity, only data from the outbreak visits, and not from the cross-sectional study were used for further analyses.

However, even when only the 41 herds that underwent outbreak investigations were considered, there was large variation in reported morbidity (IQR for cattle 21.9-35.8%, for small ruminants 0-50%).

Both cattle morbidity and virus isolation data were available for 31 outbreaks (24 agropastoral and 7 pastoral). Herd size and outbreak serotype explained a small of the variability reported for both cattle (Table 3.11) and small ruminants (Table 3.12), whereas livestock practice and season did not help explain cattle morbidity levels. However, similarly to the morbidity model with the larger dataset, much variation in morbidity remained unexplained (Deviance with random effects and intercept only: 306.5 on 29 degrees of freedom, residual deviance: 290.7 on 26 degrees of freedom).

Table 3.11: Variables explaining variation in cattle morbidity using data from herds with virus isolation and typing.

Variable Difference in

AIC LRT Χ² p Estimate (95% CI) Odds ratio (95%

CI)

Herd size -3.93 5.93 0.0149

Per extra ten cattle

-0.046 (-0.083--0.01) 0.955 (0.92-0.99)

Small ruminant morbidity and virus isolation data were available for 16 outbreaks (9 agropastoral and 7 pastoral). For the sample available, livestock practice, herd size, season or outbreak serotype did not help explain the variation in morbidity.

Morbidity levels in different species

Lactating cows had the highest reported levels of morbidity, followed by other types of cattle (Figure 3.9).

Figure 3.9: Proportion of animals that households reported to show clinical signs of FMD in each species and age group.

The most commonly reported clinical signs of FMD in livestock were foot and mouth lesions, salivation, anorexia and depression. These signs were reported by over 90% of households that had outbreaks. Over 85% reported lameness and weight loss. Milk loss in female cattle, goats and sheep was reported by 90.6%, 90.0% and 69.2% of households,

Sheep < 1 year Adult Sheep Goats < 1 year Adult Goats Cattle < 1 year Other Female Cattle Adult Male Cattle Lactating Cows

0.00 0.25 0.50 0.75 1.00

Proportion of animals reported to show clinical signs

four pastoral) reported animals aborting during FMD outbreaks. Two of these households reported abortions in cattle only and the other three reported abortions in both cattle and small ruminants. The proportion of cows in each herd reported to have aborted ranged from 0.3 to 19.2%. For small ruminants, the proportion ranged from 7.5 to 14.3%.

Of the 89 households in the cross-sectional and longitudinal studies that reported on long-term effects of FMD on their livestock, 22 households (24.7%) reported heat intolerance syndrome in one or more of their livestock.

Clinical signs recorded during veterinary examination

Individual animal data from clinical examinations by veterinarians on the field team were available for 238 animals with FMD lesions from 19 different herds in the outbreak tracking study (11 agropastoral and 8 pastoral). Of the 238 animals, 90.8% had foot lesions and 88.2% had mouth lesions. Of 37 cows over three years that were in their lactation period, four (10.8%) had FMD lesions on their udders. Detailed data on clinical signs were available for 213 of the 238 animals examined for lesions. These are summarised in Table 3.12.

Table 3.12: Clinical signs recorded in animals with FMD lesions that were examined in detail.

Clinical Sign Number (%) affected

Weight loss 148 (69.5 %)

Lameness 136 (63.8 %)

Anorexia 130 (61 %)

Depression 117 (54.9 %)

Salivation 111 (51.9 %)

Heat intolerance 33 (15.5 %)

Diarrhoea 19 (8.9 %)

Loss of milk (Lactating cows > 3 years old, N=37) 26 (70.3%)

Abortion (Cows in calf > 3 years old, N=36) 1 (2.8%)

Overall, levels of reported livestock mortalities due to FMD were low (median and IQR of 0% for all species). Out of 118 households (84 agropastoral and 34 pastoral) that reported on livestock morbidity and mortality due to FMD, 29 (24.6%) reported that animals in

their herd died due to FMD. There were 23 agropastoral and six pastoral households amongst these.

There were 25 households that reported bovine mortalities due to FMD. Of these, 19 households reported mortalities below 5%. A further three households reported bovine mortalities between 5% and 10%. Two households reported bovine mortalities between 10% and 20%. Only one agropastoral household reported mortality in cattle of 36.5%.

Eleven households reported small ruminant mortalities. Of these 3, 6 and 9 had mortalities below 5%, 10% and 20% respectively. Two agropastoral households had small ruminant mortalities above 40% (Figure 3.10). One of these was the same household that reported the high cattle mortalities. The majority of small ruminants that died during outbreaks were juveniles, with 100% mortality in this group in two households. Six of the herds with mortalities had virus isolation data. Three of these had outbreaks caused by SAT2, two by SAT1 and one by serotype A.

Figure 3.10: Reported livestock mortality due to FMD in 118 households.

Reports of human illness during FMD outbreaks

Of the 88 households that commented on whether or not they perceived people to become ill from FMD during outbreaks in livestock, nine (10.2%) pastoral households reported symptoms in household members that they believed were caused by FMD. Fourteen

Cattle Small Ruminants

0.0 0.1 0.2 0.3 0.4

Reported mortality

Species

Small Ruminants Cattle

mouth, on the lips and in the nose, coughing, sneezing, headache, fever and muscle pain.

Of 97 respondents commenting on whether they believed people got FMD, 23 (23.7%) believed that people could become infected. When asked how people contracted FMD, ten respondents attributed it to drinking milk and thirteen were unsure. Nineteen respondents of the 23 listed similar clinical signs in people as above and four did not list symptoms.